Gases that are nearly transparent to solar AND thermal radiation? I've been curious about if there are any gases in the atmosphere that are nearly transparent to both solar and thermal radiation. $CO_2$ for instance is nearly transparent to solar radiation but is partially opaque to thermal.

I've tried to find information on internet, but the large amount of information about global warming is effectively hijacking my google searches.

Edit: When I say solar radiation, I am not just referring to that which is visible. Please consider at least infrared, visible, and UV in your answer.

Any help or insight will be greatly appreciated.

Google Radiative (or radiation) absorbtion coefficients for gases (or enter specific gas of interest). Most of this data relates to applications in combustion and refrigeration so that is the area to look at. To avoid "contamination" from all the global warming stuff try looking at older things like papers from the 1950's. I have some detailed refrigeration books from the 50's which I think had this data but not to hand right now. Or see if you can get hold of some books like that from your library or a bookstore.

Many gases were studied in great detail with proper experimental measurements to verify well before global warming was a thing. You can find graphs of lots of useful things which can help you with an understanding of how the various gases might work in the atmosphere. For example using the emissivity of CO2 to calculate radiative heat transfer in the atmosphere with the standard Stefan-Boltzmann equation when you know the concentration of CO2 is, say, 400ppmV. Emissivity of CO2 can be surprisingly low at atmospheric concentrations, temperatures and pressures, less than 0.002 typically.


What is this long mark undersea Visiting Google Maps, I came across this long, sinuous, while pretty regular mark undersea that looks like an ancient river, when the sea was way lower, or a big (big!) boulder that could have rolled down to the bottom (?).
Given the location (ring of fire), it could also be a "crack" made during a major (and ancient) earthquake that, with time, has been filled with sediments.
This looks like this question, but the shape is very different, and much less sinuous than the one in Japan.
The mark:

The location:

It looks like a submarine canyon incised into the seafloor and shelf by repeated sediment "flushing". Given the location, earthquakes probably flush huge quantities of sediments from the low angle plains to the north, through the canyons, and into the abyssal plain to the south. You might find these canyons in any tectonically active seafloor that sees heavy sediment loading from, say, a mountainous tropical region. This one's not that big, compared to New Zealand's Hikurangi Channel, at nearly 700 km.
There's another one off the SE coast of Hokkaido Island. What, precisely, locally controls the formation of these canyons is an interesting question.


What does the unit cell of petitjeanite look like? The question in Chemistry SE What is the crystal structure of bismuth oxyhydroxyphosphate (BOHP)? is about a catalyst synthesized by accident. A link in this comment points to the page https://www.mindat.org/min-3329.html which is for the mineral petitjeanite, or $\ce{Bi3(PO4)2O(OH)}$. There are about 38 photos available there, and there seems to be quite a diverse range of appearances to my untrained eye.

I was wondering if a drawing or computer-generated image of a unit cell for petitjeanite would exist in any database or website for mineralogy and crystal structures, something like those shown in these questions 1, 2, 3.

Should one assume that the mineral petitjeanite and the chemical discussed in the recent Chemical & Engineering News article Photocatalyst shreds drinking water contaminant PFOA are probably the same crystal configuration and unit cell, or can there be some variety?

The paper also includes this SEM image of microcrystals of the "inadvertently produced bismuth oxyhydroxyphosphate (BOHP)."

  The accidentally synthesized BOHP (shown) can break down the toxic industrial contaminant PFOA faster than any other photocatalyst. Credit: Environ. Sci. Technol. Lett.

Should one assume that the mineral petitjeanite and the chemical discussed in the recent Chemical & Engineering News article Photocatalyst shreds drinking water contaminant PFOA are probably the same crystal configuration and unit cell, or can there be some variety?

No you cannot assume the structure from the formula, many materials have polymorphs (think graphite vs. diamond). To know if the structures are the same you must look at the diffraction pattern from the paper. In the paper the synthesized bismuth oxyhydroxyphosphate matches that of petitjeanite so in this case that is the prototype structure.

Using the information about diffraction, from the ICDD Databse (pdf 01-082-8058)we find that petitjeanite is a triclinic system of the $\mathrm P\bar 1$ space group (#2). with lattice parameters of:

$\require{mediawiki-texvc}$
$$a = 9.798\AA; ~ b =  7.250\AA; ~ c= 6.866 \AA; \qquad \alpha = 88.280^\circ \beta = 115.270^\circ ~ \gamma = 110.700^\circ$$

and atomic positions of:
$$\begin{array}{c|lll}
\text{Atom}&x&y&z\\
\hline
\ce{Bi}&~~~0.52327&~~~0.41421&~~~0.7523\\
\ce{Bi}&~~~0.29838&~~~0.74044&~~~0.55549\\
\ce{Bi}&~~~0.07735&~~~0.1609&~~~0.28045\\
\ce{P}&~~~0.6952&~~~0.0172&~~~0.9215\\
\ce{P}&~~~0.0961&~~~0.372&~~~0.7862\\
\ce{O}&~~~0.3777&~~~0.5382&~~~0.4759\\
\ce{O}&~~~0.3066&~~~0.1549&~~~0.5579\\
\ce{O}&~~~0.859&~~~0.0275&~~~0.8943\\
\ce{O}&~~~0.5569&-0.2084&~~~0.8602\\
\ce{O}&~~~0.621&~~~0.1596&~~~0.7526\\
\ce{O}&~~~0.7684&~~~0.1052&~~~1.1811\\
\ce{O}&~~~0.2584&~~~0.5101&~~~0.7497\\
\ce{O}&-0.0468&~~~0.4637&~~~0.6902\\
\ce{O}&~~~0.0209&~~~0.1498&~~~0.6362\\
\ce{O}&~~~0.1695&~~~0.3727&~~~1.0506\\
\end{array}
$$

and last but not least this renders to an image of:

Purple: Bi
Orange: P
Red: O


How averaging works in GFS model from NOAA? We have downloaded grib2 files for GFS model from NOAA and extracted irradiance (Downwards shortwave radiation flux) data. Following is a sample output for cordinates at [52.0,4.0]:

|      Timestamp      | Value |
| 2017-01-01T03:00:00 |   00  |
| 2017-01-01T06:00:00 |   00  |
| 2017-01-01T09:00:00 |   00  |
| 2017-01-01T12:00:00 |   40  |
| 2017-01-01T15:00:00 |   50  |
| 2017-01-01T18:00:00 |   20  |
| 2017-01-01T21:00:00 |   00  |

We know that the values are averaged. We doubt that the averaging is performed over a window of 3 hours such as the values between $hour$ and $(hour-3)$ are averaged and assigned to the timestamp at $hour$.

We haven't found any documentation explaining this fact. Can you please explain the principle behind averaging and timestamping? A reference will be very helpful.

The GFS is a model, and the model have a given time-step equal or smaller than the time-step of the output, that in this case is 3 hours. Different processes can be computed using different or even multiple time-steps.

Some of the reported variables are instantaneous, others are cumulative, and others are time averaged.

According to the documentation for the GFS radiation driver module in the GFS Operational Physics Documentation, the Downwards shortwave radiation flux correspond to a time averaged output quantity, meaning that for each model grid cell, its value is stored every internal time step (deltim) to then report the time-weighted average of all stored values, which is what you get in the 3-hour output.
However, I don't know what is the exact value used for deltim or how the time weights are computed.

Therefore, what you said seem to be pretty much the case. This is that the value reported for timestamp hour is the average of all the intermediate values computed between hour-3+deltim and hour using some time weights schema that is unclear to me.

In the link above, you can find all the source code for GFS, so it seem that to figure our the details of the time averaging you might need to search in the code where the values of the array fluxr (that store the intermediate time-step radiation flux values) is averaged and see there how it is done.


Can small-scale backyard gardening produce more food per acre than broadscale [grain] farming? Mark Shepard in his book "Restoration Agriculture" proclaims

[...] small-scale backyard gardening which has shown in study after study to produce more food per acre than broadscale grain farming.

Unfortunately, he doesn't cite any studies or goes into more detail. Is the main point here that grain farming is particularly low on biomass production, or is there a reason why backyard gardening can in generally have higher yields than industrial farming? References would be very welcome!

Efficacy of food production per square foot/acre differs from soil quality and rate of regeneration. It's also a case of if you can produce year round. Some permaculture specialists, monitored one case in an article of "Green America" A 500 sq foot garden producing 300 lbs of produce per year. Among other's. Soil nutrient recycling is a key aspect of producing food year round, along with temperature (Green houses).

Composting
Soil/air temp
Growth rate of produce involved
So the answer is "Yes" if dedication is involved.


How rare are double rainbows? We have all seen rainbows in our lives. But the other day, I saw a double rainbow! How rare are double rainbows and what causes them to appear?

A normal single arc rainbow is caused when sunlight enters a raindrop with a light-path refracted>reflected>refracted. A double rainbow occurs when sunlight hits a part of the raindrop at a different angle of incidence, at which the light-path is refracted>reflected>reflected>refracted. Some energy is lost with each reflection, so the double internal reflection emerges as less bright than the primary arc. Also, because there is another internal reflection the colours are inverted. So every rainbow has a primary and seconday arc. Hence the question becomes: 'Is the observer in a position to see the secondary arc', which  is a matter of geometry between the sun, raindrop and observer.

So the answer to your question is 'no', it isn't rare at all, in fact a secondary arc is always present somewhere, but is not always visible to the observer for reasons of geometry and background light intensity.


Why does helium-3 stay in the moon and not escape from it? So the moon is full of helium-3.

Since it's a gas in the moon's vacuum... Why doesn't it escape?

The Moon is not "full" of helium-3. 3He is at most fifty parts per billion of the lunar regolith1 and that "high" concentration pertains only to permanently shadowed craters. The Moon is bombarded by a steady stream of helium-3 while sunlit. Some of this incoming helium-3 is temporarily embedded in the lunar regolith. Without this steady supply, the helium-3 content would dissipate at a temperature-dependent rate proportional to the amount of helium-3 in the lunar regolith.

The quantity $q(t)$ of in a cubic meter of lunar regolith is thus dictated by a simple differential equation, $\dot q(t) = \alpha(t) - \beta(T)q(t)$. Time averaging the bombardment and escape rates yields $\dot {\bar q}(t) = \bar{\alpha} - \beta(\bar T)q(t)$. This differential equation yields a steady state value of $\bar q = \bar{\alpha}/\beta(\bar T)$.

1 Cooks, "3He in permanently shadowed lunar polar surfaces", Icarus, 206:2 778-779 (2010).


SEGD and SEGY recorded data What is the difference between a segd recorded data and a segy recorded data and can we convert from segd to segy and vice versa?

SEG-D is a specialized format, while SEG-Y is a general-purpose format.

In general, SEG-D is intended for field recordings of seismic data, and SEG-Y is intended for 'seismic data exchange'. Having said this, SEG-Y is so general-purpose, and so ubiquitous, that I'm not surprised to hear (anecdotally) that people are using it for data acquisition. Certainly, the recent release of Revision 2 — which allows for high sample rates, variable trace lengths, long records, and large files — facilitates this.

As an interpreter, I use SEG-Y all the time, whereas I've never come into contact with SEG-D. Thus, I don't know enough about it to go into any detail, but a quick look over the SEG-D specification suggests it has better support for describing receivers, channels, sources, and including things like observer logs. Which is what you'd expect in an acquisition format.

SEG's formats are notoriously, er, flexible. So converting directly between the two formats may or may not be possible, depending on which fields have been used, and the lengths to which you're prepared to go to 'adapt' the target format to your use case. The usual way to convert, as it were, would be to process (i.e. demux, sort, image, and maybe stack) the field data in the SEG-D file(s), and write out one or more SEG-Y files.

Good luck!

References

SEG-D Rev 3.1 description, SEG Technical Standards Committee, 2015.
SEG-Y Rev 2.0 description, SEG Technical Standards Committee, 2017.


Are there any other sites that allow users to search for historic hurricanes within a given area? Once upon a time I seem to remember there being a plethora of sites with very graphical interactive tools for quickly searching Atlantic hurricane data by time range, locations impacted, and storm type and get quick answers.  Some I remember as being very intuitive, and offerings from tv stations, government sites, and independents.

These days I know of exactly one, https://coast.noaa.gov/hurricanes/.  However I find this site to be difficult to comparably difficult to navigate in finding the location, filtering, and interpreting.  I believe NOAA once offered a top-notch option at http://hurricane.csc.noaa.gov/hurricanes/, but it's long gone, and I have trouble finding any others.  There's great such tools that have developed for severe weather, and perhaps with the millions of sites out there, other good ones for hurricanes exist, and I just don't know it.

Even better would be if such a site also included other basins to boot.  But these days, even for the Atlantic, I usually just look through pages on like Unisys Weather or the archives on Clark Evans' model website or Wikipedia annual maps.  But searching for "when is the last time a storm affected X" has proven surprisingly hard these days.  Any help to offer?

There is this atlas for the North Indian Ocean basin - Indian Ocean Cyclone Atlas and while I am not sure about the cyclone tracks for the pre satellite era cyclones the site is comprehensive and covers all cyclones in the Indian Ocean up to the current period. After you register yourself here - Registration  then you can view the cyclone tracks.

Here is a sample of cyclone tracks between 2012 and 2016


Why the $\delta \, ^{18}\text{O}$ in foraminifera shells decrease with temperature even if the oceanic $\delta \, ^{18}\text{O}$ stay constant? I understand why foram shells contain more $^{18}\text{O}$ when there are ice sheets present, since $^{16}\text{O}$ evaporates more readily and gets trapped in the ice, increasing the relative abundance of $^{18}\text{O}$ in seawater. However, in the absence of ice sheets: What is the reason for there being more $^{18}\text{O}$ in the foram shells in colder climates? Since I assume the evaporated $^{16}\text{O}$ would just get returned to the sea by rain and rivers if it's not being trapped in ice.

PS: This is an adaptation of a question asked in the private discussion board of a first year university course on Earth Sciences, that I'm copying here so a wider community can benefit from it and the corresponding answer. As suggested by the moderators, I'll donate any reputation received from this question in the form of a bounty awarded to exceptional answers (in particular by new or low-rep users).

That is because the chemical reactivity of $^{18}\text{O}$ is slightly higher than that of $^{16}\text{O}$. For that reason, the biochemical reactions that produce calcium carbonate in foraminifera prefer $^{18}\text{O}$ over $^{16}\text{O}$.

However, the temperature dependence arise from the fact that the difference in reactivity is smaller when temperature increase. Therefore, in warmer temperatures the $\delta ^{18}\text{O}$ will be more similar to seawater (no preference for any isotope), but at colder temperatures the chemical preference for $^{18}\text{O}$ will be stronger and, therefore, the $\delta ^{18}\text{O}$ will increase.

This correlation with temperature is also known as the "paleotemperature equation", but as it is an empiric equation there are many slightly different versions, however all of them are pretty consistent. Several ones are summarized in figure 5 of the paper Oxygen isotopes in foraminifera: Overview and historical review (Pearson 2012) copied below, showing how the excess of $\delta ^{18}\text{O}$ in shells ($\delta ^{18}\text{O}_{\text{cc}}$) relative to the $\delta ^{18}\text{O}$ in seawater ($\delta ^{18}\text{O}_{\text{sw}}$) correlates with water temperature.

The deeper reason that explain the chemical preference for $^{18}\text{O}$ come from a process named "equilibrium isotope fractionation", associated  to the vibrational characteristics of the light and heavy isotopes related to covalent atomic bonding.
As explained by Gussone et. al (2003):

  "Equilibrium fractionation occurs as a consequence of covalent atomic
  bonding. During molecule formation the incorporation of heavier
  isotopes is preferred because covalent atomic bonds formed with
  heavier isotopes show larger bonding energies and, hence, are more
  stable than covalent bonds formed with lighter isotopes."

There is a competing effect called "kinetic isotope fractionation", that that leads to a correlation with temperature in the opposite direction (because heavier isotopes have slower diffusion times and are slower crossing membranes), but in the case of Oxygen isotopes, its effects is overcome by equilibrium fractionation.


How do tropopause folds form and do they have any impact on synoptic scale weather? What is the process that creates a tropopause fold?  Do these features have any significant impact(s) on weather patterns or the atmosphere?

I am not not an expert in meteorology, but do study the chemistry involved in these types of events.  My understanding is that the folds in the tropopause generally occur below the front of the jet stream, when the potential vorticity is strong enough to transport stratospheric air down through the tropopause/inversion.

Please see the relevant quote from Q. J. R. Meteorol. Soc. (2004), 130, pp. 1195–1212 doi: 10.1256/qj.03.21
Convective mixing in a tropopause fold
By H. J. REID and G. VAUGHAN∗
Institute of Mathematical and Physical Sciences, University of Wales, Aberystwyth, UK

"Mixing between stratospheric and tropospheric air can occur most readily in deep
intrusions of stratospheric air into the troposphere, such as tropopause folds (Danielsen
1968). They occur because of the ageostrophic circulation at the jet entrance (Hoskins
1982) and coincide with the frontal zone beneath the jet. Deep folds can extend down to
the top of the boundary layer (Browell et al. 1987; Vaughan et al. 1994), while smaller
folds, extending only into the upper troposphere, are ubiquitous around the polar jet
stream (e.g. Vaughan et al. 2001). They also occur beneath the subtropical jet stream
(Gouget et al. 1996), where it has been suggested that mixing between the subtropical
fold and tropospheric air promotes the generation of new aerosol particles (Zahn et al.
2000). Turbulence within folds can result from shear instability beneath the jet (Pepler
et al. 1998; Hartjenstein 2000) or from convection extending up from the boundary
layer (Browning and Reynolds 1994)."

As for synoptic scale weather, I don't think a tropopause fold affects the synoptic scale weather events much, but are rather a part of the weather events.  The downward mixing of stratospheric air will introduce drier air, leading to lower humidity in the general vicinity.  Of course, ozone will be entrained into the tropopause as well, which has air quality implications.  And there are certainly feedbacks in the fold phenomena that will affect heat, radiation, and kinetic patterns... but the synoptic weather in the region is going to be more driven by the jet stream itself rather than a fold that may occur.  A meteorologist, though, might have better information on that.


What would be the phase shift and polarity of a seismic wave upon reflection What would be the phase shift and polarity of a seismic wave a) when it hit the free surface
b)when the free surface reflection goes down and hit a reflector and returned to the receiver placed on the surface.

In general, the answer is not simple as it depends on the angle of incidence of the wave and the properties of the medium.
The Zoeppritz equations are used to understand the behavior of seismic waves incident on reflectors (or the free surface). The solutions give the reflection and transmission coefficients for P and S waves, which depend on the densities and wave speeds of the lower and upper media as well as the angle upon which the wave is incident. In general, the coefficients are complex valued; the phase shift is encoded in the phase of the complex number.
I have used the Zeoppritz explorer program for this calculation.


Need help identifying rock formation so this is my first time here because I need help in identifying the features on this rock formation.
https://www.flickr.com/gp/158064920@N05/6USrY9

Thank you in advance.

in picture 11 there is erosion by water and wind.

it is sandstone and this is easily eroded by water each time it rains the water takes particles of the sandstone and moves them down the mountain.

sorry for this short and bad answer,it was a simple question so the answer is simple too.


Is there conclusive evidence for the Antarctic Circumpolar Current developing after the glaciation of Antarctica? The Antarctic Circumpolar Current (ACC) is the continuous oceanic current that encircles the Antarctic continent, as is often explained in the literature as being the cause of the onset of glaciation in Antarctica.

However, a study in 2013, in the article A potential barrier to deep Antarctic circumpolar flow until the late Miocene?, suggest that the ACC did not fully develop until the late Miocene, due to the current being blocked by a volcanic arc in the early Drake Passage, and that the ACC importance was not in the global cooling on the Eocene-Oligocene boundary, but in the intensification in the late Miocene of the glaciation of Antarctica.

Is there conclusive evidence for the Antarctic Circumpolar Current developing after the glaciation of Antarctica?

Lyle et al. (2007), prior to the paper you mention, also came up with this idea that the ACC initiated with its modern setting (i. e. with strong currents and mixing throughout the water column)  during the Late Oligocene (ca. 25 Ma), so roughly 10 Myr after the Eocene-Oligocene when the antarctic glaciation is thought to have occurred. Their evidence is based on sedimentology, specifically the presence of erosional structure associated with deep current flow. They however don't discard in this paper the idea that a surface ACC existed prior to this.

The original idea (Kennett 1977) according to which the ACC started near the Eocene-Oligocene transition was based on the observation of biogenic sedimentary facies pattern (classically siliceous south of the ACC and carbonaceous north) coupled with the observation of the opening of the Drake Passage around that time. Later, observations of the establishment of an endemic antarctic planktonic fauna during the latest Eocene (e. g. Lazarus & Caulet 1993, Lazarus et al. 2008) and measurement of Nd isotopes (Scher & Martin, 2006) at Agulhas Ridge (i. e. south of Africa) that coincides with Pacific waters values strengthened that hypothesis.

However, the idea that the antarctic glaciation was a consequence of the setting of the ACC has been somewhat challenged (De Conto & Pollard, 2003, and later Barker & Thomas, 2004) based mainly on numerical modeling, as they show that, although a developed ACC would have participated in the cooling triggering the glaciation, it is not a necessary condition for it: the glaciation could have entirely been caused by the observed drop of atmospheric $p_\mathrm{CO_2}$, even without a developed ACC.
Additionally, some of the evidences for an early setting of the ACC (namely the facies change argument) could very well be a consequence of the glaciation rather than the consequence of the ACC (Barker & Thomas, 2004).

So, as far as I see, we are at a stand-off, where we have arguments in favor of a late settling of the ACC (mostly sedimentary and tectonic arguments) and at the same time arguments in favor of an early settling (in particular paleontological and geochemical arguments) and no real reason to discard any.

References:
Barker & Thomas, 2004. Origin, signature and palaeoclimatic influence of the Antarctic Circumpolar Current. Earth-Science Reviews, 66: 143-162.
De Conto, R.M., Pollard, D., 2003. Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric $\mathrm{CO_2}$. Nature 421, 245 – 249.
Kennett, J.P., 1977. Cenozoic evolution of Antarctic glaciation, the circum-Antarctic Ocean, and their impact on global paleoclimate. Journal of Geophysical Research, 82: 3843–3860.
Lazarus, D. B. & J.-P. Caulet, 1993. Cenozoic Southern Ocean reconstructions from sedimentologic, radiolarian and other microfossil data. In J. P. Kennett and D. A. Warnke (Eds), The Antarctic Paleoenvironment: a perspective on global change. Antarctic Research Series, 60: 145-174.
Lazarus, D. B. et al., 2008. Patterns of opal and radiolarian change in the Antarctic mid-Paleogene: clues to the origin of the Southern Ocean. Micropaleontology, 54(1): 41-48.
Lyle et al., 2007. Late Oligocene initiation of the Antarctic Circumpolar Current: Evidence from the South Pacific. Geology, 35: 691-694.
Scher, H. D. & Martin, E. E.,  2006. Timing and Climatic Consequences of the Opening of Drake Passage. Science, 312: 428-430.


What are "x-cutting relationships"? This tweet by Daryl Blanks asks:

  Day 1 VTMR trip @GeologyLeics -First stop Laxford bridge! gneiss with amphibolite and granitic pegmatite intrusions - can u spot all x-cutting relationships?!

What are cross-cutting relationships in this context, and how many are there?

Cross cutting relationships.

Here's a very rough sketch. You had the black stuff, which was then cross-cut by the red intrusion (grey in the original photo), and finally intruded by the blue intrusion (pink the in the original photo).

This is the law of superposition. For more fun follow #SuperpositionPuzzle on Twitter!


Oldest to Newest Bedrock in the USA "road trip" I am supposed to design a road trip (using major highways) across North America. I have to design a route that starts with the oldest rock of Archean age and finishes with the youngest rock of Quaternary age. I have to include the following in sequence from oldest to youngest:

Archean
Proterozoic
At least two periods in the Paleozoic
Mesozoic
At least two periods in the Cenozoic

I've tried a few things (USGS, Macrostrat, OneGeology) to help me but I am really lost, can anyone recommend a possible highway route or areas to focus on?

If you were hoping for a smooth succession from Archean all the way down to Quaternary, you're going to be disappointed. Geology is messier than rocks being serenely laid down continuously through time like that. A drive from the Appalachians to the East Coast would get you everything but the Archaean rocks, although the only Proterozoic rocks would be found in the Piedmont.

The tough part is finding rocks of Archaen age. Although the North American craton contains Archaen rocks, they are only at the surface in northern Wisconsin and Minnesota (That is, if we restrict ourselves to the United States as you asked), and the Upper Peninsula of Michigan. There are a few outcrops in the Black Hills of South Dakota.

Here's a link to a large detailed geological map of the three states.

But this is just the bedrock geology. The trouble with looking for Archean age rocks in northern Wisconsin and Minnesota, of course, is that these areas are mostly covered by glacial till from recent ice ages (although you might find an Archean glacial erratic that the ice sheets carried down from Canada). Archean outcrops might be small and inaccessible.

(Source: Wikimedia commons)

Minnesota has early Archaen ("Superior" craton) rocks and a whole succession of Paleozoic. It has some Cretaceous rocks but lacks other Mesozoic/Cenozoic bedrock. North Dakota has some Jurassic age rocks in its northeastern corner.

(Source: Steven Dutch, University of Wisconsin Green Bay)
https://www.uwgb.edu/dutchs/index.htm

Wisconsin has late Archaen ("Penokean" craton) rocks and the same lack of later rocks as Minnesota. Wisconsin has a field-trip planning site with an interactive outcrop map at this link.

If you could get access to the Black Hills outcrops (uplifted bits of the "Wyoming" craton), you might be able to approximate what tou want with a trip east through South Dakota, starting in the Black Hills. I haven't found an image of South Dakota geology appropriate for embedding, but
Here is a link to a large, detailed PDF of South Dakota geology, and  here is another link to an interactive site with generalized SD geology.


Continuous lightning for over an hour; is this phenomenon common and does it have a name? A few months ago, I witnessed something off the coast of Florida that I have never seen in my life. From my apartment, from about 10PM - 12AM, I saw pretty much continuous cloud to cloud lightning. I don't really remember how many strikes a second it was, or if it was once every couple seconds, but there was never a time when there was not one or more lightning strikes in the air. I had a video but unfortunately the file is corrupted.

Is there any name of this phenomena, and how common is it?

In Norwegian we call it kornmo (grain ripener); it happens in the late summer at a distance of more than 20 km so there is no sound.

The English translation is: "sheet lightning - heat lightning - summer lightning". I am not sure if this covers the meaning we have for it in Norwegian; it is said that Thor, the god of thunder, swung his hammer over the fields to get the grain ready for harvest.

This type of lightning is at more than 20km from the viewer and often 10-20 times this distance from you. It is really beautiful to see it.

This type of lightning happens high up in the atmosphere so one needs good viewing conditions to be able to see it. I do not think it is rare in itself; what is rare is the the atmospheric conditions that allow us to see it.

I guess this does not answer your question fully so I hope others post their answers too.


Have Russian Drilling Operations in Lake Vostok Succeeded Yet? A couple of years ago the Russians began drilling through about 2km of ice to reach Lake Vostok in Antarctica. It was hoped that they would find living organisms there which had ben entombed under the ice for many millions of years. They will be gaining information from the ice cores extracted on the way, but the big discoveries are expected to come when they reach the bottom, predicted to be a vast and deep lake of liquid fresh water.

The Russians did "succeed" to reach the water at borehole 5G-2 in 2012. However, the lake water flooded into the borehole due to overpressure, and refroze. They drilled again during the next campaign to sample this refrozen lake water, but found that it was contaminated by drilling fluid (DF). From Alekhina et al. 2017:

  As expected, the level of contamination of the frozen water core with the DF constituents decreases as the depth of sampling increases. However, even in sample 3450, the deepest and cleanest of all those studied, the concentration of foreign organic compounds (16.7 mg l−1) indicates significant chemical contamination, especially for water as pristine as that which we expected to obtain from Lake Vostok [...] After the rising water in borehole 5G-2 reached the junction of the two boreholes and continued to rise in 5G-1, the drilling fluid that remained trapped in the abandoned borehole began to be displaced by the heavier water. As a result, about 1 t of DF rose from the bottom of 5G-1 to the top of the lake water column that had already filled the borehole. During this process, the rising DF mixed with, and thus contaminated, the freezing water.

Because of this contamination, any biology result from these ice cores would be invalid for the scientific community. After that, the Russians have drilled a new borehole (5G-3) where they allegedly managed to sample pure, uncontaminated water in 2015 (here is the press release from RT, which is not considered a neutral source...). However, I could not find any published results from this sample. And the same year, Russia cut Vostok project's budget... So I doubt we will see anything coming out of this in the future.

On a more positive note, scientists did manage to drill through 800 meters of Antarctica ice to reach another lake, lake Whillans, without contaminating it (they used only hot water to drill, not drilling fluid). And they did find "a diverse assemblage of bacteria and archaea". From Christner et al. 2014:

  Our data show that SLW supports a metabolically active and phylogenetically diverse ecosystem that functions in the dark at sub-zero temperatures, confirming more than a decade of circumstantial evidence regarding the presence of life beneath Antarctica’s ice sheet [...] Given the prevalence of subglacial water in Antarctica, our data from SLW lead us to contend that aquatic microbial ecosystems are common features of the subsurface environment that exists beneath the ~10$\small\mathsf{^7}$ km$\small\mathsf{^2}$/s Antarctic ice sheet.

However, there is a major difference with lake Vostok: lake Whillans is connected to a hydrological system, while lake Vostok is "closed" and has a water residence time of over 10,000 years. So if life is trapped in there, it could have evolved differently...


Noctilucent clouds and anthropogenic climate change In reading about observing noctilucent clouds, several articles about this phenomena, such as Science Daily's Spectacular 'Night-shining' Clouds Could Be A Harbinger Of Climate Change, suggest that changes in their frequency and latitudinal-occurrences may be linked to anthropogenic climate change.

Is there evidence of a link between anthropogenic climate change and changes in the frequency of noctilucent cloud occurrences?

The current answer is uncertain, especially with recent observations.

Zahn (2003) outlined that despite the possibility of noctilucent clouds (NLC) being sensitive to water vapour mixing ratios and temperature, there are 3 main concerns as to the link between the frequency of NLC occurrences and climate change:

NLC observations have shown a great variability (including in frequency) since they were first described in 1885.
There has been no significant variation in altitude
The timeframe of observing this phenomena is too short to fully delineate natural and anthropogenic forcings.

In 2007, the AIM (Aeronomy of Ice in the Mesosphere) mission was launched to explore NLC and related phenomena, in particular, the SOFIE (Solar Occultation for Ice Experiment) instrument.

In recent observations, reported in the NASA article Unexpected teleconnections in noctilucent clouds in 2014 found that the winter air temperature over the USA and Arctic stratospheric conditions have a direct link to the frequency of NLC over Antarctica (as per the image below from NASA):

Note: PMC is often used synonymously with NLC

This suggests that changes in winter temperatures on the opposing hemisphere may indeed alter the frequency of NLC occurrences.

However, other influences are being investigated, such as solar cycles, observations and research from the CAWSES II Climate and Weather of the Sun-Earth System mission have found that there appears to be a correlation between NLC frequency and solar flux, as seen in the graph below:

Image source: Project 3 PMC/NLC altitude, frequency and brightness changes related to changes in dynamics and chemical composition (Thomas et al.).

This all ties in with Zahn's 3rd doubt - more data from multiple observations are needed in order to fully determine whether or not the frequency of NLC has any relationship with climate change.

Reference

Zahn, 2003, Are Noctilucent Clouds
a "Miner's Canary" for
Global Change? EOS


Where do the electric charge carriers for the current for earth's magnetic field come from? I have some trouble trying to understand, why streams and convections in the outer liquid earth core, coriolis forces etc. would create an electric current?
Because you probably need an electric potential first and what then is the cause of the electric potential?
Is it perhaps a property of the earth mantle to have regions that are polarized?

Although Temperature boundary conditions at the mantle do affect the dynamo that sustains itself in the earth's core, it is unlikely that the dynamo's genesis came out of polarized regions in the earth's mantle.

Regardless of the manner of genesis of the core, it is now a self-sustaining dynamo where electric current creates a magnetic field which in turn generates electric current owing to rotation of the earth much as in an electric generator. If you want to read more about it in detail, I would recommend an excellent review paper by Prof. Binod Sreenivasan available at http://ceas.iisc.ernet.in/~bsreeni/currsci10.pdf


Increase Evaporation from oceans I would like to ask you about evaporation from sea water. Can you increase evaporation by spraying seawater to the air? Is there any difference compared to freshwater spraying (aerosol particles)?

Yes, you can increase evaporation by spraying the sea water as an aerosol because this increases surface area. It's the same with fresh water too, but why would you want to do it? It wouldn't have any noticeable effect on the humidity of the general area. The only useful effect that I can see concerns fresh water only. Spraying the water from a pond or small lake as fine droplets would increase the oxygen content and benefit the fish. Hot weather depletes the oxygen in the water and sometimes fish become distressed, so if you want to save your valuable coy carp it might be a good idea. In the ocean it doesn't work, the sea is too vast.


Dependence of solar irradiation through the atmosphere on Sun's altitude I want to show that the higher the Sun's altitude, the higher the solar irradiation through the atmosphere, through simple experiments. However, I don't have the instrument that measures irradiation. Is there a good approach?

I believe you could use pyranometer data at various elevations to get a non-spectral measurement of the total irradiance received at the Earth's surface.  From here: http://en.wikipedia.org/wiki/Pyranometer

  A pyranometer is a type of actinometer used to measure broadband solar irradiance on a planar surface and is a sensor that is designed to measure the solar radiation flux density (W/m2) from a field of view of 180 degrees.
  Pyranometers are frequently used in meteorology, climatology, solar energy studies and building physics. They can be seen in many meteorological stations - typically installed horizontally and next to solar panels - typically mounted with the sensor surface in the plane of the panel.

If you want something more accurate, a pyrheliometer or radiometer is used.  From http://www.esrl.noaa.gov/gmd/grad/starmeas.html

  Direct solar irradiance is the solar radiation that passes directly though the atmosphere from the sun without being scattered or absorbed by the atmosphere. Typically it is measured on a surface that is kept normal to the direction of the center of the sun's disk. That surface is held normal to the sun's position by a solar tracker. Pyrheliometers are most commonly used to measure total direct solar irradiance. The most accurate measurements of this quantity are obtained from absolute cavity radiometers which serve as calibration standards and are being increasingly used operationally.


Do rising CO2 levels change the appearance of the sky in infrared? Atmospheric carbon dioxide levels have been rising, recently passing 400 parts per million.

CO2 is a greenhouse gas; it absorbs and emits radiation in the thermal infrared range. It is, as far as I know, quite transparent in the visible range.

If we could see in the infrared range that's most affected by CO2, would the increased levels be visible? Would the sky appear darker because more infrared is being absorbed? Or perhaps brighter because more is being emitted and/or reflected? Or just a different color?

Would an infrared photograph of the sky taken, say 100 years ago in an unpopulated area look significantly different from one taken today?

Due to man made climate change, from space, the Earth currently looks a little darker in Infra-red (IR) and a little colder (longer wavelength), but the change is small and would be hard to notice without sensitive photon-counting equipment.   The earth doesn't exactly glow in steady color in IR either, it swirls and looks like a circulating, 100% cloud covered planet, which makes sense when you consider that our atmosphere, mostly the H2O and CO2 in the atmosphere is opaque to much of the infrared spectrum, so it looks a little like Venus in the IR, but not quite as dense with clouds.   What's more, you'd see seasonal variations and day/night variations, so it would be hard to notice a pretty small climate variation over that.

See YouTube video and article of the Earth in IR: Planet Earth in Infrared (Synchronized)

and the article: Our Planet Has the Vapors.

The video isn't quite right, because it's only one wavelength designed to track water-vapor not the entire IR spectrum, but I thought it was close enough to use as a starting point.

The short answer is, at least for now, the Troposphere is warming but the stratosphere is cooling and contracting, so from space, in IR, Earth is both a little smaller and a little colder/darker, at least, for now.

The longer answer is that when the Earth is in energy equilibrium, that is, not undergoing climate warming or cooling, the Earth gives back to space  the same amount energy it receives from the Sun, at least, more or less.  There's some variation, but it's largely the same.

The only way Greenhouse driven warming can happen, is for the Earth to hoard heat, and gives back less heat to space than it takes in from the sun.   When the Earth grows colder, it's the opposite, the Earth needs to return more energy to space than it takes in from the sun.  This variation doesn't have to be all that big, for example, a fraction of 1% variation over enough time can be enough to start or end an ice age, but that's the only way warming or cooling can happen.  It has to be an imbalance in Earth's energy equilibrium (technically, also, it could be a change in Earth's orbit or a solar minimum), but Earth's orbital changes take tens of thousands of years and Earth's climate changes mostly take 1,000 or so, and solar minimums are relatively weak and thought to only last a couple hundred years or so.  So the primary driver for climate change, warmer or colder, man made or natural, is the Earth hoarding or losing energy.

This doesn't have to happen entirely in infrared.  Changes in albedo/reflection can play a role too, for example, as snow cover and permanent glaciers grow, the visible light reflected off earth gradually but steadily increases resulting in the Earth giving back more energy than it takes in, leading to a cooling, sometimes an ice age, and the energy imbalance continues until the Earth is sufficiently cooled to reach a new equilibrium.

Currently, the Earth is hoarding heat and it's albedo is relatively unchanged, meaning that it's giving back less IR into space than it used to, so, in IR, the Earth looks a little bit darker than it used to before man made climate change.   Ballpark, about 1% darker in the IR.   As to changes in color, there's some variation in wavelength on both warmer and colder, but on average, slightly colder/longer wavelengths.

Estimates vary, but, ballpark, Earth is trapping roughly 2 extra watts of energy per square meter due to climate change and most of that trapped energy/heat goes into the oceans, very gradually warming them.  The lower atmosphere is more effectively absorbing and reflecting thermal radiation from the surface so less IR is reaching the upper atmosphere and less is going into space, so while the surface of the Earth does grow brighter in IR what is mostly seen from space is the cooling upper atmosphere.

Over time, as the Earth's surface and lower atmosphere grows warmer, it will emit more IR and the upper atmosphere will, in time, give back into space just as much IR as it used to before climate change, and probably more, but that will take 100 years or so, perhaps longer.   Also, as Earth's ice cover drops and it's oceans rise, Earth's albedo will mean less visible light is being reflected into space, so the thermal radiation will need to increase to make up for that.  So, in a century or two, the warmer Earth should glow brighter in IR and on average, a bit warmer/shorter wavelength, too.   How much will depend mostly on how much ice cover melts, but we're probably not looking at more than maybe a 1% increase, 2% tops.

For some numbers and pretty charts, see here.

Earth is hit by about 340–341 watts per square meter of energy from the sun, that's on average, summer/winter, equator/poll and night/day.  Direct sunlight on a perpendicular surface to the Sun's rays is about 4 times that.

Of that 340–341 watts, currently about 29% or 100 watts is directly reflected back into space as mostly visible light.  The remaining 240 or so watts (per m2) leaves the Earth in the form of infra-red or thermal radiation.

About 170 watts of that 240 comes from the high atmosphere.  About 30 from cloud tops and about 40 watts from surface radiation.   While the Earth's surface does grow warmer during climate change and brighter in IR, 90% of that gets re-absorbed by or reflected back by the atmosphere and only 10% reaches space, so the added brightness you might expect to see off the warmer surface makes up only a small part of the total.

If we say the Earth's surface has warmed about 0.8 °C, say from 288K to 288.8K, using the 4th power rule, that should emits about 1% more thermal energy than it did before climate change, but 1% of 40 watts comes to about 0.4 watts per square meter increase, and perhaps decreased overall due to the more opaque atmosphere with higher CO2.   The biggest factor for the earth's IR image is the temperature of the upper atmosphere.

As an FYI, there are other imbalances to the heat in/heat out equilibrium equation, for example, a really big volcano might release enough heat into the surface to unbalance the ratio temporarily and following a big volcano there's an increase in the amount of light reflected off earth which leads to a relatively rapid but temporary cooling.   A large enough meteor impact could also create a variation, and the Earth is hit by solar wind and cosmic rays and it loses some heat in very fast moving particles that exceed escape velocity (mostly hydrogen from water molecules).  The Earth also has internal heat coming from it's warm interior, which means the Earth does emit a bit more heat than it receives overall, at least on average, which does throw off the expected equilibrium a little bit.

And, final and curious sidebar, you might ask, how the Earth's surface can emit 400 watts per square meter, which is more energy than Earth receives from the sun.  That has nothing to do with your question though, but it's a curious statistic I think.   It's because our atmosphere acts like a blanket, warming the Earth overall.

Hope that wasn't tl;dr.


Whitecapping in ocean surface waves Even though the physics of wave breaking for ocean surface waves may not be well understood, what wave breaking is and what it looks like is no mystery to the average beach-goer. However, I am confused to as what "whitecapping" is, in the context of "whitecapping dissipation" of waves that appears in literature.

What is whitecapping? Is it the white "stuff" that is created when a wave break?
If so, what causes the white "stuff"? Is it the same as "foam", a term that is found in the literature as well?
Are the terms "whitecapping" and "wave breaking" synonymously used? Are they in fact one and the same?

Relevant references would also be appreciated.

Whitecapping refers to the steepness-induced wave dissipation in deep water during which some air is entrained into the near-surface water, forming an emulsion of water and air bubbles (foam) that appears white. It occurs when the velocity of individual water particles near the wave crest exceed the phase speed of the wave, causing the front face of the wave to become too steep and "break". Steeper and more vigorous breakers are more efficient at entraining air bubbles into the water column, and they generate more foam.
Whitecapping is an essential process for air-sea gas exchange.

In the wave modeling community, because current spectral wave prediction models do not resolve air entrainment by the breaking waves, we use the term "whitecapping" to describe all steepness-induced deep-water wave dissipation. For example, see Hasselmann (1974).

Waves also break due to shoaling as they enter shallow water, and these are usually referred to as plunging breakers. While plunging breakers without doubt generate a lot of foam, we don't use the term whitecapping to describe them. Thus, whitecapping is a specific kind of wave breaking, as described in the first paragraph.

See a comprehensive review by Cavaleri et al. (2007) for a description of all the processes represented by current wave models.


What are the challenges in predicting lithology directly from acoustic impedance? Seismic inversion methods help to visualize the subsurface layers of the earth in terms of petrophysical properties (e.g. impedance). Still some geophysicists use the final inverted impedance model in company with various seismic attributes (like amplitude envelope, instantaneous frequency, and phase) to predict lithology or paleogeographic features.

If seismic inversion transforms the reflection amplitude into acoustic impedance (lithology) than why can't it be used to predict the lithology independently?

Yes, lithology interpretation/classification directly from seismic inversion products is something people do.  I've seen it work very well in oil and  gas exploration and development of fields.

I personally think that there are two main challenges involved in predicting lithology from seismic inversion impedances. It would be a bit of a cop out to say that the whole inversion and lithology prediction process is challenging, so I won't, even though it is. So, assuming that you achieve good inversion results, by which I mean that your inversion synthetics match input seismic angle stacks and your inversion products (estimated elastic properties) match calibration points (upscaled well logs), I think that the challenges are the uncertainties associated with the:

ability to discriminate rock types in study area, and
low-frequency model

Below I go into a little more detail regarding these two factors. Just remember that I'm talking about lithology prediction from an absolute inversion. Also, I will talk about "elastic properties" a lot, by which I mean the P-impedance, S-impedance and density, or their derivatives like Lambda, Mu and Poisson's ratio if you're that way inclined.

Discrimination of rock types

Before you attempt to predict lithologies from seismic inversion results, you need to know the expected elastic properties of the rocks in your study area. If the various rock types in your study area have the exact same elastic properties, distinguishing them from inversion products is going to be impossible, no matter how good your inversion is. To make a good lithology prediction you need to know the elastic properties of the measured or predicted rocks in your study area. If the rocks have similar (e.g. overlapping) rock properties you need to account for this uncertainty in your lithology prediction.

For example, say you are targeting gas and the predicted reservoir is sandstone. Does a gas filled sand have different elastic properties to a brine filled sand? What about from the sealing shale? What are the expected range of elastic properties for these rocks? By doing forward modelling experiments (e.g. Gassman fluid substitution and/or lithology mixing) you could answer questions that address risk-cases like: what are the expected elastic properties of a low saturation gas sand or a high porosity brine sand? If high porosity brine sands and gas-sands have similar/overlapping elastic properties and I end up predicting a gas-sand from my inversion, what is the probability that the gas-sand is 'real'?

(source)

The above image shows the elastic properties for three lithologies: sandstone, shale and limestone, in terms of P-wave velocity** (Vp) and the ratio of P- to S- velocity (Vp/Vs). Provided your inversion results are accurate, these lithologies would be distinguishable because their property populations do not overlap.

The mean P-wave velocity (Vp) for the limestone is approximately 5800 m/s. But what if the mean Vp was 4000 m/s? The limestone population would then overlap with the shale, meaning that it would be difficult to discriminate between the two lithologies from your inversion results with great confidence.

A thorough rock physics study is necessary before attempting any seismic inversion project to understand the elastic properties of your rocks and to ensure that your target rocks are distinguishable. If your rocks have sufficiently different elastic properties then lithology prediction from seismic inversion is feasible.  You can use your rock physics study to define how your lithologies can be classified from the inversion results (e.g. depth dependent probability density functions of P-impedance versus Vp/Vs for each lithology/fluid type).

** Vp can only be estimated from seismic inversion if you also get a good density result, which is uncommon. I'd prefer it if this graph showed P-impedance (Vp * density), but beggars can't be choosers.

Low-frequency model

So, you know the elastic properties of the rocks in your study area and you know that they can be theoretically discriminated, and you want to predict lithologies from seismic inversion results? I think that the next challenge in lithology prediction are the uncertainties associated with the low-frequency model, because the low-frequency model:

determines the absolute value of estimated elastic properties

so has a very big influence on the predicted lithology

is built by interpolating/extrapolating sparse data (e.g. well logs or rock physics trends)

i.e. a lot of the spatial variation of the low-frequency model is not measured

A low-frequency model is used to fill in the low-frequency elastic property gap not measured by seismic data, and allow absolute elastic properties to be estimated. For conventional marine seismic with a bandwidth of, say, 10-60Hz, the low-frequency model will provide the inversion with elastic properties of the study area between 0-10Hz (see picture below). What kind of geological information is captured within this low-frequency range? Large scale geological changes, like compaction trends, or the elastic property changes associated with low-order sequence stratigraphy cycles.

(source)

Without a low-frequency model, inversion can only provide the relative impedances of two layers; this is called a relative inversion. Inversion with a low-frequency model is called an absolute inversion, and it seeks to estimate the total elastic property of the layer, independent of impedance of above/below layers. If you get the low-frequency model wrong, your absolute elastic properties will also be wrong and therefore you will predict incorrect lithologies.

A low-frequency model can be built by extrapolating low-pass filtered well logs (P- and S-sonic and density), rock physics trends, etc throughout the study area, creating a 3D distribution of elastic properties. How can you be sure that you have a good low-frequency model?

Blind well testing can give you confidence in your model.
Use a robust method for extrapolating your well logs or rock physics trends.
Even better would be to improve the low-frequencies of your seismic data through deghosting, to reduce the influence of the low-frequency model on your final interpretation.

Final thoughts

You can create different criteria for classifying lithologies, run an absolute inversion and predict lithology fairly easily these days. But if you don't have confidence in your ability to discriminate between different rock types or you're not sure if your estimated absolute elastic properties are correct, you cannot be sure that the lithologies you have predicted are useful. So what to do? Firstly you need to do a really good rock physics study first to understand the elastic properties of the rocks, and rocks you predict to be present, in your study area. Secondly put in a lot of effort to making sure you have a robust low-frequency model.


Methane remote sensing? I'm trying to compile a list of remote sensing (Earth observing satellite) instruments capable of detecting methane in the atmosphere or near surface of Earth. After some search I have found:

Japanese Greenhouse gases observing satellite (GOSAT), launched 2009, measuring CO2 and CH4.
European Sentinel 5 and Sentinel 5 Precursor, measuring wide variety of atmospheric contents, 5P to be launched in 2016.
Beginning private company GHGSAT, measuring greenhouse gas (GHG) and air quality gas (AQG) emissions.

Are there any other satellites?

I found a great paper named Remote Sensing of Particulate Pollution from Space: Have We Reached the Promised Land? and collected some remote sensing instruments doing CH4 measurement in the chart below.

It contains the information about the satellite, orbit types, instrument and the data time-range.

Satellite       Orbit       Instrument    Years

Nimbus-7        Polar       SAMS          1978-1983
UARS            L56.9       CLAES         1991-1993
UARS            L56.9       HALOE         1991-2005
ADEOS           PS          IMG           1996-1997
Terra           PS          MOPITT        1999-
AQUA            PS          AIRS          2002-
AURA            PS          HRDLS         2003-
Envisat         PS          SCIAMACHY     2007-


How is abundance of elements in the Earth's crust estimated? In an quiz app I surprisingly learned that aluminium has a larger abundance then iron. When researching this on Wikipedia, I found this article,
which also had the comment:

  Note that numbers are estimates, and they will vary depending on source and method of estimation.

Now I wonder what methods exist and were used to estimate this? The only idea I had, that they took probes from different places and averaged the result, but that sounds like a very vague guess, because you would need a lot of probes from different places and depths (up to 50km deep), so I guess they used another method to estimate this. If somebody knows how the numbers are estimated, can he also say how accurate this estimations are?

can he also say how accurate this estimations are?

Let's begin by saying that the crust is heterogeneous. There is no one "composition of the crust". If you go to a place rich with limestones, then Ca and C are the most common elements (excluding O), if you go to a place rich with granites then Si and Al are the most common. Go to places with abundant basalt and you get lots of Mg. That means that the accuracy is irrelevant. If you have the average of an entire continent, there is no one rock or one area that has this composition. And if there is, it is by pure coincidence.

what methods exist and were used to estimate this?

One way to find an average is to know how much of each rock you got (which is easy if you have geological maps of everything) and what's the composition of each rock. However, there is a more clever way of doing it. You can sample sediments. Take major rivers that have huge areas in their drainage basin. These rivers transport the fragments of those rocks as sediments and deposit them in one place. All you have to do is to analyse those sediments. Surprisingly (or not), when you actually do this for rivers in Europe, America, Australia, etc, the composition of them turns out to be almost identical! So that's one way to derive an approximation.

up to 50km deep

You can't directly probe that deep. Our deepest drill hole was just over 10 km, and that was almost impossible (and extremely expensive to do). Fortunately, we have an indirect method of sampling rocks from 50 km and even deeper. Sometimes magma erupted from depth tears away pieces of rock from the walls of the conduit. This rock is then embedded in in the volcanic rock. Here's an example:

Source: James St. John, flickr
You have the black basalt and in it a rock that came from several tens of km below the surface (or more). By collecting a lot of those deep-seated rocks from volcanic rocks, we can get a good idea of what the lower crust and the upper mantle look like.


What is the best way to split strike and dip data on the image provided into "domains" in order to interpret folding on a stereonet? Link to the original image: https://postimg.cc/v4bRqxxR
I believe this image represents two folds which are overturned and plunging. I would like to analyse these folds on a stereonet, but I am unsure how to split the data.
I have annotated the image (link below) to show my thoughts on splitting the data into domains. What I am finding confusing is the relation of the data in the "northern domain" to the "southern domain".
Link to annotated image: https://postimg.cc/Wtc7JBD3
Any advise on how to split the data into domains would be helpful and reassuring in my understanding.

I think you may have more than 2 domain based on satellite image. Maybe you have three limbs of folds (green) and a fault (red). Please consider this interpretation carefully, I don't know where your study area is, what are its geologic units and structures and plutonic intrusions may deform other rocks (sedimentary, metamorphic and vulcanic), which its satelite images will look like your area, specially in old terrain (Archean ones as part of Brazil, Australia, Canada, United States, Russia, Sweden, among others).

I recommend:

Try to draw the morphostructural lineaments in the topographic raster of your area. You should use the shadow relief to help you in this task. Then, based on its directions, you can have a ideia about the spacial distribution of the domains.
The relief texture (I don't know if these are right words) can also be used to define domains. The roughness of the mountain terrain is the highest in your area.
The units with similar ages as Paleoproterozoic ones and Neoproterozoic ones define two domains, at least. It can also improve or subdivided your domains.
Plot all data of a specific structure* in some stereogram program as Stereonet, OpenStereo or Georient. The Georient has an advantage, you can enter the data by clipboard. The similar structures will be plotted nearby. Based on the clustering, you may improve the domain boundaries.

*Please, do not plot foliation (Sn) and bedding (S0) in the same stereogram. Each structure should be interpretate individually.
About stereogram interpretation, you should see the book of Marshak & Mitra (1988) that show excelent description about this.

Marshak, S. & Mitra, G. 1988. Basic Methods of Structural Geology. Enlewwod Cliffs, Prentice Hall

However, the best way is observed the relationship between foliations of different order (Sn and Sn+1) and/or foliation and bedding (Sn X S0) in field. This relationship will indicate the vergence. And then, you must proceed to the interpretation of stereogram.
I don't think there are easy way to split. You should to do this manually. I commonly import the data to Excel and classify by domains following the dip direction (or strike), location and, more important, vergence.
And, please, read about the geology of your area before you start. This help a lot. I hope that I could help you. I have listen what I wrote to you several times from my teachers during my graduation :). Best luck in your studies.


How are daily precipitation totals computed? I would like to use ASOS data from Iowa State University   to compute daily rainfall totals for specific locations. Using ASOS, I am unable to match the official NWS totals. I am assuming that the definition of a day is midnight to midnight, local time.

For example: KLGA had a record rainfall total of 3.33"  on June 7, 2013. An excerpt of the ASOS data covering June 7 is below. The "D" and "H" columns are EDT. It appears that rainfall totals are cumulative and reset hourly at 51 minutes (see hours 12 and 13 EDT for example). But I am unsure how to interpret certain cases. What do I do with hour 21, which reports 0.21" at 36 minutes, 0 at 48 minutes, and 0.24" at 49 minutes. Does that 0 denote a reset prior to 51 minutes, implying a total of 0.45" for that hour? Or does it indicate something else, such as a temporary cessation?

The general questions are: a) how does one parse the p01i column, and b) should it be possible to use ASOS precipitation data to match official NWS totals? Thanks!

Excerpt from ASOS data:

GMT                     M   D    H   M  p01i
...
2013-06-07T16:23:00Z    6   7   12  23  0.11
2013-06-07T16:43:00Z    6   7   12  43  0.19
2013-06-07T16:51:00Z    6   7   12  51  0.21
2013-06-07T17:35:00Z    6   7   13  35  0.18
2013-06-07T17:51:00Z    6   7   13  51  0.22
...
2013-06-08T01:16:00Z    6   7   21  16  0.18
2013-06-08T01:29:00Z    6   7   21  29  0.21
2013-06-08T01:36:00Z    6   7   21  36  0.21
2013-06-08T01:48:00Z    6   7   21  48  0
2013-06-08T01:49:00Z    6   7   21  49  0.24
2013-06-08T02:47:00Z    6   7   22  47  0.22
2013-06-08T02:51:00Z    6   7   22  51  0.22
2013-06-08T03:51:00Z    6   7   23  51  0.11
2013-06-08T03:58:00Z    6   7   23  58  0

Edit: See below. Note that the value of p01i at 6:59 (0.01") is less than that at 6:51 (0.05"), and greater than that at 7:40 (0"), which in turn is less than that at 7:51 (0.09"). What exactly is being reported here?

GMT                     M   D   H    M  p01i
2013-06-07T10:51:00Z    6   7   6   51  0.05
2013-06-07T10:59:00Z    6   7   6   59  0.01
2013-06-07T11:40:00Z    6   7   7   40  0
2013-06-07T11:51:00Z    6   7   7   51  0.09

Edit #2: @JeopardyTempest  confirms the importance of 51 minutes past the hour. I have an algorithm that (almost!) works. Assume:

The day is measured from midnight to midnight local time, without a DST adjustment. So in June, LGA remains at -0500.
Precipitation totals are accumulated to 51 minutes each hour

The official daily 2013 rainfall totals for June 2, 3, 6, and 7 are 0.11, 0.96, 0.10, 3.33, 0.79. Using the algorithm above with the ASOS data for the same days yields 0.11, 0.96, 0.10, 3.32, 0.80.

Typical synoptic (hourly) obs come in about 51 past the hour (sometimes a couple minutes off).  The other reports you're seeing are generally subops (SPECIs) which generally only report precip since the last ob given, but the total of which should always be reflected in the hourly.

So for 2136/2148/2149 timed obshour... you just use the 0.24 from 2149, and it should include the others in it (so skip the others that would lead to double-counting).

On the other hand, the 659 ob being smaller than the 651 ob makes sense... as 659 is in the NEW hour... so would be reflected in the 751 ob (which is indeed higher).

I didn't get a chance to look too closely, but looks like all of these are unfortunately altered forms of the data.  I believe typical full data should have METAR or SPECI in it to indicate which obs you want?

But no big deal, if you look back at the rawer-looking data you gave, looks like you can find which ones you want by looking for the ones with SLP reported right about the end.  Or, even better, just look for the 6**** fields right about the end, which are the 6 hour total precipitation.  Just add the four of those up, and you'll have the daily total.

If you're trying to accomplish all this in Excel, some formulas could be worked up to automatically take what you need from the day's data, or you could use a regex in any of the variety of online regex testers.  Or writing some sort of script could save a lot of time if you're downloading a lot of data.  But the rawer data is often safer and more easy to work with.

I think I used a page like this for more info back in the day when I had to do it.


Barotropic vorticity equation I came across the barotropic vorticity equation (below) in Sakamoto (2002) and I cannot figure it out. The notation is not clear to me. How can it be derived from the Navier-Stokes equation?

$$ \beta\psi_x=\frac{\tau_x^y-\tau_y^x}{\rho_0H}-r\zeta+A_H\nabla^2\zeta-\frac{f_0}{H}w_D $$

where

$\psi$ is the streamfunction

$\nabla$ is the horizontal gradient operator

$\zeta=\nabla^2\psi$ is the vertical component of relative vorticity

$(\tau_x,\tau_y)$ is the zonal wind stress

$f=f_0+\beta y$ is the Coriolis parameter

$\rho_0$ is the mean density

$H$ is the depth of the model ocean

$r$ is the inverse time scale for vorticity decay by bottom friction

$A_H$ is a horizontal eddy viscosity

$w_D$ is not explained in this paper.

This equation is a form of the Shallow-water equations, which are derived from Navier-Stokes in the incompressible limit and the vertical direction is integrated out.

One then takes the equation for the vorticity (which has only one component then) from the Shallow-water equations. The vorticity is split into planetary vorticity, as is the Coriolis term with the $\beta$-sheet-approximation.

Additionally it looks like they're using a velocity streamfunction.


Making Sense of Coldwater Ocean Currents The basic understanding of ocean currents is that warm currents carry moisture whereas cold currents carry nutrients.  This is why some scientists believe in the connection between the Arctic ice caps and the warm Gulf Stream and the frigid Humboldt and Benguela currents turning the tropical lands of Chile and Namibia bone-dry.

With that, there are some confusions with the workings of coldwater ocean currents.  Antarctica is surrounded by the Antarctic Circumpolar Current, a coldwater current, yet it is covered in mile after mile of frozen water.  The Pacific coast of North America is nurtured by coldwater currents, yet we see temperate rainforests.

So what's going on?  Why are there habitats that require a lot of moisture near coldwater ocean currents that can't carry that much?

The currents run counterclockwise. That's why the Humboldt Current cools the Pacific coast of South America, because the water is coming from the "six o'clock" position in the Antarctica. But in the Northern Hemisphere, the "six o'clock" position is warm water near the equator, which warms Oregon and Washington.

In the northern hemisphere, the cold Labrador current cools land to its west. That's because the water is coming from the "12 o'clock position near the Arctic. On the other hand, the west coast benefits from warm water currents running in a counterclockwise direction. That's because the "6 'oclock" position in the northern hemisphere is near the tropics, which brings warm water to Washington and Oregon at the "2-3 o'clock" position.

All other things being equal, colder air carries less moisture than warm air, and land near cold water currents is dryer than land near warm water currents.


What sort of geological features would you look for to find copper? What sort of geological features would you look for to find this precious resource?

Two types, low volume high concentrations, and vice versa. For high concentrations start with gravity mapping, and check out high Bouguer anomalies. Generally speaking basic and intermediate igneous, and metamorphic terraines are a better bet than sedimentary terrains - though circulating groundwaters and water-rock interaction can produce local copper shows almost anywhere. Regional mapping of surface water and sediment chemistry should highlight the areas worth exploring. Search for oxidized copper minerals like malachite, azurite, brochantite, etc.

In Australia one of the richest copper mining areas was famously discovered by a dog chasing a rabbit into its' hole. The dog owner found malachite in the excavated spoil of the rabbit warren.

On the big industrial scale, (high volume, low grade) look for copper porphyry of Andean type, which should be obvious from general geological mapping.

A crude but novel way of exploring is to dump bits of scrap iron in local streams, then check them out a few weeks/months later to see if iron-copper exchange has occurred.


Horizon letter for bedrock What is the official letter for the bedrock soil horizon? I know that the letters to represent the A, B, and C horizons are widespread, but the fourth layer (bedrock) is referred to with different names. Some call it the D-Horizon, some the R-Horizon, and some just say bedrock. Is there any standard or official term, and if so, what is it?

According to Wikipedia and Nature.com, "R Horizon" is the official letter for bedrock.

CAPTION: Example soil with designations that communicate the soil formation processes occurring in each horizon.


How far up do you have to go before most of the atmosphere is below you? If I wanted to make an air shield around the earth to contain exactly half the planet's atmosphere (by mass), how far above sea level would I have to build it?

It's slightly complicated to me because you have to take into consideration the change in pressure as well as the geometric growth of the volume of a sphere as you increase the radius.

Thank you.

Roughly 5.5 km, although the exact value depends on the weather.  All you need to do is to solve the hydrostatic equation and find the height at which the pressure is 50% of the height at sea level (or perhaps average elevation of Earth surface instead of sea level).  Any answer actually performing the calculation deserves upvotes more than I do ;-)

See, for example, Thickness of Earth's Atmosphere:

  Using boundary layer theory as an example, we can define the thickness of the atmosphere to be the altitude that encloses 99 percent of the total mass of the atmosphere. Looking at the chart, we can see that this seems to be about 31 kilometers. The halfway point, where half the mass of the atmosphere is below and half above occurs at 5.5 kilometers. Another interesting fact is that when you are cruising in a modern jet transport at 11 kilometers, you are above 77.5 percent of the atmosphere. The total mass of the atmosphere turns out to be 5.3 zettagrams (5.3 Zg).

I'm not entirely sure how the calculations in the linked article are performed, but I recall calculating this as a student and ending up somewhere around 5 km, so it sounds right.  Simple calculations often assume an isothermal atmosphere, which is of course not accurate, but good enough if you don't need to know the answer more precisely than within several hundred metre.

This page at Stanford reaches the same number.


Terrain correction for gravity data using Nagy, 1973 I am working with an algorithm for terrain correction of gravity data. I am using Nagy, 1973. However, I could not get the results I need.

So, this is the problem. I have this function

where x,y,z are the coordinates of a prism corner.
the equation 2 is the numerical method, where $S(xi) =  -1 for x< 0,  1 for x > 0$ and $0$ for $x=0$. same applies $y$
but $F(x,y,z) = 0$ when $z = 0$
The equation 3 gives the $z$ component of the gravitational attraction

It looks pretty simple to implement but I can't get a consitent result.

then, I know that I have to multiply by $G$ the gravitational constant and the density of the earth.

I have the following coordinates

$(x1,x2) = (-500,500)$
$(y1,y2) = (500,1500)$
$(z1,z2) = (500,1500)$

The earth density is $1000\ kg/m^3$. I should get a result of $2.360\ miliGals$. But I didn't.

I attach the code in python, Anyone with an answer?

def nagy1973(x, y, z):
from math import log, sqrt, atan

# computes the total gravitational atraction of a rightrectangular Prism
# input x =  tuple with x1 and x2 coordinates
#       y =  tuple with y1 and y2 coordinates
#       z =  tuple with z1 and z2 coordinates
# output GravCorrect = a terrain correction for a right rectangular prims.
def Fz(a,b,c):
    # this is the numerical method for the gravitational
    # attraction over the Z component
    # input a = x
    #       b = y
    #       b = z
    # output F = GravCorrect    terrain correction
    a = abs(a)
    b = abs(b)
    c = abs(c)
    r = sqrt(a**2 + b**2 + c**2)
    r0 = sqrt(a**2 + b**2)

    GravCorrect = a * log((b+r0)/(b+r)) + b * log((a + r0)/(a + r)) + c* atan(a*b/(c*r))
    return GravCorrect

GravCorrAcum = 0 # this gives total z component of a prism
for k in range(1, 3):

    for j in range(1, len(y)+1):

        for i in range(1, len(x)+1):

            if x[i-1] < 0:
                sgnX = -1
            elif x[i-1] == 0:
                sgnX = 0
            else:
                sgnX = 1

            if y[j-1] < 0:
                sgnY = -1
            elif y[j-1] == 0:
                sgnY = 0
            else:
                sgnY = 1

            sgnIJK = (-1)**(i+j+k)

            RealSign = sgnIJK * sgnX * sgnY

            #print(sgnIJK, sgnX, sgnY, RealSign)

            GravCorr = Fz(x[i-1], y[j-1], z[k-1])

            FinalFz =  RealSign * GravCorr

            GravCorrAcum += FinalFz*6.67408e-11*1000*100000 #multiply by the gravitational constant
                                                            #density 1000 kg/m3,100000 conversion constant to miligals
                                                            # output miligals
           # print  FinalFz, GravCorrAcum

return GravCorrAcum

Call the function:

x= (-500, 500)
y = (500, 1500)
z = (500, 1500)
FZ1 = nagy1973(x, y, z)
print FZ1

Instead of the Nagy prism formula, I suggest you to use the formula quoted in the following paper:

  B. Banerjee, S.P. Das Gupta (1977):
  "Gravitational attraction of a rectangular parallelepiped"
  Geophysics, vol. 42, n. 5, pp. 1053-1055
  doi: 10.1190/1.1440766

I wrote, in Fortran, a TC program based on that formula. If you read the paper you better understand why the algorithm proposed by Banerjee-das Gupta is easier to program, but in any case, I would like to point out some features that are described at the pp. 1055:

1)"...our expression contains only a tan inverse term facilitating computer work in all respects".

2)"The argument of the tan inverse term of our expression is simpler than the argument of sin inverse term in Nagy’s formula"...

3)"...in the Nagy's formula when the signs of x1 and x2, for example, are opposite (i.e., the y-axis is crossed), the prism is divided in two, and the integral is separately evaluated from 0 to x1, and 0 to x2, and finally they are added. In this process, some logical control is required in programming his formula. But from our expression (3), it easily follows that separation of the r.h.s. term into two is not required; similarly, when the x-axis is crossed or both x- and y-axes are crossed. This is because the signs of x’s and y’s are automatically taken cam of in our subroutine".

The formula to be programmed is quoted at pp. 1055 n° 3), but in any case I could provide you the code (in Fortran) that I wrote 30 years ago writing to palmieri.gravimetry@libero.it

Kind regards and best wishes to all, Francesco


Why is helium only found in wells mixed with natural gas? Does all commercially available helium come from natural gas wells?
Is it theoretically possible to have a pure helium well?

Helium is produced by the radioactive decay of primordial uranium and thorium.  It should not be strongly associated with non-primordial 'fossil' hydrocarbons.

Helium is produced by the radioactive decay of primordial uranium and thorium. It should not be strongly associated with non-primordial 'fossil' hydrocarbons.

The first statement is correct. The second is not. There are several reasons that helium should be strongly associated with non-primordial hydrocarbons. Both are fluids found predominately in the crust due to the highly lithophilic nature of uranium and thorium in the case of helium and the fossil origin in the case of hydrocarbons. Being a gas, helium is somewhat soluble in hydrocarbons. Like most gases, helium solubility in hydrocarbons increases with pressure. Unlike many gases, helium solubility in hydrocarbons increases with temperature.

Trapped hydrocarbons thusly act as a trap for helium. In places where hydrocarbons aren't present, helium might be trapped by some capping rock, or it might escape through the tiniest of pores. As the smallest gas (even molecular hydrogen is larger), helium is wont to find a way to escape to the surface -- unless temporarily trapped by a trapped liquid.


'Peak water' in the Ogallala Aquifer, USA? According to the United States Geological Survey Report (USGS) Groundwater Depletion in the United States (1900–2008), the Ogallala Aquifer (or High Plains Aquifer) is a vital source of groundwater for a major agricultural region in the United States.

In the USGS report, there is evidence of significant and ongoing depletion of the aquifer.  From the USGS report, the total depletion at the end of 2008 is about 341 km$^3$ and the rate of depletion at the time of writing the report was "continuing as high a rate as ever".

The Ogallala Aquifer is labelled as number 13, in the above USGS map.

Given the effects of climate change on aquifer recharge and drought cycles, coupled with the human depletion of the aquifer, is there any evidence that 'peak-water' could occur in the Ogallala Aquifer?

By 'peak-water', I am referring to a point where it becomes practically and economically impossible to pump water from the aquifer

This question is related to Recharge a dry aquifer?

It is definitely possible to completely drain an aquifer.  However, as the potentiometric surface (water level) in the aquifer drops, extraction of water becomes less economical, but the perceived value of the water increases. It is possible to apply "unconventional" drilling techniques like directional drilling and fracking to extract groundwater. You could potentially get philosophical and argue that there is a point where the aquifer no longer meets the definition of an aquifer.

Your question is really a matter of scale.  The USGS Principal aquifer map depicts the Ogallala aquifer as a complete and continuous hydrostratigraphic unit because that map is a national-scale map.  It would be more appropriate to call it the Ogallala aquifer system, to remove implications that it is one continuous, well-connected aquifer system that runs across several states.  It is much more likely that this aquifer is a group of hydrostratigraphic units separated by faults, confining units, and lateral discontinuities.  Because of this horizontal heterogeneity and because pumping influence such as cones of depression is generally localized, you could potentially completely deplete some portion of the aquifer system while leaving other portions with some water.

In terms of the water budget, as you have shown in the above USGS figure, discharge is already outpacing recharge. In their Public Information Circular 18, the Kansas Geological Survey projects that some parts of the aquifer system will be depleted within as soon as 25 years, while other regions have a life expectancy of between 50 and 200 years. In an interview with the Lubbock Avalanche-Journal, the Center for Geospatial Technology at Texas Tech said that some regions of the aquifer in Texas only have 15 years of water left.

As water is removed from an aquifer, the pressure that water exerts to help hold up the aquifer skeleton is reduced.  The reduction in water pressure can cause deformation in the aquifer. Some component of this deformation is recoverable (elastic). However, if the stresses on the aquifer exceed that of what the dewatered material can handle, then the dewatered aquifer/confining layers could undergo permanent compaction, leading to a decreased ability of the aquifer to store water. See USGS Circular 1182 for more information on these concepts.

While the technology exists to implement artificial recharge, either via injection well or infiltration ponds/galleries, this technique requires adequate geochemical conditions and an appropriate recharge source. Once an aquifer system is stressed to the point of compaction, its storage is permanently decreases, reducing its value as a candidate for artificial recharge.  For more information on artificial recharge, see the USGS website.


"New" cloud types: Can they be used as markers for climate change observations? This question was originally posted on Physics SE, (now deleted) but I think this community is a better fit.

This article "New" type of Clouds, reports that a revision to the  International Cloud Atlas will include 12 extra examples of cloud shapes.

  This time around 12 new terms have been added. The best known of these is asperitas, meaning rough-like in Latin, as the clouds can look like the tossing of the waves at sea when viewed from below.

I am aware that these are not new cloud types per se, rather the article is referring to a reclassification system.

These cloud types in all probability have been in existence for a long time, and it is due to the increasing use of cameras on smartphones that has contributed to their new prominence in the Atlas. The article I cite above includes references to the well known jet contrails, but does not ascribe any more significance to these cloud classifications than that.

  In terms of the way the WMO classifies clouds, they have also added one new "species" - the volutus, or roll-cloud, a low horizontal tube-shaped cloud mass that appears to roll about a horizontal axis.

My question, promoted by this reclassification of existing cloud types,  is: could new cloud types be associated with human activity and, (a  tenuous connection I admit), could we use the amount of these putative new cloud types to act as a crude marker of our impact on the current atmospheric environment?

I would stress that the website of the International Cloud Atlas makes no obvious, at least on initial reading, link to my question above.

I am aware of the  Penn State Jet Trail Research regarding jet trails, in particular their absence from the atmosphere following the 9/11 attacks and subsequent temporary flight ban.

My answer is no. The reclassification of clouds is not affected by climate change. It is more of our understanding of how they work, formation mechanisms, etc. Cloud classification can generally be broken down into altitude and shape (cirrus-type, cumulus-type, and stratus-type). The subtypes of those describe the behavior, and may be combinations of types (such as cirrostratus, pyrocumulus and cumulonimbus). There are other types, such as the new asperitas cloud (formed by gravity waves), the Kelvin-Helmholtz instability cloud (formed by the Kelvin-Helmholtz instability), contrails (formed by jet exhaust), fog (formed by either advection or radiation), etc.

That is not to say that clouds don't affect climate. For example, cirrus clouds, and other high clouds, are optically thick, preventing the low temperature from dropping. It has been debated what the net effect clouds have on the environment, newer research seems to indicate net warming (see latest IPCC report), despite the traditional thought being cooling. Being that water vapor is a greenhouse gas with generally greater concentrations than the famed CO$_2$, it is extremely important to consider in climate discussion.


Making a local geological field trip an interesting and educational event for children? I have no expertise in geology or earth science, but I would like to do a "field trip" with my home-schooled young children (under age 10) where I could teach them about geology from a hands-on perspective.

What could I do on this field trip that would make this event memorable and special for the children, that would not be possible just at home at the dining table?

If you are unfamiliar with small children, here are some outside things they like to do that I think may be compatible with this kind of event:

digging (and hopefully finding pretty rocks, crystals, fossils, etc)
hiking, walking, and running
exploring "the wild"
caves
creatures

I had a few ideas, but I don't know if any of them are practical or possible, or where I could gain the skills to make these really happen?

Use our knowledge of geology to predict what kind of rocks we'd find if we dug in one place. Go there and dig, and see if we are right.
Somehow actually find something that is uncommon: iron, shark teeth, crystals
Find an area with 2-3 distinct kinds of rock, so it is very easy for the kids to distinguish this sedimentary rock over here from that igneous rock over there.
Bring back something that would be more interesting when viewed under a microscope

I would hope that any answers could be generally applied anywhere, but if it is helpful I live on the Wasatch Front in Utah, USA

You live in an very good state for interesting geology, rock collecting, etc.  In regards to looking for things the kids can collect, view and otherwise analyse the PDF, "The Collectors Guide to Rocks, Minerals, and Fossil Localities of Utah" would be a good start to your research.  The publication is from the Utah government and covers a large number of areas in the state.  Over 30 years ago I made a trip to the Caineville just east of Capital Reef National Monument and collected pelecypods, they where laying on the soil with the occasional gypsum spars.  I believe the area is in the document I suggest you read, I doubt I could find it now but there was lots to find in the area in general including some evaporative type minerals, agates, and fossils.

You also have the Great Salt Lake, some areas would be good to collect and view brine shrimp, protozoa, and algae with a microscope, many would be easily viewable with a dissecting microscope.  You could also discuss the geological history of lake Bonneville of which the Great Salt Lake is but a remnant.

Finally the Gem Trails of Utah guide can provide some sites where collecting might be appropriate, though this publication is getting old and doesn't focus much on geology.

The land status and access to these areas change frequently and sometimes it is difficult to locate the sites, expect some failures in your adventures.  I would also suggest that you field check the surrounding areas because published areas often get damaged by careless individuals.  Finally, would also suggest you follow leave no trace principals as much as possible within a collecting trip, the scenery and wildlife in many of these areas are really impressive and it is a shame to see it all dug up by collectors.

As a final thought most states have some form of Geological Road Maps, there are some listed on this government site.


How to read NOAA/NASA GOES satellite data? I requested satellite image data (GVAR_IMG) for a project that I am working on from the GOES satellite, but I don't know what format it's in or how to read it.  When I open it with a text editor it is hexadecimal.  The files are end in .BAND_01, .BAND_02, etc.  The website that I requested the data from said that the data is available in different formats: "Data distribution formats available are raw, AREA, NetCDF, GIF, and JPEG." However, I do not see the option for selecting different formats.

Go to the user preferences.  From there you will be able to choose different formats and data options.  If you choose netCDF, you will be able to read these filetypes with most map readers.  For Python, you can use netCDF4-python.


What are the formula weight and gram-formula unit (gfu)? I'm reading Shaw's "Trace Elements in Magmas" and in his page 16 he writes the following:

  ...It is necessary to look at the relationship between $c_i$ and
  $x_i$, i.e. the weight and molar concentrations. In any phase of
  weight $W$ the weight of component $i$ is $w_i$ and if the formula
  weight of $i$ is $M_i$, then the number of gfu (gram-formula unit
  concentration) of $i$ is $n_i$, where $n_i = \frac{w_i}{M_i}$...

What does he mean when he mentions the "formula weight" ($M_i$) and the gfu (gram formula unit)?

$M_i$ is the molar mass of the ith element. Dividing $w_i$ by $M_i$ yields the number of moles of that element in the sample.

There are two primary ways of looking at abundances. One is by weight (or mass), the other is by number of atoms. Consider beryllium and uranium. Their abundances are very similar when looked at in terms of mass: 1.9 parts per million (ppm) for beryllium versus 1.8 ppm for uranium. In terms of molar abundance, they aren't so similar. In this sense, beryllium's abundance is 4.3 ppm; for uranium, it's only 0.15 ppm.


Is there any way to measure the amount of radiation the earth receives from the sun? My understanding is that it is difficult to measure the amount of radiation the earth receives to the sun and that due to variability in a number of different quantities such as the changing distance to the sun, the tilt of the earth, and the variable amount of radiation emitted from different parts of the sun's surface, it is not currently possible to measure solar irradiance. Is this correct?

Your understanding is half correct. Yes, we can measure the amount of radiation the Earth receives from the Sun.

Yes, it is difficult to get an extremely precise measure of how much radiation the Earth receives from the Sun in any one time interval. But there's not really much value in such extreme precision anyway.

However, it is fairly easy to measure solar irradiance at any one place (on earth, in the atmosphere or in space); as NASA and others currently do (kudos to farrenthorpe for the link). These measurements account for the changing distance to the sun, and the tilt of the earth, and to a very large extent the variable amount of radiation emitted from different parts of the sun's surface, because the Sun's diameter is tiny compared to the distance between the Earth and the Sun (just under 1%).

And having measured solar irradiance at one or more places, it is then easy to get a fairly precise estimate of how much radiation the Earth receives from the Sun in any one time interval.


How do I calculate Oxygen requirement in an aerobic waste water pond? Assuming I have data of BOD, COD and water discharge. How do I calculate the O2 requirement?

you can actually calculate the theoretical oxygen requirement using the following formula:
O2 req (kgO2/d) = [Q * (S0-S) / (BOD5/BODL)]/ 1000
Where:
Q= flowrate m3/day
S0= infulent BOD/COD concentration (mg/L)
S= efulent BOD/COD concentration (mg/L)

FYI Successful decreasing of BOD and COD can be obtain by using high volume Oxygen Generator such as Submersible Aeration


Is there a maximum size for a single snowflake? Just based on my previous experiences a wetter snow, in general, has larger flakes.  Some online sources say that raindrops do have a maximum size before they start to break apart when surface tension can no longer withstand air resistance, however the maximum size of a snowflake is less defined (1&2).  One source also states that light winds and a wetter snow is more conducive to larger flakes because the light wind helps keep them from breaking into pieces, and the additional moisture creates a film which helps the flakes stick together (2).

I understand that it may be difficult to measure a snowflake before it melts and that may be why the only non-confirmed size that I have found is from the 2014 Guinness Book of World Records of an eye witness account in 1887 of a snowflake 15" wide by 18" deep (3).

So my question is twofold:

Is there a theoretical limit to how large a single snowflake can be?
If there is a reliable way to measure snowflakes, what is the largest
snowflake ever measured?

Sources:

http://www.theweatherprediction.com/habyhints/261/
https://www.reddit.com/r/askscience/comments/32e2nf/what_is_the_maximum_size_of_a_raindrop/?st=jhi2ljz8&sh=25942d8e
https://www.reference.com/science/big-can-snowflakes-a119e8a009c4d4ac

According to Caltech physics professor Kenneth G. Libbrecht's site SnowCrystals.com

  This monster is, to my knowledge, the largest snow crystal ever photographed. It measures 10.1 mm (0.4 inches) from tip to tip (averaged over the three axes). ... Note that this is a snow crystal: a single crystal of ice ... Larger snowflakes have been reported, but those were puffballs made of huge numbers of individual snow crystals stuck together. During very calm conditions, these puffballs can grow into pancake-shaped agglomerations as large as a dinner plate

He has a paper Physical Dynamics of Ice
Crystal Growth, but I don't see any discussion of theoretical maximum sizes of crystals or agglomerations.


Where can I find information about monthly seasonal change in a given area? I have searched Google for almost an hour with no result. I'm looking for something like, "Indonesia, January to August is rain season, September to December is hot season".

I can't use the old information in books about seasonal change that now seem to have shifted and I can't find any updated information anywhere.

You can try climatemps.com for easy access and plots. There they have a map you can click on or a list by countries.
More data and analysis tools are available at the KNMI Climate Explorer, a more reliable and scientifically sound source.

This is one of the outputs for Jakarta from jakarta.climatemps.com


What structures form due to the melting of subducting plates? What structures form from the melting of subducting plates?
Plutons, Accretionary wedges, Deep sea trenches, Faults?

The subducting plate never really melt. It just gets recycled into the mantle (the Asthenosphere to be more precise), which is in solid state. It is plastic and deformable enough to allow convection flows, but it is solid.

Beside more mantle, something that forms from the subducting plate is magma. The water contained in the subducted slab (that was once ocean floor) can lower the melting point of the mantle and allow it to melt and form magma. The magma is liquid and less dense than the surrounding mantle, therefore it rises through it, and then through the continental plate. Once there it can create plutons, batholiths and feed volcanoes if it make it all the way to the surface.

But what melts is mostly the mantle mixed with water from the subducting plate, not the subducting plate itself.