Can reforestation sequester our annual carbon emissions? Forests sequester and store substantial amounts of carbon every year, while each year humans emit substantial amounts of carbon into the atmosphere. Is it possible for forests to sequester as much carbon as we're currently emitting each year, and if so is there a rough estimate of how much reforestation would be necessary?

Of course with such drastic land use changes as it would require to reforest much of the Earth, humanity's carbon emissions would surely change. This is basically a thought experiment, or a rough analysis to highlight the potential (or lack thereof) for trees to sequester our carbon emissions.

Reforestation is a one-off gain in carbon storage. Once a forest is fully mature, the carbon cycles back into the atmosphere as trees die and decay or are burned. So no, this will not sequester all the emissions from fossil-fuel burning. It could help offset it in the short term, but probably mainly just offsets the carbon dioxide from deforestation.


North Indian ocean tropical cyclones Why are tropical cyclones in the Bay of Bengal more frequent and stronger than those in the Arabian Sea?

During the Indian Summer Monsoon, a low level jet covers the Arabian Sea. This causes vertical wind shear to increase over the Arabian Sea and inhibits cyclogenesis in the region. Hence, less tropical cyclone activity compared to the Bay of Bengal.

http://www.meted.ucar.edu/tropical/textbook_2nd_edition/print_3.htm#page_5.3.0
(Need account to login)
http://www.nature.com/nature/journal/v479/n7371/full/nature10552.html#ref1
(First line)


Gypsum saturation index I did some geochemical modelling and found groundwater samples I have are saturated with respect to the mineral gypsum. I need some help with interpretation, more information is given below.

The groundwater comes from an engineered aquifer that is comprised of sand. Prior to construction, the sand was in contact with water containing high sulfate and calcium concentrations (dissolved gypsum). There was also some pyrite oxidation occurring which undoubtedly lead to increased sulfate concentrations.

Does my geochemical modelling work give evidence that the groundwater dissolved $Ca$ and $SO_4$ concentrations are in equilibrium with solid phase gypsum? meaning the mineral is present even though it was completely dissolved initially?

thanks

A geochemical model, like phreeqc calculates the saturation index (SI) for minerals based on the composition of the solution, temperature, and possibly pressure. These are used to calculate the activities of the ions, based on the activity coefficients. These are then compared to the activities that would be present at saturation as defined by the solubility product (Ksp). The saturation index is < 0 if the solution is undersaturated with respect the mineral, = 0 at saturation, and > 0 if supersaturated.

So when you say the model shows you are saturated with respect to gypsum, it indicates that by definition you are in equilibrium with solid phase gypsum. It does not indicate if you got there by dissolving gypsum or by precipitating gypsum. It is highly unlikely (but theoretically possible) that your SI is exactly 0 without one of those things happening.


When did the last rifting / break-up event occur? When thinking about the formation of the current continents from a super-continent, it's clear that this is a gradual process, but there must be certain areas on earth which were once joined and were the "last" to break apart from Pangea.

Do we know when and where these rifting / break-up events took place?

Rifting is an ongoing process. At the moment, e.g. East Africa is rifting apart from the Nubian plate, we also see rifting of continental plates elsewhere, eg Rio Grande. New continents are being formed, but it doesn't happen on a human time scale. Modellers of future geography have a difficult task to decide what rifts that will stop and what rift that eventually will result in a new continent.

See yellow marked faults and rifts:

Madagascar is sometimes refereed to as the eight continent, not only of biogeographic reasons. It was rifting away from Africa and later India during mesozoic time, starting 160 Ma.

The last rifting that resulted in the present continents I can think about (probably the community can come up with a later event!), would be the North Atlantic breakup, that is still ongoing, but the last part of separation of present continents was the opening of the Fram Strait 16-10 Ma. This separated Greenland from the European plate and had a large impact on the Arctic Ocean conditions.


To what accuracy and precision do we know the volume of the Earth? Satellites such as GOCE and GRACE measure the geoid with unprecedented accuracy.  Altimeters can determine local surface elevation with millimetre-precision.  This makes me wonder: to what precision and accuracy can we measure (or calculate) the volume of the Earth?

I'm a lay when it comes to solid Earth, and I find it surprisingly hard to find even the order of magnitude of an answer ($10^0$ metre?  $10^3$ metre?  $10^{-3}$ metre?).  Wikipedia is extremely limited on the question and links to a surprisingly poor NASA factsheet that doesn't include any error estimates, cites no sources, and is imprecise in providing context or defining what it's talking about.

One can calculate the volume of Earth using semi-major and minor axes obtained from reference ellipsoids, but I have no idea how large an error is introduced by this approximation.

What are the precision and accuracy do we know the shape of the Earth?

One way to approach this is to treat the Earth as an oblate ellipsoid. This would mean the errors arise from the uncertainties in the Earth's equatorial radius and the flattening. From Groten, "Fundamental Parameters and Current (2004) Best Estimates of the Parameters of Common Relevance to Astronomy, Geodesy, and Geodynamics," Journal of Geodesy 77:10-11, 724-797 (2004), the Earth's equatorial radius in the mean tide system is 6378136.72±0.10 meters, and the inverse flattening is 1/f = 298.25231±0.00001. The uncertainty in volume due to the uncertainty in equatorial radius is about $3 V \frac{\Delta a}{a}$, where $V=\frac 4 3 \pi (1-f) a^3$, or about 51,000 cubic kilometers. The uncertainty in volume due to the uncertainty in inverse flattening is tiny in comparison, about $V \frac {\Delta 1/f} {1/f (1/f - 1)}$, or about 120 cubic kilometers.

That 51,000 cubic kilometer figure sounds like a lot, but it's not. It means the volume of the Earth can be expressed to seven places of precision.


Could this study "totally dismantle" Global Warming claims? Could this study "totally dismantle" Global Warming claims?

That's the assertion made in the article ‘Bombshell’ climate-change study could totally dismantle the claim humans are causing global warming.  Quoting from the study:

  "The conclusive findings of this research are that the three GAST data
  sets are not a valid representation of reality,” the authors wrote.
  “In fact, the magnitude of their historical data adjustments, that
  removed their cyclical temperature patterns, are totally inconsistent
  with published and credible U.S. and other temperature data. Thus, it
  is impossible to conclude from the three published GAST data sets that
  recent years have been the warmest ever — despite current claims of
  record setting warming."

On reading that article I noticed that they name but do not link to the article nor it's publisher. I was able to find it here: On the Validity of NOAA, NASA and Hadley CRU Global Average Surface Temperature Data & The Validity of EPA’s CO2 Endangerment Finding (pdf), but that's on a Wordpress site, not a credible scientific journal, as far as I can tell.  Further googling only turned up more references in political-influence sources like TheBlaze.com.

The one place that may be presenting as something that they published is the Heartland Institute (here), but I cannot tell if they are legit or not.

There is no publication information in the paper itself, nor any evidence of formal "peer-review" other than the list of scientists(?) on page 2 who affirm that they agree with the conclusions (which is not my understanding of what peer-review means nor of how it works).

I also have some trouble following the reasoning of their findings and conclusions, which seems like a bit of a logical leap.

So, my questions are:

Is this a legitimate peer-reviewed scientific paper as they claimed
How legitimate/credible is their methodology?
How legitimate/credible are their findings?  And is this really something new?
Is it published anywhere, and has there been any open scientific review, critique or commentary of it?
Does this paper really represent a credible threat to current climate change theories?

There is several credibility problems with this work.

First, they mention after the title:

  Abridged Research Report

but I cannot find any related full work from the authors on the matter. As a comparison, in this case, a short, simplified article was prepared as a companion for a full paper. The former is useful for news agencies and general public, and the latter for interested peers.

Second, references are poor. Data sources are cited, from government or agencies FTP sites, which is probably legit (I did not verify the linked data in great detail). GAST dataset are publicly available, as the freedom to publish possible misinterpretation in a proper peer reviewed journal, which remain to be done for the authors actual work.

Third, there is no real methodology. The abridged paper is presenting results and interpretations, but there is no real method.

Fourth, p17

  Clearly the historical GAST data adjustments that have been made have been dramatic and invariably have been favorable to Climate Alarmists’ views regarding Global Warming

This type of statement is having no place in a scientific paper, as this is poorly opinionated based on nothing of substance (Clearly, dramatic, Climate Alarmist) and does not prove much, except that the contribution is not scientific.

Fifth of less importance. the formatting is very poor, which is not helping with the credibility of authors - not that it is very hard to prepare nice and efficient looking reports these days. In a few words, poor communication (in this case, this paper) is not helpful to convince colleagues of alternative ideas (or any ideas).

Sixth until this work reach the stage of being published by an independent peer reviewed medium, I don't see how this could even begin to be a 'threat' to current climate science.


Wave train 200 m/s meaning I ran a 60 m line intended for surficial seismic refraction. Energization with hammer. 12 (10 hz vertical 5 m spaced) geophones and 5 shots (15 m spaced). Record length 0.5 s. Thanks to a borehole near a strata of man-made gravelly silt (0.40 m) and very soft silty clay (to 5 m) and then clay improves its consistency deeper were identified. My seismic traces seemed to be ok, but at office the principal wave train gives 200 m/s and first arrivals refractions are so weak that they cannot be easily identified. I think the principal train wave shadows them.

My question: What is the meaning of a 200 m/s train wave?

I've seen data like this before. My research focused on acquiring/processing both vertical and horizontal component data in subsurface environments characterized mainly by saturated and/or unconsolidated facies. So, it's entirely possible even for a that kind of surface-wave to display such low apparent velocities.

What I think you are seeing at that particular offset and traveltime is the Rayleigh-wave beginning to 'disperse' - AKA seismic dispersion beginning to manifests itself as a results of the wavefield convolving with layering and near-surface heterogeneity.

As for a refraction arrival, if it's indeed present, it should be extremely weak and probably only discernible via some kind of gain (e.g. AGC).


Information on this rock, and identity? My aunt gave me this rock.  She has had for years.  She was given it by a relative who passed many years ago.  She said it was called a Tuffy (not sure which way it should be spelled) and that it came from Neveda.  I couldn't find any info on it.  Could you help.  Thank you.

Typically we are not answering Rock Id questions, though this is a somewhat unique question because the rock is unique.  Your rock is likely a tufa (never heard it called tuffy).  It is a rock that is formed when water with high carbonate content is released to the surface.  Depending on the conditions at the surface the dissolved carbonate comes out of solution, this can be through cooling, depressurization and reduction of the partial pressure of CO2, or through biological precipitation by organisms such as blue-green algae.  There may also be other means that the deposition occurs but overall the water solution is initially oversaturated with the carbonate minerals.  These deposit out in the patterns shown on your sample.  If you were to perform an acid test your rock should show a strong reaction.  The area around the California Nevada boundary has a large number of locations with this type of deposit both active, Mono Lake, and inactive like the Trona Pinnacles.  Nevada itself has some of these deposits in the Black Rock Desert, Pyramid Lake and Fly Ranch areas.  Deposits are likely found world wide but these are the ones I am familiar with.  The pattern of deposition on your rock suggests to me an association with algae when it was deposited.  See the following sites:

https://en.wikipedia.org/wiki/Tufa

https://www.blackrockdesert.org/wiki/index.php?title=Geology


How many supercontinents have there been? With plate tectonics, supercontinents split up into smaller continents, and then the smaller continents get mashed up together to form a new supercontinent. There used to be a single supercontinent Pangea, and before that there was Rodinia. How many times in the past have all the continents been smashed up together into a single supercontinent?

There's a fairly decent Wikipedia page about this: https://en.wikipedia.org/wiki/Supercontinent
In short, though, the question of "how many times has this happened?" is very difficult to answer because the further you go back in Earth's history, the less evidence is still left today from that time. Not everything can or will ever be reconstructed with certainty.


Why do we recycle paper? Recycling metal and some plastics makes complete sense to me. Why bury something in a landfill that you'll have to find and dig up more of later. What I don't get is why we recycle paper products, especially those created with plant matter.

My understanding is that the fossil fuels we use for energy were generated during the Carboniferous period by burying carbon rich plant matter in anoxic swamps. If we are causing climate change by reversing this effect, dumping tons of carbon back into the carbon cycle... why recycle paper, or other products created, necessarily, by pulling carbon from the atmosphere?

Wouldn't a more beneficial method of disposing of such waste be to find a method of isolating them from the effects of weathering and keeping the carbon they contain locked up as long as possible?

Wouldn't a more beneficial method of disposing of such waste be to find a method of isolating them from the effects of weathering and keeping the carbon they contain locked up as long as possible?

You are ignoring a number of factors here.

A good deal of energy, much of it non-renewable, is needed to turn trees into paper. The trees need to be cut down (requires petroleum), transported to the saw mill (more petroleum), sawed and chipped (requires electricity), transported again (more petroleum). Once it gets to the paper mill, it needs to be pulped (requires petrochemicals, which need to be transported (requires petroleum)). The pulping process also consumes a good deal of electricity, as does the process of turning pulp into paper.

Bottom line: Paper has a positive carbon footprint.

If you send that paper to a landfill after using it, the carbon in that paper will be released to the environment, and in fairly short order. On the other hand, recycling paper bypasses a number of the steps involved in turning trees into paper. Turning paper into pulp is easy. Recycling paper reduces paper's positive carbon footprint by a significant amount.

The question specifically asks about finding a method of isolating wastes from the effects of weathering. That's not easy. Anaerobic bacteria find paper to be quite yummy. A deep ocean trench might work, but it would be better to not make paper in the first place. Growing and harvesting trash trees and then sending them into the deep would be more effective. A number of early geoengineering proposals suggested doing just that. There are big problems here, mostly unintended consequences. Deep sixing trees in deep ocean trenches is no longer viewed as a viable carbon sequestration scheme.


What is it about ancient craton geology that results in associated kimberlite pipes containing economic diamond deposits? According to the Australian Geological Survey Organisation paper Kimberlite and lamproite diamond pipes (Jaques, 1998), economic deposits of volcanically-formed diamonds are

  restricted to ancient cratons (typically >2.Ga) or cratonised provinces older than 1.8 Ga

Ga = billion years

and that rarely do younger accreted cratonised belts contain economic deposits.

This relationship can be seen in the Greenland Mineral Exploration Newsletter map below:

What is it about the ancient craton geology (and geochemistry) that results in the associated kimberlite pipes containing economically important diamond deposits?

The Science Daily article How diamond-bearing kimberlites reach the surface of Earth: Acidification provides the thrust (Ludwig-Maximilians-Universitaet Muenchen (LMU)) reports of research completed by an international research team led by Professor Donald Dingwell, Director of the Department of Geo- and Environmental Sciences at LMU.

They state that ancient cratonic crust provides silicate minerals that result in the originally basic magma to become more buoyant and as they are forced through the pipes, it causes the buoyant magma to move fast.  With the authors describing that as the magma ascent increases in velocity, the more silicates it gathers (entrains), increasing the dissolved silicate concentration - until the amount of released $\mathrm{CO}_2$ and $\mathrm{H_2O}$ greatly increasing the velocity of ascent, as the authors state 'like a rocket'.

A more thorough geochemical description is provided in the article Kimberlite ascent by assimilation-fuelled buoyancy (Russell et al. 2012), the proposed model mechanism as the original kimberlite melt to be carbonatite-like - poor in silica content, this magma assimilates materials during its accent through the upper mantle and crust, becoming more silicic, causing the $\mathrm{CO}_2$ solubility to decrease, reducing density and increasing buoyancy, causing the magma to accelerate.

In terms of why cratonic crust is the locale of many diamond rich kimberlite pipes is described from Professor Dingwell as being due to the silica rich cratonic crust is thick enough to provide the magma to make contact with the silicate rich minerals therein.


What is the loudest thunder ever recorded (dB) at ground level and where did it occur? Sound travels fastest through warm air and conditions such as temperature inversions can help to amplify the sound of thunder (source).  Conversely, during a thundersnow event the falling, and accumulated, snow can act as an acoustic suppressor (source). Originally I was thinking that the loudest thunder at ground levels would simply be at higher elevations, however the atmospheric conditions mentioned above, and others that I'm not aware of, have me wondering where the loudest thunder would actually occur.

Thunder 1 mile away-117 dB
Thunder 1/2 mile away-121 dB
Lightning strike just meters away from you-125 dB


Which ocean evaporates the most water per surface area? I guess the Pacific Ocean evaporates the most water because of its size.
But which of the major oceans evaporates the most water per square meter?

When push comes to shove, the highest evaporation rate per unut area corresponds to the highest average temperature.
As this pair of illustrations from NASA shows, that would be the Indian Ocean.

Simply put, the Indian Ocean misses both polar regions and hits the tropical and subtropical latitudes squarely, so it is warmer overall.  Ergo more evaporation.


Why don't pyroxenites and peridotites appear in Streckeisen's QAPF diagram? Wikipedia says for QAPF diagrams:

  "A QAPF diagram is a double ternary diagram which is used to classify
  igneous rocks based on mineralogic composition."

Why don't pyroxenites and peridotites appear on this diagram?

Aren't they igneous rocks?

Why don't pyroxenites and peridotites appear on this diagram?

Because they do not have any quartz, feldspars, or felspathoids.

The same Wikipedia page also says this:

  QAPF diagrams are also not used if mafic minerals make up more than 90% of the rock composition (for example: peridotites and pyroxenites).

Instead, we use a different diagram, that has olivine, orthopyroxene, and clinopyroxene at the vertices. Like this one right here.

  Aren't they igneous rocks?

Not necessarily, actually. But that's a completely different question.


what is the best way to detect spatial and temporal pattern of precipitation in mountainous region? The study area rang from 500 to 8000 m above ground and distributed into 4 elevation classes, above 5000,4-5000, 3-4000, below 3000 m above ground. This region has different climate zone/precipitation zone in term of amount and pattern.
What is the best way to detect the spatial and temporal pattern of precipitation in such region with monthly satellite data?

This is a non-trivial problem.  Short answer:  I don't think it can be done with monthly satellite data to a useful precision.

Here's where I started:

https://earthobservatory.nasa.gov/Search/index.php?hq=site%3Aearthobservatory.nasa.gov%2FFeatures%2F&q=measuring+rainfall

They now have a tropical rainfall project.

https://earthobservatory.nasa.gov/Features/TRMM/

It uses space borne precip radar.  In the article above I didn't find specs on the resolution.  Looking elsewhere, it's temporal resolution is 1 month, and horizontal is .25 degree (about 18 miles) If your study zone has latitude under 35 degrees, it may be of use, but overall it seems too coarse.  I would expect a montane environment would require a resolution on the order of a kilometre.

Even a simple rain gauge is problematic.  Go look at the siting requirements.  I suspect that parking one on a cliff at 6700m is going to give you non-conformant data.

I think synthetic aperture radar is being used to determine snowpack depth.
In the bad old days they hired people to go measure snow packs.

Using corner reflectors on the surface where they would be buried in snow may give you better results.  You measure the attenuation from the snow on top of them.  Take substantial time and effort to calibrate. Big win:  You are measuring the mass of ice in the column, not the depth.

Rainfall is much more difficult.  Water doesn't pile up and wait to be measured.
Or maybe you could stack it:  Consider a corner reflector at the bottom of a cone.  Choose a frequency that is somewhat absorbed by liquid water.  The cone is deliberately angled so that reflections off of it miss the transmitter.  So the corner reflector's signal is attenuated by the pile of water on it.  The cone magnifieds the water depth.

Weather radar can determine precipitation intensity, but using it in the mountains would mean getting returns of the mountain too.  Hard to sort.

Possibly put the radar on top of a mountain, and give it zero angle of elevation. In essence you would be measuring the amount of water passing through a disk. I don't think these instruments come in crackerjack boxes.

However, you said satellite.

If you have known chokepoints in stream channels, you can monitor them using very high resolution imagery -- in effect you are using a natural weir.  However you need resolution in inches. I'm skeptical about the folks at Langley lending you their satellites.

Might be possible to monitor the rise and fall of lake and ponds.  This requires a precision that I don't think is possible right now.

Might be possible using a pair of corner reflectors.  One is fixed to the ground, the other floats in a plastic open top barrel.  Bounce microwave pulse and measure the difference in time.  This requires accurate timing.  A nanosecond is about 9 inches at speed of light.  You want to reliable measure 1/10 of this.  Centimeter band microwave should be able to do this.  You still have to place the instruments, and I suspect you will need to visit them to clean out dead leaves, bird nests, and replace instruments that have been damaged by moose and woodpeckers.  You will also need to do calibration measures to compare what the instrument in the open measures compared to ones under the tree canopy.

Your upper levels are well above tree line, which means that as often as not, precipitation travels horizontally.


Why is it that "With higher CO2, the dry gets drier and the wet gets wetter"? The Phys.org article CO2 dip may have helped dinosaurs walk from South America to Greenland quotes Dennis Kent, "adjunct research scientist at Columbia University's Lamont-Doherty Earth Observatory" in the following:

On Earth, areas around the equator are hot and humid, while adjacent areas in low latitudes tend to be very dry. Kent and Clemmensen say that on a planet supercharged with CO2, the differences between those climatic belts may have been extreme—perhaps too extreme for the sauropodomorph dinosaurs to cross.
"We know that with higher CO2, the dry gets drier and the wet gets wetter," said Kent. 230 million years ago, the high CO2 conditions could have made the arid belts too dry to support the movements of large herbivores that need to eat a lot of vegetation to survive. The tropics, too, may have been locked into rainy, monsoon-like conditions that may not have been ideal for sauropodomorphs. There is little evidence they ventured forth from the temperate, mid-latitude habitats they were adapted to in Argentina and Brazil.

The article references Dennis V. Kent el al., "Northward dispersal of dinosaurs from Gondwana to Greenland at the mid-Norian (215–212 Ma, Late Triassic) dip in atmospheric pCO2," PNAS (2021). https://www.pnas.org/cgi/doi/10.1073/pnas.2020778118
but currently the link to the article is not working; perhaps it's not actually been published yet.
Question: Why is it that "With higher CO2, the dry gets drier and the wet gets wetter"? Does this adage come from modeling, from data, or from both? Is it a well-accepted rule of thumb?

To my best knowledge, the paper by Held & Soden (2006) is the first paper that discussed the concept of the rich get richer. They used the climate change experiments generated for the Fourth Assessment of the intergovernmental panel on Climate Change or in other words, climate projections using climate models forced with different CO2 scenarios.
One of their findings is that:

Assuming that the lower-tropospheric relative humidity is unchanged
and that the flow is un-changed, the poleward vapor transport and the
pattern of evaporation minus precipitation (E - P) increases
proportionally to the lower-tropospheric vapor, and in this sense wet
regions get wetter and dry regions drier.

To explain, assuming warming earth leads to more evaporation and an increase in the air capacity to carry water vapor, therefore, relative humidity can be assumed unchanged in the lower-tropospheric. Simoustanly, with warmer mid and higher latitudes the act of the atmosphere (through General Circulation) to redistribute the heat is reduced. Thus, more water vapor remains in the regions of evaporation leading to wet regions get wetter and dry regions drier.
Yes, this result is widely accepted in the community.


State of Stress in rotated 2D system I'm working on the rotation of the state of stress using the book Geodynamics of Turcotte page 101. The 2D coordinate system $x'$ and $y'$ is inclined at an angle $\phi$ with respect to the $x$, $y$ coordinate system (see Figure 2.14).

The force in the $y$-direction on face $AO$ is

$$ \sigma_{yy}AO $$

and the force in the $y$-direction on face $OB$ is

$$ \sigma_{xy}OB $$

The force in the $y$-direction on face $AB$ is

$$ -\sigma_{x'x'}AB\cdot\sin\theta -\sigma_{x'y'}AB\cdot\cos\theta$$

I don't understand why the force in the $y$-direction on face $AB$ is equal to the above equation?

I think the negative signs are there because the stresses are not oriented in the same direction than the $y$-direction. I don't know why it is necessary to subtract the two lengths.

You are correct in your intuition regarding the signs of the forces.  The reason for two terms is due to the direction of the force.  The y-direction is not aligned with the face AB (it is aligned with y') so the force on this face is a combination of the forces normal to AB ($-\sigma_{x'x'}AB$) and the force along the face ($-\sigma_{x'y'}AB$).  Because the question wants only the force in the y-direction, we need to find the projection of these forces along that direction.

If the angle between the coordinate axes is $\theta$, then the contribution of $-\sigma_{x'x'}AB$ in the y-direction is $-\sigma_{x'x'}AB\sin\theta$ and the contribution of $-\sigma_{x'y'}AB$ in the y-direction is $-\sigma_{x'y'}AB\cos\theta$, thus the total force in the y-direction is the sum of these contributions:

$$-\sigma_{x'x'}AB\sin\theta-\sigma_{x'y'}AB\cos\theta$$

Here is a quick figure to help visualize the geometry:


What was the size of the Aral sea in year 1000 CE? I understand that since the rise of the Soviet Union the Aral sea has dried up more and more due to irrigation from rivers diverting its water to other areas for the sake of agriculture.
But is it possible that a drying process started long before the Soviet Union?
This question gives some input on believed depth and salinity in the past.
But what, allegedly, was the size of Aral sea in like the year 1000 CE (or even before that), and what information leads to that conclusion?

Before the 1960s, the size of the Aral Sea was relatively consistent. However, the Aral Sea went through some "dry spells" during the 1st and 3rd centuries BCE. Going even further back, the Aral Sea dried up during the Early Pleistocene and was "refilled" during the Early Holocene. In other words, the Aral Sea probably looked the same in 1000 as it did in 1950. (Encyclopædia Brittanica)


Is this classification of mineral formation environments correct? I am writing an app for students that consist in 180 sheets of the most common minerals on Earth's Crust.

One of the fields of the sheets is environment of formation.

It is important to me to correctly classify environments because I generate with code thousands of questions for a quiz type:

  In wich environment would you found calcopyrite?

  a) Sedimentary

  b) ....

This is my classification of environments of formation of minerals:

Sedimentary: diagenesys minerals etc (calcite, halite...).
Magmatic: sensu stricto igneous minerals (quartz, plagioclase...).
Metamorphic: minerals formed on metamorphism (muscovite, clorite...).
Tardimagmatic: stockworcks, IOCG, VMS, etc, derivatived from magma.(copper, pyrite...).
Hydrothermal: basin fluids, veins of hig-medium-low grade (quartz, serpentinite...).
Exogenous: neoformation minerals on surface by (alteration clays...).

My question is: is this classification correct?

I am particullary worried about tardimagmatic environment. I am sure the term is used at Spain, but it migth not be very accurate at anglo saxon Universities, for the english version of my app.

Update from answers

Thank you very much for answers. Exogenous was totally an inaccurated term and I suspected tardimagmatic was not a very used term, so my clasification will be:

Sedimentary
Magmatic
Metamorphic
Hydrothermal
Supergenic

My users will thank it.

As answering Gimelist yes the sheets have multiple environments as you can see for pyrite. This is taken in count when I generate the questions (not to show two correct options).

I know to memorize is not a good way to learn, but for first courses they should associate quickly eg heidenbergite as inosilicate.
I add a description of the environment so I think the quiz has some pedagocical value for first courses students.

A genetic classification.

Endogenic: Magmatic, Metamorphic, Hydrothermal
Exogenic: Supergene, Sedimentary

For more on this please see Wenk, H. R., & Bulakh, A. (2016). Minerals: their constitution and origin. Cambridge University Press (second edition)
or the first edition of this book(2004).


Is there evidence to suggest that the release of methane clathrates in permafrost regions will impact climate change? We can see that there are large buildups of methane clathrates in permafrost regions.

Climate scientist James Hansen has predicted that the release of the permafrost methane clathrates could cause runaway climate change.

We know that some have related the Triassic Extinction event to the release of Permafrost Clathrates.

Do we know how much methane is stored in the permafrost? Do we know at what temperature it will be released? Can we model the release of methane into the atmosphere in the same way we can model the release of carbon dioxide?

My question is: Is there evidence to suggest that the release of methane clathrates in permafrost regions will impact climate change?

Your first two links don't seem to mention clathrates.

Much ado about methane says:

  What methane are we talking about?
  The largest methane pools that people are talking about are in sediments of the ocean, frozen into hydrate or clathrate deposits (Archer, 2007). The total amount of methane as ocean hydrates is poorly constrained but could rival the rest of the fossil fuels combined. Most of this is unattractive to extract for fuel, and mostly so deep in the sediment column that it would take thousands of years for anthropogenic warming to reach them. The Arctic is special in that the water column is colder than the global average, and so hydrate can be found as shallow as 200 meters water depth.
  On land, there is lots of methane in the thawing Arctic, exploding lakes and what not. This methane is probably produced by decomposition of thawing organic matter. Methane could only freeze into hydrate at depths below a few hundred meters in the soil, and then only at “lithostatic pressure” rather than “hydrostatic”, meaning that the hydrate would have to be sealed from the atmosphere by some impermeable layer.
  ...
  The possibility of a catastrophic release is of course what gives methane its power over the imagination (of journalists in particular it seems). A submarine landslide might release a Gigaton of carbon as methane (Archer, 2007), but the radiative effect of that would be small, about equal in magnitude (but opposite in sign) to the radiative forcing from a volcanic eruption. Detectable perhaps but probably not the end of humankind as a species.


What is the erosion rate of mountains? How much height of a mountain or any topographic high, decreases for a million year averagely? What is the range? (min / max)

This may not answer your question, but it indicates that erosion is extreme at high altitudes.

  More than 60 percent of the sediment delivered to the world's oceans in the prehuman world originated from erosion in mountainous areas with elevations greater than 3 km above sea level.
  Muddy Waters -
  More sediment is entering rivers, but less makes its way to the sea
  - Sid Perkins

Only about 1% of Earth's area is above 3 km.

  (Fig. 2.4 of Deep-Sea Biology: A Natural History of Organisms at the Deep-Sea Floor) (via DavePhD)


Is it true that "All life on earth gets its energy from the sun"? How much biomass is not derived from photosynthesis? In helping my son with his college biology I ran across some statements that I think are wrong according to updated data.  The copyright is 2017 so it is supposed to reflect the most current knowledge.

It makes the following assertion
"All life on earth gets its energy from the sun"

We know this is not true since extremeophiles that thrive on alternate energy sources were observed in the deep ocean volcanic vents where no sunlight can penetrate and in subterranean environments.

In fact, it is speculated that the subterranean biomass is greater than the familiar surface biomass of the earth.  What are the most recent estimates of the size of  biomass that does not derive it's energy from the photosynthesis originated food chain?

As you say, the existence of organism that live out of chemical compounds expelled by hydrothermal vents (Chemoautotrophs), immediately render the sentence "All life on earth gets its energy from the sun" as an approximation. However, some approximations are pretty good for all practical purposes. Nevertheless, this approximation (even if right), have some deep implications when it comes to assess the likelihood of life in other celestial bodies, like Jupiter's moon Europa, which is the kind of concerns through which I got involved into this topic.

First, there is a very important distinction to make regarding your question,  that is really about

  biomass that does not derive it's energy from the photosynthesis

As you describe it. But that's very different than "subterranean biomass". In particular, the following sentence that you mention:

  ...it is speculated that the subterranean biomass is greater than the
  familiar surface biomass of the earth.

Refers to the biomass within soils (i.e. roots, fungus, bacterias, arthropods, etc.), which is indeed very large. You might include deep ocean ecosystems also. But in all those cases, the energy used by organism was originated by photosynthesis and ultimately by the Sun. The energy get to those sub-surface ecosystem in the form of buried dead organic matter or marine snow. Some works hypothesize about other massive subsurface ecosystems living deep within the oceanic crust, hosting perhaps up to 1/2 to 2/3 of the global biomass. However, as pointed by Whitman et. al. (1998) (the source for the above figure): "current evidence suggests that most of the subsurface biomass is supported by organic matter deposited from the surface". Therefore, it would constitute just one more photosynthetically supported ecosystem.

That been said, the core of your question is "What is the size of biomass that does not derive it's energy from photosynthesis?" And that can be boiled down to: What is the fraction of global net primary production that come from chemosinthesis?.

I don't know of any estimation of that fraction, but to calculate an upper limit for it should be pretty straight forward, at least to have a sense of how good is the approximation of saying that "all life gets its energy from the sun", and how important could be chemosynthesis for the global biomass at most. Let's crunch some numbers:

First consider how much energy is there available for chemosynthesis. To do this it is important to note that no organism can get its energy from the energy gradient within the Earth, so the amount of energy available IS NOT the Earth's internal heat budget. Instead, it correspond to the amount of energy available to life in the form of chemical compounds that come from Earth's interior. According to Gaidos et al., in the most active hydrothermal vent fields, it correspond to 0.157 $MJ/m^2 year$ (read as Mega Joules per square meter per year). The same paper point that

  For comparison, the primary production in the upper ocean is
  equivalent to a biological energy flux of ∼315.36 $MJ/m^2 year$, and this
  is only 0.01% of the total energy available in sunlight.

However, the upper ocean ecosystem is nutrient limited, so the efficiency could be much higher at hydrothermal vents. Perhaps the most efficient ecosystem is the tropical rain forest, with efficiencies in the order of the few percent (~1-3%). So as we are looking for an upper limit, let's say that the ecosystem at the hydrothermal vents have an efficiency of 10%. That leaves us with 0.016 $MJ/m^2 year$ to transform to organic matter.

Now: How much energy is there in a kilogram of organic matter? It varies, but given we are aiming to an upper limit a reasonable (low) typical value is ~10 $MJ/kg$.

We need also to know the surface of hydrothermal vents. To aim again for an upper limit, let's say that all mid-oceanic ridges have the energy availability cited above (referring to the most active hydrothermal vent fields). With 80,000 km of mid-oceanic ridges and about ~15 km wide, we have about 1.2$\times 10^{12}$ $m^2$. Keep in mind that looking at the global distribution of known hydrothermal vents in the figure below, this is most likely a massive overestimation:

Putting all together, our upper limit for the chemosynthetic biomass would be:

$\frac{0.016 MJ/m^2 year \times 1.2 \times 10^{12} m^2}{10 MJ/kg}=1.92 \times 10^9 kg/year$

Now, if we compare that with the 1.7$\times 10^{14} kg/year$ that is produced by photosynthetic primary producers. We get that chemosynthesis produce AT MOST a 0.001% of the biomass.

It can be argued that chemosynthesis happens also outside of hydrothermal vents. But those other locations, like geysers and hot springs, are much smaller. Other more extensive chemosynthetic ecosystems have been proposed, like SLiMEs (Subsurface Lithoautotrophic Microbial Ecosystems), but even if they exist over extensive areas, their productivity would be very small.

To summarize, it would be more correct to say that "More than 99.999% of the life on Earth gets its energy from the Sun". And given all the over estimations we made, I would not be surprised if a more detailed calculation would add a few extra "9's" to that figure.


Earthquakes PGA/PGV in time? Good day! On USGS web-site I can get co-called PGA/PGV (Peak Ground Acceleration/Velocity) values in the region of earthquake. It is possible to get the map of velocities with respect to time (to see how earthquake developed in time)?

Thank you.

No. However, you can look at backprojection results which show where the energy is coming from. It gives you some idea about how the earthquake evolved in time, e.g., see here (click play to see the video).

The only other way to get what you want is to use observations from dense arrays. E.g., see here, but this is only possible in certain regions.

EDIT (answer to your comment below): Codes like SPECFEM3D are good for simulating low frequency ground motion (e.g., 0.1-1Hz). High frequency (1-10Hz) ground motion, that affects smaller structures like 1-2 story houses or even mid-rise buildings is very difficult to simulate (you need a very accurate, very high resolution, velocity model with the right soil/geotechnical layer etc., a highly accurate source model with the 'right' slip distribution, rise time, rupture velocity etc., and finally, a very large supercomputer). You're better off using GMPE's like USGS but that will not tell you how things evolve in time.

Bottomline is that statistics of high frequency ground motion are rather well understood (scales with distance) but not for lower frequencies where effects like rupture directivity/velocity, path/basin effect etc. become even more important.

Finally, Okada's elastostatic solutions are for calculating the final displacement field and doesn't have time component, i.e., you can simulate the final slip but not how it evolves with time which is an elastodynamic problem. Also, the final displacement field alone doesn't tell you anything about PGA/PGV.


What are these lines on this stone? I found this on Lake Ontario in Canada. I was wondering is there is anything special/out of the ordinary about it?

You don't say which lake, but these are almost certainly crinoid stem fossils. Crinoids, or sea lilies, are echinoderms (relatives of starfish and sea urchins) that anchor themselves to the sea floor and feed on plankton.

In some crinoids, the animal's sea urchin-like calyx is connected to the anchor by a long stem to a holdfast which anchors it. The stem part of the crinoid's endoskeleton is a stack of calcareous rings or pentagons (called "ossicles") which look almost like a little spinal column. (However, vertebrates are not descended from crinoids, even though Echinoderms are deuterostomes, placing them closer to chordates than arthropods or molluscs).

When the animal dies, it falls into the bottom sediment and the stem can become disconnected as the sediment is compressed into limestone. Sometimes the rings stay aligned, and show assemblages like you see in your rock. Other times, all you see are disconnected rings or little pentagons, like the ones all over the rest of the rock.

Crinoids have been around since the Ordovician period
485 million years ago, so they appear in (and sometimes entirely make up) limestones throughout the world.

Source: GeoKansas

And, just because it's there, here's  a video of a crinoid crawling across the sea floor.


Data sets for historical sea level estimates I am looking for data sets for historical global sea level estimates. How would I go about doing this the best way? Are there any publicly available resources for this?

The timespan I am looking at are the following: Preferably from 300 000 - 200 000 years ago to today, or from 15 000 - 10 000 years ago to today.

There are a number of publicly available proxy records for sea-level/temperature curves, I'd start with Google Scholar if you want refereed articles but a straight Google search can give you good results if you use the right search terms, like "sea-level over time" gave me some useful results; I'd recommend the Wikipedia result as most useful to you.


Peak season for Thunderstorms What causes different locations to get their peak season for thunderstorms at different times of the year like some locations get the most thunderstorms in a July some in June and some in August and some get the most thunderstorms in September. What causes the peak season for thunderstorms to be different in different locations?

What you are really asking is why the weather varies from place to place, sometimes in places which are only a few miles apart (in the hills of the Dhofar region of S.Oman, you have a transition from monsoon scrub and grassland to arid desert in the space of only 2 or 3 hundred metres!). Weather is such a complex thing it is impossible to enumerate all the factors which cause local variation, except to say that the presence of hills and mountains often has something to do with it.

Matter is made up of sub-atomic particles containing positive and negative charges. They are usually evenly distributed, every positively charged particle  being balanced by a negatively charged particle, which means these charges cancel each other out.  Nearly everything we see around us is therefore electrically neutral. This disguises the enormous power of the electromagnetic force, which is trillions of times more powerful than the gravitational force, so even a very slight imbalance between positive and negative charges, such as occurs in thunderstorms, can produce dramatic results.

These electrical imbalances can be produced by air turbulence such as takes place in rising plumes of hot air called thermals, of which the strongest happen in summer. Particles of dust or moisture in the rising air currents rub against each other and cause separation of charge.  The condensing raincloud becomes negatively charged, while the ground below becomes positively charged. Positive and negative charges hate to be separated, as they have a very strong attraction for each other.

The positive charges on the ground are pulled along by the negatively charged cloud, and tend to build up on church steeples and similar pointed objects that reach into the sky. When the two masses of separated charge become sufficiently strong, and especially if they pass over a tall, pointed object, they cannot resist the urge to recombine and an electrical discharge takes place. Why one place should have more of these events in August and another in September is a complex question which cannot be answered without knowing all the many variables which influence the weather in both of these places.


How is ocean salinity measured from space? Since 2009, two satellites (SMOS from ESA and Aquarius from NASA) are providing global salinity measurements. While ocean temperature is easily derived from infrared radiation for instance, what parameter is measured by those satellites to estimate the salinity of the ocean?

In a nutshell:

The instrument measures microwave radiances (after calibration)
If we know the sea surface temperature, we can use radiances to calculate emissivity.
The emissivity at 1.4 GHz is itself a function of near-surface ocean salinity.

However, in reality, it's more complicated, because there are other factors that come into the equation, such as surface roughness, which depends on wind.  Remote sensing problems are often underdetermined, and we need to make assumptions in order to retrieve the desired quantity.  Measuring ocean salinity from space is a classical inverse problem.

You can find details in the highly cited paper:

  Kerr, Yann H., Philippe Waldteufel, J-P. Wigneron, J. Martinuzzi, Jordi Font, and Michael Berger. "Soil moisture retrieval from space: The Soil Moisture and Ocean Salinity (SMOS) mission." Geoscience and Remote Sensing, IEEE Transactions on 39, no. 8 (2001): 1729-1735. (weblink).

which addresses both soil moisture and ocean salinity.


Can atmospheric conditions cause carbonated beverages to fizz more? For some reason today, carbonated beverages have been fizzing up more than usual. It's happening with beer and club soda. Very strange, no gremlins either - the beer was from the back of the fridge, been there since yesterday. The club soda was still for plenty of time.

I was thinking low atmospheric pressure could be at hand. There are stratocumulus clouds in the sky, the AC is on. In Chicagoland area.

This is physics rather than Earth Sciences, but differential pressure between tinned liquid and atmosphere is by far the dominant factor. In Scotland I remember opening a can of 7-up at sea level with almost no effervescence. Then I climbed Ben Nevis, 1344 metres, and celebrated reaching the summit with another can. The resulting 'geysir' ejected about half the can in spectacular fashion. Temperature also has an effect in that the solubility of CO2 on a cold day, say 10 deg C, is about 30% more than on a hot day of ~30 deg C. So if the outside temperature is warmer than at the time the drink was canned, then there will be an excess of free gas that has come out of solution, but is still in the can waiting to be released. If we say two grams of excess CO2 in the can, that will yield about a litre of gas at one atmosphere and 21 deg C.

I'm wondering what the effect of a high sugar content would be. Could large organic molecules act as foci for gas bubble formation? Maybe a fun  school experiment!


Is there a database of the geologic/stratigraphic units of France? Is there a page where I can look up rock unit definitions for France similar to:

https://www.bgs.ac.uk/lexicon/home.cfm
http://www.bgr.de/app/litholex/index.php

I did some searching for this, but because of my poor French I couldn't find anything.

The best I have been able to turn up is the paid BD-logs service, which provides standardised lithology for borehole data. Open Geospatial Consortium data all appears to be listed on the Geoservices page, and does not appear to include a lithological database/lexicon. The French Geological Reference Platform does not appear to include a standalone database. The BRGM's list of resources also does not appear to provide pointers to any relevant information. Given that the FRGM is in active development, it seems plausible that this is not in fact a dataset that currently exists.


What fraction of dry land is below sea level? Someone just asked me if it would be practical to counter the rise of sea level by pumping water into storage on land. It struck me that if there is enough land below sea level, this would require construction of aquifers, but would not require using energy to pump the water as the destination of the water would be below its current level. But I have no idea how much land below sea level is available.

This question is intriguing. At the current rate of sea rise (about 3 mm per year), all of the Earth's dry land below sea level would be submerged in just a decade. There are an estimated 49 countries around the global with at least some real estate below -0- metres elevation, but the sum of all the potential volume (around 7,500 km^3) is insignificant compared to the volume of water generated by glacial and ice cap melt:  "A meter of sea level rise is a volume 50 times greater than all of the depressions that are below sea level in the world", according to this link: http://mountainmystery.com/2015/08/17/hiding-rising-seas-in-sunken-deserts/.


Shouldn't we encourage consumption of single-use plastics? Plastic is a good way to sequester carbon I've heard a bunch of impractical proposals for ways to sequester carbon:  pump CO2 gas into the ground, grow trees for the sole purpose of burying them underground where they won't decompose...   and these proposals all seem impractical to me.

By contrast, it seems quite doable to allow people to consume single-use plastics, and dispose of them in well managed landfills.  (I wouldn't exactly say we should encourage the practice, not until we have bioplastics in widespread use and green energy powering plastic production).  Stringent efforts should be made to ensure the plastic is not burnt and is kept out of the marine environment.

Plastic is very chemically stable, it won't decompose and form methane or anything else, it won't bubble up to the surface, and mixed in with garbage it becomes unattractive for future generations to dig it up.

I'm also making the assumption that any oil not used for plastic production would be used instead in the transport industry or at least somewhere where it'll be put straight into the atmosphere. I think it's naive to think that if I forgo my plastic drinking straw, there'll be one more drop of oil remaining forever in the ground - it won't be left in the ground, instead it'll be made available to the transport industry.

I've tried to get an answer to this question from New Scientist, Australia's Dr Karl and basically every chemist or physicist I encounter and no-one can explain why I'm wrong.  So it seems to me governments everywhere who are banning single-use plastics are doing the opposite of what they should be doing.

Plastic isn't a good way to sequester carbon the sense that this term is usually meant.

Carbon sequestration is normally assumed to mean

  [...] the long-term removal, capture or sequestration of carbon dioxide from the atmosphere to slow or reverse atmospheric CO2 pollution and to mitigate or reverse global warming.

(From Wikipedia, my emphasis.)

This is not how plastic production works: the great majority of plastic is made from petrochemicals.  So almost all plastic is made from fossil carbon, not from carbon extracted from the atmosphere recently.

With plausible assumptions about the energy used in making plastic and its source, then turning fossil carbon into plastic which is then not burnt is probably better in terms of carbon emissions than just putting the fossil carbon straight into the atmosphere.  But it's worse (again in terms of carbon emissions) than just not making the plastic at all.

Note that there have been plastics made from plant materials, and many early plastics were made like that: Celluloid is a good example.  I thought Bakelite was as well, but it turns out it's the first one that wasn't.


NCDC Snowfall Data - Interpretation? This is my first time using this dataset, so I have probably made an elementary mistake. I am having trouble understanding a file from the NCDC's climate normal dataset:

http://www1.ncdc.noaa.gov/pub/data/normals/1981-2010/products/precipitation/ann-snwd-avgnds-ge010wi.txt

Here is a sample of a few rows from the above file:

USC00064767         105P

USC00065077          31P

USC00065445         370S

USC00069388          66S

From the documentation:

ann-snwd-avgnds-ge010wi.txt Long-term averages of number of days during the year
                             with snow depth >= 10 inches

From the readme and the above, I am assuming that the numerical portions of the entries in the second column in the above sample should all be numbers of days per year, so at most 367. However, some of the values listed above are greater than 367.

Any ideas for me, or other places to look? Did I miss any threads on this forum that discuss how idiots can understand NCDC data?

The readme file for all the datasets has a section on units.  In this section, they describe how to interpret the numbers (which exclude decimal points in the data files).

For the "number of days" data it says:

  [units are] "tenths of days" for the number of days per [time] above or below certain threshold, such as days above 90F. e.g., "256" is 25.6 days.

So, you need to divide all those numbers by 10 to get the actual values.  Also, take note in the readme file of these pieces that correspond to the data file in question:

S = standard (no more than 5 years missing and no more than 3 consecutive
    years missing among the sufficiently complete years)

P = provisional (at least 10 years used, but not sufficiently complete to be
    labeled as standard or representative). Also used for parameter values on
    February 29 as well as for interpolated daily precipitation, snowfall, and
    snow depth percentiles.

-9999: missing or insufficient data; values cannot be computed
-7777: a non-zero value that would round to zero, for variables bound by zero.


What are the advantages in looking at an OLR map versus looking at IR satellite imagery? Conceptually they seem to be showing the same information. But in the context of a Madden Julien Oscillation (MJO) or equatorial waves  especially over the equatorial oceanic layers which one is more useful to look at:
1) OLR Map or,
2) IR Satellite Imagery (black and white satellite pictures of clouds)?

First OLR map is usually graded in flux units (W/m2) thus it is quantitative data, not just a visual picture.

Clouds themselves are not a very reliable indicator of high convection and thunderstorm activity. They could form elsewhere and get blown into a dry region. Also with an OLR map students would not be distracted with the shapes of the clouds.

AIRS OLR products combine infrared and microwave data. Microwave data helps to distinguish between areas of strong convection and nonprecipitating clouds.

Here is a typical OLR product from GOES satellite (taken from Hai-Tien Lee presentation). Such images can be generated with 15 minute interval so the movement of the MJO pattern can be easily observed.


Is there a convenient place to get vertical wind shear info for my location? Now that it's thunderstorm season here in New Hampshire, it would be nice to be able to find out what the vertical wind shear is like at the altitudes that affect thunderstorm formation, to guess whether they'll form.  Once cumulus clouds have started to form, it's usually easy to see by just looking up.  But when planning one's day in the morning, there often aren't big enough clouds yet.

Can anyone direct me to an easy-to-use source for this?

Yes, NOAA's Storm Prediction Center's soundings page is a great source for the information you are looking for, especially the skew-T diagrams and wind hodographs. This site provides current soundings as well as a past archive of 1 week. For the explanation of the soundings diagrams and numbers provided, see the soundings help page.


Is there a name for the process of producing positional data for cartography? Map-making requires two distinct processes, first to produce the data -- latitude, longitude and elevation -- of the points to be mapped; and second to represent this data on a flat surface as a map.

Cartography nicely covers the science of creating the map from the data -- plotting points to give an accurate representation of desired properties, realising that at least one of shape, area, direction or distance, has to be sacrificed.

Is there an overall name for the initial gathering of data? Terms like "surveying" seem to me to be too specialised or limited to cover all the processes involved, and "topography" seems too broad.

Surveying is the process of taking topographical measurements of latitude, longitude and elevation. It is also the process of marking out lines for engineering/construction designs of such things as roads, tunnels, fence lines, boundaries & foundations of buildings.

Surveying provides the topographical data that cartographers, engineers and other professionals use for their purposes.


Why would Google's map of areas affected by Hurricane Harvey have advisories for the west coast and other far away areas? What behavior of this hurricane would lead to advisories for the west coast and even parts of Canada and Alaska, when the hurricane is in the South?

I have little experience in meteorology or any of the earth sciences really, so I am interested in how this would affect the weather or other conditions far away from where the hurricane is severe.

It seems like there is more than just a hurricane going on. According to the National Weather Service there are excessive heat advisories, gale warnings, etc.


How to properly setup a domain in NWP model (WRF) according to meteorological input data I want to setup a mesoscale weather prediction model (WRF or something else) to work with NCEP/GFS meteorological input data with resolution of 0.25deg. My question is how to choose a proper size for the parent domain, considering the resolution of the input data. In my case GFS resolution is around 20km in mid latitudes, is it necessary for my parent domain to be around this value - for example 18km (or 21km) and then use nested domains to go down to 2km.

18km>6km>2km

Or i can start directly with parent domain size 2km?
What will be the effect of this big gap 20km to 2km?
Do i need a longer spinup so i can resolve clouds for example, if i choose to start straight with 2km resolution?
Am i going to miss some kinetic energy from the coarse meteorological input because of dissipation not represented properly?
I suppose computation time is not much more if i use 18>6>2km compared to starting directly with 2km. From my experience with WRF, finer domains take most of the time to be computed -ar. 85% in my specific setup.

A good rule of thumb for down-scaling with WRF is not to interpolate down more than 3 or 4 times; with 3 being the standard recommendation. So while 18 km is probably overkill for an outer domain (this is a personal opinion, there are some operational models like HWRF that start at 18km), 2km would definitely be too fine for a parent domain. The main reason for this is the boundary conditions: your wrfbdy_d01 file is interpolated from the original data down to your model's resolution, so for a 2km domain you will be constantly having very low resolution features imposed upon your boundaries, which will cause fairly unphysical conditions at the boundaries throughout your forecast period. By having a wider, lower-resolution "buffer" domain between you and the outer boundary conditions you avoid unphysical artifacts entering your domain.

There are 5 overlap gridpoints at the edge of each domain, so your inner domain should be at least 5 (outer) gridpoints away from the outer domain.


Most corrosive seawater areas in world I am looking for any studies or maps detailing the average salinity and temperature for areas of the Earth's oceans. As an extra if anyone has data or maps on areas with large amounts of in-trained silts or aggressive sea life (muscles/barnacles) that would be a huge help.

Purpose: I would like to write a paper for Navy engineers on specific world areas of concern for equipment operation utilizing seawater cooling systems. That way we can gear our preventive maintenance to account for these problems.

Sea water is all very corrosive; the precise composition is not significant. Steel structures are cathodically protected with impressed current and/or sacrificial anodes, usually aluminum. For equipment to be cooled with seawater there are a few choices ;However, for the Navy where reliability is more important than the cost , titanium would be the material of choice ( Type 2 , but types 1 and 3 or the Pt alloy - forgot the number- are also good).The variables for sea water corrosion are : temperature, velocity, sediment, and marine growth, not composition. Inco/Huntington probably evaluated every possibility for sea water corrosion at the La Que labs in Wrightsville Beach NC. Work done before Harvard MBAs' in management eliminated "research" from "research and development". Papers will be published under "Seahorse Institute" and NACE ( National Association of Corrosion Engineers). NACE will have various current publications available for sea water corrosion ( located in Houston TX). Most of this R & D was done before the internet so it won't be available on-line.


Single-layer water content variables In different reanalysis products (ERA 20C and NOAA/OAR/ESRL/PSD 20th Century daily data specifically) one can find the following variables:

Total column water (ERA)
Total column rain water (ERA)
Total column water vapor (ERA)
Total column cloud liquid water (ERA)
Cloud water content (NOAA)
Precipitable water content (NOAA)

How are they calculated? What are the differences between them? Could you please cite a reference or book in which this is explained in details?

Which of these may serve as a best approximation to represent large-scale patterns of rainfall (monsoonal cycles)?

Which of these is the vertically integrated specific moisture?

Are any of these equivalent to the vertically integrated moisture flux divergence as an approximation for precipitation, as in Banacos and Schultz (2005)?

The ERA Interim reanalysis is made by ECMWF and the other reanalysis is made by NOAA. Reanalyzes of the past are made by running global climate models and these differ because NOAA and ECMWF use different models and perhaps even slightly different data. The models on the other hand can be very different for example on implementation of data assimilation, parametrization and even grid cell size.

All of these variables are vertically integrated. The ERA variables in the order you mention them contain:

-Total column water: all water

-Total column rain water: all liquid and solid water in droplets large enough not to be considered cloud droplets (my guess)

-Total column water vapor: all gas phase water

-Total column cloud liquid water: all liquid cloud water

The NOAA variables:

-Cloud water content: all liquid and solid cloud water

-Precipitable water content corresponds to Total column water

From these the Total column water vapor corresponds the Vertically integrated specific moisture. None of these is the divergence of the total column water vapor phase that you need. Although the paper you are referring approximates precipitation from moisture divergence, you could use just the Total column rain water and no approximation is needed (I didn't read the paper so I don't know if this is makes sense).

Edit, added sources:
The ERA variable list can be found here and you can search variables there and press them to get the definitions too. For NOAA I couldn't find a source for the definitions of these variables. If someone finds please edit this answer


Weak flashes of light in the sky On a recent, late-evening flight from New York City to San Fransisco, I was seated on the right side of the plane. We were flying over lake Michigan - about 2 hours into the flight. When we were over the mid-west I looked out of the window and could see these continuous flashes in the sky. At first I thought it was lightning, however this continued for almost 30 minutes or so and seemed to be silent too. What is this phenomenon?

You were most likely seeing lightning (to be sure, a date/time and your location would be necessary).  Lightning can be visible from quite a distance and storms can be incredibly active with lightning within the clouds and from cloud-to-cloud.  Given a large distance and being inside a (relatively) loud airplane cabin it is no surprise that you couldn't hear the thunder associated with the lightning flashes.


Marks on boulders of volcanic origin I am working in a catchment in the southern Ecuadorian Andes, about 3700 m.a.sl. Rock outcrops at the upper part of the catchment, as massive blocks varying their size from one meter up to five meters, as shown in the first picture. Based on my limited knowledge of geology I would say that the rocks are of volcanic nature, probably andesite/rhyolite, very massive, dark in color with visible white crystals (Picture 2). I noticed that a lot of the rocks,  present scars/marks on their surface (Picture 3) and I would like to now their possible origins.

These areas are suspected that were covered by glaciers during the last glaciation. The catchment is located close to the rim of an old caldera.

The rocks are undoubtedly of volcanic origin, and I would attribute the marks on their surfaces to shrinkage while their interiors were still in a semi-molten condition but rapidly cooling. The white crystals are probably quartz.


What is a Rotating Shadowband Radiometer, and how does it work? This answer explains that the device labeled "B" in the photo below is a "Ultraviolet Multifilter Rotating Shadowband Radiometer."

What is a Rotating Shadowband Radiometer, and how does it work?

Screenshot from https://vimeo.com/315754123

A rotating band shadow meter will give you the diffuse radiance as well as direct radiance.  When the band is in the lower location the sensor will measure all the radiance from the sun both direct and indirect.  when the band is raised it blocks the direct sun into the sensor giving an indirect radiance measurement.  The total radiance - the indirect radiance will give you direct radiance.  In this case the meter is setup to capture the UV portion of the spectrum.  Multifilter suggests that it can record radiance for bands of UV radiance so it would be tracking radiance on two or more ranges wavelengths.  The model described in this link supports six distinct frequencies though none are in the UV band.

The band rotates above the sensor occluding the light from the sun, when the radiance is at its lowest during the band rotating you are, typically, capturing the point where the direct sunlight is being filtered by the band.  When the band is not occluding the sun you would be capturing the highest radiance. The sampling rate would be setup in the datalogger or computer to allow radiance values at specific time intervals.

A short video of one in operation can be seen in this tweet.


Formation of limestone without living organisms? Limestones are formed mostly from skeletal fragments of marine organisms.

However, calcium carbonate dissolves naturally in water, so the living organisms are not the only source of it in water.

Is it possible for limestone to form without living organisms? Are such deposits observed? Or is the presence of limestone a clear indicator that life is, or was present on given planet?

Oolites are limestones that are usually considered as in-organic, although they may have bits of shell/etc in them.  These form by the precipitation of calcium carbonate around particles (sand, broken shell, etc) with a process comparable to that of an oyster.

Some oolite references:

http://www.sandatlas.org/2012/09/oolite/

http://en.wikipedia.org/wiki/Oolite

Recently I saw a reference that limestones do not deposit when Fe2+ is present. Unfortunately I can't find the reference now. If this is the case, then for the Earth, limestones require the indirect presence of life. The evolution of cyanobacteria created free oxygen in the atmosphere and the dissolved in the oceans. Hence all dissolved iron was oxidised from Fe2+ (a green colour) to Fe3+ (orange colour).


What is the Pleniglacial age? I'm sorry if this is a stupid question. I was wondering if someone could briefly explain what the Pleniglacial age is and how it fits in with the geologic time scale.

Additionally, if someone could recommend a way to keep track of all of these names I would appreciate it.

Thank you!

The Pleniglacial is a stage of the Weichselian Chronostratigraphy which is divided in three stubstages (early, middle and late). You can compare the absolute age to the geologic time scale.

(Data from:
Kasse, C., Huijzer, A. S., Krzyszkowski, D., Bohncke, S. J. P. and Coope, G. R. (1998), Weichselian Late Pleniglacial and Late-glacial depositional environments, Coleoptera and periglacial climatic records from central Poland (Bełchatów). J. Quaternary Sci., 13: 455–469. doi: 10.1002/(SICI)1099-1417(1998090)13:5<455::AID-JQS398>3.0.CO;2-T)


Does a hurricane classification exists where estimated rainfall is taken into account? Hurricanes are classified with the Saffir–Simpson hurricane wind scale. However an extreme  amount of rainfall can cause a disaster although the windspeeds are not extreme. Is there some sort of classification where estimated rainfall caused by a hurricane is taken into account?

At the current moment, none that are in operaational use. The problem with using expected measurements is that there may be multiple drastically different estimates, and then there is the problem of errors creating misclassification. There have been attempts, but none of them that are noteworthy or operationally used, that I know of.

This article may be relevant to your question. This article may also be relevant, but is obviously dated considering the events of Hurricane Harvey. Harvey also highlighted the problem of rainfall relative to runoff, which is significant in urban areas and concave/parabolic topography.


Tipping point theory, historical examples This article gives a wonderful overview of tipping point theory, where a large system can be brought into a different state by a small perturbation.

Searching online I have found mostly articles on theoreticly based studies on tipping point theory and some speculating on the consequences that may occur due to global warming.

I am wondering if these tipping point theories are still all theoretical or are there any historical examples that provide as a base for these anticipated changes? For example, area the transitions between Eras and Periods also caused by tipping points or are they more gradual changes of the system because they occur on a very large timescale?

Tipping point events have occurred throughout earth's history and parts of the earth system are currently being monitored for signs of abrupt change. Past earth system tipping points include The Great Oxygenation which brought molecular oxygen (O2) into the atmosphere and Snowball Earth events where the earth's surface became ice-covered. Tipping points can occur on a planetary scale, as in the previous examples. These events can also occur on a regional  scale. For example, the West Antarctic Ice Sheet is a regional feature that is currently being monitored for signs of collapse.


Definition of Surface-based atmospheric duct I am writing a literature review for a project and I have a problem. Namely, I cannot figure out the the condition required for surface-based duct to occur. Literature does not help either. In one of the journals I find:

"Surface-based ducts are mostly caused by advection of warm and dry  air over the ocean or land, which creates humidity and temperature inversion." [1]

And in other

"Surface ducts generally appear in sunny weather with relatively stable atmosphere. At this time, the atmosphere often has a relatively stable temperature inversion layer, and the humidity generally decreases with height." [2]

So one paper says there is humidity inversion while other says that humidity decreases with height. So which is it?

[1] E.  Dinc  and  O.  Akan, “Beyond-line-of-sight  communications  with  ducting  layer,”IEEECommunications Magazine, vol. 52, no. 10, p. 37–43, 2014.

[2] W. Tang, H. Cha, M. Wei, and B. Tian, “The effect of atmospheric ducts on the propagationof ais signals,”Australian Journal of Electrical and Electronics Engineering, vol. 16, no. 2,pp. 111–116, 2019. [Online]. Available:  https://doi.org/10.1080/1448837X.2019.16224918

Both situations are possible. Normally, the atmosphere gets colder and more rarefied with height, and cold air holds less moisture than warm air. Inversion layers trap the lower air mass closer to the ground, so there is a reversal of what you might normally expect: temperature and humidity rises as you get higher, rather than the normal decrease. Inversion can occur in several ways, for example, if a mass of warm air moves in over a cold surface, an inversion will take place. Bothe statements you quote are correct, but the second one is more usual.


Use of Neodymium in Paleoceanography $\varepsilon_{Nd}$ (i. e. the relative deviation of $\frac{^{143}Nd}{^{144}Nd}$ from a standard) is often used as a proxy in paleoceanography to identify the basin of origin of oceanic currents.

But what is the model behind this idea? Is this proxy purely empiric?
Why would the Neodymium isotopic ratio vary among basins and why would this variation be stable in (geological) time?

A part answer to your question.

According to the article Palaeoceanography: The briny deep (Martin, 2008), explains the reason for the use of the neodymium ratio as being

  The isotopic signature of a water mass is imparted from weathering of continental material in the region where the water mass sinks below the surface. Radiogenic Nd isotope values reflect a contribution from relatively young volcanic material, whereas non-radiogenic values are a consequence of inputs from old continental crust. The water mass carries its distinctive signature as it circulates through the oceans.

Its stability is described in the paper Temporal stability of the neodymium isotope signature of the Holocene to glacial North Atlantic (de Flierdt et al. 2006), as being due to the observations that Nd isotopes

  are not thought to be altered in any significant way by biological processes, and thus can serve as a quasi-conservative water mass tracer.


Which CMIP5 models give the highest and lowest warming for RCP8.5? Question is in the title.  I'm doing impacts research and need to pick a couple of scenarios before downloading GCM runs.  Want to pick a low one and a high one and one in the middle of the road.  I'm an economist, rather than a climate scientist.

In my experience, HadGEM has been fairly pessimistic.  But I'd appreciate a reference to something citable, ideally plotting climate sensitivity by model.

To add, I'll be downloadading a few of several model runs from a dataset of publicly available downscaling experiments.  I'll then analyze each climate model, and then average the results of each experiment to form an ensemble. It is known that one should not average GCM runs until the final step in one's analysis.

There is no model that consistently yields either highest or lowest warming because each model has strengths and weaknesses which depend upon the conceptual emphases. This varies with latitude, continentality, proximity of water/lakes, presence/absence of ice and mountains, regional significance of atmospheric processes - both physical and chemical, regional airflow strengths such as monsoonal and hurricanes, etc. Each model calibration works either brilliantly well, or downright dubiously, according to the model conceptualization. There is no 'one size fits all' (environments).

That said, however, I routinely use the CMIP-5 ensemble as listed in the World Bank Climate Change Knowledge Portal - just because it is convenient and readily available. You can find it at http://sdwebx.worldbank.org/climateportal/index.cfm - just click on the world map for your region / country / area of interest, and select the parameters you want. This is not the full ensemble, but 16 selected models that seem to work well - at least most of the time.

So here is a recent example from Nepal: scanning the maximum and minimum monthly temperatures, 'giss-r' generally yielded the hottest temperatures, although for occasional months the hottest was 'ccsm-4'. The coolest temperatures were mostly given by 'noresm 1-m' though for occasional months the coldest was from 'miroc esm'. However, this is just a random example. I do not believe that such conclusions are consistent everywhere in the world.

Why concentrate on the coolest and hottest models? Doesn't it make more sense to work with the ensemble median? I find that the relative distribution of model results is roughly similar regardless of the RCP. I usually quote RCP 4.5 or 6.0. RCP 8.5 is too pessimistic. Does anyone still seriously think that RCP 2.8 is attainable?

My advice is to spend a day picking temperature trends from the WB-CMIP model portal for a wide range of environments, and only then draw your conclusions.


Permafrost thickness Studying for a midterm and I came across the following question. Is aspect more or less important than material type in determining permafrost thickness?

In physical geology, aspect is the compass direction that a slope faces. So the trail of the sun from east to west in the Northern hemisphere would provide more sunlight to the South than the North, but I would think that material type for determing permafrost would be more important. Not sure how but looking for a explanation

This is a non-exhaustive list of factors influencing the permafrost thickness :

latitude
altitude
aspect
material type
nature of the regional climate (dry, oceans, continental)
geologic history of the permafrost (formed after the last glacial maximum, or before?)

Time is important: older permafrost can be very deep, especially in areas such as in Siberia, Yukon/Alaska where the effect of glacier was limited, thus exposing the ground to cold conditions for long time. Some areas in the Canadian archipelago are in excess of 1 km deep, and more than 500 m is not uncommon, largely depending on local and time conditions.

Yet, huge discrepancies in permafrost depth can be found between western Canada/AK, eastern Canada, Northern Europe and Siberia, given a constant latitude, and therefore isolation and thus comparable aspect. As an example at Svalbard (78N), permafrost depth was reported to be less than 400 m, while regional depth in the central canadian archipelago north of Baffin Island is more than 500 m (for 73 - 75 N) and 1500 m in northern Siberia (which is at a lower latitude than Svalbard).

To get back to your question, aspect (or solar radiation input) is pretty much uniform for a given latitude - but in this case, for the same latitude, permafrost depth vary.

On the other hand, material type vary locally. If wetlands, mosses and vegetation will contribute to cool the ground, enabling deeper permafrost in those areas. Areas were there is a lot of snow (snowbanks) will have a warmer permafrost compared to crests nearby. Lakes change how heat can be extracted from the ground (latent heat effect) so permafrost will be thin under a lake compared to around the lake (lake being a type of material in the context of your question). Desert ? Rock outcrop ?

Each type of environment behave in a certain way regarding heat extraction and ultimately heat exchanges, which have a lot to do with the nature of the surface..


Please help me identify the inside of this stone please could you help me identify this stone I found on the beach, it almost looks like it has tiny eggs inside but they definitely aren’t as they are solid and aren’t removable
Thank you in advance

Your rock is chalcedony, a Cryptocrystalline variety of quartz.


Need help understanding rain rate formulas from drop sizes I have come across different formulas by which the rain rate [mm/s] or [mm/h] can be computed from the drop size distribution.
I'm somehow unable to convert the different formulas into each other. It is maybe a stupid question with some unit error, but I cannot find it.

A well-known formula seems:
\begin{equation}R_1 = \frac{\pi}{6} \int_0^{\infty} v(D) D^3 N(D) dD
\end{equation}
This should be the instantaneous rain rate in [mm/s]?? Unfortunately most publications just quote the formula without units...

I'm supposing that $D$ is in [mm], $N(D)$ in [mm$^{-1}$ m$^{-3}$], and $v(D)$ in [m s$^{-1}$].

$v(D)$ is usually approximated as $3.778\cdot D^{0.67}$.

Another formula I have come across is
\begin{equation}
R_2 = 6\pi \cdot 10^{-4} \int_0^{\infty} v(D) D^3 N(D) dD,
\end{equation}
which is said to be [mm/h], then.
Also for $D$ in [mm], $N(D)$ in [mm$^{-1}$ m$^{-3}$], and $v(D)$ in [m s$^{-1}$].

Now apparently $R_1 \cdot 0.0036 = R_2$. But why?

If $R_1$ is in [mm/s], then we should multiply by 3600 to get to [mm/h].
Can someone spot where I am wrong?
Is it right that $R_1$ is in [mm/s]? (given the units of D, N(D) as above)

The first equation does not match up with the units. But first things first... What you're calculating when you calculate rain rate is an accumulation rate, which is volume flux through a plane (mass flux divided by density) divided by the area of that plane. For this reason, it doesn't matter whether it is computed over a square meter or a square kilometer -- since volume flux is proportional to the area, it cancels out

Also it doesn't really matter whether $N(D)$ has units of $mm^{-1} m^{-3}$ or $cm^{-1} m^{-3}$, since that first unit cancels out in integration.

If the units are as you say they are in the first example, then the expression should read
$$R_1 = 10^{-6}\frac{\pi}{6} \int_0^\infty v(D)D^3N(D)dD$$
to get a result in $mm/s$.

Multiplying this by 3600 to get a result in $mm/hr$ yields the the second expression.


Could Rumblings From Plutons be as Ominous as Rumblings From Volcanoes? Mount Kinabalu in North Borneo is a 10 million year old pluton. A pluton is a magma plume from the mantle which was not able to reach the surface and erupt as a volcano, but solidified underground and has since been exposed by erosion.

It is reported that Kinabalu is rising at a rate of 5mm per year, pushed up by forces from below. In 2015 there was a powerful earthquake which killed 18 people. With volcanoes, rising terrain and earthquakes are often a portent of more dramatic things to come, though not necessarily imminently. Could this also be true of plutons?

I searched the mentioned earthquake, and if i understood it right it is attributed to a fault line formed by two laterally moving crustal units (a "normal fault"). Mount Kinabara itself is not to blame, though the earthquake triggered landslides as secondary effects at its steep flanks. I also found papers on the geological history of the area that offer explanations of the causes of the earthquake. As to portents and the future, if only i knew ... :-)

There is this publication (Wang et. al. 2015, open access) about the earthquake attributing it to a normal fault directly beneath Mt Kinabalu. The epicentre's position is marked on a profile in the publication.


Are there any weather services that provide hourly forecasts beyond 7 days? I'm working on a small project and am trying to find a way to get the very extended hour-by-hour forecast for a location. Most services (Darksky, etc.) seem to offer 7-day extended hourly forecasts, but I'm not able to find anything beyond that.

Does anyone have suggestions?

The trouble is, any skill above climatology beyond about 5-7 days is very very low.

So sites could offer such forecasts, but they wouldn't be worth much of anything.

The main thing they could offer that has any use that is an indication of what typically happened in previous years (i.e. climatology)... but unfortunately I don't know any site that offers such on an hourly basis.  We could use more of that!  Still, if you're familiar with the area you're looking up for, you're probably fairly used to the typical weather for a given time of year.

There has been some small skill at making blurrier longer range forecasts... basically estimating either within a large range (such as hurricane forecasts) or (more often) giving probabilities of whether the weather will be above or below that climatological expectations.
(Basic summary for those wondering about how successful some such probabilities are: on these graphs, 0 is no skill, 100 is perfect skill... so 8-14 days temperature and precip have a bit of skill, but lower for temperature and almost no skill for precipitation for a monthly forecast given 2 weeks ahead of time)

But such long-range forecasts don't have nearly the precision to offer hourly forecasts to be of any legitimate use.

So basically if you're eagerly planning for a trip in 10 days or a wedding in a month or two, you're much better off staying far away from such novelty longrange forecasts until the event gets much closer.  Until then, all you can really figure on is what's typical for the given time of year.


Can we separate a sandy, clayey & salt layer on basis of their rheological properties? Since, given enough compaction, salt is able to behave like a fluid & buoyant too if it's overlain by a higher density rock (it could be fine grained clay or a sandy sequence). But in another case, when a layered sandstone is inter bedded with shale, & given enough pressure and temperature, the shale becomes mobile & flows while the sandstone shows brittle properties. Do the above two situations work on different principles or same, or are these two completely different processes?

In your question I think you are mixing up metamorphic conditions such as the conditions that gneiss forms from sedimentary rock with the formation of diapirs.  Diapirs occur where a less dense layer of a relatively plastic rock has denser overlying formations create sufficient pressure so that the less dense substance deforms and rises over time.

Diapirs of salt occur where thick salt deposits over overlain by dense sedimentary shales and sandstones.  Because of the slowness with which salt deforms the sedimentary deposits will be buried sufficiently deeply that they will have lithified, turning to rock and becoming more dense.  The salt layer will have some trapped water in it that helps the salt to recrystallize as a response to a pressure gradient.

Diapirs can also occur where water saturated sands are overlain by muds (sand volcanoes) or where water saturated clay layers are overlain by dense silts (mud lump islands).  In these cases the layers are relatively shallow and the sands and clays are not lithified.

In conditions of deep burial and high pressure differentials the sedimentary rocks will recrystallize into denser rocks and will deform, producing folds in some lithologies and faults in other rock types.  The slow speed of the deformations and high pressures and temperatures (mostly due to deep burial) give the mineral grains the rocks are made of time to recrystallize and move around each other.  Only if this sub-microscopic recrystallization is not happening fast enough will there be faulting in a layer.


What voltage and/or amps cannot be found naturally? Electricity can come in many forms on Earth but when is amps and/or voltage limited physically on Earth? In other words, what voltage arises naturally on Earth?

The maximum voltage which can possibly occur depends on the materials involved and the distance.

When the breakdown voltage of an insulator is exceeded, the electric potential difference is large enough to force the material into becoming a conductor.

This means that for example when the voltage between two points on the surface of the earth, or two in the sky, or anywhere else connected by air, exceeds about 3kV/ḿm (depending on e.g. humidity) the air between them starts to conduct and the potential will tend to equalize. The same principle applies when the points are separated by materials such as rock.

It turns out, however, that we are not here interested in the properties of the atmosphere since lightning is insignificant compared to the geodynamo. I am not aware of any easily digestible summaries which put the numbers in terms of raw amperage, unfortunately. I did manage to find this lecture which (p. 30) has some estimates of total current in the inner magnetosphere (so in space surrounding the planet, not on it unfortunately) in the multi mega-ampere range.


Do trees capture more CO2 during a fast growth stage? I understand that trees capture CO2 from the air and use that carbon to grow. As trees reach mature height, do they begin to capture less CO2 as they would only need carbon for "maintenance" as opposed to "growing taller"?

I am trying to understand how to model expected CO2 capture for a given tree (my background is in math, not biology). I'm pretty sure my logic is flawed but not sure where...

Trees capture CO2 primarily to get carbon for growth and maintenance.
Therefore, trees need less carbon once mature.
Therefore, mature trees capture less CO2 from the atmosphere.

Right, there are a lot of misconceptions about this. They are mostly to do with the difference between the magnitude of carbon storage and the rate of carbon uptake, and also the difference between whole site carbon storage and above ground biomass carbon storage. There is also ongoing research taking place which (as you might imagine) takes a very long time because of the life expectancy of most tree species.

The standard forester's response is: a hectare of new forest will tend to grow on a Sigmoid / logistic curve (well described by Paine et al. 2011) which looks like this:

This is based on an even aged stand (so, multiple trees, planted at the same time).

Interpreting this, we can see that the greatest rate of carbon uptake is between years 25 and 75 (for this site, species, etc.) but the greatest level of carbon storage is not really achieved until year 150+. You can read more about this in the infamous "Blue Book" by  Forest Research.

Based on this alone, we would assume that mature forests do not sequester much more additional carbon per ha per year, but they do store a lot more than if we simply felled the forest to maximise carbon uptake. However...

1) Below ground carbon (soil carbon, roots, stumps etc.) doesn't follow the same rules. Carbon can remain sequestered in soils (particularly peat) for very long periods and can continue to be laid down (depending on site conditions) more or less indefinitely. When soils are disturbed (for example by felling operations or drainage) they release carbon. So any forest disturbance will tend to release soil carbon.

2) It doesn't scale well to individual trees as pointed out in in Stephenson et al. (2014). This is because the total tree population per ha is of a variable size (tree mortality and thinning means that there are fewer trees per ha over time).

This means we end up with a trade off between storing the carbon we have already sequestered and drawing down new carbon into the system. The degree to which the carbon sequestration rate decreases over time depends a lot on the forest soil, climate, species, and other local conditions. There is an academic discussion taking place over the difference between a simple measurement of above ground woody biomass (as shown above) and a whole-site carbon balance.

It can get quite complicated, and how you look at it can result in different results. Do you definitely want to model individual trees? Or are you thinking about forests in general?

Hope this helps.


Characterizing earthquakes using accelerometer data Is there a way to use accelerometer data to characterize earthquake intensity, e.g., on Richter scale?

Yes, you can measure seismic energy with accelerometers. Most people do.

There are three ways to measure seismic energy: by displacement $x$, velocity $\dot{x}$, or acceleration $\ddot{x}$. Loose-spring devices like geophones measure velocity; stiff-spring devices like MEMS and relative gravimeters measure acceleration: they are accelerometers. Those used in seismology and exploration geophysics are very precise.

I wrote about the various instruments used to measure seismic energy in a blog post a while back. An excerpt about seismometers:

  Seismometers [are] precision instruments not used in exploration
  seismology because they are usually quite bulky and require careful
  set-up and calibration. [Most modern models] are accelerometers, much
  like relative gravimeters, measuring ground acceleration from the
  force on a proof mass. Seismometers can detect frequencies in a very
  broad band, on the order of 0.001 Hz to 500 Hz: that's 19 octaves!

Short story: When digital seismic receivers arrived on the scene in Calgary in the early 2000s, there was a lot of skepticism. We spent a lot of time comparing them to traditional geophones. The conclusion: they were about the same. Here's one comparison by Michael Hons at CREWES, and here's another; here's yet another from one of the big manufacturers, Sercel (now CGG). Finally, here's a presentation more oriented around earthquake seismology.

Okay, but I was talking about the accelerometers in iPhones!

Oh, sorry. As @Fred points out in his answer, consumer-grade MEMS accelerometers (as you might find in a phone or latop) may not have the sensitivity or calibration that a researcher would want, but one might compensate somewhat for this with multiple measurements, e.g. an array of devices. In other words: quantity, not quality. (This is perfectly legit: we do it in exploration seismics too.)

Dashti et al. (2013) in Earthquake Spectra Journal found you could get useful measurements (e.g. for emergency response) from networks of phones with a few tricks:

The more measurements the better.
Horizontal orientation is best.
Prefer high-friction phone covers.
Don't expect to get great data for small quakes.
Treat small groups of phones as arrays.
Don't use data for phones that fell off a table!


What's the difference between a crater and a vent? Crater is above a vent
whereas a vent is below it.
All the best....

A vent opens through the side of a volcano, somewhere on its slopes. The crater (and neck) can seal itself up, solidify over a period of inactivity, then re-open anew nearby to form a new crater. Magma will more readily move through the interface between a solidified neck and surrounding ash matrix than it will through the center of a solidified neck alone.