How can radiometric dating of meteorites determine the age of the earth? Wouldn't this only determine the age of the decaying nuclide in each rock? How can the radiometric dating of different meteorites determine the age of the earth? Wouldn't radioactive decay have already been occurring in all of those  meteorites long before they hit earth? Wouldn't dating only show when the unstable nuclides in that meteorite were created, not when the earth was created? If you went and measured a decaying nuclide in a metiorite which had traveled for 500 million years before striking earth, then the dating of that metiorite would not tell us the age of the earth it would instead give us an age measurement at least 500 million years older then the earth actually is because that nuclide was decaying long before it managed to hit earth's surface.

Also assuming this does somehow get accounted for, how would determining the age of all these various meteorites allow us to estimate the earth's age? Wouldn't this only give us a lower bound on the earth's age? How do we know there doesn't exist some older meteorite out there indicating the earth is older then 4.5 billion years?

This is not a duplicate of the question asking about why measure meteorites not rocks, I am talking about meteorites and my question is regarding how dating can take into account when the rocks became part of earth as opposed to when the nuclides being dated first came into existence. Its not like the unstable nuclides within a metiorite suddenly decided to start decaying when they hit earth. They started decaying the minute they came into existence, including the time before they hit earth.

Many of your questions are answered in this question and associated answers:

Why is Earth's age given by dating meteorites rather than its own rocks?

To add to some of your other questions:

  Wouldn't radioactive decay have already been occurring in all of those meteorites long before they hit earth or our moon?

Yes. We have an assumption that the Earth formed at about the same time as the meteorites. The age obtained for meteorites is not the time when they hit the Earth, it is the time when they formed. Which is reasonably assumed to be close to the age of the Earth.

  Wouldn't this only give us a lower bound on the earth's age? How do we know there doesn't exist some older meteorite out there indicating the earth is older then 4.5 billion years?

Because we haven't found one. We have found thousands of meteorites and none have an age older than that. Yea, there could be something that we simply having found. But the more you look, the more a pattern emerges.
Furthermore, there are other systems like 26 Mg-Al which do not date how long ago things formed, but rather how soon after the supernova things formed. This allows us to know that meteorites that formed 4.5 billion years ago, also formed within a few million of years after the supernova that made the nebula and all materials in the solar system. Therefore, Earth could not be older than 4.5 billion years.

Al-26 forms abundantly in supernovae and is radioactive with a half-life of almost a million years. Minerals which contain both Mg and Al (such as spinel: MgAl2O4) will initially incorporate Al-26 which will then decay to stable Mg-26. When measured, the mineral will have an excess of Mg-26 relative to what is expected, and then it can constrain its formation time to the time when Al-26 was still around (without a few million of the supernova). The same meteorite can then be dated using other methods (usually U-Pb) to determine how long ago it formed, and the answer is usually ~4.5 billion years.


If plants convert a greenhouse gas into a non-greenhouse gas, do they cool? Plants turn Carbon Dioxide into Oxygen, that is not a greenhouse gas. But Carbon Dioxide is.

Therefore, wouldn't plants cool the area?

Plants are natural machines that convert $CO_{2}$ into $O_{2}$ when there is sunlight. This process is known as photosynthesis because photons provide the energy that triggers the reaction,
$$6CO_{2} + 6H_{2}O -> C_{6}H_{12}O_{6} + 6O_{2}$$

The question then is where do the plant products,such as leaves, fruits, flowers,roots that are composed of $C_{6}H_{12}O_{6}$  stored? If these plant remains are stored in the ground more than they are decomposed and then release $CO_{2}$ into the atmosphere, then we can positively say they are the natural cleaning robots, sorry super-robots or cleaning freaks!


Open source well information viewer I am in the middle of a hobbyist experiment and would like suggestions on an open source HTML viewer for mud loggging, FMIs, lithology and seismic. I have used INT before but for this project I would like an open source alternative.

Your best bet is probably OpendTect.

It's not quite what you asked for. OpendTect is a desktop application and does not use HTML/JavaScript for display. It is dual licensed; the free version is licensed under the GPL. It will read wells and seismic no problem, but I'm not sure about FMI in the free version.

Agile started G3.js, a JavaScript library based on D3.js for logs and seismic, but we didn't get very far. (I'm the founder of Agile; I'd welcome a reason to start that project up again.) Agile also has welly, a Python library for well logs and lithology.

There are lists of other open source tools for geophysics and geology on Wikipedia.


How to estimate the settling time of atmospheric particulates as a function of aerodynamic size? Understanding the behavior of particulates in the atmosphere is important for modeling climate, weather and public health. They can be nucleation sites for rain, fog and smog, they can have thermal impact due to absorption of sunlight and possibly radiation in thermal infrared, and the smallest can deposit chemicals deep inside our lungs.
Their behavior can be characterized by their particulate aerodynamic diameter, one way to characterize their size according to their aerodynamic behavior.
The rate at which particulate matter deposited in the atmosphere settle to the ground is a strong function of size. Throw a handful of sand into the air and it returns to the ground within second, create soot with fire and it rises in the column of hot air produced and may take weeks, months or even years before it returns to Earth.
Of possible interest:

High-flying bacteria spark interest in possible climate effects
Microbes Survive, and Maybe Thrive, High in the Atmosphere
Living Bacteria Are Riding Earth’s Air Currents

Is there any way to estimate at least approximately as a function of size the time it takes airborne particulates found high in the atmosphere to return to Earth, and which ones return due to gravity and which due to formation of precipitation? I know it's a complex topic and it may depend strongly on the altitude at which they start. Perhaps some rules-of-thumb or examples might be sufficient to get an idea of what's involved in such estimates. That may be helpful in order to formulate more specific follow-up questions.

I took a class once, and we had an approximate equation for an particle (equation sheet is still up):
$$\frac{d\vec{v}}{dt}=\frac{\rho_{particle}-\rho_{air}}{\rho_{particle}}\vec{g}-\frac{3\rho_{air}C_D}{4\rho_{particle}CD_{particle}}\vec{v}|\vec{v}|$$ where $\rho$ is density, $\vec{g}$ is the gravity vector (usually $=g\hat{k}$ but can be changed if the particle has a charge), $C_D$ is the surface drag coefficient, $C$ is the Cunningham correction factor, $\vec{v}$ is the particle velocity, and $D_{particle}$ is the aerodynamic diameter of the particle.
Solving for $\frac{d\vec{v}}{dt}=0$ to get the terminal velocity is one option. I can't remember if the above equation considers environmental motion. You can work through the other equations in the equation sheet and see that even getting a terminal velocity is complicated and requires an iterative method since $C_D=C_D(\vec{v})$. This might work for engineering purposes, but may not practical for atmospheric modeling.
There is another take on this issue of deposition. One parameterization for dry deposition is the (see pgs. 6-9): $$v_{deposition}=\frac{1}{r_a+r_b+r_a r_b v_s}+v_s$$
$$r_a=\frac{1}{ku_*}\left[\ln\left(\frac{z-d}{z_0}\right)-\Psi_h\left(\frac{z}{L}\right)\right]$$
$$v_s=\frac{D_p\rho_{particle}g}{18C\mu}$$, where $v_s$ is the settling velocity, $\mu$ is the dynamic viscosity, $L$ is the Monin-Obukhov length, $\Psi_h$ is the integrated similarity/Businger-Dyer function for heat, $k$ is the von-Karman constant, $z_0$ is the roughness length, $d$ is the displacement height, $u_*$  is the friction velocity, and $r_b$ is the viscous  sub-layer resistance.


Historical NWS GFS forecast data The National Weather Service (NWS) makes the results from its Global Forecast System model (GFS) available for download as GRIB2 files.

While accessing current (or recent) forecasts is straight-forward, I am looking for the archived forecasts over at least the last year, better multiple years back for the purpose of statistical analysis of predominant weather patterns in certain areas.

Does anybody know how to access this information?

It all depends on the region you are interested on. For the North America region, you could use the North American Regional Reanalysis (NARR).

NARR is a "high resolution combined model and assimilated dataset. It covers 1979 to near present and is provided 8-times daily, daily and monthly". The best and easiest way to access the data is through NOMADS. There you will find data in several different formats (netCDF, GRIB...) and it has a resolution of around 32km.

If your interest is in global data, then you could try the NCEP/NCAR Reanalysis. It is a global reanalysis of the atmosphere from 1948 to the present with a resolution of 2.5 degrees. There is also the NCEP/DOE reanalysis with a similar footprint. I think you can get both of them from NOMADS.

All these products are reanalysis (therefore not forecast) products. If your interest is in forecast products, then you can use the North American Mesoscale (NAM) product. It has a resolution of 12km and it is available through NOMADS. The model they are currently running is a version of the Weather Research & Forecasting - Nonhydrostatic Mesoscale Model (WRF-NMM).

There is a complete list of NOAA model products available and a brief description of each in the NOAA NOMADS page.


Ground water is almost every where, then how do mines and other holes are digged so that ground water doesn't drain into it Water finds it way to the lowest point because of gravity.
So if we dig a mine or something same, then how we take ground water in account, so that it doesn't fill in.

We pump it out. Open and closed pit mines usually have pumping installations to get the water out.

Look up Mine dewatering on Wikipedia.

There have also been numerous accidents in the past where mines were flooded (YouTube: Turkey mining accident: 18 workers trapped after underground water floods mine), and when left alone many abandoned mines will fill up with (ground) water.
Sometimes these are nice diving objects.

Or (as Trond Hansen commented) we try to prevent it from coming in in the first place, by using cement, grout or bulkheads to 'plug the holes'.

If you are really interested:

Mine Water: Hydrology, Pollution, Remediation by P.L. Younger, S.A. Banwart, R.S. Hedin.

Design of Water Holding Bulkheads for CoalMines by V.S. Mutton and A.M. Rememnikov


Have there ever been any islands that disappeared due to rising sea level? With global warming comes rising sea levels. This has been going on for at least fifty years.

So haven't there been some islands that have been swallowed by now? An island could be nothing more than a rock jutting up a few centimeters out of the sea. There are many such "rock" islands that surround larger islands, and I'm wondering if any have been devoured by now.

I don't need a whole list of such islands, although a link to such a list would be probably the best answer one could hope for. What I'm really looking for is a few examples, or maybe the largest island known to have disappeared thanks to the rising sea.

Definitely, there are lots.

As you say, sea-level is rising in most (but not all) coastal areas. Indeed, at the end of the last ice age ca. 12,000 years ago, sea-levels rose about 120 m. Many islands and land bridges — such as Beringia across the Bering Strait, and Doggerland across the North Sea — drowned.

I can't find any lists of drowned islands, but here are some places you will find them today and in the geological past:

'Banks' on the eastern seaboard of North America would have been emergent during the ice age — Georges Bank and the Grand Banks for example. As they drowned, they would have formed islands — lots, in the case of Grand Bank.
The Hawaiian archipelago is part of a famous chain of drowned islands, but the change in sea-level is not the only thing that's drowning them. As the plate moves over an upwelling in the mantle — the same thing that's causing the volcanism there — it subsides and cools. I'm sure there are many drowned islands in other extinct and active volcanic provinces and seamount chains: the Zubairs, Canaries, Azores, Iceland, the South Pacific, etc. Sometimes life keeps up for a bit as a coral reef grows around the sinking island, perhaps forming an atoll.
Near-sea-level islands like atolls abound in places like the Maldives. These atolls are volcanic and actively subsiding. Sea-level may or may not inundate them, depending on whether the coral growth can keep up. Another fragile island is Sable Island off Nova Scotia — clinging to the edge of the continental shelf.
Volcanos can explode as well as sink slowly into the sea. Krakatau Island is probably the best example. This one has nothing to do with sea-level.
Rift basins start as mountainous tears in the crust, then subside and flood. Global sea-level change will often act to accelerate this. An example might be the various island groups on the shores of the Red Sea. These will likely sink into the sea eventually.
Salt-domes in Louisiana (e.g. Avery Island) form hills, but the domes continue offshore for hundreds of kilometres. Many of them would have been exposed in the past, some even more recently than the last ice age.

Maybe others can chip in some other scenarios; I'm sure there are dozens.

The point is that sea-level is not the only factor — subsidence, sediment accumulation rate, and erosion also play their rôles. But sea-level always plays some part, and can change quickly relative to the other factors.


What is the furthest observable phenomenon from Earth that is Earth Science? Guessing that the Earth's magnetic field is the furthest observable Earth Science related phenomenon from Earth itself, though not completely sure.

It appears the Earth's magnetotail, which is a part of its magnetosphere, is on the Earth's nightside; lengthwise exceeds 6,300,000 kilometers (3,900,000 miles); and is the furthest known observable feature of Earth.

I am unable to explain why is it commonly not included in the "spheres" of Earth Science.

Note: The gravitational pull of Earth in theory spans the known Universe, though it's unlikely to have any observable affect, unlike the Earth's magnetotail.


How much has the total transport of the Antarctic Circumpolar Current changed over time? The Antarctic Circumpolar Current (ACC), the oceanic current that flows around the Antarctic continent, has many links to weather and climate processes (e.g., Is there conclusive evidence for the Antarctic Circumpolar Current developing after the glaciation of Antarctica?).
My question is how has the total transport of the current changed in time at different time scales? Clearly, it has changed since its potential formation in the late Miocene. My interest is in both short time scales (seasonal), decadal (e.g., ENSO effects) and longer time scales.

From reading the literature on the subject, my impression is that we don't know that much on the subject, primarily due to a scarcity of measurements. My understanding is that the first and only year-long time-series was made at the Drake Passage in 1979 (e. g. Whitworth & Peterson, 1985) by the ISOS programme (International Southern Ocean Studies). In addition to that NOAA's WOCE (World Ocean Circulation Experiment) added yearly data from 1990 to 2002.

According to Rintoul & Sokolov 2001 and Rintoul et al. 2001, most of the variability south of Tasmania is due to changes in currents north of the ACC itself.
Cunningham et al. 2003 show that the moderate interannual variation in baroclinic transport they observed seem to be coeval with variations in the location of the Polar Front (it moves north or south on a 90km range). But overall the variability seems to be relatively low, and the ACC relatively steady.

White & Peterson, 1996 showed an interesting phenomenon that they called the Antarctic Circumpolar Wave: it is a "wave" in the ACC circling the globe in ca. 8 yrs with a period of 4yrs at any location and it is defined by anomalies in sea-suface temperature, sea-level pressure and sea-ice extent. However no evidence for corresponding anomalies in volume transport was showed, to my knowledge.

So, to summarize, as far as I can see:

not enough data for seasonal trends (only one yearlong time-series);
some interannual variability (possibly as a consequence of variabilities in other water masses);
not enough data to study decadal variation.


Can there be ice in the core because of pressure? Because there is so much pressure in the earth's core, the inner core is solid but what happens if you manage to add some water in the inner core or near it. Does the pressure make the water solid or does it evaporate? do iron and nickel only turn solid under pressure?

what happens if you manage to add some water in the inner core or near it.

It will probably react with the solid iron to form iron (oxy)hydride:

Our observations indicate that H2O is likely introduced into the deep Earth through reaction between iron and water during the accretion and separation of the metallic core. Additionally, reaction between Fe and H2O would occur at the core‐mantle boundary, given water released from hydrous subducting slabs that intersect with the metallic core. Accumulation of volatile‐bearing iron compounds may provide new insights into the enigmatic seismic structures observed at the base of the lower mantle.

(source: https://doi.org/10.1002/2017GL075720)
In other words, the question of whether the water would be ice, liquid, or vapour is a non-question because water as molecules of H2O would cease to exist.
You don't need the core for this. Take water, put it on a piece of iron, and the water would be absorbed into the iron in the form of rust:
$\ce{Fe + 0.5H2O + 0.5O2 = FeOOH}$
Regarding the question of what would happen to just water if you would put it in core-like pressures and temperatures, the answer is simple: we don't know. I don't think anyone attempted that experimentally. It will probably not be a gas - pressures are way too high for that. Since the melting point of H2O is much lower than that of iron, I suspect it will be a liquid.
Something from the comments:

On quora, they said that high pressure would lower the melting point of ice, not as expected, probably making it vapor

This is only relevant at relatively low temperatures because of the anomalous crystal structure of ice. For most compounds, you need greater temperature to melt something which is at pressure. It's actually opposite for water, and closely related to the fact that ice floats on water (which is very counter-intuitive - usually solids are denser than liquids). But at high temperatures, of hundreds and thousands of degrees, water starts to behave normally under high pressure.


Why is the ocean paleotemperature trend downwards? In The Encyclopedia of Paleoclimatology and Ancient Environments by Vivien Gornitz (2008, Springer) it is found that 50 My ago the sea temperature was about 13ºC above the present value.

.

AFAIK the several proxies gave consistent answers.

Why is the temperature always decreasing ?

I recommend you read the original paper Lear et al. (2000). In it they explain that the results are controlled by processes in polar regions and likely associated with the polar surface temperature. The surface temperature will vary considerable depending on the proximity and extend of the deep water formation areas. As these areas are fairly local, relatively small changes in the location and extend of deep water formation can result in deep water temperature being altered. The uncertainty associated with using single cores to estimate global temperatures is thus quite large. What the authors suggest is a predominantly ice-free world during most of the Paleocene and Cretaceous periods and several ice-sheet expansion events during the Oligocene, Miocene and Pleistocene. If there is no ice, the polar and sub-polar deep-water formation is limited and the water temperatures in the deeper part of the ocean is much warmer.

The temperature record shows a general cooling trend for the past 50 My, but its resolution is too low to define abrupt temperature extremes. Assuming that the process of deep water formation at high latitudes prevailed throughout the past 50 My, these deep-ocean temperatures can be inferred to represent polar surface temperatures (1). The temperature trend (Fig. 1C) appears to comprise four main cooling phases separated by periods of more stable temperatures. These cooling phases occur during the early Middle Eocene, the Late Eocene through Early Oligocene, the late Middle Miocene, and the Plio-Pleistocene.
Alternative evidence supports the existence of these principal cooling phases. A sharp cooling in the early Middle Eocene has been invoked to explain the abundance of siliceous sediments of this age (20). The Early Eocene warm climate is thought to have promoted in- tense chemical weathering of siliceous rocks at
high latitudes, which resulted in high concentrations of dissolved silica in the oceans. The subsequent cooling stimulated upwelling of nutrient-rich water and intense biosilicification. The cooling over the Late Eocene through Ear- ly Oligocene is coincident with the transition from “Paleogene” to “transitional” benthic foraminiferal faunas and high extinction rates in planktonic and terrestrial faunas. The initiation of this deep water cooling also coincides with a reduction in the extent of tropical rainforests on land (21, 22). The cooling in the late Middle Miocene is marked by a narrowing of tropical and warm subtropical biotic provinces in terrestrial and marine environments (23). Warmwater diatom assemblages were replaced by cold-water species at this time (24). The Plio-Pleistocene cooling is not represented by an extinction phase in benthic foraminiferal faunas; instead, faunal groups adapted to the changing bottom water conditions by migration (21).

When you use data from other regions, you get a much different result. For instance, Elderfield & Ganssen (2000) showed how different the temperature changes can be for different species and locations.
Their data are much more recent and suggest an increase in temperature over the last 20,000 years. As always, everything depends on the temporal scales. One issue that tends to be true is that estimates for periods long time ago tend to have larger uncertainties.


Can climate change cause earthquakes, tsunamis, or volcanic eruptions? Different scientists have brought forth a theory that climate change can cause earthquakes, tsunamis and volcanic eruptions. For example:

Professor Bill McGuire of University College London in his book Waking the Giant: How a changing climate triggers earthquakes, tsunamis, and volcanoes (OUP, 2012).
Giampiero Iaffaldano of the Australian National University, for example in this article or this article.

What is the general view among Earth scientists on this theory? How strong is the evidence that supports or refutes this theory?

A quote from the summary of the book you listed:

  feeding torrents of freshwater into ocean basins that rapidly filled
  to present levels. The removal of the enormous weight of ice at high
  latitudes caused the crust to bounce back triggering earthquakes in
  Europe and North America and provoking an unprecedented volcanic
  outburst in Iceland. A giant submarine landslide off the coast of
  Norway sent a tsunami crashing onto the Scottish coast while around
  the margins of the continents the massive load exerted on the crust by
  soaring sea levels encouraged a widespread seismic and volcanic
  rejoinder.

Could not access the other links.  This is clearly bordering on pseudoscience.  I admit I have not read the book but the summary makes it sound like junk science.  As a scientist I am skeptical and all of this seems like a stretch. I sure would like to know how crustal rebound (isotasy) affects a volcanic hot spot in the middle of the ocean.  The hot spot is most likely generated at the core-mantle boundary where convective cells in the core meet the mantle and melt it. The whole scenario sounds like a bad movie. Is there anything that someone will not blame on global warming? And how would we ever know that a landslide in Norway was due to crustal rebound/global warming?

But the author is disingenuous.  Even if he is correct, he implies that the changing climate in the past and any potential events associated with that changing climate might be related to changing climate today.   But climate change of the recent past has been due to the earth cycles set out by Milankovich and not to man-made global warming.  How can the two be compared when in the past we had a 6 degree change and now we are looking at only about a 1 degree change up until now.  Sounds like he is desperate to sell his book and hypotheses.


Digitalizing precipitation data from the image of weather map I have a set of very old precipitation anomaly maps, from 1995-2006 for Brazil. The data of these maps, is to the best of my knowlegde, lost.

I would like to have them digitalized, ie, to NetCDF or another similar gridded format. Is there any tools recommendend for this job?

The figure below is a recent plot, similar to my files.

You can convert the image to NetCDF data using gdal_translate. The command line looks something like:

gdal_translate -ot Int16 -of netCDF jpeg_filename nc_filename

You can use ncl example: click here


How to check the recurrence intervall of heavy rain events Heavy rain or flood events have recurrence intervalls. I.e. 100 year, 50 year or 25 year events. However, with increasing data and global warming and other factors these intervalls change.

How can I check wether a heavy rain event from 2015 with a recurrence intervall of 50 years still has the same intervall? Or wether it already has a 48 year intervall.

In engineering it is common practice to build intensity-duration-frequency (IDF) curves, which basically map out the frequency of a given rainfall event based on its average intensity (mm/hr) and duration of the event. This addresses the issue of needing to classify a 'heavy' rainfall event. In general, the duration and intensity are inversely related (more intense rainfall events tend to last a shorter time).

There are many examples of calculation and software packages to actually build these curves, which are used often for engineering design to help decide the storm a given piece of infrastructure is being designed to (e.g. 5 year storm, 25 year storm, etc.). Most municipalities will have developed their own IDF curves to set standards for design.

There are also examples of online tools to help generate IDF curves for a given location, such as this one in Ontario. This tool is neat as it calculates the IDFs for a given year, and uses trend analysis to predict future changes to the IDF curve, allowing you to also pick the target year for generating the IDF curve.

If you see that the intensity/duration changes for a given frequency storm event (e.g. 50 year), that would indicate a shift in the rainfall patterns due to climate change. You may need additional statistical tests to check if these changes are statistically significant (examples of this type of analysis applied here and here). You will likely not see much change in these curves over a few years as the datasets overlap quite a bit and the trends will not change rainfall patterns in that short a time frame, however, over a 25 or 50 year period you will likely see some changes in the IDF curves, depending on the location.


How to graph gravity as a function of depth, given radius and density? I need to do this for a planet that has uniform density, and a planet that has two layers. For the first part, I was given that the density was 550 kg/m³, so I made one column in an Excel spreadsheet that gave mass as a function of radius, then made another column that plugged that $M$ value into $g = \frac{GM}{r^2}$. Then I graphed my $g$ values against my radius, which gave a linear function. I'm not sure if that was the right approach, or of how to make a function for the planet that has more than one density. Does anyone have any ideas on this?

As long as we deal with a spherically symmetric planet, the mass of the shell above you does not influence the observed gravity; the little mass close by exactly cancels the large amounts of mass far away (you would float inside a planet if it looked like a pingpong ball and had all its mass centered on the surface!), this is called Newton's Shell Theorem.

You can then compute $g$, acting as if the mass $M$ is concentrated at a point on the centre of the sphere. Thus, combining your knowledge of the mass $M$ underneath you, and the radius $r$ towards the center of this planet, you can compute the gravity field using the equation you give!

For a constant density we have a volume $V=\frac{4}{3}\pi r^3$, thus mass $M=\rho_1 V$, and the gravity is given as $g(r)=\frac{GM}{r^2}=G\frac{4}{3}\pi r \rho_1$, linear like you found. For two layers, it is a sum of this first mass $M_1=\frac{4}{3}\pi_1R_1^3$ and second mass $M_2=\frac{4}{3}\pi_2(r-R_1)^3$ but ONLY when this mass is below you, i.e.
$$g^*(r) = \begin{cases}G\frac{4}{3}\pi \rho_1 r & r\leq R_1 \\ G\frac{4}{3}\pi( \rho_1\frac{R_1^3}{r^2}+\rho_2\frac{(r-R_1)^3}{r^2}) & r>R_1\end{cases}.$$
This should not be linear anymore due to the $R_1^3/r^2$ contribution!

Good luck!


How do I convert kg·kg⁻¹ to ppbV (parts per billion volume)? I am using the CAMS model output data to figure out the ground level ozone at a particular place. It is given in mass mixing ratio, and I want to convert to parts per billion volume mixing ratio (volume/volume).

Shown above are ozone values from a model – basically the given values on the right beside the dates are in $\mathrm{kg} \cdot \mathrm{kg}^{-1}$. How can I convert them to ppbV?

So if you have a mass-mixing ratio, you effectively $\frac{ \text{kg pollutant}}{\text{kg dry air}}$. PPBV is parts per billion volume, or number of molecules of pollutant per billion molecules of dry air. Since not all particles weigh the same, you must use a conversion factor. Consider molar mass, which is the ratio of moles (a unit describing the number of molecules/photons/atoms) to mass. Ozone has a molar mass of 48 kg mol$^{-1}$. Dry air doesn't have a molar mass per se, but an effective molar mass may be computed by a weighted sum of the molar masses of the consitituent chemicals (or you can Google it). Afterwards, you may have to multiply by a billion.$$\therefore \frac{ \text{kg pollutant}}{\text{kg dry air}} \times\frac{\frac{\text{mols of pollutant}}{\text{kg of pollutant}}}{\frac{\text{mols of dry air}}{\text{kg of dry air}}}=\frac{\text{mols of pollutant}}{\text{mols of dry air}}$$


Is Cape Canaveral really the lightning capital of the US? Today's SpaceX webcast featured an interesting quote, that Cape Canaveral is the lightning capital of the US. Is that really the case? If not, how does it compare in lightning strikes to other areas in the US?

It's pretty likely. Florida has the highest lightning strikes of anywhere in the US, as can by seen by this map from lightningsafety.com This is the area near Florida, with the highest levels.

It's hard to see, but the highest density is actually just to the west of the Cape, but it's not too far of a stretch to say it's the lightning capital of the US.


"Obicular" structures in basalts I found spherical or globular structures, structures in basalts of a greenstone belt which underwent alteration and deformation. However, in thin section, these structures have undeformed pyroxene and olivine. Below is a field picture of the structure. Would anyone know what these structures are called and how they form?

.

These globular structures are called varioles, and there is not complete agreement as to how they are formed. The most likely theory is that the basalt has been hydrothermically altered by millions of years of water infiltration bringing in tiny amounts of other minerals, but the jury is still out.


correct way to calculate transport through a section in an ocean numerical model Suppose that I want to calculate the transport across a certain transect (green line) from the outputs of an ocean numerical model. The model has the $u$ values at the center of the grids (crosses) and the $v$ values at the corners (circles), as it uses a C-grid.

Should I use the velocity values closest to the transect? Should I average the values at the corners? Interpolate?

Side question: does anyone know some Matlab toolbox to analyze numerical model outputs?

I have been using the routines in nctoolbox (also check here) that do all the slicing (vertical, horizontal, following a track).
The repository is in GitHub.

The one you should looking at is vsliceg.m.

You can follow the logic there or develop your own.


Transformation of soil moisture units I have soil moisture data from Regional Climate Models expressed in $kg/m^2$. Τhis quantity is the total soil moisture that is estimated for the land column. The depth of this column is dependent on the land surface model that was used.

How could I transform soil moisture units expressed in $kg/m^2$ to $m^3/m^3$ so that model outputs are comparable to remote sensing soil moisture data that are expressed in $m^3/m^3$? Is there a way of doing this transformation without taking into consideration the soil depth?

The other answers are correct that you need to know the soil depth to convert from mass units (kg m-2) to volumetric units (m3 m-3).  However, when comparing these variables you should also be aware that satellite soil moisture is typically measured only over the top few centimetres of soil. Total column soil moisture from a climate model will typically be the sum over several metres, so the dynamics of these two variables are likely to be quite different (contrast the red and light blue lines in the upper plot).

It's more common to compare satellite data with top-layer soil moisture and even then to normalize each dataset in some way, e.g,

$$NWI = \frac{SM - SM_{min}}{SM_{max} - SM_{min}}$$

or as normalised anomalies,

$$NWI = (SM - \overline{SM}) / \sigma_{SM}$$

I've used the latter to normalize the lower plot.  Normalization gets around the units problem, but doesn't get around the fact that you're comparing physically different quantities.


How can I identify "tough" (mixed) granites? I am trying to parse an old geologic description of stone suitable for use as road metal:

  Care must be taken to distinguish the difference between the hardness
  of a stone and its toughness...Toughness in granites, syenites, and
  the like is occasioned by the disposition and size of the crystals
  forming them, these crystals being more interlocked in the tougher
  varieties of these stones than in the others.... Although we have
  described syenite as being made of quartz, feldsparand hornblende
  (excluding the few accessory minerals, for simplicity), we have not
  stated in what particular quantities these may exist, and this is an
  important factor in the inquiry. It will be found that the proportions
  vary considerably and on this the differences in durability and
  specific gravity are largely dependent. There cannot be much doubt
  that in the syenites commonly used as road metal, the rate of
  decomposition of the feldspar is the principal source of the
  superiority of one kind over another. The most durable syenite, then,
  is that which has the least feldspar, and, we may add, the least iron
  in that mineral. Syenites which contain an excess of feldspar,
  generally have a low specific gravity, unless the hornblende is
  superabundant. Those hornblendic granites, in which the feldspar has a
  tendency to occur in rather large crystals here and there, cannot be
  expected to make such good road-metal as those kinds of syenite which
  do not exhibit this feature, are fine-grained, have comparatively
  little feldspar, but much hornblende.

So, the question is how to figure out which rocks meet the criteria in the quote. For example, in New Hampshire some of the available syenites are as follows from sources like minedat:

Hornblende-biotite quartz syenite to syenite (Late Ordovician)
Hornblende (or alkalic amphibole) syenite (Jurassic)
Nepheline-sodalite-hastingsite syenite (Jurassic)
Porphyritic syenite - Hastingsite or hornblende and (or) hedenbergite are present. (Jurassic)

So, the question is how can I tell if a minedat description of a plutonic rock is favorable according to the criteria of the quoted passage?

So, the question is how can I tell if a minedat description of a plutonic rock is favorable according to the criteria of the quoted passage?

No. The description doesn't say how much feldspar is in the rock. It could be 5%, or it could be 20%. It also doesn't say anything about the iron content of the feldspar (although with some petrological hand waving you can assume by the presence of other minerals).

The nepheline syenite is going to have no feldspar (or very little), because it's usually either nepheline or feldspar, not both. But, we don't know whether nepheline is any good for the purpose.

I'm also wondering why is hornblende considered superior because it is a mineral that cleaves and breaks very easily.

One thing that is important is that they stress the fine grain size. Usually rocks with fine grain size are tougher than those with coarser.


What's a frost-gley? I've noticed this term in a book about Pleistocene East Europe. It's apparently a soil which was formed during the interstadials, but that's all my book says, and I can't find much more on the internet. So what more can be said about frost-gley, preferably with sources?

A frost-gley is a waterlogged permafrost soil. IOW, a gleysol that has undergone cryoturbation.


How gold deposits can be formed in Himalayas? I have heard that gold is found in the water coming out of glaciers in Skardu region of Pakistan.

Given that this area is part of Himalaya, what processes could result into ores of gold in this area?

Similar questions have been answered here and here but I need more specific and detailed answers, considering the geology of this area.

Himalayas represent a huge area with a complex geological history which I suspect has large areas that have never been adequately mapped to allow for an ore deposit evaluation. Nevertheless, placer gold might be found within any region of the  Himalayas.

Placer gold deposits are an accumulation of gold formed by gravity separation during sedimentary processes of the gold bearing host rock.

Reference: https://www.britannica.com/science/placer-deposit

Many granite bearing mountains containing quartz-feldspar porphyry dykes/veins associated with elevated concentrations of sulfur and arsenic can be found  in many parts of the world. I would assume these deposits would also found in the Himalayas.

Reference: http://www.minelinks.com/alluvial/goldDeposits.html


By what objectively correct process could we determine the truth about the actual severity of anthropogenic climate change? I began to do the best that I could to boil the key facts down to the most basic essence of proving significant anthropogenic climate change:

(1) It is a verified fact that since 1959 $\small\mathsf{CO_2}$ increased 98 PPM which is 126 times faster than the next fastest increase of at least 90 PPM in the prior 800,000 years.

(2) It is a verified fact that $\small\mathsf{CO_2}$ is currently 37% higher that its prior 800,000 year high value of 298 PPM.

(3) It is a verified fact that global temperatures have increased  about 0.75C since 1970.

(4) It is a verified fact that the only reason the Earth is much warmer than the Moon is the greenhouse effect of greenhouse gases.

(5) It is a verified fact that a significant increases in greenhouses gases cause a corresponding significant increases in global temperatures.

It does seem to be the case that within the premise that all of the above facts are true that significant anthropogenic climate change is proven.

The only pushback that I have gotten from global heating deniers is that they simply do not believe the temperature record.

By what objectively correct process could we determine the truth about the actual severity of anthropogenic climate change?

There are two key goals of the above question:
(1) To make sure that the above five points sufficiently prove AGH.
(2) To find very succinct and compelling ways to validate these five points.

We have reasonably good observations of the present.  We have moderately decent observations of the past (with larger uncertainties the further back we go).  Unfortunately, we have no observations at all of the future.

There are fundamentally only two ways to know about future impacts:

We can wait.  20 years, 50 years, 300 years.  We will know for sure, but it will be far too late to act on the knowledge to prevent the worst consequences.
We can model the impacts.  All models are wrong, but some are useful.  There is no "objectively correct process to determine the truth about the actual severity", because "actual severity" is not an objectively defined quantity.  However, we can model the impacts on biodiversity loss, sea level rise, desertification, food security, economic losses, and other measurable quantities that we care about.  From a strictly mathematical point of view, we can never be 100% sure.  However, if we are 99% sure of net impacts that most people would consider to be very bad indeed unless we act, the precautionary principle suggests acting is the wisest thing to do.

Source: USA Today, but has been published in many newspapers.


Would the shaking of an earthquake be visible to somebody in a low-flying aircraft? If you are in an airplane well above ground level, but low enough to see the faces of people relatively easily, and an earthquake happens, will you see the ground shake?

It depends largely on how deep, or shallow, the earthquake is, how large, and what kind of terrain you're looking down on. Some fairly large earthquakes, magnitude 6-7, can have very little surface effect, when they are centred 5+km down as many earthquakes in New Zealand often are. The finer the sediment on the surface, and the thicker the sediment cover, the greater the ground shaking is at the surface and the more motion is usually visible. Different ground covers will also make shaking more or less visible, long grass, or cereal crops, on a windy day will look like they're in motion even without a 'quake.

Shallow earthquakes often result in apparent L-wave activity, by which I mean that you can actually watch the ground wave coming towards you if you're outside on relatively flat ground, even during relatively small 3-4 pointer 'quakes. These waves also make parked vehicles rock from side to side, I would expect these effects to be the most visible from the air in the case of small to moderate earthquakes.

Larger 'quakes will cause noticeable shaking of buildings, power poles, aerials etc... even when quite deep and possibly distortion to large linear features such as roads, railways, waterways, and crop and orchard rows. These distortions would be visible as they form, and, when large enough, from very high in the air.


Why doesn't the whole volcanic cone appear black? Cooled lava looks black, but why the whole volcano, even near crater, doesn't always appear black like cooled lava?

The cooled lava might be covered by ashes. So depending of the amount of ashes and the wind you might have a black volcano or a gray volcano. Many volcanoes are formed by layers of lava and ash.

https://en.wikipedia.org/wiki/Volcano#/media/File:Volcano_scheme.svg


Wind speed, precipitation, extreme daily precipitation I am trying to figure out what type of precipitation lifting mechanism occurs in a area that is unknown but I know some facts about the climate. So I know that there are 4 precipitation lifting mechanisms - frontal, convection, convergent and orographic. So based off the extreme daily precipitation I need to choose one of these and back up my statement. So I have concluded that the area is inland because the temperature range is from -10 to 20, which is larger than most coastal temperature ranges. So I am hoping that this fact will eliminate one of the lifting mechanisms. So the extreme daily precipitation goes as follows.

Jan:65mm
Feb:54mm
Mar:64mm
Apr:75mm
May:80.3mm
June:92.8mm
Jul:92mm
Aug:86mm
Sep:90mm
Oct:87mm
Nov:82mm
Dec: 76.4

What type of lifting mechanism is responsible for the most extreme precipitation events? Then I need to back it up with the amount of days with the winds greater then 52km/hr which is only 8, and the yearly average wind speed is only 12.9.

My thinking is that I don't believe its orographic. But I am not sure which it is out of the other 3. There is not much wind all year around so this must be a factor, and there is a moderated amount of extreme precipitation all year around(shown by the data I provided)

Sometimes it is obvious, but it may not be possible to attribute the rainfall mechanism from the daily rainfall. Also, the four lifting mechanisms are not 'either / or'. There are frequently combinations of the above, particularly in respect of the most extreme events.


How did this stone become encased within different rock? My father, in his younger years, was a stone mason in Cincinnati Ohio. A couple of decades ago he was building a wall of some kind. He would fetch rock from a creek bed, haul it to the construction site, then shape it with what he calls a brick hammer.
After giving one rock a good whack, he found that it contained a smooth gray stone about the size of a child's fist. One side of the stone is a little darker than the other. When cracked open the stone appears fairly homogeneous.
How did this stone find its way inside the larger rock?
EDIT: Removed my speculation (cited by one answer) and other clutter. Added example of stone used for the wall.

(click to enlarge)

it was simply an older stone smoothed by water that had fallen into sediment.

This is exactly what happened. There's a name for that: a conglomerate.


Why do we see the limestone on top of Cambrian layer? The official story says like Cambrian Ordovician transition was caused/accompanied by animals learned how to build the Ca-based skeletons. These skeletons and shells started to fall upon the sea bed causing the rich and durable limestone formations on top of earth crust. I wonder didn't limestone form itself in pre-Cambrian epochs? You already had the CaO in the primordial crust (I wonder why do you give the leverage to he people who chronically cannot understand a question even after it was answered). You do not need animals for the CaO to react with CO2. Actually, there was much more CO2 even before Cambrian, billions of years ago. But we do not see any limestone formations at that time. So, why do we see the limestone on the top layer sediments 460-60 mln years ago rather than at the very bottom of the crust?

No.  CaO will not exist in most environments for any significant time in the presence of CO2, it will react to form CaCO3.  I doubt CaO is the primary source of Ca in our world.  Silicates are likely the original source of Ca in our oceans https://en.wikipedia.org/wiki/Silicate_minerals.  CaCO3 will partially dissolve or corrode in water to form an aqueous solution of Ca +2 + 2 HCO3 -.  The dissolution of the CaCO3 in water is an equilibrium reaction based on the acidity and temperature of the water, this is why the acidification of the oceans is a concern for our marine life.  I am not a chemist or a biologist but organisms will extract the aqueous Ca +2 ions found in the water to form shells etc.  Because these organisms are not evenly distributed in the ocean their shells and skeletons will and have accumulated the CaCO3 in distinct areas.


Methods and Software for Interpolating/Modelling of Stratigraphic Well Data in 2D/3D I have some geologic well data. The lithologies have been interpreted, and stratigraphic columns have been drawn. The columns have been adjusted for elevation, and correlation has been done between seemingly continuous layers.

Is there a more sophisticated 2D/3D program, preferably open source or free trial (I'm a student), that could be used to map the area better with an interpolated or block diagram result?

OpendTect may do this, however getting to that stage would be a painful experience.

Petrel can do this very easily, however, that is not anywhere near free...

If you're a student, your department may have access to a few decent programs to achieve this. If you could find out what you have available, we might be of more help!


How do we know the asteroids formed at the same time as earth? In continuation of the question Why is Earth's age given by dating meteorites rather than its own rocks?, what evidence do we have that the asteroids indeed formed at the same time as earth? Is there any physical evidence, or is it a conclusion reached mostly through simulation?

what evidence do we have that the asteroids indeed formed at the same time as earth?

It depends on what is your definition as "the same time". The formation of the solar system and Earth did not happen at a particular second in time but was rather a continuous process. It also depends on what you define as "asteroids".

I'll try to put some things in order.

The oldest known material from Earth is a zircon from the Jack Hills in Australia. Its age has been recently refined to be 4382 million years. We know that because we measured it.(1)
The moon forming event occurred sometime between 4348 and 4413 million years ago.(2) Now, that zircon should be younger than the moon (because the moon forming event would destroy any already-existing minerals on Earth). Yet, there is a slight overlap between the ages. This is due to the fact that analytical capabilities have their uncertainties and error.

This means that the Earth has been here at least ~4.4 billion years ago, because you need the Earth to have a moon. The Earth didn't just pop into existence, but it formed over a period of time, in which small planetesimals collided with each other and accreted to form a larger body.

The question now is, what is the age of the planetesimals? We can't know for sure because they are all integrated into Earth, but we can look at asteroids and see their age. We do that by dating the meteorites that fall on the Earth, which in some cases are blasted off asteroids by (even more) collisions and impacts.

When you look inside a specific type of meteorites called chondrites, you can see objects that are called CAIs (calcium-aluminum inclusions). These things are solids condensed from vapourised gas that existed in the solar nebula before any planets and planetesimals formed. These are basically the first solid to form in the solar system, and they define the birth of the solar system. We know that they formed 4568(3,4) or 4569.5(5) million years ago.

Planetary bodies (which for this discussion will be considered as km-sized chucks or rock with the ability to melt and differentiate to mantle and crust, and accrete to form proper planets) began forming around 4566.2 to 4567 million years ago(5,6,7). We know that because we can date meteorites that we know originated in asteroids. This is just 2 million years after the formation of the first solid droplets in the solar system. Now, while 2 million may seem like a long time for your daily commute, it is not too long for planetary processes (considering Earth is 4.5-4.4 billion years old).

Now there is a time gap - what happened between 4566 (formation of planetesimals and asteroids) and 4413 (formation of the moon)? There are about 150 million years that I haven't talked about yet. Was the Earth gradually growing in a linear fashion during that time or did it form rather quickly? Luckily, there are answers to that as well. Based on some measured geochemical data it was shown that most of Earth's mass actually accreted ~10 million years after the formation of the solar system(8). That's rather quick! So the Earth has been sitting there, all by itself, around 100 million years until the moon formed. As to how the Earth itself formed, it could be just amalgamation of small planetisimals, collision of larger bodies, or something completely else. Chemical evidence and physical models do not always agree, and it's all highly debated.

This is a field which is rapidly evolving and discoveries are made all the time due to better analytical capabilities and better models. Just look at the years of the papers below. This is all cutting edge and a highly exciting field of study. Everything that I wrote here can be inaccurate or even plain wrong, but that's the fun in science.

  Is there any physical evidence, or is it a conclusion reached mostly through simulation?

So it is a combination of both. You find physical evidence: rocks from Earth and parts of meteorites and their minerals. You measure their isotopic composition to find their age and other characteristics. Then you make a model (or a simulation) that tries to see what has to happen in order for the physical properties to agree.

Further reading:

An introduction to Meteorites and the origin of the Solar System - a very accessible and interesting read.

Chronometry of Meteorites and the Formation of the Earth and Moon - a more technical review, may be paywalled.

Refs:

1 Valley, J. W., Cavosie, A. J., Ushikubo, T., Reinhard, D. A., Lawrence, D. F., Larson, D. J., … Spicuzza, M. J. (2014). Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nature Geoscience, 7(3), 219–223. doi:10.1038/ngeo2075

2 Carlson, R. W., Borg, L. E., Gaffney, A. M., & Boyet, M. (2014). Rb-Sr, Sm-Nd and Lu-Hf isotope systematics of the lunar Mg-suite: the age of the lunar crust and its relation to the time of Moon formation. Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences, 372(2024), 20130246. doi:10.1098/rsta.2013.0246

3 Bouvier, A., & Wadhwa, M. (2010). The age of the Solar System redefined by the oldest Pb–Pb age of a meteoritic inclusion. Nature Geoscience, 3(9), 637–641. doi:10.1038/ngeo941

4 Burkhardt, C., Kleine, T., Bourdon, B., Palme, H., Zipfel, J., Friedrich, J. M., & Ebel, D. S. (2008). Hf–W mineral isochron for Ca,Al-rich inclusions: Age of the solar system and the timing of core formation in planetesimals. Geochimica et Cosmochimica Acta, 72(24), 6177–6197. doi:10.1016/j.gca.2008.10.023

5 Baker, J., Bizzarro, M., Wittig, N., Connelly, J., & Haack, H. (2005). Early planetesimal melting from an age of 4.5662 Gyr for differentiated meteorites. Nature, 436(7054), 1127–31. doi:10.1038/nature038825

6 Greenwood, R. C., Franchi, I. A., Jambon, A., & Buchanan, P. C. (2005). Widespread magma oceans on asteroidal bodies in the early Solar System. Nature, 435(7044), 916–8. doi:10.1038/nature03612

7 Amelin, Y., Kaltenbach, A., Iizuka, T., Stirling, C. H., Ireland, T. R., Petaev, M., & Jacobsen, S. B. (2010). U–Pb chronology of the Solar System’s oldest solids with variable 238U/235U. Earth and Planetary Science Letters, 300(3-4), 343–350. doi:10.1016/j.epsl.2010.10.015

8 Rudge, J. F., Kleine, T., & Bourdon, B. (2010). Broad bounds on Earth’s accretion and core formation constrained by geochemical models. Nature Geoscience, 3(6), 439–443. doi:10.1038/ngeo872


Coriolis effect and Cyclones The Coriolis force predicts that winds in the northern hemisphere should be deflected in a clockwise pattern and winds in the southern hemisphere should be deflected in an anti-clockwise pattern.  Why is it that in the case of cyclones however, the cyclones spin anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere?

Don't think of the Coriolis force as deflecting motion clockwise/counter clockwise, but to the right (NH) or left (SH), when looking in the direction of the motion.

So this is sort of 'by definition'. A cyclone is a low pressure system, and air will move from a location with high pressure towards a location with low pressure. The Coriolis force will deflect this air to the right in the Northern Hemisphere, creating a counter-clockwise motion around the low pressure.
Around high pressure systems the direction of the motion is opposite, anti-cyclonic.

A very simple sketch, with a low pressure in the centre, and higher pressure around it:

Another way of looking at this is through the equation for geostrophic motion. The wind around a cyclone is (nearly) geostrophic, so the equation of motion can be simplified to

$$
f\mathbf{k}\times\mathbf{v} = -\frac{1}{\rho}\nabla p
$$

where $f$ is the Coriolis parameter, $\mathbf{k}$ is the vertical unit vector, $\mathbf{v}$ is the wind speed vector, $\rho$ is density and $\nabla p$ is the pressure gradient.

So, looking at a sketch of a low pressure system on the northern hemisphere, the pressure gradient force will look like

The gradient itself goes from low to high pressure, but the force has the opposite direction. To achieve a balance between this and the Coriolis term, we need this situation:

(Note the negative sign for the Coriolis term here. In the above equation we have equality, so with the negative sign the direction is opposite that of the pressure gradient force.)

As $f$ is positive on the northern hemisphere, when we use the right-hand rule for cross-products, this means that $\mathbf{v}$ must be directed as

i.e., giving a counter-clockwise motion around the low pressure.


Geode-like rock but it's empty inside. Why does this happen? I found this geode-like rock (spheroidal shaped with empty spheroidal cavity inside) near Dickson Tennessee, USA. Comments suggest that this is in fact geode, but it is empty and featureless inside.

The white on the outer part is soft and can be flaked off.

Can this still be a geode? Assuming it is, why might this one be empty inside instead of being full of crystals?
Would this be indicative that most geodes in this area are likely to be empty as well, or would there be no correlation between one and another?

Click any image for full-size view, scale is in inches:

Geodes form where there is a gas bubble or some other sort of cavity in volcanic or sedimentary rocks. I once found scores of them eroding out of a sea cliff in Oman, and they looked very similar to yours. I can tell that your geode was formed in sedimentary rock like mine were. What happens is that over millions of years, water seeps in, sometimes bringing in sand and clay particles which line the cavity when it occurs in sedimentary rock. This mineral rich water, sometimes from hydrothermal sources, seeps into the cavity and precipitates various minerals, mostly silicon dioxide, around the sides of the hollow. This usually results in a lining of quartz crystals, but can produce amethyst or opal, both of which are composed of silicon dioxide. Very rarely, opalized fossils are found inside geodes. As for your empty geode, I presume that either the necessary seepage of mineral-laden water never happened, or it never had time to happen. The process takes millions of years.


Is the urban heat island effect stronger during a particular season or part of the year? It is known that cities tend to be warmer than the surrounding landscapes, and this is known as the "urban heat island effect".

In the summer there is greater heat output from air conditioning systems. In the winter there is greater heat output from heating systems (heat pumps aside). Are these a substantial contributor to the effect, or are there other causes?

Summary of question: What are the causes of the urban heat island effect, and are there specific times of the year when the effect is stronger?

As with so many concepts in geography, I don't think there is a definitive answer -- it would very likely vary from city to city and from year to year. Urban heat island (UHI) effect is affected by so many different variables, such as albedo (reflectivity of surfaces), specific heat of the materials receiving and releasing radiation from the sun, thermal conduction into the ground, cloud cover, wind, and as you mentioned, anthropogenic heat production.

Throughout the year in a city with four distinct seasons, most of these variables change independently of each other (except for probably the specific heat of the materials). For instance, in a hypothetical city that receives a great deal of snow, albedo might be much higher in winter due to the high reflectivity of snow covering low-reflectivity surfaces (such as asphalt, roofs, etc.), which might reduce its contribution to UHI by causing fewer surfaces to absorb radiation from the sun. However, as mentioned in the question, anthropogenic contributions to UHI Effect might be higher in winter in the hypothetical city from latent heat from buildings, water/sewer pipes, vehicles, and so on. Further, wind patterns might shift in winter, bringing in more cool air in winter rather than summer, which would counter the increase from the anthropogenic sources.

Also, impacts from urban heat island are actually generally most pronounced during dusk, which is when much of that short-wave radiation from the sun (which was being stored all day in the sun) is released as long-wave radiation. With that in mind, another factor that could contribute is day-length. Many cities with four distinct seasons are in the mid-latitudes, which have variable day lengths between the seasons. Longer daylight in summer, then, would suggest that the UHI Effect would be worse in summer, as there would be more time for the surfaces to absorb short-wave radiation from the sun.

Great question - sorry for not definitively answering it. It appears there are some gaps and conflicts in the limited research on this topic.

A grad student at UMN suggests that UHI effect is worse in winter (without really explaining why), while TR Oke suggests it is worse in summer, while James Voogt  suggests that UHI effect is generally stronger in summer and winter compared to spring and autumn (in the mid-latitudes).


What is the geothermal potential of a volcano? If there were lots of geothermal plants—even mobile ones—near a volcano, how much power could this provide? Could the sapping of some of the heat energy make the volcano less likely to erupt?

Volcanoes erupt due to increase in pressure, within the magma chamber (often 3-10 km deep), due to exolusion of volatiles. The magma chamber is usually heated from below. Geothermal plants in volcanic regions exploit heat from hot water in the "shallow subsurface", few hundreds of meters deep (and rarely exceeding 1-2 km). So as far as your second last question is concerned the impact on the volcano will be little as deep hydrothermal circulation can only transport so much heat.

There are many such plants around the world, e.g., Iceland, Philippines, Indonesia, New Zealand etc. However drilling in hot rocks has its own set of problems. It is also not easy to build large plants near volcanic areas due to lack of accessibility, infrastructure, market etc.


What is the difference between chalcophile and siderophile elements? As it is described (W. M. White, Geochemistry):

  Siderophile elements have an affinity for a metallic liquid phase
  and
  chalcophile elements have an affinity for a sulfide liquid
  phase.

What is the exact difference between them? It just seems to be the same thing as sulfide liquid must contain metals as well. As far as I know, siderophile elements are: Fe, Co, Ni etc and chalcophile ones are Ar, Mg, Sr, Ba etc.

First, a small correction: Fe, Co and Ni and considered chalcophile. Mg, Sr and Ba are lithophile. Ar is atmophile.

Here's the classification, just in case you need to have it in front of your eyes: source: the Wikipedia article on Goldschmidt classification

  What is the exact difference between them? It just seems to be the
  same thing as sulfide liquid must contain metals as well.

This is a bit confusing because most siderophile metals are also chalcophile. Let's begin by defining what are metal and sulfide liquids in the Earth.

Metal liquid: Siderophile elements are concentrated in molten Fe. Not just any metal, but specifically molten Fe. This is truly molten metal, where most of the atoms are neutral, the bonding is metallic, and there are no ionic bonds. The only place that a liquid like this exists to any significant proportion today is Earth's outer core.
Sulfide liquid: Chalcophile elements are concentrated in molten sulfide. In the Earth this will mostly be Fe-rich sulfide, the liquid analogue of pyrrhotite and pentlandite (known as mss in high temperature). This liquid is dominated by the presence of sulfide as S2-. This is no longer a metallic liquid with neutral atoms. This is a liquid where the bonding character is a combination of ionic (because you got Fe2+, Ni2+ and S2-), metallic and covalent. Sulfide liquids can exist in the core (we do not know), but they exist in the mantle and the crust where they are how you move the chalcophile (and siderophile) elements around. Ore deposits of these elements almost always form from sulfide liquids, or their alteration products.

Because of the contrasting bonding properties of the metallic and sulfide liquids, trace elements partition differently to them. For example, Te and Cu will "feel more comfortable" in sulfide liquid, whereas Ir and Au will prefer the liquid Fe metal.

How does this fit in the bigger picture? The main importance of the siderophile-element category is that there are not enough of them. When you look at how much siderophile elements there are in the solar system, and then compare to how much we have in the crust and mantle, there are not enough. This is especially true for the highly siderophile elements (HSE: Au, Re, Ru, Rh, Pd, Os, Ir, Pt). This is unfortunate, because these are very useful metals. We could all use some more Au, Pt and Ir. The accepted explanation is that when the Earth formed, the liquid Fe metal that sunk to the core scavenged the siderophile elements from the surrounding silicate (lithophile-nearing) magma ocean and locked them in the core, far away from us.

But this occurred a very long time ago, and has little relevance for moving the siderophile elements around in more recent times, and in places closer to us. In the absence of liquid metal, siderophile elements actually behave as chalcophiles. Ore deposits of HSE and particularly the platinum group elements (Ru, Rh, Pd, Os, Ir, Pt) occur in sulfides.


Relative Humidity approximation from Dew Point and Temperature I would like to find a formula to approximate RH based on known air temperature and dew point. I need the approximation to be valid at least between -20...+40 degrees Celsius. I read the accepted answer on this question, but unfortunately

the link for the document where the tabulated values were retrieved from is no longer working
using those values yield weird results. I tried it (the RH formula with the constants in the first row of the table) with T = 16.15 and TD (dew point) = -4.45, and it gives 215% RH (could it be $100^{m*...}$ instead of $100 *10^{m*...}$?...)

Any help would be appreciated. Thanks.
UPDATE
Thanks @BarocliniCplusplus for his answer. If anyone reading this needs an implementation in Python to approximate the RH, here is one:
RH = 100*(math.exp((17.625*TD)/(243.04+TD))/math.exp((17.625*T)/(243.04+T)))

where T is the temperature, and TD the dew point. This approximation is taken from this article (see "Conclusions" in the article for more details).

The equation for relative humidity is $$RH=100\times \frac{e}{e_s(T)}=100\times \frac{e_s(T_d)}{e_s(T)} \tag{1}$$
Where $T_d$ is the dewpoint temperature and $T$ is the temperature, $e$ is the water vapor pressure, and $e_s$ is the saturation vapor pressure, which is also known as the Clausius Clapeyeron equation. While the previous link has a decent definition and equation, my preferred equation (particularly because it is derivable) is the low temperature approximation:
$$e_s(T)= e_s(273 \mathrm{K})\exp\left[\frac{L_v}{R_v}\left(273.15^{-1}-T^{-2}\right)\right] \tag{2}$$
where $T$ is the temperature or dewpoint temperature in Kelvin, $L_v$ is the latent heat of vaporization,$e_s(273 \mathrm{K})=6.11 hPa$, and $R_v$ is the specific gas constant for water vapor. Note that $(2)$ is for liquid water. You may be able to replace $L_v$ for $L_s$ for sublimation/deposition. Also note, that this is the "pure" form of the relative humidity equation. The presence of solutes (Cloud condensation nuclei) may lower the saturation vapor pressure, increasing the actual relative humidity. I'll let combining $(1)$ and $(2)$ be an exercise left for the reader.


Has there ever been a study done on the effect of steam/thermal pollution on climate Most people are well aware of the idea of greenhouse warming. Carbon dioxide receives particular attention, do to the uncertainty of sources, sinks, and inert properties. However, combustion, which produces carbon dioxide, also produces water vapor, another greenhouse gas. I am aware of the paper on contrails, but generalizing that idea beyond contrails.
Given that water vapor is a greenhouse gas, and assuming the produced quantities are comparable to the quantities of carbon dioxide produced, has there been a study using climate models, with only water vapor emissions inventories, as compared to only carbon dioxide emissions inventories?

A second aspect to this is thermal aspects of anthropogenic steam. Because steam is produced with a temperature higher than the environment, how much of an impact does the mixing of this steam have on the climate, particularly the microclimate?

While the effect might be measurable (just barely) it's small.   We add about 30 billion tons of CO2 to the air every year.   About half of that gets absorbed into the oceans (give or take), the remaining 15 billion tons remains in the atmosphere for a long time.

280 PPM CO2 the post ice-age, pre industrial revolution number works out to about 1,000 billion tons of CO2.   Adding 15 billion tons per year, at the current rate, it would take about 66 years to double the 280 PPM to 560 PPM.   That's, of-course, very much an approximation and the ocean absorption rate probably doesn't remain constant it depends on the change in concentration and change in ocean temperature.

Water vapor, however.   While the output varies depending on fuel the mass of water added by burning fossil fuels is about 1/2 the mass of CO2, so 15 billion tons per year.   The amount of water vapor in the atmosphere at any given time is by this estimate about 5,700 billion tons.    Adding 15 billion tons of water vapor to the atmosphere per year might be enough to be significant, but as pointed out in the comments, water vapor leaves the atmosphere very quickly.  Unlike CO2, which takes a long time to filter out.   The half-life of water is days, the half-life of CO2 is probably a century or more.

If extensive driving or fossil fuel burning is done in low humidity areas, it seems feasible that some warming could be added by the increase in water vapor, but I expect that effect would be small but perhaps measurable.   In high humidity areas it would be irrelevant.   I've never heard of a study that looked at this in any detail.    That said, the intuitively obvious answer is that the effect would be tiny.   A tiny fraction of of the effect of CO2.    That said, water vapor does need to be included in the study as warmer temperatures hold more water vapor, so, as the Earth warms, water vapor in the atmosphere increases and pushes the warming along even more.   That's a well known feedback mechanism.    The effect of water from burning fossil fuels is likely very tiny because it's too little and too temporary and the net total amount of water vapor in the air is still primarily a factor of temperature, weather patterns and wind direction.    It is, however, probably not zero.  There's likely some tiny effect, but I've never heard of a study that looked into it.


Intuitive definition of the Monin-Obukhov length? The Monin-Obukhov length (L) is defined as:

$$L = - \frac{\rho C_p T_v u^3_*}{kgH}$$

where $\rho$=moist air density; $C_p$=air specific heat capacity; $T_v$=virtual temperature; $u^3_*$=wind friction velocity; $k$=0.41 (von Karman constant); $g$=gravity; and $H$=sensible heat. Note that there are lots of different formulations - this one is taken from this video on eddy covariance.

It is used when describing how turbulence is affected by bounancy, e.g. from rising thermals from the earth's surface. I would like to get some intuition for what the length actually physically represents. The wikipedia page states that:

  A physical interpretation of L is given by the Monin–Obukhov similarity theory. During the day -L it is the height at which the buoyant production of turbulence kinetic energy (TKE) is equal to that produced by the shearing action of the wind (shear production of TKE).

However, that is still pretty opaque to me. To me, that sounds something like a parameter of a distribution that describes at what height wind shear starts to break up up-welling packets of air, but I really don't have any idea. Is there a good intuitive description of this quantity?

The way I understand it is the height above the surface at which buoyant (heat) production of turbulence first equals the mechanical (shear) production of turbulence.

A more useful definition is given by the American Meteorological Society:

  A parameter with dimension of length that gives a relation between parameters characterizing dynamic, thermal, and buoyant processes.

  At altitudes below this length scale, shear production of turbulence kinetic energy dominates over buoyant production of turbulence. It is defined by

  where k is von Kármán's constant, u* is the friction velocity (a measure of turbulent surface stress), g is gravitational acceleration, Tv is virtual temperature, and Qv0 is a kinematic virtual temperature flux at the surface. The parameter was first described by Obukhov in 1946, and therefore should not be called the Monin–Obukhov length, even though there is a Monin–Obukhov similarity theory that uses it. The Obukhov length, of order one to tens of meters, is the characteristic height scale of the dynamic sublayer. The Obukhov length is zero for neutral stratification, and positive (negative) for stable (unstable) stratifications. The dimensionless Obukhov length z/ L (where z is height above the surface) is used as a stability parameter, with z/L = 0 for statically neutral stability, and is positive (negative) in a typical range of 1 to 5 (-5 to -1) for stable (unstable) stratification.


Is it possible to get trapped in a circle of water in a rip current? According to the YouTube video Rip Currents: How to Survive the Deadliest Ocean's Trick, a rip current occurs when there are two circles of water spinning close to shore in opposite directions such that the water between them is flowing away from shore. My question is

  Is it possible to put yourself in a position where you're inside a spinning circle of water associated with a rip current and there's no way to escape from it without swimming underwater until you're rescued?

I don't know if that's possible or not. Maybe the water on the surface in a spinning circle is flowing around the circle and towards its centre and the water below the surface is flowing away from the centre. I won't get into the question about whether it's possible to escape the circle by swimming underwater. I think in that situation, the best thing is to swim directly away from the centre and not to swim against the current and let yourself keep being dragged around in circles. Even if you do that, the rate that water is flowing towards the centre might still be too fast. This is pretty much a yes no question so I think it should be easy to provide an answer that actually answers my question. Researchers might then be able to use the answer to invest in research on the best strategy to escape from a rip current.

Ok, i try an answer based on your clarification.

Diving in a straight line in such a regime is near impossible, because sight is obstructed. A specially trained free diver may have more of a chance but will have to go to the surface several times.

Now let's assume that an unlucky swimmer finds him-/herself in exactly the depicted situation and quickly analyzes and realizes what's going on (unlikely). If they are cold blooded enbough they can try and swim to one side, then with the stream either once around or back again towards the beach. But ... things aren't usually like in a picture book. There are coast parallel streams, waves and rocks can make it difficult to get out of the water unhurt, and maybe the stream turns too far outside or not at all. There may be undertow or a breaking wave throws the swimmer on the rocks. And when outside, even in 20° warm water the survival chances are low, until a helicopter or the rescue boat arrive. And even then, finding a head of a swimmer between the waves is pure luck for the rescue forces. People have actually drowned in the middle of regattas and dense trafic searching for them. That is why it is strictly forbidden to go overboard ;-)

There is a reason why people do die in such or similar situations. In any case, the answer to your question is "Yes", a swimmer can easily find himself in a situation where reaching the land is impossible. A snorkler with fins may have better chances.

Edit: just so that you know what i am talking about, 3 random videos. Medium conditions, waves 1-2m. Dynamic conditions, waves 6-8m. Calm conditions, .5m waves.


Could the Grand Canyon be flooded by the ocean if it got deep enough? The Colorado River has been carving the Grand Canyon for a few million years now, such that the canyon floor is around 6000 feet lower in elevation than the surrounding area, at about 2400 feet above sea level. If things continue as they have, the Colorado River will continue to make the canyon deeper. If the river eroded away enough rock so that the river's bottom got to sea level, and this process continued to go upstream the river from where it empties into the Pacific Ocean so that the floor of the canyon eventually eroded below sea level, would the canyon gradually be filled in by the ocean? Would this even be possible? If not, why don't we see the mouth of the Colorado (or any river for that matter) gradually  move upstream, with ocean filling in where the river once was?

It is unlikely just from erosion. There are a couple reasons for this but because of the time scale over which this process would occur, other phenomenons might change the geologic picture completely.

The reason the canyon formed in the first place is because of tectonics that uplifted the rocks. From this page:

  Uplift of the Colorado Plateau was a key step in the eventual formation of Grand Canyon. The action of plate tectonics lifted the rocks high and flat, creating a plateau through which the Colorado River could cut down.

Erosion is much quicker when the slope is steeper so the carving of the canyon slows down as the river flow gets gentler. So the deeper the canyon carves, the more potential force it loses. From the same source as the earlier quote, a stratigraphic profile:

Another reason erosion has slowed down significantly is that the type of rock the water has to carve through is much different the deeper it gets. The river has now reached metamorphised layers that are much harder than the limestones and sandstones from the upper layers. The Vishnu Group is practically bedrock. This page has a nice explanation:

  The steeper the slope, the faster the runoff flow and the more force it will have to move material. The less vegetative (plant) cover and leaf material on the ground, the more open the soil will be to the flowing runoff water. Four things cause slope erosion: the amount and rate of rainfall, the steepness or gradient of the slope, the amount and nature of plant cover, and the type of soil and bedrock underneath.

Regarding this question:

  why don't we see the mouth of the Colorado (or any river for that matter) gradually move upstream, with ocean filling in where the river once was?

Erosion takes material away but this material has to go somewhere. Sediments are carried downstream and deposited at the mouth of those rivers, becoming what we call river deltas. The deltas usually advance into the sea as the mass of sediments is incredibly huge. Take a look at this picture:

This is the eastern end of Lake Mead where the Colorado river would flow when the reservoir level was higher. The entire flat brownish area is deposited silt from around 50 years of flow. I rafted through that now exposed silt and the walls on either side of the new channel were over 30 feet high. The same thing occurs in the oceans, but over much longer timescales.

So, to summarize:

There is much less water flowing through now than in the past. If Colorado winters become too mild and dry, then the river's power will be even further diminished.
The slope gradient of the river can only get gentler, so erosion will slow down.
The river has reached much harder rock that resists erosion much better.


What is the meaning of seismic spectral blueing? What is the meaning of seismic spectral blueing? Please cite any good introductory materials if possible.

It is a kind of spectral shaping, intended to increase the vertical resolution of seismic reflection data.

The logic goes like this:

Seismic data is band-limited and lacks high frequencies. This limits its vertical (travel time, and thus thickness) resolution. This is annoying because we often care about thin beds.
The spectral peak of seismic data tends to be at a fairly low frequency compared to its total band. That is, the longer wavelengths are disproportionately strong compared to the short ones. Thinking of an analogy with the electromagnetic spectrum, we could say that the spectrum is reddish.
We assume that geology is whitish, or scale free, so all 'frequencies' are represented (when we're in the time domain, they are frequencies; when in depth they are wavenumbers).
So maybe we can reshape the seismic spectrum to more closely match the geological spectrum, as derived from logs, by boosting the higher seismic frequencies a bit.
One way to do this is to design an operator, a sort of wavelet, with which to convolve the seismic data. The result would be the seismic with the boosted frequencies.

Here's one example of the application of the method [PDF] from Yadav et al. (2010).

It's just my opinion, but I'd treat the idea and the method with the same skepticism as any method claiming to enhance seismic resolution. That said, I'm sure there's a champion of blueing for every detractor. Caveat interpretor.


could a rhyolitic magma melt a ferromagnesian mineral like olivine? if the temperature of a felsic magma is about 800-650 °C and olivine melting point oscillates between end members forsterite and fayalite near 1900-1200 °C, Does this mean that an olivine crystal in the magma would never melt, even if it were very small in relation to the amount of magma?

This is an excellent question.

What does happen when you drop a crystal of olivine into liquid rhyolite?

There are several answers which all depend on the exact composition of the olivine, how much magnesium is in the rhyolite, temperature, size of the olivine, how much olivine are you dropping into how much rhyolite, and more.

Let's take the most extreme case of dropping pure Mg olivine (forsterite) into pure felsic rhyolite (a feldspar–quartz liquid mixture). For argument's sake let's assume full thermodynamic equilibrium.

First, rhyolites can dissolve some amount of Mg. Not much. Maybe 1%, maybe 2%. If it's only a tiny bit of olivine, the olivine will dissolve as a liquid into the rhyolite (you might call it "melt", but that's not the correct term), making the rhyolite a bit more magnesian.

If you add a bit more olivine, you saturate the melt with Mg. This means that a certain magnesian mineral will form in equilibrium with the rhyolite liquid. This could be biotite, amphibole, a clinopyroxene, etc. But because our simple system has no water and no calcium, pure solid olivine sounds like a good choice.

However, forsterite is not stable in felsic systems. It will react according to the reaction:

$$\ce{Mg2SiO4 + SiO2 = 2MgSiO3}$$

This is the reaction of forsterite (Mg-olivine), reacting with quartz, to form enstatite (orthopyroxene). Therefore, your olivine doesn't melt. It converts to a different mineral: orthopyroxene!

This is well illustrated by the following phase diagram, coming from this website:

Some more related questions and answers:

Melting point of minerals

Why do felsic materials have lower melting points than mafic?


Can anyone explain the reason why CO$_2$ increases global temperatures (not the simplistic greenhouse analogy provided for public consumption)? The greenhouse effect analogy of global warming is that atmospheric carbon dioxide CO$_2$ absorbs some of the infrared radiation emitted by the Earth, and redirects a portion of that radiation back down to the Earth's surface, thereby heating the surface more than it would have done if that radiation had been able to escape into space.

Global warming is then simplistically explained to the general public by the idea that as atmospheric CO$_2$ concentrations rise, more infrared radiation is absorbed by CO$_2$ and re-emitted back down to Earth, causing increased heating of the Earth.

However, this explanation is not technically correct, because at present atmospheric CO$_2$ concentrations, just one kilometer of atmosphere is sufficient to fully absorb all the infrared radiation emitted by the Earth, at the wavelengths at which CO$_2$ absorbs.

Carbon dioxide absorbs infrared at the wavelengths of 2.7, 4.3 and 15 µm, and the CO$_2$ in the first kilometer of atmosphere alone is able to completely absorb all infrared at these wavelengths.

So the infrared absorption process is already fully saturated, and thus further increases in atmospheric CO$_2$ will not lead to any additional absorption. This is why the simplistic explanation provided for the general public does not seem to be technically correct, even though it roughly outlines the idea.

I found one blog article by Clive Best that tries to explain the actual process behind CO$_2$'s ability to cause global warming. Judging from that article, the actual process is more complex than the simple explanation provided for public consumption. However, I don't fully understand the explanation given in the article (and from what I did manage to understand, I am not sure if it is fully correct).

So I wonder if anyone here can provide an easy to understand explanation of the actual mechanism by which increased atmospheric CO$_2$ leads to global warming. Or perhaps if you know any good articles that explain it, please can you post the links.

I tried to find some info on the actual mechanism of global warming via Google, by using search terms such as "mechanism of greenhouse effect in global warming", but was surprised to find very little information available.

I also asked this question on physics.stackexchange.com here.

Borrowing an explanation from one of my other answers, the basic mechanism of the greenhouse effect is roughly as follows (note this is also a simplified model)

  The Earth is in (to all intents and purposes) a vacuum, so it can only
  gain or lose heat via radiation. The sun emits most of its radiation
  at visible and UV wavelengths. The Earth's atmosphere is fairly
  transparent at these wavelengths and so the Sun's radiation mostly
  passes through it and hits the surface. Some of this radiation
  (determined by the Earth's albedo) is reflected from the surface back
  out into space, but the rest is absorbed by the surface, which causes
  the surface to be warm. The surface loses heat by radiating in
  infra-red wavelengths. Greenhouse gases absorb some of the IR
  radiation, which causes the atmosphere to warm up (the GHG molecules
  transfer some of this heat to non-greenhouse gasses by collisions, but
  heat is also transferred upwards by convection). The warm atmosphere
  re-radiates some of this energy both upwards into space and downwards
  back to the surface. The part that is radiated downwards is also known
  as "back-radiation" (and is directly observable). Now the important
  factor is not the amount of outbound IR radiated from the surface that
  is absorbed, but the altitude at which there are not enough greenhouse
  gases above to absorb the IR radiated upwards from that layer, so that
  it can escape out into space. The lapse rate means that the
  temperature of the atmosphere decreases with increasing height. This
  means that the more CO2 we put into the atmosphere, the higher this
  emitting layer becomes, and the colder it is. As the amount of IR
  radiated depends on the temperature of this layer, if this height
  increases then the amount of IR radiated from the planet falls,
  leading to an energy imbalance, with the planet absorbing more of the
  sun's radiation than it emits as IR, and so the planet warms up. This
  continues until the radiating layer warms up enough for the outbound
  IR to be in balance with the incoming radiation from the sun. So the
  more CO2, the warmer the mean surface temperature, all things being
  otherwise equal.

Thus it is irrelevant that most IR emitted by the surface is absorbed by the atmosphere, it is the height from which IR is not absorbed that matters.  If it is colder than the surface, it will emit less IR than the surface is emitting and hence less energy is radiated into space.

For a more detailed explanation of why absorption at the surface is of little relevance, see this RealClimate article by Spencer Weart.

Just to add a historical note, this explanation goes back at least as far as Ekholm's paper of 1901 "On The Variations Of The Climate Of The Geological And Historical Past And Their Causes":

  The atmosphere plays a very important part of a double character as to the
  temperature at the earth’s surface, of which the one was
  first pointed out by Fourier, the other by Tyndall. Firstly, the
  atmosphere may act like the glass of a green-house, letting through
  the light rays of the sun relatively easily, and absorbing a great
  part of the dark rays emitted from the ground, and it thereby may
  raise the mean temperature of the earth’s surface. Secondly, the
  atmosphere acts as a heat store placed between the relatively warm
  ground and the cold space, and thereby lessens in a high degree the
  annual, diurnal, and local variations of the temperature.

  There are two qualities of the atmosphere that produce these effects. The
  one is that the temperature of the atmosphere generally
  decreases with the height above the ground or the sea-level, owing
  partly to the dynamical heating of descending air currents and the
  dynamical cooling of ascending ones, as is explained in the mechanical
  theory of heat. The other is that the atmosphere, absorbing but little
  of the insolation and the most of the radiation from the ground,
  receives a considerable part of its heat store from the ground by
  means of radiation, contact, convection, and conduction, whereas the
  earth’s surface is heated principally by direct radiation from the sun
  through the transparent air.

  It follows from this that the radiation from the earth into space does
  not go on directly from the ground, but on the average from a
  layer of the atmosphere having a considerable height above sea-level.
  The height of that layer depends on the thermal quality of the
  atmosphere, and will vary with that quality. The greater is the
  absorbing power of the air for heat rays emitted from the ground, the
  higher will that layer be, But the higher the layer, the lower is its
  temperature relatively to that of the ground ; and as the radiation
  from the layer into space is the less the lower its temperature is, it
  follows that the ground will be hotter the higher the radiating layer
  is.”

 [Ekholm, 1901, p19-20]

(h/t Steve Easterbrook's blog article)


Can anyone explain this frost phenomenon? Look at this amazing frost I woke up to in Sooke, BC, Canada. This was so very cool to wake up to.

I am going to take a guess and say these are Frost crystals. There are few conditions that need to be present in order for these to develop

1) Light wind

2) Relatively high humidity(some water vapor source perhaps nearby)

3) Depending on your elevation - was this somewhere near a mountain basin ?

As opposed to snow crystals frost crystals form more near the surface

You can read this article  Frost crystal and if the answers are in the affirmative
then you know these are the conditions that caused these crystals to form.


Why don't weather forecast models normally take solar eclipses into account? Since there is a total solar eclipse somewhere almost every year, I would have thought it would be included as a standard option in weather forecast models.  However, I've learned that is not really the case.

The moon does not normally affect weather, but during a solar eclipse, there is reduced solar radiation reaching the surface of the Earth.  This causes cooler temperatures and changes in wind speed/direction than would not otherwise be predicted.   The NOAA ESRL HRRR took the solar eclipse of August 21, 2017 into account when doing the weather forecast and found cooling of up to 6 degrees Celsius in some places.  Do any other weather forecast models take solar eclipses into account?  Or, is this the first time?  Why don't weather forecast models normally take solar eclipses into account?

Total solar eclipses are rare.  Globally, they only happen every 18 months.  In any given spot, they are much, much rarer, with a recurrence period of many hundreds of years.

Solar eclipses are localised in time and space.  Although model resolution may be just about small enough (in time) to resolve the totality, it only has a limited impact.

One could implement solar eclipses in weather forecast models, but there's plenty of more important things to worry about improving.  Operational weather forecast models are complex beasts, so you really want to change things only if it may yield a significant improvement.  The potential improvement of implementing a consideration of solar eclipses is minimal, so it's simply not worth the effort or the risk.

Experimental models are a different category and as you have seen, eclipses have been implemented in those.  But the risks involved are much smaller; nobody really cares if experimental models go totally wrong, but you really don't want to be responsible for breaking the operational weather forecast model.

You might be interested in this article on The weather’s response
to a solar eclipse that  my colleagues wrote.


What are the differences between implicit and explicit methods when applied to modelling Earth systems? I am struggling to understand the difference between implicit methods and explicit methods in numerical modelling of Earth processes, particularly when applied to modelling Earth systems in 2 or more dimensions, such as in NWP (Numerical Weather Prediction), for example.

I understand the basic principle for the explicit method: that an explicit model would calculate the new value of each grid square independently for each time step, for example. The application of the implicit method puzzles me though – it seems to require knowledge of both the current state of a system and the latter  state, before the latter state is even calculated? Is it somehow extrapolating the outcome?

The answer by @IsopycnalOscillation explains some implications of using explicit and implicit schemes and in what applications one is preferred over the other. Here, I describe how these two methods actually work, and how does the implicit scheme uses knowledge of the later state.

Take the ordinary differential equation:

$$
\dfrac{\partial u}{\partial t} = f(u,t)
$$

and for simplicity, let $f(u,t) = -cu$, where $c$ is a positive constant and $u = u(t)$. The equation is then:

$$
\dfrac{\partial u}{\partial t} = -cu
$$

often called the linear drag equation.

Again, for simplicity, we consider the simplest two schemes, a first order forward Euler differencing (explicit), and a first order Euler backward differencing (implicit). As you know, forward Euler differencing yieds:

$$
u_{n+1}=u_n-c\Delta tu_{n}=u_n(1-c\Delta t)
$$

This method is called explicit because the future state is evaluated as function of the present state. From the von Neumann stability method where the growth factor is defined as:

$$
\lambda = \dfrac{u_{n+1}}{u_n} = 1-c\Delta t,
$$

the scheme is stable when $|\lambda|<1$, neutral when $|\lambda|=1$, and unstable when $|\lambda|>1$. We see that the forward Euler method applied to the linear drag equation may be unstable.

With the implicit Euler backward differencing, we have:

$$
u_{n+1}=u_n-c\Delta t u_{n+1}
$$

Rearranging the terms leads us to:

$$
u_{n+1} = \dfrac{u_n}{1+c\Delta t}
$$

Notice that the $u_{n+1}$ is not found on the right-hand side anymore. Here, the growth factor is:

$$
\lambda = \dfrac{1}{1+c\Delta t}
$$

We see that, in this case, $|\lambda|<1$ holds for any value of $c$ and $\Delta t$.

Thus, if one is concerned about stability, an implicit method is advantageous for solving this equation. However, notice that the implicit method is more computationally heavy, even in this simple case, because a division is significantly more expensive operation than multiplication. This is especially true in larger and more complex systems of equations where $f(u,t)$ may be a large matrix that need to be inverted.

A good introductory text on these methods and there applications in atmosphere and ocean modeling can be found here: Mesinger and Arakawa: Numerical Methods Used in Atmospheric Models (1976). For more references, see the answer to this question.