Could earth run out of O2? Death in a closed environment due to lack of O2 is actually not that bad:

https://www.youtube.com/watch?v=kUfF2MTnqAw

And as far as I know as we are cutting down our life saving woods and jungles less $O_2$ is being produced and more $CO_2$ is not converted back to $O_2$.
Greenpeace and others tell us how bad this fact is.

But: If it continues like this, is it possible for humanity to extinct itself because we run out of $O_2$ and breath in too much $CO_2$?

Wouldn't it be much nicer than like burning to death if the $O_2$ would disappear?

No, that will not happen. There is just too much oxygen in the atmosphere.

Over 20% of our atmosphere is oxygen.
Only about 0.04 % of our atmosphere is CO2, so too much CO2 would kill us much sooner than the lack of oxygen.

If you reduced the oxygen concentration in the atmosphere from 20.8% to 19.8%, you wouldn't even feel the difference. If you reduced it to 15 %, you would still survive it. You could even survive 10 % for short time periods.

However, let's see what would happen if you added CO2 as a replacement for the oxygen you removed: at 1%, you would feel extreme dizziness. At 5% you would lose consciousness and die.

But the real danger in CO2 lies elsewhere. Even an increase from our current 0.040 % to 0.045 % could cause a lot of damage to the climate, and an increase above 0.055 % could be disastrous. Unless you are locked in a small room, the reason why the increase of CO2 and decrease of oxygen will be dangerous won't be because you wouldn't be able to breathe. Changes significantly smaller than those required to make breathing difficult, would be enough to wreck the ecosystem, cause drought, desertification, starvation, and economic collapse.

Also note, that trees are very important for the water cycle, as a habitat for many species, and for preventing soil erosion, but they play an insignificant role in producing oxygen. Most of our oxygen is produced by algae.


How does one determine the optimum offset in a seismic survey? I was going through a report on MASW (Multi Station Analysis of Surface Wave) and found this

  "To avoid the aliasing in the space domain, geophone spacing (Δx) needs to be less than half of the minimum wavelength of interest but channels of the seismograph are limited. As a consequence, geophone spread length (L) is constrained in a certain range. However, on the other hand, a sufficient geophone spread is required for mode separation and the investigation depth."

I understand that this may depend a lot on optimization but is there any approach or research which can be used to make this decision considering both small and large offsets might be useful based on what we are trying to determine.

It depends.

Caveat: my experience is with reflection seismic surveys, but I think many of the principles are similar to MASW.

As you guessed: it's an optimization problem. There are lots of factors at play. It's up to the geophysicist to balance the various needs of the survey:

You need to image the target with useful accuracy (small natural bin size).
You want useful signal:noise levels (high fold and trace density).
You want near offsets for good estimates of P-wave reflectivity.
You want far offsets for good estimates of elastic properties (e.g. density).
You may need far offsets to image certain types of geology.
You want the acquisition crew to have enough receivers for the design.
You want to be able to afford the acquisition and processing!

A while ago, I wrote a blog post on the subject: Fold for sale. It's about balancing fold (how many traces go into the stack, basically, a big driver of signal:noise) with cost.

My colleague Evan Bianco and I also did a series on modelling seismic acquisition. If you're into Python at all, there's some code to play with:

The race for useful offsets
Laying out a seismic survey
It goes in the bin
Seismic survey layout: from theory to practice

The greatest minimum offset in a bin is an important consideration, as you guessed. Also notice the spider plots, which try to visualize both maximum offset in a bin, and the range of azimuths going into that bin (which could be important for stress analysis, for example):

It's hard to go into a lot more detail, other than pointing at more things to read. There are a couple of really good books on this subject:

Cordsen et al. (2000), Planning Land 3D Seismic Surveys. SEG Books.
Vermeer & Beasley (2012). 3D Seismic Survey Design. SEG Books.

For a quick overview, I recommend reading this great paper by Norm Cooper:

Cooper, N (2004). A world of reality—designing land 3D programs for signal, noise, and prestack migration: a 2-part tutorial. The Leading Edge 23, October and December, DOI:10.1190/1.1813357 and DOI:10.1190/leedff.23.1230_1.


Distortion-free map of all continents I've been searching for a map that shows all continents in their actual size that is free of projection distortion, to no avail. Every map I found was of a particular projection type and as such showed continents out of proportion. Even this one, that claims to "not lie" seems rather distorted.

I am no expert in the area, but I do have some 3D graphics background, so I decided to give it a go. I took a spherical projection map of the continental plates, projected it onto a sphere, then created a polygonal mesh encompassing all continents onto the sphere, then brought that into 2d space and relaxed edge length to correspond to their relative length in 3d space as much as possible and transferred the pixel information to the resulting UV map. Note that I did not account of the planet being an imperfect sphere, so that may be a source of minor inaccuracy. And the result:

It does look a lot like a Dymaxion projection, although my result seems less distorted, probably because the former is project onto a rather low resolution mesh before unfolding:

Is my result accurate enough, or is my workflow missing something? And in case of the latter, I'd appreciate a reference to an accurate representation, or at least some info on what I did wrong and how to improve my result.

I've been searching for a map that shows all continents in their actual size that is free of projection distortion, to no avail

That's because such a thing does not exist. A projection by definition has distortion, otherwise it would not be a projection.

The only way to have a distortion free view of the planet is by having a physical globe, and looking at it with both eyes so your brain gets the three dimensional perception (assuming going to space is not an option). Anything else will result in distortion.

Now that we have this covered, there are all kinds of projections with all kinds of distortions. Distortions can affect areas, distances, shapes, etc. to various degrees. It's your choice to determine which types of distortions and their magnitudes are acceptable to you, personally. There is no need to reinvent the wheel, there are enough projections out there already.


As the earth's core cools, will the size be affected? Objects can change in size when their temperature changes. I'm wondering whether the cooling of the earth's core will affect it's size? Or will the change be insignificant due to the elements and states involved or the pressure acting on the core etc.?

Over the 4.6 billion years of the Earth's evolution, so far, the inner/outer core interface has "cooled" to a mere 6000 deg C. Of course, other things being equal, the core will contract as it cools, but the rate of cooling will be massively delayed by the slow radioactive decay of uranium 235, U 238 and Thorium. Delayed, in fact by many more billion years. The mantle will cool with it, and being plastic, will deform to take up the space of the thermal contraction. However, by the time the radioactive heating decays to much lesser values, the sun will have blown up into the red giant phase. Even if the Earth is not actually engulfed by the expanded sun, it will be so heated that the oceans, and more volatile fractions of the crust will have boiled off into space, to become  part of the enhanced solar wind.

If we assume that the Earth's core will eventually cool by 4000 deg C, then Earth will eventually have a reduction in radius of about 10 km (my very rough back of an envelope calculation) from thermal contraction alone. How much of the surface will have boiled off into space by then is anybody's guess.


Can living where (rare) earth magnetic ore is abundant provide any protection from cosmic radiation? Can living in a region that is rich in (rare) earth metal that has an inherently strong magnetic field provide any protection from cosmic radiation? Where are the strongest magnetic field other than the north or south pole and is there a map of these areas?

Related: How would our weather change in the event of a magnetic pole shift?

Absolutely not.
First of all, "rare earth magnet ore", meaning the ores of metals like neodymium (Nd) and samarium (Sm), is not magnetic at all. It only becomes a magnet once you make a magnet out of it. For example, one such magnet is Nd2Fe14B  and it only becomes a magnet after neodymium is combined with iron and boron.
Naturally occuring neodymium ore is usually in the form of minerals such as bastnäsite (a rare earth carbonate) or monazite (rare earth phosphate) that are not magnetic.
It gets even worse!
Even if by some force of magic the rare earth ore would protect you from cosmic radiation, you now have two problems:

Most rare earth ore also has significant amounts of the radioactive thorium and uranium. You do not want to live in these areas, as any "protection" from cosmic radiation will be more than compensated for by the background radiation of the place you are now living in.
These are not nice places to live in. The three operating or recently operating rare earth extraction operations (aka mines) are in the desert. Bayan Obo in China, Mount Weld in Australia, and Mountain Pass in the United States.


How long could a steel artifact last? Would man-made steel artifacts be able to be preserved like fossils for millions of years, or would corrosion make them dissipate? What about metals such as aluminum that don't corrode as easily?

The short answer is no.

Most metals do not fossilize well, they are too reactive/water soluble. Metals are usually what is doing the fossilizing, dissolved metal in groundwater is being attracted to the electrical properties of organic material and filling in or swapping places with a porous material. You might have a stain left or some of the shape as a natural casting, but not material preserved. The exception might be in amber, but it could also be really bad: amber preservation is tricky chemistry, so I am not comfortable saying yes or no. Metal objects have good short term preservation but horrid long term preservation. there are some low reactivity metals that might survive like gold, but not as fossils. But even gold is water soluble over millions of years, so even that would require some unusual conditions.


How will axial precession affect the weather in the northern hemisphere (UK latitudes)? Unless there's a twin star to our sun in which case axial precession might be an illusion the Earth's wobble won't effect the total amount of energy received from the sun as is expected from increased ellipticity, but will effect the amount of sun's energy to the Northern and Southern hemispheres in a cyclical 26000 (and diminishing) year period with periodic further exacerbations caused by variations in tilt.

How has Precession and variations in tilt been factored into the weather change model if at all?

As a side question: On the Salisbury Plain 6500 yrs ago according to wobble theory the East-West alignment going by the apparent motion of the sun across the sky must have been different to today. Can anyone tell me how to calculate the difference in respect to Grid North  please?

Background:
I'm building a picture of Neolithic Britain and want to know the orientation of East-West in this time period to check for orientation practices if any. The particular time period I'm interested in lies about half way along the Axial Precession's swing so I'm interested to know A) Whether the axial precession exists or not and B) How the theory is in agreement with the weather patterns for the last 24000 yrs on Salisbury Plain.

You may be better off getting a more precise answer by cross-posting this physics if you want a precise mathematical explanation of the model.

First, axial precession, as mentioned above, is different than axial tilt. Both change over time, but on different time scales.

That said, the answer is it has most certainly been explored: Milankovitch cycles are an attempt to explain patterns of solar forcing on climate. The wikipedia article does a fairly good job of laying out the foundation of the theory, which is that there are three key components influencing solar forcing: eccentricity (how elliptical our orbit is), axial tilt (the change in amount of tilt of the earth), and axial precession (the actual change of direction of the poles). All three components operate on different time cycles.

Unfortunately for us, the nice Milankovitch theory leads to a huge conundrum: the predictions don't play out as expected. Physics dictates that eccentricity would have the weakest effect of the three, but the largest fluctuations are seen in roughly 100ky intervals (tilt and precession operate on roughly 25k and 50k intervals, eccentricity roughly 100k). This leads to the 100,000 year problem.

Now, all of this is in the context of climate on the global scale, but the point applies just as well: nobody has a conclusive answer as to what exactly is going on, hence the entire field of paleoclimate. Unfortunately for scientists, the Earth is far from a simple rock: our physical (ocean, atmosphere) and biological systems are so complex that it is often too simplistic to pin down changes on one particular phenomenon on a geological time scale. People can study the temperatures  of individual sites over time, but determining the big picture cause of those fluctuations is tough enough for the planet as a whole, much less for a location as specific as the Salisbury Plain.


Is the Principle of Fossil Succession accurate? After wondering on the validity of the principle of Original Horizontality, I'm now focusing on the principle of fossil succession.

This principle states that :

  Fossils of species that did not coexist in the same geological period were found to be in different strata. The principle provided a way for geologists to determine the age of a particular rock layer based on the fossils embedded in it.

This principle seems illogical to me. Let's say that in South America, fossils of a certain species are found, and dated to be from Jurassic. Now, same fossils are found in Europe, and therefore we should conclude that stratum are from Jurassic too.

As we know that Earth is all the time disrupts by inner motions of its cores, what if those motions implied a fossil to move over stratum? It would imply a miscalculation here. How can I prove that this principle is safe?

(For better understanding, imagine that I bury a box at a certain place. If you come 2 years later, nothing proves that you'll be able to find it again, because 'things move in the inside')

Your analogy with burying a box is not as accurate as you think. It needs specific sedimentary conditions for the remains of an organism to fossilize: being buried in soil is far from enough.

Fossilization is such that, eventually, the fossil will be embedded in its stratum, meaning that tectonic events (as you suggest) that would displace the fossil will also displace the stratum around it.

However you are right to question the principle of succession in the sense that, things can happen before the fossil is embedded in its stratum. Namely you have three common phenomena: reworking, downworking, and time averaging.

Reworking, the more common phenomenon. It can occur when the sediment that originally contain the fossil is being eroded. What the sediment contained is therefore once again put in the system and need to be either dissolved or re-sedimented in a new stratum.

Downworking is (I think) more frequent in marine settings: before the sediment is consolidated, the fossil sinks into it, into an as-well unconsolidated but older sediment.

Time averaging. It can take a lot of time for a sediment to consolidate into a stratum, time during which organism remains continue to rain on the sediment. The stratum will therefore not represent a point in time but a time-span corresponding to the time it took to the sediment to consolidate.

Of the three phenomena, only reworking is really problematic (the two other being only moderate time displacement, rarely more than a couple of $10^5$ years). However it is usually manageable to recognize the fact that a fossil was reworked (different alteration compared to other fossils in the same stratum for instance, and if the sediment was already consolidated when the fossil was displaced you will find bits of the old sediment still attached to it).

There is also another problem (regarding your example of a Jurassic species deposited in South America and the same species deposited in Europe), which is biogeography: a species does not appear and disappear at the same time everywhere on Earth (see illustration below). In most cases the time discrepancy is small but in some case it isn't: this is what we call, in biostratigraphy, diachronism.

Taken from Peter Sadler's short course on biochronology. The grey area represent the taxon extent in time and space.


Why was there a negative temperature anomaly between 1950 to 1980? If I understand the information from this link correctly,
Instrumental temperature record
between 1950 to 1980 there were negative temperature anomalies in the years of those decades.

decade
difference (°C)
difference (°F)

1950–1959
−0.02
-0.0360

1960–1969
−0.014
−0.0252

1970–1979
−0.001
−0.0018

This seems odd considering massive oil consumption started in 1880 IIRC, and by 1980 over 350 billions of oil barrels were already consumed (much more probably, since the data before 1950 isn't considered because there weren't reliable records).
Why was there a negative temperature anomaly between 1950 to 1980?

This phenomenon is known as global dimming.

It was due to the particles and aerosols mostly released by combustion of fossil fuels such as diesel. Those particles block the radiation from the sun, so they have a cooling effect. For some decades this effect counterbalanced the warming effect of greenhouse gases, although it is no longer the case at a global scale (see for instance Wild et al. 2007). Particles emission has been reduced thanks to better engines and new regulations, which stopped their masking effect on global warming. Which is a good thing since those particles have a serious impact on health.


Interpolate Gaussian grids to regular fixed grids using bilinear interpolation? I want to regrid GCM data available on Gaussian grids to regular grids, say at 1 deg X 1 deg.
How to do this using CDO or Python or MATLAB.

Edit 1: Data format is netcdf.

climate data operators (CDO)

define grid

We define a lat-lon target grid with 1°x1° grid cell size 30x30 grid cells starting at 40°N and -10°E (=10°W):

gridtype = lonlat
xsize    =  30
ysize    =  30
xfirst   = -10
xinc     =   1
yfirst   =  40
yinc     =   1

This text is written into a text file. See section 1.3.2 CDO Manual for details and further examples.

If you already have a netCDF file which has data on your target grid, you can also extract the grid definition from that file:

cdo griddes FILE_WITH_TARGET_GRID.nc > myGridDef

myGridDef is a text file.

interpolate data

I assume that we do a bilinear interpolation. This is done with the remapbil operator via:

cdo remapbil,myGridDef INPUT_FILE.nc OUTPUT_FILE.nc

The grid of your input data needs to be properly defined in your input file (that is often a problem).

'properly defined' grid

Alternative 1

The spatial dimensions of the data variable (SST in the example below) need to be named lon and lat. Additionally, coordinate variables lon and lat have to exist (time independent!). These need to have correct coordinate variable attributes (see example below).

Example:

dimensions:
    lon = 30 ;
    lat = 30 ;
    time = UNLIMITED ; // (24 currently)
variables:
    double lon(lon) ;
            lon:standard_name = "longitude" ;
            lon:long_name = "longitude" ;
            lon:units = "degrees_east" ;
            lon:axis = "X" ;
    double lat(lat) ;
            lat:standard_name = "latitude" ;
            lat:long_name = "latitude" ;
            lat:units = "degrees_north" ;
            lat:axis = "Y" ;
    double time(time) ;
            time:standard_name = "time" ;
            time:long_name = "time" ;
            time:units = "seconds since 1900-01-01 00:00:00" ;
            time:calendar = "standard" ;
            time:axis = "T" ;
    float SST(time, lat, lon) ;
            SST:long_name = "sea_surface_temperature" ;
            SST:units = "degree celsius" ;
            SST:_FillValue = NaNf ;
            SST:missing_value = NaNf ;
            SST:var_desc = "sea surface temperature" ;

Alternative 2

The spatial dimensions and corresponding variables exist in the source file but are not denoted as lon and lat. Then each data variable (SST, in this example) needs to have an attribute coordinates that holds the names of the coordinate variables.

SST:coordinates = "lon lat" ;

Example:

dimensions:
    TSTEP = UNLIMITED ; // (24 currently)
    COL = 112 ;
    ROW = 106 ;
variables:                     " ;
    double lon(ROW, COL) ;
        lon:standard_name = "longitude" ;
        lon:long_name = "longitude coordinate" ;
        lon:units = "degrees_east" ;
        lon:_CoordinateAxisType = "Lon" ;
    double lat(ROW, COL) ;
        lat:standard_name = "latitude" ;
        lat:long_name = "latitude coordinate" ;
        lat:units = "degrees_north" ;
        lat:_CoordinateAxisType = "Lat" ;
    double time(TSTEP) ;
        time:standard_name = "time" ;
        time:long_name = "time" ;
        time:units = "seconds since 1900-01-01 00:00:00" ;
        time:calendar = "standard" ;
    float SST(TSTEP, ROW, COL) ;
        SST:long_name = "sea_surface_temperature" ;
        SST:units = "degree celsius" ;
        SST:coordinates = "lon lat" ;
        SST:var_desc = "sea surface temperature" ;

Note:

If the coordinate variables are missing, then they can be created via the setgrid operator. If we want to add a grid definition to the source file then we need the source file's grid definition in the text file (see 'define grid').

cdo setgrid,mySourceGridDef INFILE_NO_COORDS.nc INFILE_WI_COORDS.nc


Is the cause of Old Faithful's bimodal distribution for eruption times straightforward? From wikipedia:

  With a margin of error of 10 minutes, Old Faithful will erupt 65 minutes after an eruption lasting less than 2.5 minutes or 91 minutes after an eruption lasting more than 2.5 minutes. The reliability of Old Faithful can be attributed to the fact that it is not connected to any other thermal features of the Upper Geyser Basin

Relatively recent discoveries led scientists to believe that there is a substantial underground chamber where the water and steam build up:

  A previously unknown underground cavity might help trigger the timely eruptions of the famous Yellowstone geyser Old Faithful, a new study shows. The researchers who uncovered new evidence of a chamber suspect that it stores the pressurized near-boiling water, steam, and other gases that propel Old Faithful’s eruptions.

Are the 65 minute and 91 minute values given for the eruption times simply a byproduct of needing more time for the steam to "recharge" after a larger eruption, or is there a deeper interplay between the underground cavity and the main channel that causes some sort of a vortex that has a (somewhat) regular periodicity?

First I would like to say this is not my area of expertise, so this should perhaps be a comment but I am not allowed yet to comment on this site.

In a simplistic view a geyser has heated water chamber with a column of water above it.  The water is heated above the normal boiling temperature but is kept liquid by the pressure of the water column above it.  When the water eventually starts to vaporize this reduces the pressure on the water in the chamber resulting in more rapid vaporization of the water in the chamber resulting in the eruption.

For Old Faithful assume two chambers, one chamber is lower than the other. If the temperatures in both chambers are high enough the vaporization in the upper chamber would also reduce the pressure in the lower chamber allowing it to vaporize resulting in both chambers emptying, resulting in a longer eruption.  Assuming the infill and heating rates are essentially constant then the time before the next eruption would take longer because both chambers are "empty".  On the other hand if the upper chamber vaporizes and but the lower one does not, either because it is not hot enough or the pressure hasn't dropped enough or back pressure from the upper chamber keeps the lower chamber liquid, then only the upper chamber will empty resulting in less time to infill and reheat.

Again not my area.


In terms of the greenhouse effect, what is the Earth's heat capacity? (Question moved from physics to earth science)

Has the earth’s atmosphere reached an equilibrium at which the input radiation energy roughly equals its output, or is the output significantly lower than the input because the energy is being used to heat up stuff? In other words – if the atmosphere’s composition remains exactly the same as it is now, will the atmosphere continue getting warmer, or will the temperature remain as it is now?

If Chuck Norris removed all man- and cow-made greenhouse gases from the atmosphere in an instant – would the atmospheric temperature return to "normal" in a few years, or would there be a significant lag due to the high heat capacity of atmosphere, oceans, and land?

Edits to make my question more precise are appreciated.

For the greenhouse effect, the problem is not a matter of heat capacity. For example, Carbon Dioxide has a specific heat capacity of 0.843 J g$^{-1}$ K$^{-1}$ while $\ce{N_2}$, which is the largest component of the atmosphere, has a specific heat capacity of 1.039 J g$^{-1}$ K$^{-1}$ and water vapor, the most common greenhouse gas on earth, has a specific heat capacity of 1.865 J g$^{-1}$ K$^{-1}$. Thus, the warming isn't necessarily a thermodynamic problem, with regards to heat capacity (though it is, in a ways, a problem of entropy).

The reason that some gases are greenhouse gases is more of a radiative transfer problem than a thermodynamic problem, but the two overlay with regards to molecular structure. Water vapor's absorption spectrum shows that it absorbs most infrared radiation. This graphic demonstrates how much radiation of each wavelength is absorbed by different gases.

You may ask "well, that's dandy, but why do some gases absorb only some parts of the spectra?" Well, that is a bit more complicated, and is dependent on the molecular structure, quantum mechanics, and spectroscopy.

To answer your hypothetical questions directly:

  Has the earth’s atmosphere reached an equilibrium at which the input radiation energy roughly equals its output, or is the output significantly lower than the input because the energy is being used to heat up stuff?

In a ways, yes, that is a fundamental assumption, per Kirchoff's law.

  if the atmosphere’s composition remains exactly the same as it is now, will the atmosphere continue getting warmer, or will the temperature remain as it is now?

There would be a lag before major changes are seen, per Fourier's law. But since water vapor is a greenhouse gas, we would do best not to deus ex machina all greenhouse gases away. Additionally, we need greenhouse gases for survival- too little and we all freeze.

  Has the earth’s atmosphere reached an equilibrium at which the input
  radiation energy roughly equals its output, or is the output
  significantly lower than the input because the energy is being used to
  heat up stuff?

Well, we are almost always at some sort of radiative equalibrium, per Kirchoff's law. For example, the hotter an object becomes, the faster it will cool, per Stefan-Boltzmann Law.


Possibility to influence oceanic evaporation to protect Sahel/Sahara When reading about the projects that want to plant trees on the Sahel-Sahara border, for protection of the Sahel, I wonder what other possibilities there are.

Like, would it be possible to influence precipitation in the Sahara desert by enlarging the evaporation of seas and oceans.

This question would combine a number of different sub-questions.

First of all, would moistening the air help at all? When reading Wikipedia, it looks like the air in the Sahara is extremely dry, but there's also a lack of precipitation generation mechanism. Can rain be generated there if the air would be wetter?

Secondly, when it rains in the Sahara, where does the rain come from? The main wind over the Sahara desert is an eastern to northeastern wind. So it comes from over the Asian mainland, and can't carry a lot of water.

Does it mainly come from different winds (like an occasional western wind)?
Does it mainly come from evaporation of the red sea (though that has a small surface)
Does it get carried all the way over Asia, so coming from the Pacific ocean?
Anything other ideas?

Thirdly (this is more a physics question), is it feasible to alter the evaporation rate of a large water body (feasible as in comparison to the tree-planting project, so it can cost a few billions). The experiments I've found wrt the relation between water-surface temperature and evaporation seem to suggest an exponential relation. Which is at least nice,

Water doesn't have a colour, so it doesn't extract a lot of energy from the solar rays (at least not at the surface, but the energy gets spread over the entire depth). If we could let an energy-absorbing coloured surface (a black surface) float just a few inches under water, it could heat the water surface and make it evaporate more.

By making it evaporate relatively near the coast (as opposed to evaporation in the middle of the ocean), the majority of rain will also have to fall on land

When this technique could be applied to a decent portion of the Red Sea, the surface temperature could be enlarged sufficiently, which could let the Red Sea act as a big ocean, thus result in a wetter Sahara and Sahel.

This might of course be a very stupid idea (like the majority of fresh ideas).

I thought someone would have studied this thoroughly before me (at least before planing millions of trees), but I couldn't find a lot of info on it (not even on the basic questions like how strongly surface colour influences evaporation).

Thanks for reading through this, and trying to answer (a part of) it.

Changing ocean evaporation would impact weather & climate globally. While that may benefit some regions, it would be detrimental to other regions - robbing Peter to pay Paul.

One of the risks would be the effect on rainfall intensity, rainfall duration and the amount of rain falling in any location. It could have disastrous consequences for landslide prone regions or low lying areas prone to flooding.

Increased rainfall would result in accelerated soil leaching requiring soil nutrients to be replaced at a great rate to allow the continuation of farming and for forests to keep developing.

The accelerated soil leaching would also have an impact on the oceans and marine life and land based life reliant on marine life. Additional phosphates would result in increased algal booms, particularly in estuarine waters. Excessive algal blooms can make such waters toxic to life than can only live in such waters.

In addition to accelerated soil leaching there will be associated soil run-off and silting of rivers, estuarine systems and coast outflow regions. For marine wildlife parks such as the Great Barrier Reef, that would have a devastating consequence and may lead to the destruction of all biodiversity with such reefs.


Tsunami Characteristics I got datasets about Tsunami events.

According to International Tsunami Information Center and Indian Ocean UNESCO Tsunami center, for an earthquake to cause Tsunami it should have a large magnitude (> 6.5) and shallow focal depth ( < 100 km ).

But there are entries in NOAA tsunami dataset with focal depth of 260 km and a magnitude of 6.8 occurred at sea with the epicenter located at 21.1 km from the nearest coast. There are also entries with magnitude range of 4-5 causing tsunamis.

Are there some other characteristics of earthquake that may cause tsunami?

The rupture velocity of earthquakes is another factor that determines the magnitude of a tsunami.  The term tsunami earthquakes was coined by Hiroo Kanamori in 1972 to describe when an earthquake having a slower rupture velocity (~1km/sec), compared to a more normal velocity (2.5-3.5 km/sec) of a typical earthquake, causes a tsunami greater in magnitude than expected.

This paper investigates the effect of a horizontal movement of sediments due to an 1896 earthquake that may have created a tsunami earthquake.


Why are pyroclastic flows ground-bound? This bugged me for a while:

Pyroclastic flows are fast (up to 700 km/h (430 mph) according to Wikipedia) and typically roll down the slopes of a volcano. E.g. here https://www.youtube.com/watch?v=Cvjwt9nnwXY.

Also according to Wikipedia, and other sources, they are hot, up to 1000 degrees Celsius, and consist of gasses.

This makes me wonder, why do those hot gasses not ascend up into the atmosphere? This is what hot air does, so there must be something very special about theses gasses.

Now, I know that C02 and CO are heavier than air, but at 1000 degrees?

Volcanic plumes and pyroclastic flows are two behaviours of basically the same thing. A volume of hot gasses and tephra (a.k.a. a mix of ash, pumice, and volcanic rocks of different sizes).

If the gas is hot enough and the tephra content is light enough the mix will be buoyant and it will rise as a volcanic plume. On the other hand if gas is too cold to support the plume, or the weight of the tephra is too heavy. It will collapse and rush downhill as a pyroclastic flow. That is referred to as a "Fountain collapse", and is the most common cause of pyroclastic flows.

That is why the are also referred as density or gravity currents.


How will increased $\ce{CO2}$ affect forests and other vegetative areas? Some researchers contend that increases in atmospheric CO2 (e.g., from anthropogenic emissions) will enhance plant growth in general.

What is the level of that enhancement?
Does the associated climate change simply make it easier for invasive species to propagate?
Or is there really a valid case to be made that at some point, if concentrations of CO2 get high enough, forests and vegetative zones will somehow benefit?
In general, how will increases in CO2 and related climate change affect forests and other vegetative areas?

If you increase CO2 concentration and keep all other parameters at there current level, then biomass production should go up. The reason is simply that CO2 is one of the building blocks biomass is made of in photosynthesis.

In the real world it's trickier than that of course. Here you have to take into account how natural cycles will be affected by increased CO2 levels. Temperatures e.g. will go up which is expected to be beneficial for biomass production for moderate increases and becomes increasingly bad for higher increases. Precipitation patterns change, wind patterns and therefore soil erosion change etc. etc.

Chapter 7 of the IPCC report deals with the question how climate change affects biogeochemical cycles; biomass production is one of the parameters that go into the carbon cycle.

To my knowledge biomass production is one of the parameters that benefit from moderate temperature increase but are expected to turn to their opposite around the 2-degree benchmark.


Quantitative mapping of air pollution Sifakis and Paronis I am reading this paper about deriving AOT and I have found this

This grid dimension proved to be an optimum compromise:
It is large enough to include some visible ground structure and sufficiently
small to allow consideration of a homogeneous atmosphere inside the grid cells

What does it mean...  homogeneous atmosphere inside grid cells?

Homogeneous simply means “the same”. In the paper you have read about AOT (Aerosol Optical Thickness, I'm assuming?), the software used to process the data requires the user to select a grid cell size – at a sufficiently small size, the properties of the atmosphere can be assumed to be the same everywhere inside the cell, i.e. homogeneous, to allow the software to perform its calculations. There's little point in selecting a grid cell size smaller than the distance scales that are interesting and/or meaningful, or smaller than the scale on which anyone could/would measure the properties of the atmosphere you are interested in.  As an extreme example, there would be little point in finding/calculating the Aerosol Optical Thickness for every square centimetre across a geographical region!


What is the tallest fully underwater seamount in the world? I am wondering what is the tallest fully underwater seamount in the world ? When I say the tallest, I mean the one that is the nearest of the sea level.
EDIT : The highest that I found would be at about 50m below the water's surface do you know any other seamount that would be even higher ?

According to the Oxford Dictionary of Earth Sciences,

  seamount Isolated, submarine mountain rising more than 1000m above the ocean floor. The sharp, crested summits of seamounts are usually 1000-2000m below the ocean surface. Seamounts are of volcanic origin.

To avoid classifying seamounts by arbitrary sea level (dependent on availability of surface water), the key point is then that seamounts are features of volcanic origin that rise over 1000m above oceanic crust.

The Hawai'i-Emperor seamount chain is of volcanic origin; all of the islands in this chain are seamounts. Mauna Kea only rises 4207m above sea level - but measured from its base on the oceanic plate it is 10100m high, much taller than Mt Everest. Mauna Kea is - pretty conclusively - the highest seamount in the world. The Woods Hole Oceanographic Institute agrees.


What color is the Sahara desert, as seen from orbit? In images of the Earth taken from spacecraft (or composite images thereof), the color rendering seems to be really inconsistent.
Examples

(Source: NASA, https://visibleearth.nasa.gov/images/57735/the-blue-marble-land-surface-ocean-color-sea-ice-and-clouds)
This is one of NASA's composite images. Here, the Sahara is yellow.

(Source: NASA, https://visibleearth.nasa.gov/images/55418/the-blue-marble-from-apollo-17)
This is a photo from an Apollo mission. Here, the Sahara is an orange/red ochre. This is a very different color.
I realize that there are annual variations to be expected in the color of the landscape, but the above differences seem to be too large to be accounted for by that effect.
Is the Sahara ochre or yellow?

Neither. The Sahara Desert is heterogenous. It’s yellow, red, orange, brown, black, and even green in certain places and at certain times of year.

Slightly less cheeky answer: neither. Both examples are both approximations of human vision, displayed on computer screens that can be highly variable. The 2002 version of the Blue Marble is a composite of 4 months of atmospherically-corrected data in narrow wavelength bands. The composite data is scaled to approximate the nonlinear response of human vision. In particularly bright areas the image is clipped in some bands, leading to incorrect hue and loss of contrast.

For all the gory details, here’s the user’s guide for the MODIS land surface reflectance product (which has always looked slightly greenish to me): http://modis-sr.ltdri.org/guide/MOD09_UserGuide_v1.4.pdf

The Apollo 17 Blue Marble is a color-corrected scan of 40-year-old film (stored in a freezer at NASA’s Johnson Space Center) and is also not a particularly good representation of what an astronaut would see (as Pont commented earlier). The best description of the appearance of the Earth from space is from astronaut Piers Sellers, who said it’s “brilliant blue, and too bright to look at directly—like sunlight reflected off snow while skiing at high altitude”.

Brutally honest answer: neither. To paraphrase Mapbox’s Charlie Loyd, there’s an irreducible subjectivity to color. How we perceive color is affected by ambient light, adjacent colors, overall amount of light, individual physiology, our age, and probably mood and what we had to eat for breakfast. Viewed from space there are even more variables: particularly atmospheric conditions (which influence both incident and reflected light) and viewing angle.

Current state-of-the-art is probably NOAA View, http://www.nnvl.noaa.gov/view/#TRUE which uses a multi-band algorithm to simulate true color with Visible Infrared Imaging Radiometer Suite (VIIRS) data. According to that algorithm, the Sahara is more red than yellow.

For the record, I’ve worked on color-correcting MODIS imagery, the Blue Marble datasets, and astronaut photography on the NASA Earth Observatory & Visible Earth sites (including the referenced version of AS17-148-22727—unfortunately I can’t find the original TIFF.) Perhaps that means I think the Sahara is both ochre and yellow. I also wrote the guide to color-correcting Landsat imagery linked by Jezibelle (thank you).


If rocks are stones, what type of rock are gallstones? From Wikipedia:

  Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a common rock, is a combination of the minerals quartz, feldspar, and biotite. The Earth's outer solid layer, the lithosphere, is made of rock.

From Wikipedia page about gallstones:

  A gallstone is a stone formed within the gallbladder out of bile components

So if rocks are stones, what type of rock are gallstones?

Igneous rock is formed through the cooling and solidification of magma or lava.
Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earth's surface and within bodies of water.
Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism

Gallstones don't fit into any of these categories so what type of rock is it?

The nature of this question is more about biological chemistry than it is about earth science. This is because gall stones have nothing to do with geology, but chemical processes in the body.

Consequently, it would be inappropriate to apply geological classifications, such as igneous, sedimentary or metamorphic, to gall stones.

Due to the way gall stones are formed - layers of bile coating a nucleus - they could be describes as being concretions.


Water vapor content versus specific humidity I am wondering the difference between water vapor content and specific humidity to determine the moisture availability in the atmosphere. Which one is more acceptable variable to determine the moisture availability in the atmosphere?

I need to show the moisture availability in the atmosphere in my study. So should I explain it through water vapor content or through specific humidity?  I will explain the rainfall deficiency over a region

For a study relating to rainfall, I would be inclined to look at total column water vapour (TCWV), also known as integrated water vapour (IWV) or precipitable water.  They're all (more or less) the same thing.

The company Remote Sensing Systems describes it as:

  Total column water vapor is a measure of the total gaseous water contained in a vertical column of atmosphere. It is quite different from the more familiar relative humidity, which is the amount of water vapor in air relative to the amount of water vapor the air is capable of holding. Atmospheric water vapor is the absolute amount of water dissolved in air.  When measured in linear units (millimeters, mm), it is the height (or depth) the water would occupy if the vapor were condensed into liquid and spread evenly across the column. Using the density of water, we can also report water vapor in kg/m2 = 1 mm or g/cm2 = 10 mm.

For rain to form, clouds need to form first.  Clouds need cloud condensation nuclei, but crucially, for clouds to form, the water vapour partial pressure needs to reach the saturation vapour pressure.  The latter is strongly dependent on temperature (Clausius-Clapeyron relation), so a profile of relative humidity is not the most directly useful quantity.  The total column water vapour describes how much liquid water might form, which is why it is sometimes even described as precipitable water.

You can get this product either from reanalysis (like ERA-5) or retrieved from hyperspectral infrared sounders, such as IASI, AIRS, or CrIS.  Depending on where and when in the world you're looking at, there may also exist products from geostationary instruments.


How does a 'fire tornado' form? A 'Fire tornado' or 'Firenado' or 'Fire whirl' are a fearful feature of forest fires world wide.  Having seen one up close, I can attest that they are both awesome and utterly terrifying, but I am aware that these vortices are not strictly speaking, actual tornadoes.

An example, filmed in fires in 2012 around Alice Springs, Northern Territory, Australia, as in this YouTube Clip.

The Wikipedia page for this topic rather vaguely states

  Often, fire whirls are created when a wildfire or firestorm creates its own wind, which can turn into a spinning vortex of flame.

But, the page does provide the following public domain image of a 'fire tornado':

How does the vortex of fire in a 'fire tornado' form?

They form due to strong convective forces, coriolis effects, local wind and weather, and local topography.  The fire effectively creates an intense localized low pressure cell due to the heating of the air which can behave similar to any low pressure system.  I haven't seen one on flat terrain like your picture shows but when performing slash burns for silviculture purposes you can have very large tornados form along ridges as the fire burns uphill.  These tornados can extend outside the fire zone under the right conditions but generally die out soon once removed from the source of heat.


Are there standards for tropospheric NO2 levels considered low or high? I'm working with  Ozone Monitoring Instrument (OMI) $\ce{NO_2}$ vertical column density (molecules/cm2) data. To help interpret the values, I'm wondering if there are standards that show which values are considered low vs high, or good vs hazardous (similar to the air quality index/ AQI). Have any agencies (e.g., EPA, WHO, EU) published anything related to this?

The OMI tropospheric NO2 retrieval algorithm does not provide surface concentrations of NO2, but rather a column density.  So, it isn't appropriate to directly correspond those OMI retrievals to health standards that are based on ambient concentrations at the surface.  There have been many attempts to correlate surface concentrations of NO2 to tropospheric NO2, but the correlation is fair at best.  Furthermore, the tropospheric column inherently changes depending on elevation, since the amount of atmosphere in the tropospheric column decreases as the surface elevation increases.   There are also several assumptions that go into the retrieval that create a large amount of error (e.g. stratospheric column subtraction, a priori profiles, surface albedo, etc.).

As I discuss in this post, it is possible to distinguish clean, polluted, and highly polluted tropospheric NO2 columns.  However, the exact thresholds are specific to location and sometimes season as well, since the retrieval algorithm responds differently depending on parameter assumptions.  In general, if you are seeing values over ~5x10^15 molec/cm^2, you can be sure there is real NO2 pollution.  Anything over 1x10^16 molec/cm^2 is highly polluted.   The higher the values are, the more confidence there is in the retrieval.

You can see the responses from the creators of OMI for similar questions here:

  Does the red colour signal smog at the surface?

  No, since OMI does not measure the concentration at the surface directly. Instead, OMI measures the total amount of nitrogen dioxide (NO2) in a column up to about 10 km.

  However, research has shown that high NO2 column amounts in OMI measurements (red colours) usually coincide with high concentration levels at the surface. This concentration is usually not as high that you can it moderate or heavy smog, but it does still indicates an elevated level of air pollution. The OMI measurements clearly show that The Netherlands suffers from a significantly higher level of air pollution by NO2. See also the answers to the next questions.  Note that smog does not exist only of NO2. Other important ingredients are aerosols, ozone, sulphur dioxide and hydro carbons.

  The OMI map shows a red colour over The Netherlands but according to surface measurements of the Dutch National Institute of Public Health and the Environment (RIVM) it just minor smog. What causes the difference?

  The surface measurements from RIVM are related to the European norms for smog. Those norms are related to a peak level surface concentration. The threshold level is an average concentration of 200 microgram/m3 NO2 during one hour. The peak levels should not exceed this threshold more than 18 hours per year. Peak levels concentrations are most of the time well below the threshold values and therefore one speaks of minor smog.
  OMI does not measure the concentration at the surface directly. Instead, OMI measures the total amount of nitrogen dioxide (NO2) in a column up to about 10 km. For this column amount there are no direct European norms. The relation between column amounts as measured by satellites and surface concentrations is complicated. Therefore, a red coloured area in the OMI map cannot be related directly to European norms and no conclusion with respect to exceeding some norm can be drawn from the OMI maps.
  The colours in the OMI maps are chosen in such a way that you can clearly see the difference between different areas. Column amounts of 20 x 10 power 15 molecules per cm2 and higher all have same red-purple colour.

  Can OMI measurements be related to ground level concentrations, like those being measured by the Dutch National Institute of Public Health and the Environment (RIVM)?

  The largest contribution to the measured NO2 column amount is located in the boundary layer. This is the bottom layer of the atmosphere in which air is mixed quite rapidly and in which the NO2 concentrations are relatively constant. The height of boundary layer varies between a few hundred meters till a few kilometres. The height varies during the day and depends on the weather and season of the year. A rough estimate of the NO2 surface concentration can be calculated by dividing the column amount with the height of the boundary layer.
  A study, using a chemical model of the atmosphere, showed that NO2 measurements by satellites are consistent with surface measurements and that the red-purple coloureds area roughly have surface concentration of 40 microgram/m3 NO2. This value is similar to the European threshold norm for the year-average concentration.


Does muscovite occur as a contact metamorphism mineral? Does muscovite occur as a contact metamorphism mineral, with dacitic intrusion into dacitic rocks?

Yes, wikipedia page for muscovite tells:

Muscovite is the most common mica, found in granites, pegmatites,
gneisses, and schists, and as a contact metamorphic rock or as a
secondary mineral resulting from the alteration of topaz, feldspar,
kyanite, etc.
Source: Muscovite, Wikipedia.

As always, you need to corroborate wikipedia is correct, but there are several papers that talk about muscovite on contact metamorphism environments, you can do your own search on a scientifical database.
Here is an example about a paper that deals with muscovite found on contact aureole of Duluth Complex, Minnesota.
So yes it is a mineral phase formed in that conditions of increased temperature due to an intrusion.
For you specific question about contact metadacites, yes too, they can develop muscovite as shown in this book about US geology.


Paper result validation and the scientific method in earth science The context of this question is computational earth science specifically meteorology/climatology but I am sure it applies to all the scientific disciplines where numerical methods are used.

Recently I had asked the author of a peer reviewed paper for the software that was used in the publication of his paper. He not only  immediately provided the software but also gave me test data to verify the results of his paper. The same was done by a climate change institute affiliated to NOAA. They gave me their software and asked me to download the relevant data from the NOAA site to validate their conclusions and perhaps reuse their software for solving my problems. In both these cases the only requirement was that the software had to be cited in any paper that I publish in the future.

These two instances are not the problem. In another couple of cases when I asked the authors of the peer reviewed paper for their software to validate their work they refused claiming that is "private". My questions are therefore:

Which one of these two  occurrences is more common in meteorology/climatology?
As somebody who is originally from a CS background (where code reviews are extremely common) I'm curious what is the current standard of reproducibility in meteorology/climatology?

Let's start with the trivially true: programming is not earth science; earth science is not programming. Programming is one tool of many in earth science. In programming, the end result is the program itself. In earth science, that's never the case: but one end result is algorithms developed that inform us about the real world, and implemented in a progam.

What if there is a bug in a peer-reviewed paper? Well, of course there is, just as there are bugs in pretty much every program that does anything useful in the real world. So what?

Validating source code is  the domain of programming. Validating algorithms and observations is the domain of earth science. Re-running someone else's code with the same input data is barely any kind of validation at all, and rarely the interesting kind. Taking someone else's algorithms and implementing them yourself, that's the sort of validation I see across the physical, life, social sciences.

So I don't see someone else's source code? No big deal. Indeed, that's often a good thing: it means I can genuinely clean-room their algorithm.


Cleavage of minerals What is the difference between 3-dimensional cleavage and cubic cleavage?
I think, they are the same, but I am not sure about if I was right or not.

The short answer: cubic cleavage is a specific example of 3D cleavage.

A cleavage plane is a direction along a crystal splits preferentially when exposed to mechanical stress.

3D crystals are objects where the spatial arrangement of atoms is described in  a parallelepiped (a unitcell) with three outer dimensions $\vec{a}$, $\vec{b}$, and $\vec{c}$.  The crystal literally builds by translating this unit cell along $\vec{a}$, $\vec{b}$, and $\vec{c}$.

The relative lengths of $\vec{a}$, $\vec{b}$, and $\vec{c}$ and the angles these vectors enclose define the outer symmetry of this unit cell.  Any of the following seven crystal classes is possible: triclinic, monoclinic, orthorhombic, tetragonal, rhombohedral, hexagonal, and cubic.  In this set, starting from triclinic and moving to cubic, the inherent symmetry increases.

With $\vec{a}$, $\vec{b}$, and $\vec{c}$, equally crystallographic planes may be defined; some of them parallel to / coincide with the cleavage planes observed at macroscopic scale.

Thus, as listed e.g., in Wikipedia you may discern:

Basal or pinacoidal cleavage occurs when there is only one cleavage plane. Graphite has basal cleavage. Mica (like muscovite or biotite) also has basal cleavage; this is why mica can be peeled into thin sheets.

Cubic cleavage occurs when there are three cleavage planes intersecting at 90 degrees. Halite (or salt) has cubic cleavage, and therefore, when halite crystals are broken, they will form more cubes.

Octahedral cleavage occurs when there are four cleavage planes in a crystal. Fluorite exhibits perfect octahedral cleavage. Octahedral cleavage is common for semiconductors. Diamond also has octahedral cleavage.

Rhombohedral cleavage occurs when there are three cleavage planes intersecting at angles that are not 90 degrees. Calcite has rhombohedral cleavage.

Prismatic cleavage occurs when there are two cleavage planes in a crystal. Spodumene exhibits prismatic cleavage.

Dodecahedral cleavage occurs when there are six cleavage planes in a crystal. Sphalerite has dodecahedral cleavage.

Intentionally, the description above was constrained to 3D crystals which eventually are (typically) described in one of 230 3D space groups. Note, there equally are seven planar space groups, and a growing body of work about 2D crystals, too.


Fossil or Beef Limestone? I found the below sample on Monmouth Beach near Lyme Regis and I am unsure if it is a fossil or simply beef limestone. The beef limestone is from fibrous calcite layers within a shale (known as shales with beef). For those that are not familiar with the area the local geology consists of marine limestones, shales and mudstones of Jurassic age which are highly fossiliferous.

Apologies for lack of a scale, it is 3 cm high and 2 cm wide, rounded like a tooth with a prominent rim around the base. Part of the back of the sample is flat as though it has been broken.

"Front" view

"Rear" view

Thanks for looking and please let me know if you would like any further information.

Looks like cone from cone in cone limestone, a uncommon texture of limestone rock.
It is most likely not a fossil.

I have found very similar pieces here in Ohio that are Cambrian age.

An accurate description of cone in cone limestone can be found at:
https://en.wikipedia.org/wiki/Cone-in-cone_structures

Also, I have found a number of fossil teeth from fish, sharks and mammals over the years and teeth are most often not the same color as the rock they are found in.


Why are there no hurricanes in the southern Atlantic basin? We see tropical cyclones (going by different names e.g. hurricane, typhoon, cyclone) all over the tropics, but it seems that there are never any storms in the southern Atlantic.  See this map of tropical cyclone activity and note the lack of activity in the south Atlantic and also in the south Pacific until you near Australia.

source

Where are all the tropical cyclones in the southern Atlantic basin?

There have been tropical storms and hurricanes in the south Atlantic, with, according to NOAA's webpage Subject: G6) Why doesn't the South Atlantic Ocean experience tropical cyclones?, with a hurricane forming in the south Atlantic making landfall in Brazil in 2004 and a strong tropical depression/weak tropical storm that formed off the coast of Congo in 1991 - but these are exceedingly rare.

The reason why these storms generally don't occur in the south Atlantic, according to the Penn State webpage Upper-level Lows as being:

  There are two primary reasons why tropical cyclones are rare in the south Atlantic basin. First, vertical wind shear between 850 mb and 200 mb is typically greater than 10 meters per second (check out the long-term average of vertical wind shear between 850 mb and 200 mb). To make matters worse, westerly shear dominates over latitudes where tropical cyclones would be most likely to form. Second, easterly waves from Africa do not form south of the equator (the MLAEJ is a northern hemispheric singularity.

Further, from the NASA News page The Nameless Hurricane, they provide an extension to the explanation with

  Vertical wind shears in the south Atlantic are too strong for hurricanes," Hood explains. Winds in the upper troposphere (about 10 km high) are 20+ mph faster than winds at the ocean surface. This difference, or shear, rips storms apart before they intensify too much

An article The first South Atlantic hurricane: Unprecedented blocking, low shear and climate change (Pezza and Simmonds, 2005) suggest that the implications of the southern hemisphere hurricane presents

  evidence to suggest that Catarina could be linked to climate change in the SH circulation, and other possible future South Atlantic hurricanes could be more likely to occur under global warming conditions.

Catarina refers to the southern hemisphere hurricane

SH = Southern Hemisphere

edited to add an NASA Earth Observatory satellite image of the hurricane:


What is the use of HV or VH polarization in Radar? Radar is a common tool in remote sensing, it is a so-called active instrument, hence it emits and receives energy.  Modern Syntethic Aperture Radar (SAR) systems are capable of both transmitting and receiving polarized waves. The most common polarizations are horizontal $(H)$ and vertical $(V)$ polarization, although other ones exist. Using H and V leads to 4 possible combinations of emitting and receiving signals:

$$HH, VV, HV, VH,$$

which is read as transmitted first, received later (i.e. $HV$ means transmitting horizontally polarized waves and receiving only vertical polarized waves).

I can relatively easily imagine the use of the $HH$ and $VV$ copolarized waves. They should be easier reflected by object that have a longish geometric structure. Large $VV$ and small $HH$ would probably indicate tower-like structures and small $VV$ and large $HH$ should indicate bridge-like structures.

However it is not obvious to me what structure would reflect a cross-polarized wave $HV$ or $VH$ stronger than $HH$ or $VV$? Furthermore, what is the difference between an object that reflects $VH$ and an object that reflects $HV$?

In the case of a ground looking radar, the cross-polarized signals HV and VH generally increase with surface roughness. For example, dense vegetation is one of the more depolarizing surface types because the polarization orientation of the emitted beam is scrambled over the course of multiple scattering interactions within the canopy before returning to the detector. Smoother surfaces can be thought of as having fewer (often just one) interactions and the corresponding signals are thus reflected to the detector predominately in their initial orientation (i.e. as HH or VV).

The cross-polarized signal also increases as scatters suspended in the atmosphere become less spherical in shape. This is particularly applicable in the interpretation of meteorological radar observations where it is used to estimate raindrop size, distinguish between solid and liquid precipitation and differentiate biological scatterers (e.g. flocks of birds) from hydrometers.

For a fixed target, the return signals HV and VH will have equal intensity. This is a direct result of the principle of reciprocity.


What cloud formation is this? I thought it may be mammatus, but the absence of the hanging down "udders" made me doubt.

It is mammatus. The individual cells are hanging down, but it just isn't very obvious from your perspective. Nice photo. Usually one doesn't have much time to photograph mammatus because of its inherently unstable condition.


Is there more water in solid form than in liquid form on earth? There is plenty water in the oceans, but I've read that deep in the crust/mantle  of the earth within crystals and other rockforms is water enclosed. So could it be possible that there is more water beneath the surface of the earth than above?

Clearly you are referring to water locked up in hydrous minerals. The short answer is no, not much water in the Earth at all compared to the surface. The hotter it gets the more hydrous minerals tend to dehydrate, so there are only minuscule traces of water at great depth. I suggest you calculate a rough water balance of water carried into subduction zones = length of subduction zone x thickness x sediment porosity (under pressure) x average subduction rate. This should be compared with estimates of volcanic emission of water vapour (both to the atmosphere and submarine - more difficult to estimate). I'm guessing these should be more or less in equilibrium. The water volume involved is trivial compared to the water on the oceans.


Can the overuse of geothermal energy become an environmental concern? At what power output would we be using so much geothermal energy that we cool the core enough to endanger the Earth's magnetic field and have to stop using it? Is this a conceivable concern for a future energy crisis?

No, this seems highly unlikely.

According to online sources:

Average human power consumption in 2008 was estimated at 15 TW.

Total annual heat loss from the Earth due to the surface heat flux is estimated at 44.2 TW.

Estimates of the electricity generating potential of geothermal energy around the world are consistently less than 2 TW.

So although the average power consumption is a surprisingly large fraction of the total geothermal heat flux, the part that might possibly be extracted for power is quite small.

There are much more concerning environmental impacts to geothermal power development than freezing the core and destroying the Earth's Magnetic field. These include increased rates of release of carbon and sulfur into the atmosphere and land use issues.


What do continents "lay" on? It's a simple question.. What do continents "lay" on? Do they float on water? or are they huge bodies that "emerge" from the sea floor/bed? are they connected to the bottom of the oceans?  Hope the question is clear. Don't be afraid to be thorough and scientific in your answer, I'll appreciate it and do everything to understand it.

Matan, the continents where we all live "float" on the Earth's mantle. The continents are made out of relatively brittle rock called the "Crust" and the mantle is made out of much more ductile material. The mantle, however, is NOT liquid. It is just much more ductile than the crust so, in geologic time, it can flow (like silly putty). Also, the mantle is much more dense, so the crust doesn't sink into it by gravitational/bouyancy forces alone.

Think of it as a creme brulee. We live on the little hard crust on the top. And there just happens to be a little bit of water on that crust that covers the less-elevated parts.

Now, a little more technical, the crust that makes up the continents and the crust that is under the deep oceans are actually compositionally different. This is because the magma that solidifies to form each of these crusts travels, by partially melting its way up, through different materials and different thicknesses. The consequence of this is that the crust making up the continents is less dense than that making up the bottom of the oceans.

The image above shows the process by which we get new (left) oceanic crust, (right) continental crust, and (middle) a special type of crust like that in Hawaii. Note that when two tectonic plates collide, the more dense one will tend to subduct under the other.


Why is relative sea-level falling in Hudson Bay? Why is the sea level in Hudson Bay decreasing so much? Hudson Bay is pretty far up north, much closer to glaciers. Would it make sense for it to recede at this level with sources of fresh water relatively close?

The area is experiencing post-glacial isostatic rebound.

Much of Canada was covered in an extensive ice sheet in the last glacial period (the 'Ice Age'), from about 110 ka until 12 ka. The ice in the Hudson Bay area was among the last to melt:

A thick ice sheet depresses the crust (the lithosphere), making a small dent in the uppermost mantle (the asthenosphere) in the process. Well, not that small: p 375 in Gornitz (2009, Encyclopedia of Paleoclimatology and Ancient Environments) says it could be 800 m for a 3000 metre-thick ice sheet!

Since the asthenosphere is highly viscous, it takes a long time time for the depression to 'bounce' back up. This map from Natural Resources Canada shows the current rate:

Since global sea-level is currently rising at about 3 mm/a, a local uplift at this rate will break even. Anything more will result in relative sea-level fall, as we see in Hudson Bay (as well as in Scandinavia, the UK, Alaska, and elsewhere — this map is wonderful).

Interesting, for geologists anyway, is the sedimentological record this leaves. I love this example of raised beaches and a small delta experiencing forced regression on the shores of Hudson Bay:

Last thing — you asked:

  Would it make sense for it to recede at the level that it is
  receding with sources of freshwater relatively close?

Since Hudson Bay is connected to the world's ocean, mainly through Hudson Strait, the runoff into the Bay has no measurable effect on the water level.

Credit
Ice retreat map by TKostolany, licensed CC-BY-SA. Rebound map by NRCan, free of copyright. Google Maps image contains own credit.


What kind of stone is on this photo Does anybody know what kind of stone this is?

Thanks alot in advance

Wolfgang Adamec

I believe it is metamorphic due to the absence of crystals that can indicate ignious rock, and the absence of particles that would show it as a sedimentary rock. You can make an educated guess by folowing the advice of the website Rock Identification Made Easy


Airports with longest continuous temperature records Does anyone have a resource on what airports (or other recording stations) have been recording temperature continuously (daily) for quite a while?

I remember reading that some back to the 1910s/1920s, but I am having trouble finding resources on which airports, and of course getting my hands on the records themselves. I would like very much to find such resources.

I found a pretty easy-to-digest resource from NOAA here:

ftp://ftp.ncdc.noaa.gov/pub/data/noaa/isd-history.csv

It has a list of temperature sources (including airports), with their start/end dates that they were measuring.


Can large (and wet) storms really trigger large magnitude Earthquakes? At the 2011 AGU Fall meeting, this poster claimed that the water erosion from Taiwan's wettest storms could prematurely trigger large magnitude earthquakes , $ M \ge 6.0 $. If this was true, this discovery would be incredibly important for not only our understand of earthquake mechanics but also hazard prevention. Could this theory really be correct?

The 2011 AGU poster has been cited once, by Burtin et al. (2013)1, who say in their abstract ... event activity was positively correlated with the precipitation intensity... -- but more importantly, in the body of the paper, this:

  Furthermore, it has been argued that rainfall may affect the occurrence of earthquakes, either by downward fluid diffusion from the surface [e.g., Bollinger et al., 2007] or by erosional unloading of active faults [e.g., Wdowinski and Tsukanov, 2011], but these mechanisms require exceptional or very prolonged precipitation and they are likely to entail significant delays between the meteorological driver and seismic response of up to years. For
  these reasons, we also rule out rainfall-triggered seismicity as a possible source of the near-surface activity we have detected.

Note, however, that over the course of the study they recorded 29 events, of Ml 0.7–5.7.

Meanwhile Sobolev et al. (2012)2 - in a journal I do trust - say in their abstract:

  This study is concerned with the effects of powerful Pacific cyclones on the seismicity of Kamchatka, Japan, and the Philippines. We used complete seismological catalogs for these regions that span a few tens of years. It was found that the cyclones that originate from the western Pacific generally do not exert a significant triggering effect on the seismicity of these three regions, at least in the short term, during a few weeks. The ground motion generated by cyclones, which might be treated as a trigger, does not have amplitudes above those in the motion due to numerous local earthquakes of moderate magnitudes (∼4–5) and larger teleseismic earthquakes.

The only two recent publications claiming any link at all between cyclones/extreme precipitation events and significant seismic activity (i.e. not "minor" landslips) are from sources I don't trust: a 2013 paper in a journal I've never heard of (International Journal of Geosciences) before, and a 2014 publication in "Natural Hazards and Earth System Sciences Discussion. I'm dubious about them not because they are open access but because I am concerned about methodology and sources.

While this mechanism was mentioned to me as plausible as an undergraduate at Cambridge in approximately 2012, the department's view seems to have shifted (per Burtin et al - Neils Hovius is very senior in the dept). The current evidence does not appear to support any short-term link between extreme weather events and significant seismic activity. Long-term links have not been ruled out but I have not found any substantiating evidence for such connections.

1 disclaimer: it turns out I know two of the coauthors, including one of the senior ones, personally.

2 Original in Russian also available


Why does chlorophyll only come in green? Plants do not only come in green but chlorophyll does. The pigment in the plant creates other colored plants other then green.

Could a plant grow under an alternative light spectrum like a green sun or a pure green light? Why is the green spectrum of light that of chlorophyll reflected and not absorbed?

chlorophyll is green because that was the part of the spectrum that was left when plants evolved. The bulk of the spectrum was already being harvested by other photosynthetic life. there is actually a wide variety of photosynthetic pigments chlorophyll is just one of many. You may want to check out the purple earth hypothesis.

Sauce


Historical data on world's forest area Is there long historical data (at least a few centuries back), at the world level, of forest area? I've only found data by the FAO starting in 1990 (see here). There is some older evidence for a few regions and countries but no aggregate measure (for instance, see here). Any help is appreciated.

When I need data about past and future projected land use change, I usually refer to the global dataset that was developed for the global climate simulations CMIP6.
The dataset is the Land Use Harmonization V.2 LUHv2 and it was developed by researchers at the University of Maryland.

Reading the supporting document of the dataset, among others, the following characteristics are reported:

  global domain;
  850‐2100 annual land-use states, transitions, and gridded mgt layers;
  0.25 x 0.25 degree spatial resolution;
  12 possible land-use states including separation of Primary and Secondary natural  vegetation into Forest and Non‐forest sub-types,
  Pasture into Managed Pasture and  Rangeland, and Cropland into
  multiple crop functional types

The dataset is composed of a set of simulations using different land surface models:

  These datasets are being developed as a contribution of the Land-Use
  Model Intercomparison Project (LUMIP) to the Forcing Group for CMIP6

Data can be downloaded from this page.

Of course, the layers you find here are "just" models' results, but as much as past observations made a good calibration possible, the variations reported are likely be the most accurate information about the evolution of the world forested areas currently available.


How to interpret the use of late and early Tertiary from older literature? When reading older papers how should I interpret the use of "Late Tertiary" and "Early Tertiary"?  Would these periods equate to Paleogene and Neogene, or was there a different accepted boundary age between the Late and Early Tertiary?

I think this is very hard to answer this question as it is exactly this ambiguity that caused the International Commission on Stratigraphy to discard the names Tertiary and Quaternary for there are no clear limits to these era's. For example, the name Quaternary was only introduced some 70 years after the name Tertiary (source), and Neogene covered both the last part of the Tertiary as well as the Quaternary era (source), until in 2009 the Quaternary was reinstated as a period while at the same time redefining the boundary of the Pleistocene (source), so interpretation should take into account when the article was written as well.

The meaning of Late and Early Tertiary is therefore dependent on the context, and is probably only safe to be interpreted as relative ages (unless exact ages are given, but in that case there is no question of interpretation), not well defined periods in time. It might help to look for articles by the same author or from the same year to see what the common interpretation was at that time.


Is it possible for Earth to experience Polar Shift? Many accounts claim that the Magnetic Field of the Earth has been seriously degrading for the past centuries and we are currently in the process of the so called Polar Shift. How likely would it be for Earth to experience this phenomenon. Is it really possible?

What would be the possible effect to human beings if this happens?

Is it possible for Earth to experience Polar Shift?

Yes, and it has happened before.

In the past 80 million years it happened over 150 times. The last time this happened was around 800 thousand years ago. A quick note about what a polar shift is, more properly termed a geomagnetic reversal. Earth's magnetic is such that a compass points to a certain direction. For example, a modern compass would point north. In a reversal, it would point south instead because the poles are reversed. Without going too much into detail, this occurs not by spinning of the poles but rather by decreasing in intensity until it becomes negative, thus reversing the poles.

Another important thing is the intensity. A strong magnetic field shields Earth's from some kinds of radiation, for example the stuff you can see in Gordon's answer. However, a reversed but strong magnetic field is just as fine. What you should be worried about is the change in the intensity of the field, and this is going up and down all the time, quite rapidly as you can see in the following figure:

The black bit (called Brunhes) is now - when the magnetic field is "normal". The white field in the bottom is more than ~780 thousand years ago, when it was reversed (called Matuyama). As you can see, even though the magnetic field has been normal though this entire time, the intensity went up and down. So yes, a reversal would mean that at one point the intensity would be very low, but this can happen even without a reversal.

  What would be the possible effect to human beings if this happens?

In contrast to what some people on the Internet claim, there would be no earthquake or volcanoes or other scary stuff related to it. This is simply not how this works. Also, mass extinctions from the geological history are not correlated with geomagnetic reversals, so you can take that worry off your mind. What can happen is detailed in a good way in Gordon's answer. Nothing too scary.

  Magnetic Field of the earth is seriously degrading for the past centuries and we are currently in the process of the so called Polar Shift

Not necessarily. It seriously degraded many times before without associated geomagnetic reversals.


Musing on Earth's gravity (a) What, if anything, is the difference between Earths geographic center, i.e. mid-point of the spin axis, and the gravitational center?

(b) What is the average distance between the Earth's center of gravity, and the Earth-Moon system's center of gravity?

(c) The recent 'super-moon' is a reminder that the moon's distance has an orbital wobble. So, by how much does this vary the distance between the Earth vs Earth-Moon gravitational centres, and

(d) Is the moon's varying distance from the Earth sufficient to create any noticeable effect upon sea/ocean tidal amplitudes?

For (a) through (c), consider the differences between the geoid and the reference ellipsoid, in addition to the barycentre.

For (d): A slightly higher perigean spring tide than usual, meaning in some geographical locations perhaps an amplitude difference of inches rather than millimetres.


Difference between NCEP's 20th Century daily Forecast and Analysis variables NCEP's Twentieth Century Reanalysis (V2) provides daily variables from 1871/01/01 to 2012/12/31. Monolayer analysis variables are made available in a regular grid and forecast variables in a gaussian grid. This distinction is made very clear in their list on their webpage, although I think the grid is not the main problem here, but the terms in bold.

Daily precipitation rate, for example, is a forecast variable. This makes you think weather you may use forecast and analysis interchangeably. What are the main differences? Any pros or cons? Are all of these still considered reanalysis? Any assumputions I need to make?

This question came up as a consequence of the discussion held here.

Thank you in advance.

Some variables in reanalyses have to be forecast and cannot be assimilated to allow the model to converse mass, momentum and energy. Precipitation is a good example. The model will assimilate observations which give information about moisture (someone who knows more about assimilation may want to chirp in here). This will be used in the analysis (e.g. 00z) and is forecast forward. Daily precipitation is therefore given as the accumulation of precipitation from 00z analysis -> 12z forecast and the 12z analysis -> 24z forecast.

There is a hierarchy of precipitation datasets each with pros and cons:

Gauge data is often considered the best but it very patchy (not to mentions instrument issues). You can use kriging to make spatial maps. This paper may be of interest.
Satellite datasets such as GPCP and TRMM give better spatial information but subject to issues over land, for example (I think). The are also subject to trackiness (only get data underneath/near the satellite).
Reanalyses can provide spatial and temporal homogeneity but it is a model and 'all models are wrong, but some are useful'.
Datasets are emerging combining both gauge, satellite and reanalyses such as in this paper.


How have levels of outgoing longwave and incoming shortwave radiation changed over the last 20-30 years? So as we know, climate change is associated with increased radiation flux into the Earth. In other words, the sum of (incoming shortwave radiation) - (outgoing longwave radiation) [which I will call net flux] is greater than 0.

I'm just curious though - how have all of these fluxes changed over the last 20 years? Has net flux been constantly positive over the last 20-30 years? Is it changed by El Niño? Have we seen any changes in the flux associated with the recent "slowdown" in global warming?

Have we seen any changes in the flux associated with the recent "slowdown" in global warming?

There is no evidence for such a slowdown, nor for a change in the associated flux.  Atmospheric warming has not been significant in the past 15 years (nor can we significantly state that it hasn't warmed), ocean warming has continued.  As the oceans absorb the vast majority of the excess heat, this net flux probably has not significantly changed during the "slowdown".  Note that 15 years is in any case too short to state anything about global climate change.

As for your other questions: estimates of the flux have certainly changed over the past 20 years. but estimates vary quite a bit, so I don't think we can significantly state that there has been a change in the fluxes over the past 20 years.  Nor can we state the reverse; it appears further research is needed.

For an excellent and still somewhat recent overview article on the topic, see:

Trenberth et al., Earth's Global Energy Budget, BAMS 2009


How can we calculate the total water mass that falls during a flood? I would like to know how to calculate how much water fell on California during, for instance, the mid-February 2017 flood.  I know how to look up the total rainfall at a specific weather station.  And, given a meteorological model output, I could calculate the total water precipitated over some area.  However, I don't know of any standard method (using observations) to calculate total cumulative water fallen over some area.  I've seen multi-station precipitation indexes like the one shown below.  But, I don't know how to use that to calculate total water that has fallen to the ground.

Based on observations, how can we calculate the total cumulative water volume (or mass) that has fallen on a large area during a storm?  And, using that method, can we calculate how much water fell on California during the 2017 February flooding events?  The only thing I can think of is to use the rainfall measurements at every station, interpolate across the area of interest, and then integrate.  Though, that seems like quite an intensive GIS project.  Is there a better,standardized way to make the calculation?

I don't have the answer for you, but I can point you to the tools that can be used to get such an answer.  The Advanced Hydrologic Prediction Service compiles rainfall grids using radar, surface observations, and a variety of other sources.  Options offered include daily, month-to-date, and archived data.

You can probably quite reasonably put the Shapefile download option into a GIS application, such as Grass GIS or ArcGIS, then limit it to the state (or area of interest) and compute an average or total.

Alternative, you can download it as NetCDF, which I know you'd be able to open in GrADS/OpenGrADS, mask it to a certain area using some sort of shape file or geometry, and then run an areal average on it.

I really do wish more straightforward, user-adaptable data were easily available (and no guarantee it's not, I just don't know a source).  But at least this will give you the tools to figure out.

And while you're focused on rainfall, perhaps read up on central California's Great Flood of 1852!

One other way to get an estimate of the total volume of water would be to use stream flow values combined with reservoir level changes, and attempt to estimate what percentage of rainfall escapes the reservoir system.  But at that point you're getting a very rough estimate, because the monitoring system doesn't measure every small stream emptying into the sea... and a significant (and varying) percentage of the water infiltrates the soil or evaporates.  Those complications could be incorporated into the calculation, but in the end, that seems a complicated way to solve a problem we already have more complete information on.

You asked for how much water that is.  Well, we can just as easily get a fair estimate from the map:

(month to date as of February 22nd)

If that's an average of 8" over the state of California, that's:
$ \pu{8 in} \times \pu{163,696 mi}^2 =$ 23 trillion gallons

Even if we're off by a factor of as much as 2 on the estimates, such that it's only 4" average, or alternatively 16" average, that just changes it to 11.5 trillion gallons and 46 trillion gallons.

Which begs the point... we don't often think in terms of trillions of gallons.  Trillions of gallons seems a ton, but even just a meager 0.35" over the state would equate to a trillion gallons.  Perhaps normalizing it to the area... such that it'd be $ \pu{140000 gal/mi^2}$... is a little better.  But still, a typical person would struggle to recognize whether any given value in this form would result in a flood or a droughts.

That's why we often just work in terms of percentiles, or graphs, or return periods, or just give the average in terms of inches itself.  It may not click great with everyone, but for many, such units are just a little more interpretable.

(And in case you wondered, a gallon of water weighs about 8.36 pounds, so that's about 100 trillion pounds of water, again sounding like a lot, but to most people, so does 1 trillion pounds of water from a little 0.10" inch rain system)


How can oil can escape from a shale source rock into a reservoir rock? How can oil can escape from a shale source rock into a reservoir rock if the shale itself is impermeable?

Shale typically has a low permeability but shale is not technically impermeable.
Natural occurring faults, fractures and joints in shale can greatly increase the permeability of the rock.  This is why hydraulic fracturing (or fracking) is used to increase fluid flow (for both water, natural gas and petroleum wells) in host rock with low permeability.

Fractured shale can allow a significant amount of fluid because some shale can have porosity values greater than 10%.  Given the grain size of shale, this can be a significant amount of space available to hold fluids.

References:

Physical Characteristics of Fractures and Fracture Patterns
FRACTURED RESERVOIR BASICS
Hydraulic Fracturing
Shale porosity


What are the mechanisms maintaining the Dune of Pilat? The Dune of Pilat (Dune du Pilat) is the tallest dune in Europe. The dune has been around for at least centuries. Where is the sediment coming from? Why is the dune so tall?

As per @Richard suggestion, I think the best answer comes from dune-pyla.com. They provide a complete explanation of the evolution of the dune and a couple of great summary figures:

It seems that the material comes in large part from the Banc d'Arguin to the west through aeolian transport. The sand from the bank and adjacent areas is related to the material from the river Garonne to the north.

Part of the reason for the height is that they covered the preexisting Dune de La Grave with a pine forest during the XIX century to stabilize the sand and then the forest was covered by another additional 20-30 meters of sand. The dune is still migrating east at an average rate of around 7-8 m/year and burying the surrounding forest as it migrates.


What causes this arc in the night sky where the background is brighter on one side than the other? This comment to Did nobody in the Astronomy community think 12,000 new satellites in LEO might be a problem? links to Phys.org's New ESO study evaluates impact of satellite constellations on astronomical observations which includes ESO's Areas of the sky most affected by satellite constellations shown below.
It's a fisheye lens view (FOV wider than 180 degrees)looking straight up.
There is an large arc that begins at the bottom of the image (where the elevations of 20 and 30 degrees are deonted) and extends upward and toward the left. It looks like it could be a circle about the anti-lunar point since the moon is also seen on the right side slightly above center.
Question: What is happening here? Is this an atmospheric effect of scattered moonlight? If so, what causes such a sharp transition in the amount of scattered light? Does this have a name?

This annotated image shows the night sky at ESO's Paranal Observatory around twilight, about 90 minutes before sunrise. The blue lines mark degrees of elevation above the horizon.
A new ESO study looking into the impact of satellite constellations on astronomical observations shows that up to about 100 satellites could be bright enough to be visible with the naked eye during twilight hours (magnitude 5–6 or brighter). The vast majority of these, their locations marked with small green circles in the image, would be low in the sky, below about 30 degrees elevation, and/or would be rather faint. Only a few satellites, their locations marked in red, would be above 30 degrees of the horizon — the part of the sky where most astronomical observations take place — and be relatively bright (magnitude of about 3–4). For comparison, Polaris, the North Star, has a magnitude of 2, which is 2.5 times brighter than an object of magnitude 3.
The number of visible satellites plummets towards the middle of the night when more satellites fall into the shadow of the Earth, represented by the dark area on the left of the image. Satellites within the Earth's shadow are invisible.
Crediti: ESO/Y. Beletsky/L. Calçada

What is happening here? Photoshop!

  The number of visible satellites plummets towards the middle of the night when more satellites fall into the shadow of the Earth, represented by the dark area on the left of the image. (emphasis added)


Why antarctic research stations are built above ground instead of on the ground or underground? Many online sources stresses how much the antarctic wind is dangerous for the structures and for the personnel, yet most buildings I see are built off the ground.

I suppose that is due to the different thermal conductivity of the air vs the ground.

Yet, many arctic dwelling tribes build enclosed hut on contact with the ground, as if the wind chill is actually much more dangerous than the heat lost with the ground.

Besides, building underground should guarantee an average temperature and/or depending on depth a better temperature for materials and people.

Habitats should still need insulation, but maybe they would reduce the fuel consumption to heat the habitats.

Could you point me towards research papers and/or data regarding antarctic soil temperature?

Antarctica is a whole continent and it is as diverse as any other continent.

There are two reasons buildings are often built off the ground on pillars.

1.- Avoid snow accumulation: Although in average Antarctica is a dry continent, in some coastal areas there can be massive amounts of snow accumulation. Building on pillars spare the buildings to get buried and most importantly allows the wind to blow the snow away. If you build on the surface, the snow will accumulate on the lee of the building. This happens even if there is very small snow fall, because wind transport the snow for long distance and the lee of a building is favourable for accumulation. Therefore, even it snows 1 mm, the millimiter that fell in all the ground 100 km upwind can end up piled behind your hut, and block your door.

2.- To rise buildings: Many of the bases are built on ice, and all those are buit on the accumulation area of glaciers or ice sheets. Therefore, with time the surface will rise relative to the building and will eventually swallow it. Therefore, in many cases (like the Amudsen-Scott base at the South Pole). The pillars are designed to be extended, therefore allowing to rise the building as the ice below thickens, keeping it at an optimal distance for the ground.

Regarding the inquiry about soil temperature, again that is too broad. Imaging asking about the soil temperature in North America, the answer would be quite different for Mexico than for Alaska. The same contrast can be found between bare ground areas of the Antarctic Peninsula at latitude 60°S and at almost 5,000 m of elevation on Mount Vinson plateau at latitude ~80°S


What is principle of inverse modeling? I read a few paper related to emission inventory talking about the inverse modeling. It was another method to estimate the emission from ground(called top-down method). The satellite sensor usually support the product with vertical column density(VCD) for certrain species.

The target here seems to be generate the relationship between emission and VCD. In my opinion, there are some uncertainty hidden here:

(1) the gridded VCD of certain species can be formed by different precursors, transported from neighborhood area.

(2) The chemistry system in the model also has some inherent bias which would miss some crucial source or sink process.

(3) When we set source inventory as input for chemistry transport model, the height information and the specific location are two crucial parameters. In the area of inverse modeling, we know nothing about the information of real sources(i.e fire spot, power plant).

How to generate a relative precise relationship between satellite data and source emission in consideration of these doubts?

To my understanding, the question refers to studies which aim to estimate pollutant emission fluxes using satellite retrievals of atmospheric constituents. Mathematically, this means estimating the forcing term in an advection-diffusion-reaction system given a set of tracer observations.

How well you can localize the emissions depends on the pollutant: for something shortlived, like NO2, a given observation will be influenced by a relatively small area, while for a long-lived pollutant (say CO) the effective resolution would be much lower. For long-lived pollutants, the problem is not well posed and needs to be regularized in some way. Typically, instead of reconstructing the emission from a scratch, you try to just refine an existing emission inventory.

The issues you mention regarding model errors are real and certainly do introduce biases in any emission estimates based on satellite products. This is quite well understood by people working on the field, but the difficulty is in quantifying the errors that are due to model uncertainty.

  How to generate a relative precise relationship between satellite data
  and source emission in consideration of these doubts?

Opinions vary. In my experience, few scientists believe that satellite-based emissions could replace traditional emission inventories. On the other hand, for many areas and pollutants, the regular emission inventories also involve a lot of extrapolation. Ultimately, the question is whether the inverse modeling can deliver some useful added value compared to the existing inventories.


What are these "ship wrecks" (pictured) in the old volcano crater? They consists of stone, of course, but have strange U cross section, as if they were the remaining of some ships without the head and tail section. Could anyone tell how have they formed? They almost perfectly in the center of the old, flat volcano (Strytur) near Hveravellir, Iceland. They are quite high uphill and I am surprised how lava could get into that place and then made into such a shape as it probably only flows down.

If U-shaped in cross-section, it is plausible that these are the partial remnants of lava tubes. See, for example, Morphology and mechanism of eruption of postglacial shield volcanoes in Iceland (Rossi, 1996). It is difficult to propose more detailed formation mechanisms in the absence of significantly more information about the structure.