What factors determine the height of the turbopause? The turbopause separates (by definition) the homosphere from the heterosphere.  What factors cause the turbopause to be where it is?  Is it affected by mesopheric composition, solar irradiance, global atmospheric change, and other factors that may change significantly?  Or is it mostly determined by density in the absolute sense, and therefore relatively constant?

A major consideration for any such altitude measurement, hence determination of the factors is, according to Turbopause determination, climatology, and climatic trends using
medium frequency radars at 52°N and 70°N (Hall et al. 2008), that

  measurement of the turbopause altitude is a rather different matter, primarily because direct measurements of small-scale fluctuations in neutral density, temperature or motion at altitudes of around 100km are virtually impossible.

The authors state that seasonal variation plays a significant role; the article The “wave turbopause” (Offerman et al. 2007) elaborate on this in their abstract:

  Substantial seasonal and latitudinal variations are found, with some interannual variability also present. Seasonal changes are annual at high latitudes, semi-annual at low latitudes, and a mixture of both at middle latitudes. Southern hemisphere data are similar as in the North if shifted by half a year. Latitudinal variations show a minimum in the tropics and two relative maxima at middle latitudes.

With observations made in northern Norway in the article Seasonal variation of the turbopause' One year of turbulence
investigation at 69°N by the joint University of Tromso/University of Saskatchewan MF radar (Hall et al. 1998) showing that the levels at these latitudes decreasing in summer months.

However, long term changes seem to be occurring at high latitudes, with the Hall et al. (2008) observing

  the classical radar turbopause has been at constant altitude at 52°N during the last decade. At 70°N, on the other hand it appears to be moving upward at a rate of between 2 and 7 km decade$^{−1}$.

Although the authors suggest that there may be an anthropogenic cause, the observed reasons for the high latitude change appears to be due to:

  the trend we report at 70°N is commensurable with an observed cooling of the mesosphere (and in turn a lowering of the ionospheric E region altitude) and an increasing average electron density in the ionospheric D-region.


How to prepare GrADS's .ctl file to convert grd file into .nc file in batch mode? I have lots of grd (GrADS) file and I want to convert those data into netCDF file using cdo. The operation needs all the corresponding ctl file and I will have to prepare all these. So, my question is  there any workaround for this using bash, python or R. Here is an example of ctl file:

*need to change the file name year*_rfp25.grd for each file
DSET /home/amit/climate_data/rf/year1901_rfp25.grd
TITLE Gridded rainfall
UNDEF -999.0
XDEF  135  LINEAR  66.5 0.25
YDEF  129  LINEAR  6.5 0.25
ZDEF   1 linear 1 1
* CHANGE TDEF TO 366 FOR LEAP YEARS
TDEF 365  LINEAR 1jan1901 1DY
VARS  1
rf 0 99 GRIDDED RAINFALL
ENDVARS

After some trial n error I figured it out using the following shell script

#!/bin/bash

day_number () {
year=$1
leap="false"

if [ $((year % 4)) -ne 0 ] ; then
   :
elif [ $((year % 400)) -eq 0 ] ; then
     leap="true"
elif [ $((year % 100)) -eq 0 ] ; then
   :
else

   leap="true"
fi
if [ "$leap" == "true" ];
then
   echo 366
else
   echo 365
 fi
}

for j in {1901..2015};
do
days=$(day_number j)
echo "DSET /home/amit/climate_data/rf/year${j}_rfp25.grd
TITLE Gridded rainfall
UNDEF -999.0
XDEF  135  LINEAR  66.5 0.25
YDEF  129  LINEAR  6.5 0.25
ZDEF   1 linear 1 1
* CHANGE TDEF TO 366 FOR LEAP YEARS
TDEF ${days}  LINEAR 1jan${j} 1DY
VARS  1
rf 0 99 GRIDDED RAINFALL
ENDVARS">year${j}_rfp25.ctl
done


How to calculate air temperature for given time, location and altitude? I would like to calculate (estimate) air temperature at given time, location and altitude.

All I have is air pressure for 20°C. The formula based on NTP (Normal Temperature and Pressure) to calculate pressure.

=101325*(1 - 2,25577*10^-5*h)^5,25588

h is height in meters` result is in Pascals.

I expect that the formula for calculation of the temperature would depend on sun position or even solar radiation. I know that the formulas for calculation of the sun position or solar radiation are complicated but maybe there are source codes/programs which can do that? So I could use such program to calculate what I need? I have found SolTrack (C/C++) on SourceForge which calculates various data like rise time, transit time, azimuth, altitude, ecliptic longitude, latitude, right ascension, declination... However I cannot use these results to calculate temperature.

Purpose of the calculation

I would like to use the calculation for game, to generate air temperatures for map. The game is not simulator it is just game. So I need to add some values to the map so when the aircraft flies it can accept some temperature changes. The values are important in vicinity of terrain, mountains and hills. I don't need include winds into the calculation.

Calculation of Solar Radiation
What I have found so far is calculation of solar radiation written in Visual Basic - it is xls table (Excel) ecy.wa.gov/programs/eap/models/solrad.zip. Where I have added the pressure for 20°C. Of sure the problem here is unsolved because I suppose the temperature and pressure changes during time. So I need to improve the formula to calculate the pressure for given location, time and altitude.

Additional information:
Site data and time info:
latitude in decimal degrees (positive in northern hemisphere)
longitude in decimal degrees (negative for western hemisphere)
ground surface elevation (m)
time zone in hours relative to GMT/UTC (PST= -8, MST= -7, CST= -6, EST= -5)
daylight savings time (no= 0, yes= 1)
start date to calculate solar position and radiation
start time
time step (hours):
number of days to calculate solar position and radiation
Bird model parameters:
barometric pressure (mb, sea level = 1013)
ozone thickness of atmosphere (cm, typical 0.05 to 0.4 cm)
water vapor thickness of atmosphere (cm, typical 0.01 to 6.5 cm)
aerosol optical depth at 500 nm (typical 0.02 to 0.5)
aerosol optical depth at 380 nm (typical 0.1 to 0.5)
forward scattering of incoming radiation (typical 0.85)
surface albedo (typical 0.2 for land, 0.25 for vegetation, 0.9 for snow)
Bras model parameter:
Bras atmospheric turbidity factor (2=clear, 5=smoggy, default = 2)
Ryan-Stolzenbach model parameter
Ryan-Stolzenbach atmospheric transmission factor (0.70-0.91, default 0.8)
Cloud attenuation parameters:
Coefficient for cloud correction (default 0.65)
Exponent for cloud adjustment (default 2)
Cloud cover fraction (0-1)

The answer that you seek does not exist. There is no easy formula that might be useful. Deriving a temperature based on solar radiation is also unrealistic since the system has very large latencies and complex interactions so that you'd end up writing a full-blown weather model. This appears to be beyond the scope of your intentions.

The question you need to ask is which effects are relevant to you and how accurate you want your model to be. Also, which quantities do you require? The answers affect your course of action. Since you mention flying aircraft, you may likely want vertical profiles of atmospheric temperature above a given location. Also, which of the following effects do you need to include:

Day/Night variation
Clouds, rain
Temperature inversions
Effect of different terrains (ocean vs land for example)
Large variations in geographical location
possibly other things

A good starting point are standard atmospheres (c.f. https://en.wikipedia.org/wiki/International_Standard_Atmosphere). Another approach would be to find real-world locations that are sufficiently similar to the locations you are interested in and provide measurements. These might be adapted to your situation.

A simple approach might be to tabulate a base temperature and height for different climatic zones and seasons and then apply the atmospheric lapse rate (-6.5K per km height) to these values.

On a final note, I don't know what you need this information for. But be aware that for many thermodynamic purposes, the errors that you make are not going to be that large anyway since even an error of 20-30K is only an error of around 10% in absolute temperature. So be sure to evaluate your precision requirements.


Could the Dead Sea dry up? and if so, when? According to recent findings, during the last interglacial period, about 120,000 years ago, the precursor of the Dead Sea (Lake Lisan) dried up perhaps entirely. Today, the Dead Sea level is dropping at rates of around >1m/year from the countries surrounding the Sea using all the runoff. Future climate change scenarios for the region suggest even more arid conditions. Even though previous studies suggested that the decrease in water level would stabilize around 100-150 m below current conditions, the Goldstein et al. (2011) core evidence might suggest otherwise.
Could the Dead Sea dry up? What conditions could lead to such an extreme? When would that occur?

The Dead Sea salt is almost equally Mg-chloride and Na-chloride at about four times normal sea-salt salinity. This combination is extremely hygroscopic whilst, at this ultra low elevation and high temperature, there is very high humidity. People who try to towel themselves dry after swimming in the Dead Sea find that they can't - the salt absorbs atmospheric moisture as fast as they can towel it off. In addition to the chemical characteristics of the salt, at such high concentrations the water vapour pressure at the liquid surface is almost nothing. Therefore, it will require extreme and very prolonged dessiccation to dry out the Dead Sea completely. On the other hand the sea-level still has a long way to drop before it becomes a sort of slushy paste.


Where can I get good raw meteorological data for Middle East? I live in the Middle East and I am really fond of understanding meteorology and using raw data make my own weather predictions. However, a limitation I encounter here is that most raw meteorological data providers e.g. radars are only limited to the US or UK. I would like to know if there are any sources that provide professional raw weather data for the Middle East. Thank you a lot.

This work intend to consolidate climate data series from 79 stations in North Africa and the Middle East, between the 19th century to present day. Distribution of the stations are shown in Figure 1:

One challenge they had was an amount of incomplete records in the available dataset during that studied lapse. Table 1 and 2 show the name and location of the sources for the datasets, which could be useful for you to get started if your research need recent (2008-2018) records

Further they provided as supplemental material their raw datasets used in their research here, as used in their paper (-> 2008).


Is there geological evidence that the moon once collided with the Earth? I've seen models in astronomy that show how the Earth-Moon system must have come together after a collision.  However, I have not heard whether there is any actual physical evidence on Earth that points to a prior collision.  Is there geological (or other physical) evidence here on Earth that confirms the moon originated from a collision on Earth?  If so what is that evidence?

Is there geological (or other physical) evidence here on Earth that confirms the moon once collided with the Earth?

No, there isn't. This is, however, plenty of evidence that the moon formed due to a collision of a third body (sometimes referred to as Theia) with the Earth, and the moon formed from the ring of debris that resulted from the collision.

This theory is often known as the Giant Impact Hypothesis and searching for this term may help you find other links and references elsewhere.

  If so what is that evidence?

To summarise the geological evidence, much of it is indirect evidence, in that it compares geology on the Moon with similar geology or features on the Earth, and draws conclusions to explain the similarities (or discrepancies).

Because of the sheer size of the proposed impact, it would have likely reconfigured the surfaces of both bodies entirely, and so finding direct physical evidence on the Earth would be extremely unlikely. (e.g. a massive hidden crater would simply no longer exist)

Geological Evidence

Moon rocks collected from the Apollo missions that have almost identical oxygen isotope ratios to similar rocks found on Earth of the same age.
A large portion of the Lunar crust is made up of Anorthosite, which is indicative of a large melting event. (with the energy for this supplied from the impact)
Zinc. Lunar rocks contain less zinc, but with heavier isotopes of Zn than those found on Earth, which by contrast has lighter isotopes in greater abundance. This is consistent with zinc being depleted from the moon by evaporation, such as during a massive impact event.
Density and volatiles. The Moon is 25% less dense than the uncompressed density of Earth. It is severely depleted in volatiles, with practically no water and less than half the potassium abundance that Earth has. The combination of low density and lack of volatiles implies that the Moon was not a simple accretion of early solar system material, but resembles the Earth's mantle in bulk composition. Volatile material would have been vapourised by the impact.
The bulk composition of the Moon's crust. (This one does not actually involve the Earth, but I feel it is still important to mention.) The Moon's mantle and crust chemical composition could be explained if the Moon had a large iron core, but its core is actually quite small.

Other Physical Evidence

The ratio of the Earth and Moon's mass far exceeds any other planet in the solar system, and this begs the question of how did so much material become in orbit of the Earth. (Not evidence as such, but raises the question in the first place)
Getting more indirect...there are bands of warm silica-rich dust orbiting nearby stars which is interpreted as planet-sized bodies having collided with each other, so there is precedent for similar events happening elsewhere in the galaxy. (Again, I realise this is one is not strictly answering the question, but Earth Scientists often have to look well outside the Earth to answer their questions!)

Hope this gets you started!

Update:
I recently came across this short article, which provides a summary of some of the latest thinking on the Moon's formation, including the Giant Impact Hypothesis.

Sources: de Pater and Lissauer (2010): Planetary Sciences; Canup and Asphaug (2001), Nature


How do you determine the age of >60 year old water? I have been looking around at this topic recently, and it seems that it is relatively easy to determine the age of young water, by testing the concentration of anthropogenic contaminants. However, I've also heard about scientists determining the age of water as being >60 years old.

How exactly is this done, and how accurate is it?

According to this pdf: Physikalische Grundlagen der Klimaarchive Eis und Grundwasser (mostly German - some English) all methods to determine the age of groundwater bodies older than ~60 years are radiometric:

39Ar: 30 yr - 2000 yr
14C: 1,000 yr - 30,000 yr
36Cl: 100,000 yr - 1,000,000 yr
81Kr: 100,000 yr - 1,000,000 yr
40Ar: 100,000 yr - >10,000,000 yr
4He: 10 yr - >10,000,000 yr

Another source (german only) also mentions 32Si with a similar range as 39Ar.


What is the most powerful natural catastrophic event on record? Natural catastrophic events such as hurricanes, earthquakes, volcanic eruptions and meteor impacts releases vast amount of energy.

What is the most powerful single event of such nature ever recorded in human history on the planet Earth? And as a measure of energy release, how many atomic bombs or megatons of TNT is that equivalent to? What kind of event releases most energy?

How would the most powerful events compare with modern day natural disasters, to give some sense of perspective.

hard to impossible to tell. In recorded history it was for sure one of those massive volcanic eruptions from Krakatoa, Yellowstone or Tambora. But in earth's history there were some impacts from meteorites or commets that must have been a lot more powerfull in terms of released energy than any volcanic erruption. My guess is the Vredefort crater in South Africa (largest verified impact crater on Earth with a diameter of 300 km) or the Chicxulub crater in Mexico that is said to have triggered the mass extinction of the dinosaurs.


Is there a better system than latitudes and longitudes? I am a student programmer, with very little knowledge of geography and am working with maps for a project, and have to convert latitudes and longitudes to points on a screen (map to pixels).
So my principal problem with the system of latitudes and longitudes is having to specify a hemisphere along with the co-ordinates of a point on a map.
  Is there a system which provides co-ordinates without having to specify a direction, which is also widely used?  And if so, do tools to convert between the two systems exist?
For example something like the left-top corner of a map is given (0,0), and as we go right X increases, and as we go down Y increases.

Thank you!

To answer the question in the title (with another question): better for what?

To answer the questions in the body: there is another system called rectilinear or x-y-z Cartesian coordinates. This system is the same as the 3-d Cartesian coordinates you used in calculus class. The center of the Earth is (0,0,0), and generally the z-direction goes to the poles, while x and y go to the equators at right angles, and towards points specified by whatever datum you are using. For example, the North Pole could be coordinates (0,0,6353000) in meters.

As for tools to do the conversion, you should probably send those kinds of questions to the GIS Stack Exchange. However, since they tend to be snippy when I've asked questions in the past I will tell you how I do it. I use the pyproj package for python, which is a python wrapper around the C Proj4 package.

Pyproj is pretty straight forward to use, but the transformations you want might not be so easy to figure out. The information you want is the EPSG numbers of the transforms. If you are using the common WGS-84 datum, for example, the rectilinear is 'epsg:4978' while the lat-lon is 'epsg:4326'.

A code example follows from a python (3.5) interactive console. To transform the estimated coordinates of the north pole above, we want to go from rectilinear to lat-lon.

>>> import pyproj
>>> rectProj = pyproj.Proj(init='epsg:4978')
>>> latlonProj = pyproj.Proj(init='epsg:4326')
>>> pyproj.transform(rectProj, latlonProj, 0, 0, 6353000)
(0.0, 90.0, -3752.3142451792955)

What we see here is that when we transform from rectilinear to lat-lon, we get a longitude of 0, latitude of 90, and azimuth (or altitude) of -3752.3 meters. So at the North Pole, 4 km below the surface. This altitude difference is due to both the roughness of my estimate and the specifics of the WGS-84 datum. To go the other way from the lat-lon Greenwich Observatory (at 51.478 degrees north, 0 degrees west; azimuth or elevation of 0 meters) we can do:

>>> pyproj.transform(latlonProj, rectProj, 0, 51.478, 0)
(3980563.802812242, 0.0, 4966838.380583356)

We see that 90 degrees north at altitude of zero in WGS-84 corresponds to that (x, y, z) triplet, in meters. Since Greenwich lies on the 'y' coordinate axis in the WGS-84 system, the y coord is zero.

Hope this helps.


What's a reasonable flow rate/mass flux for a fumarole? Obviously, there is going to be a large amount of variability, but what are some realistic values?

Surprisingly enough most of the figures I could find were actually about thermal output but back working the figures, and assuming I read the formulas properly (not guaranteed I'm afraid) it looks like 5-7 litres per second is the ballpark average gas flow based on fifty years worth of data from several fumarole fields in the central North Island of New Zealand. I have no idea how representative that figure would be of fields elsewhere.


wavelength of seismic wave with a gaussian source I want to know how to get the wavelength/frequency of a seismic wave, if I only have a Gaussian source and the velocity (c = 4000m/s) of a medium given.
e.g. for a Ricker wavelet it would be easy to get the central frequency and max frequency of the source to compute the wavelength by c/f, but I have some issues with the Gaussian and unfortunately only signals of a Gaussian source.
Let's assume my source time function in time domain looks like this:
source = 1/(2* np.pi * 17.**2) * np.exp( - (t-100)**2 / (2* 17.**2))

So a Gaussian with variance of 17 squared and shifted to the right. In the frequency domain it will be centered around zero and I don't really get a maximum frequency as well. Is there a way to find these?

The Fourier transform of a Gaussian is a Gaussian.

If your signal is given by

$$g(t)=\frac{1}{\sqrt{2 \pi \sigma^2}} \exp\left( -\frac{(t-t_0)^2}{2 \sigma^2}\right)$$

then your frequency spectrum is

$$G(f) = \exp(-2 \pi^2 \sigma^2 f^2),$$

where f is the frequency ($2 \pi \omega).$

I'l let you do the substitution with your particular numbers. Enjoy!

https://warwick.ac.uk/fac/sci/mathsys/courses/msc/ma934/resources/notes8.pdf
http://www.cse.yorku.ca/~kosta/CompVis_Notes/fourier_transform_Gaussian.pdf


How many days has it been since the Cambrian explosion? I want to know how to calculate the number of days since an event in Earth's past, and am using the Cambrian explosion as an example.

I define a day to be one rotation of Earth with respect to the sun. The key point is that Earth's rotation has been slowing down over millions of years, so it will not be as simple as multiplying the time in years by 365.

Is there a formula for the number of days x years ago that I can simply integrate to find the answer? Or some other way to approximate?

As a very rough approximation, one could start with equation (9) from Arbab (2009), https://arxiv.org/abs/physics/0304093 to get the effective number of days per year:

$$T_{\text{eff.}} = T_0 \left(\frac{t_0-t}{t_0} \right)^{-2.6}$$

with

$t$ the time difference between now and then
$T_0 = 365.25$ the current number of days per year
$t_0=(13.799 \pm 0.021) \cdot 10^9$ the present age of the universe (from Planck Collaboration et al. (2015), https://arxiv.org/abs/1502.01589 )

Assuming the Cambrian explosion happened about $t_c =(541 \pm 0.13) \cdot 10^6$ years ago (from Bowring et al. (2007), https://core.ac.uk/download/pdf/62875.pdf), then the number of days since can be approximated as

$$n = \int\limits_0^{t_c} T_0 \left(1 - \frac{t}{t_0} \right)^{-2.6} \mathrm{d}t  = \left[0.625 \cdot T_0 t_0 \left(1-\frac{t}{t_0}\right)^{-\frac{8}{5}} \right]_0^{t_c} \approx 2.1 \cdot 10^{11}$$

(of course one has to keep in mind that the error on this value is rather large, but to have some ballpark figure it should be good enough)

For comparison $t_c \cdot 365.25 = 1.98 \cdot 10^{11}$


How is the equilibrium of 21% oxygen in Earth's atmosphere established? The atmosphere is 21% oxygen. I assume that there must be an equilibrium between processes that produce oxygen (e.g. photosynthesis) and those that consume oxygen (e.g. aerobic respiration).

Moreover, there should be a self-regulatory negative feedback which restores the equilibrium if the system is driven away from it.  If the amount of oxygen were increased, something that would subsequently cause it to decrease over time, and if the amount of oxygen were decreased, something to cause it to be replenished.

What processes are responsible for this negative feedback?

I'm not sure I can give a good technical answer. I don't think the amount of oxygen in the Earth's atmosphere is due to equilibrium but more of a consequence of the formation of the solar system, Earth chemistry and biology.

If you look at the formation, for inner planets, much of the gas and ices were blown off due to their inner orbits and the planets being too hit by very active Coronal mass ejections in the early solar system. There are 3 likely types of close to the sun planets:   1) small rocky planets (Earth, Mercury, Venus, Mars), 2) hot jupiters, which are large enough to trap hydrogen even though they're close to the sun and hot and 3) super-earths, which have enough gravity to trap hydrogen.

An abundance of hydrogen in a planetary atmosphere would likely make oxygen formation impossible.  The Oxygen would bind with the hydrogen.

The Earth didn't have the gravity to trap much hydrogen and some of the early atmosphere would have been blown off by large meteor strikes and by coronal mass ejections, which were much more common when the sun was young.

A clue to the Earth's atmosphere's formation is the formation of the oceans, because oceans would be impossible without an atmosphere.  The oceans formed 3.8 billion years ago, so we had to have an atmosphere, at least for about 3.8 billion years.

http://people.chem.duke.edu/~jds/cruise_chem/oceans/ocean1.html

The young Earth's atmosphere was mostly methane (CH4), ammonia (NH3), water vapor (H2O), and carbon dioxide (CO2) as per the link above, as soon as the Earth was cool enough, the water vapour turned into liquid water (rain) and the oceans began to form.

Fast forward to the Great Oxygenation event when cyanobacteria, pulled CO2 from the air and release O2.  Early on, the O2 binded with iron in the ocean and some of it likely reacts with CH4 and NH3 in the atmosphere when there is lightning. Over time, CO2 was pulled from the air, replaced by O2 and O2 reacted with CH4 and NH3, producing more CO2, H20, and N2 - the common elements we have today.

Oxygen levels in planets with cyanobacteria, likely depends on how much iron is dissolved in the oceans and how much hydrogen is in the atmosphere.  If there's not enough CO2 to produce enough O2 to saturate the iron and hydrogen, the planet probably never gets much O2 in it's atmosphere - so it's all about the ratio of early elements.    Super-earths might never get oxygen atmospheres - too much hydrogen.

You also get factors like the development of lignin (got that from Neil deGrass' Cosmos) - http://evolution.about.com/od/Cosmos/fl/Cosmos-A-Spacetime-Odyssey-Recap-Episode-109.htm

Lignin made trees possible, but nothing could eat trees, so trees captured more and more carbon, so CO2 levels fell and O2 levels rose.   About 100 million years later, termites evolved and the digestion of trees released much of this captured CO2 became possible and Oxygen and CO2 leveled out.

Shellfish, to make their shells, take more O2 out of the air than CO2 (calcium carbonate has lots of oxygen in it).   That's a slow process, but over time it takes some O2 out of the air, so over tens of millions of years, parts of the atmosphere are effectively sequestered and trapped in the Earths crust, but over time, some of this is also returned to the atmosphere with volcanic activity - so the type of life forms present is also a factor and the extent of tectonic activity is a factor as is, as is the presence of a Jupiter and how many comets are likely to hit the planet and the size of the planet.

It's more chance, the solar system and planetary factors that lead to a planet's atmosphere.

To answer your question:

  So if we increase the amount of oxygen, it will decrease over time and
  if we decrease it, it will be replenished.

Tough call regarding oxygen.   CO2 is easier.    Because there's a relatively small percentage of CO2 in the air, more CO2 will lead to some of it dissolving in the ocean as carbolic acid, though the warming of the ocean might also slow the oceanic absorption of CO2.     Because there's so much more Oxygen in the Earth, 21% vs 0.04% of CO2, a measurable increase, say 21% to 22%, you'd probably see a slight increase in dissolved O2 in the ocean, but beyond that, I don't think you'd see that extra oxygen go away any time soon.  My guess is, if such an increase was done, it would last a long time, hundreds of thousands of years if not millions, because oxygen sequestering is pretty slow.     Insects would get slightly bigger pretty quick.   That might be the most noticeable effect.

If you significantly increase O2 levels, say from 21% to 30%, things would become noticeably more flammable and over time, our lungs would probably get smaller and there would be other effects, probably.    But I don't believe there's any sort of equilibrium that would fairly quickly bring it back to 21%.


Need different temperature change data sets explained Nasa's temperature record is showing temperature increase. When I confronted a climate change skeptic with it, he replied that the data has been tempered with, and that there are different data sets which do not show temperature increase.

The exact reply was:

  According to RSS, UAH and radiosonde global temp anomaly datasets,
  there hasn't been a global warming trend in 20 years;

  http://www.woodfortrees.org/plot/rss/from:1996.6/to:2015.7/plot/rss/from:1996.6/to:2015.7/trend/plot/esrl-co2/from:1996.6/to:2015.7/normalise/trend/plot/esrl-co2/from:1996.6/to:2015.7/normalise

  GISS and HADCRUT4 datasets have added heat to raw temperature data to
  artificially keep the warming trend going as NOAA freely admits:

  https://www.ncdc.noaa.gov/img/climate/research/ushcn/ts.ushcn_anom25_diffs_urb-raw_pg.gif

This sounds reasonable to me.

Can anyone familiar with climate science explain why there are several data-sets, and why they are saying different things, and why NASA's set is the correct one?

There are several climate datasets around the world, two in America - NASA's GISTEMP, and NOAA's MLOST, and one in the UK - HadCRUT. These are the main datasets but there are others around the world, China, Japan etc.

The datasets differ slightly in the starting date, number of met stations included, degree of interpolation, and the way they get round the problem of lack of met stations in oceanic areas.

As to being 'tampered with', this is a subtle malicious implication that the data has been fudged. It is also an insult to the scientific integrity of the thousands of climate scientists involved, whose aim, as in all of science, is to get at the truth. Of course, the data have been 'processed'. This is an essential part of data quality control to interpolate missing data, and to ensure consistency of the data set. But no data has been 'tampered with' in the sense of trying to lead to false conclusions.
One of the striking features of all the global datasets is that, despite minor differences, they all show the same basic characteristics of an accelerating global temperature - the 'hockey stick graph'.

There is much dishonesty about, but not with the climate scientists. It is the climate skeptics who are being dishonest (not to mention scientifically incompetent).


Where are old Himawari weather satellite images available to the public? Is the 18-Dec-2018 Bearing Sea fireball still there? In Scott Manley's new video 173 Kiloton Explosion Over Bering Sea Was Asteroid Breaking Up a bit after 01:30 he says

  The good news is that in these days of near-limitless data storage capabilities the internet has a long memory, and we can look at the Himawari satellite which is a weather satellite in geostationary orbit that covers the area in question.

I normally view Himawari images from https://www.jma.go.jp/en/gms/ and if you open an image in a new window and look at the URL you can guess how to change the date and time into the past. That works for several days or a week, but not three months.

Question: Where are three-month-old or possibly even year-old Himawari weather satellite images available to the public?

As an exercise, per:

How was the 18 December 2018 Bering Sea Fireball detected and characterized? Was it a serendipity or a weather satellite?
https://cneos.jpl.nasa.gov/fireballs/

the event was at 2018-12-18 23:48:20 UTC and 56.9N 172.4E.

You need to go this site - Himawari Archive and then it depends on what category of user you are and then obtain the imagery that way.

UPDATE -

On OP's request I am recording the information I got from JMA when I wanted to access Himawari's images. You need to specify what kind of user you are

a) research
b) commercial.

Presuming research you can obtain Himawari images from the following institutions as mentioned in the original link I provided

  The following four Japanese institutions operate Himawari-8 data archiving and redistribution services on a best-effort basis for research, development and education:

  1) JAXA Himawari Monitor (Japan Aerospace Exploration Agency)
          http://www.eorc.jaxa.jp/ptree/index.html
      Himawari-8 Data Download and Processing System (Data Integration and Analysis System Program)

  2) http://himawari.diasjp.net/expert/
      Center for Environmental Remote Sensing (CEReS)

  3) Chiba University
          http://www.cr.chiba-u.jp/databases/GEO/H8_9/FD/index_jp.html

  4)    Himawari Satellite Project (NICT : National Institute of Information and Communications Technology)
          http://sc-web.nict.go.jp/himawari/

  Users must register to download data from each institution and observe the individual data usage policies.

If you are asking how I would do it then I must mention I use a python software called
SatPy

Then I go to this URL - JAXA FTP URL( I think it is only visible if you are registered) and then download the data for whatever year I want. Then write a small script using a SatPy reader and view the data.

NOTE For the last points you are better off asking questions either on SatPy and for the data itself writing email to JAXA.


Why do deviated wells show poor correlation to seismic data? Well correlation and calibration is an important step in any type of seismic inversion. In order to obtain a good broadband frequency model, the synthetics should be correlated with original seismic data. The wavelet used for generating synthetic can be either statistical or from the data itself. But I'm facing a problem in obtaining a good correlation for those wells which are deviated. Why do deviated wells always show a lower correlation coefficient in well correlation process?

Two-way time to depth calibration is a vertical problem.

How you handle deviated wells probably depends a bit on how you are tying the wells. Here are two things to watch out for:

You should be tying to true vertical depth (TVD) anyway — make sure you're not using measured depth somehow. I expect you are using TVD — so the deviated section will be distorted (squished). It's gong to be difficult to tie, and the modeled waveform won't make much sense.
Sometimes software tries to help you by placing wells at the midpoint between the top- and bottom-hole locations. You don't want this — make sure the well is at the top-hole location, or at the midpoint between the top-hole and kick-off point.

Because of these two things, you may want to ignore deviated wells in the tying effort, if that's an option. If it isn't, focus on tying the straight hole.

Ultimately, you'll want to build a 3D velocity model, using horizons to interpolate the velocity field, and maybe even using other velocities (like stacking velocities) to 'fill in' where there are few wells. At that point you can position everything properly, deviated or not.


At what depth does the underground begin to warm up? Spring water comes out colder from being underground. But if you get deeper the temperature goes up. At what depth does the underground stop getting colder and begins getting warmer?

Is there a map for that point like a geothermal table map? I ask this because I want to build a underground water cooling air conditioner in the same manner that pipes are heated on roof tops.

Your question has an incorrect assumption built in.  Near surface ground water temperatures are not generally colder, but rather reflect the average annual temperature. This will be colder than surface temps in summer, but warmer in winter.  There is an an additional effect if your rainfall isn't evenly distributed over the course of the year, as percolating rainfall will be initially warmed by warm soil temps in summer.  As an example, in central Alberta shallow well water temps run about 10 C, while our average temp for the year is around 4-5 C

Start here: https://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm

A graph on that page shows how soil temps vary with depth depending on seasonal variation, and moisture levels.  Ball park:  30 feet gets out out of the seasonal variation, but 12 feet eliminates about 2/3 of the annual variation.

If your climate is cold enough in winter, it may be worth your while to store coolth in the form of brine.  In effect build a well insulated building with insulated foundation with what amounts to a swimming pool in it filled with either salt water brine, or calcium chloride brine.  Have a few thousand feet of 1/2" plastic pipe (drip irrigation pipe is cheap)  both outside and in the pool, and circulate antifreeze through the pipe when winter temps are below the brine temp.  In the summer, a secondary loop circulates between the pool and the heat exchangers for the house.

If you are in a desert climate, you may be able to do something similar on a smaller scale.  Under a calm clear sky, you can often get frost on the side of an insulator facing the dark sky at night.  Modifying this idea, create a large bottom insulated surface coated with a good IR emitter (Titanium dioxide white is one such.) , and run shallow water over it.  If you can routinely get 30 C colder than day time air temps, then you only have to store a few days worth of coolth instead of a years worth.

You can make the system above colder by pre-chilling the water with an evaporative cooler

Edit:  One source claims 1 degree F per 30 feet starting at around 100 feet.  Temperatures above this
however are highly variable from water movement.


Am I observing orographic rainfall? I don't know an awful lot about meteorology, so please bear with me.

My wife (who has a Geography degree) told me that rain can be generated when moist air is pushed up the side of a mountain. This makes sense from a thermodynamic point of view, but I was wondering what scale we are talking about.

It so happens we live in a mountainous area, and I often see dark clouds over the other side of the mountains. The prevailing wind is always towards us, and when it rains, it looks really bad on the other side, but somewhat ordinary by the time it gets to where we live.

The lake on the far side of the mountain is at around 400 m, the mountain is a somewhat flat ridge peaking at 1100 m, and our side of the lake is at around 700 m.

Is most of the water dumped on the far side from us?

700 m elevation difference on the windward side will be definitely enough to trigger orographic influences on precipitation. Thus from your description it seems very plausible that the mountains influence the precipitation you get.


What ice phenomenon are we seeing in this video? I don't know what this YouTube video shows, but it appears to be half glacier and half "the blob." It almost appears to be "growing" although I assume it's being pushed somehow.

Can someone tell me what this is called, what causes it, and how common it is?

Warning: Strong language in the video.

This phenomenon goes by a number of names: ice heave, ice shove, ice creep, ice tsunami, and I'm sure there are others. It is a consequence of the spring ice breakup coupled with strong sustaining winds on large northern lakes.

The warming spring weather melts the ice close to shore first, making the ice on the lake free-floating. The ice in the middle of the lake can still be close to a meter thick. Winds jostle the ice around, breaking it into chunks. With strong sustaining winds, the ice moves toward the downwind shore. With even stronger sustaining winds, the shoreline is not enough to stop the ice from moving onshore. The ice from further out (and this ice can be very thick) pushes the ice ashore, sometimes bulldozing trees and buildings.

Here's a playlist of 19 youtube videos that portray this phenomenon: https://www.youtube.com/watch?v=0EyfEDKWscg&list=PLPHgakWET6JeATJ1duoGkYItCvfPl26FU . At 32 seconds into the fifth video in the playlist you can see how thick some of the slabs of ice are.


Is pollution a contributing factor to freezing rain? I have been to different places with nearly the same freezing temperatures, around -2°C, but only at some specific places I repetitively experienced freezing rain. One common factor at these places was relatively more air pollution. Could it be that pollution is a contributing factor that causes freezing rain to occur?

If not, what are the main factors that cause freezing rain, and the regions on Earth that often experience them, especially in Europe?

Pollution shouldn't contribute to produce freezing rain. It might have an impact in the precipitation rate and location but not on the likelihood of freezing rain.

Freezing rain requires not only that the near-surface temperature is below freezing, but also that there is a temperature inversion that provides above zero temperature in the atmospheric layers above the surface.

Usually temperature drops as you go higher into the atmosphere. But in some areas, due to climate, geography and local weather patterns, you can often find that the temperature rises as you go up, that's called a temperature inversion (eventually as you go high enough the inversion dies and temperatures drops as you go even higher).

Such condition can melt the snow high in the atmosphere and then the water droplets enter an area near the surface that is below zero and cools them down but not for long enough to freeze solid (something that would produce sleet). Water droplets in such conditions gets below zero but remain liquid, a phenomena called supercooling. When the supercooled drops hit the surface (that is also below zero), they instantly freeze forming a thin layer of ice, hence freezing rain.

This figure from mprnews.org nicely summarize the phenomena:

Regarding why some places can be mor suitable for freezing rain, I'll highlight here the comment by @Anirudh pointing to this link that deals with the case of Guizhou Province in China.


Is there any evidence for higher air pressures in the geological past? I was curious about how the Earth's overall air pressure has varied over time, and tried to take a look around the internet. However, Google pops up a lot of sites with questionable science proposing that the air pressure was much higher in the past. The more outrageous claims (such as those by David Esker) are dealt with on Skeptics.SE.

However, there are more reasonable claims that air pressure was perhaps 4 or 5 times higher in the Mesozoic, thus allowing pterosaurs to fly more effectively, etc. The websites making such claims do heavily set off my pseudoscience alarms, but then some are published by the American Chemical Society by reputable sounding scientists with references to papers.

There is evidence that in the far distant past, air pressures were lower than they are currently. But after the changes to the atmosphere wrought by photosynthetic life, is there any evidence supporting the various theories of higher air pressures?

Yes, there is.
But the data is still very sparse and errors are large.

Past atmospherics pressures have been estimated by at least three different methods:

Isotopic composition of fluid inclusions trapped hydrothermal quartz ( Nishizawa ey al 2007; Goldblatt et al 2009; Marty et al, 2013)

Image from Fig. 2 of Nishizawa et al 2007.

Size distribution of gas bubbles in basaltic lava flows (Som et al 2016)

Figure 3c of Som et al (2016): Beasley River geologic context and flow detail (scale bar, 1 cm)

Size distribution of fossilised raindrop imprints (Som et al, 2012; Kavanagh & Goldblat, 2015)

Figure 1 of Som et al (2012) The 2.7-billion-year-old Ventersdorp Supergroup raindrop imprints lithified in tuff at Omdraaivlei, South Africa.

Each study is based on samples that capture the conditions at a fairly specific point in time. Therefore, different results not necessarily contradict each other, but offer a sense of how variable has been the atmospheric pressure over geological time.

The size distribution of fossilised raindrop imprints might have a large range of error due to the many factors that influence drop size beside atmospheric pressure. However, some studies suggest that the Archean (4 to 2.5 billion years ago) atmosphere was almost ten times denser than it is today (Kavanagh & Goldblat, 2015). That figure is based on fossilized raindrop imprints dated about 2.7 billion year ago, that is after the evolution of photosynthesis, but still in its early stages, when most oxygen was absorbed by the oceans and there was very little of it in the atmosphere.
On the other hand, studies based in isotopic composition of fluid inclusions and bubbles in basaltic lava have found that the atmosphere was less dense than it is today.

These studies are of great interest, as a denser atmosphere even if poor in greenhouse gasses can produce warmer surface condition, helping to resolve the faint young Sun paradox. In a nutshell, this paradox refers to how could liquid water exist on Earth in the past when the sun was much fainter than it is today.

It is important to note that the additional temperature in a thick atmosphere doesn't come from adiabatic warming as some people have suggested here. A good treatment of the phenomena is presented by Chemke et al (2016) in the paper "The thermodynamic effect of atmospheric mass on early Earth's temperature", there they say:

  We find that higher atmospheric mass tends to increase the
  near-surface temperature mostly due to an increase in the heat
  capacity of the atmosphere, which decreases the net radiative cooling
  effect in the lower layers of the atmosphere. Additionally, the
  vertical advection of heat by eddies decreases with increasing
  atmospheric mass, resulting in further near-surface warming.


Where and how can seismic data for earthquakes and volcanoes be downloaded? I need it in this format.

I went to USGS and IRIS websites but couldn't understand the downloading procedure

The easiest way to look at earthquake data that you would like in a data set you can work on (filter,plot,process,etc.) is three steps.

Get yourself a copy of Matlab
Go to the iris website and download a program called IrisFetch.m (see http://ds.iris.edu/ds/nodes/dmc/manuals/) .
Next you need a list of events and a list of stations from which to download the event, both of these can be gained simultaneously with a program from iris called Jweed. Just download both lists into a cvs file and import to Matlab and run through IrisFetch. This requires a very basic understanding of programming in Matlab but its not hard to figure out at all. Later on you will learn that you don't need Jweed at all to do this but instead can do it all through IrisFetch. Jweed is popular and easy to use though.

If this is too complicated, you can use the web-based part of iris to look at specific earthquakes at specific stations. But I don't think you get to interact with the data this way.


Convert OMI NO2 Vertical Column Density (molecules/cm^2) into Mixing Ratio (ppm) I want to convert OMI AURA data on NO2 column amounts in molecules/cm2 into ppm for comparison purposes with other literature. Can it be done? Is there a standard way of doing it?

I looked into the readme file but could not find an answer.

No, you shouldn't really do that.  A vertical column density (VCD) retrieval provides the user with a representation of the total number of molecules over some vertical slice (e.g. the entire troposphere).  A mixing ratio, often defined in parts per million, is meant to express the average number of molecules in a parcel of air.  The problem with converting VCD to ppm is that the troposphere is a whole lot more than "a parcel of air".  The density of air and mixing ratio of NO2 changes as you move vertically through the atmosphere. So, saying that NO2 has any one mixing ratio through the troposphere is really not appropriate.

There are methods you could use to estimate ppm NO2 from VCD (such as inferring mixing ratio from the shape of the a priori profile), but they would be inherently uncertain for many reasons:

The retrieval of tropospheric NO2 from OMI is not representative of the surface, but rather a well-mixed free troposphere.
The NO2 product is dependent on a global model to subtract the stratospheric contribution.
There are many quality control steps needed for quality assurance, such as accounting for clouds, terrain, surface albedo, detector issues (e.g. striping or row anomalies), etc.

In my experience with OMI tropospheric NO2 data, any expected temporal correlation to daily surface measurements is futile.  You will sometimes find temporal correlation at the seasonal or coarser scale, for what that is worth.

Spatial correlation with models and surface monitor networks should be expected, but your results will be highly dependent on your 3D spatial comparison methodology. When comparing to a model, you will want to apply the "averaging kernels" which help to remove the dependence on the a priori profile of the satellite retrieval.

In general, OMI tropospheric NO2 data is useful for identifying large emissions sources that are missing from air quality models.   It is also useful for identifying inconsistencies across political borders that appear in air quality models due to old emission inventories (e.g. mixing circa 2006 Canadian emissions with circa 2011 USA emissions).


After days of smoky air, why is it healthier to stay inside? A large wildfire has been burning for four days some distance from my town. The air is smoky, but not smokier than yesterday or the day before. General wisdom holds that we should all stay indoors.

As I enjoy my relative safety and indoor accommodations, I wonder why the indoor air is safer than the outdoor air. Even buildings that had 12-foot-wide (4-metre-wide) cargo doors open yesterday contain air less smoky than the outdoor air, or at least it smells that way.

Are still there fewer smoke particles per unit volume indoors? Do indoor environments trap the particles better? Why is the air safer indoors?

If you're in the open air you will be exposed to the full concentration of the pollutants in the air. By being inside, there's a reasonable assumption that the rate of interchange of air between inside a house and outside will be low and that inside there will be a lower concentration of pollutants.

Houses and buildings are not hermetically sealed. The gaps around windows and doors are small which results in low rate of airflow between the outside and inside of the houses and buildings. The less windy the weather the lower the flow rates.

The other way to consider it is when a room has been closed for a lengthy period while someone has been in the room, the air in the room becomes stuffy. This is because the air in the room is not being replaced by fresh air quickly enough to remove stuffy air. To remove to stuffy air the windows and doors need to be left open for a period of time for fresh air to replace the stuffy air.

The same thing happens when the air outside is heavily polluted. The air inside is cleaner and remains cleaner for a longer period if the doors and windows remain shut because the rate of transfer between air inside the building and outside is small.


Southern Hemisphere: What is the most Northern latitude where the sun can be seen for more than 24 hours? Is there a location, in the southern hemisphere, where I could pitch a tent that I would be able to see the sun at any time of day for, say, more than a week?

How far north could I go and still be able to see the sun for two days or more?

The situation in the southern hemisphere is identical to the northern hemisphere, but they occur at different times of the year.

In the northern hemisphere the arctic circle is situated at 66.5 degrees North. Likewise in the southern hemisphere, the antarctic circle is situated at 66.5 degrees South. Between each circle and its respective pole 24 hours of daylight will occur for about a month or more from the onset of the summer solstice for each hemisphere.

The southernmost settlement in South America is Puerto Williams which is located at 56 degrees 56 minutes South. This is a lot further north than the antarctic circle.

To experience 24 hour days in the southern hemisphere you will have to be in Antarctica, as is evident from this picture, acquired from Wikipedia.

The Australian base at Casey is just outside of the antarctic circle having a latitude of 66 degrees 17 minutes South. However, the Chilean base at Carvajal is just inside the antarctic circle with a latitude of 67 degrees 45 minutes South.


Plain-language summary of why Uranus and Neptune are different than Earth in having large offsets of their dipole field? This answer to Why is the magnetic axis of Uranus and Neptune off center? in Astronomy SE perplexes me, partly because I can't understand the block quotes and partly because they constrast those planets with Earth and Earth's dipole is off center as well and it's field also flips back and forth.
Question: Is it possible to write a simplified, plain-language summary of what this explanation for why Uranus and Neptune are different than Earth in having large offsets of their dipole field?

From the linked answer, which is sourced from Nellis 2017 Magnetic fields of Uranus and Neptune: Metallic fluid hydrogen:

Earth's axisymmetric magnetic field
The most researched magnetic field in our Solar System is, of course, Earth. Nellis 2017 explains how coupling between the rotational motion and convective dynamo motions in the Earth's outer core cause the magnetic axis to drive towards alignment to the spin axis:

Because rotational motion (RM) of Earth is strongly coupled into convective dynamo (CD) motions of its fluid-Fe outer core, planetary RM stabilizes convective motions that generate a dipolar magnetic field. If a convective fluctuation occurs which tends to destabilize a given dipolar axis, then strong RM-CD coupling either drives convective motions that essentially restore the initial orientation or CD fluctuations that drive the initial magnetic axes out of orientational equilibrium are so strong that RM-CD coupling eventually drives the dipolar axis into an alignment anti-parallel to its initial one.

and

Uranus/Neptune non-axisymmetric magnetic fields
The magnetic generation near the surface, as well as the H-HE envelope (again according to Nellis) means that:

local convective dynamo motions of fluids that produce the magnetic fields are essentially decoupled from global rotational motions [...]. The dynamos of U/N would then be relatively free to wander as local convective fluctuations dictate.  Thus, tilt angles and center-offsets of their fields would vary slowly over the age of the Solar System.

Earth's rotation is an important factor in contributing to the generation of the field, and helping to stabilise the form of it. The rotation influences the flow of compositionally convecting material deep within the outer core, forming cylindrical rolls that align along the rotation axis (a Coriolis effect).
While Earth's field polarity may reverse occasionally, it is to a good approximation (and we believe predominantly has always been) a roughly centred dipole, aligned roughly with the rotation axis of the Earth because of the influence of Earth's rotation.
For Uranus and Neptune, this is not the case. The centre of their dipoles are significantly offset from their centres of mass, the axes of the dipoles are significantly offset from the rotation axes.
For both Uranus and Neptune, magnetic field generation is believed to occur in flowing material much closer to the planets' surfaces (due to the very different composition of ice giants versus the terrestrial Earth). With flow constrained in a relatively thin layer near the surface, planet rotation does not have a strong influence on the form of the convective motion, so the field that results is not particularly tied to how the planet rotates.
This article gives a good idea of how the geometry of the convecting flow region can lead to Earth-like or Neptune/Uranus-like magnetic fields.


How long ago was the first limestone formed? It is readily apparent from the fossil record that the first limestone was laid down hundreds of millions of years ago, but how long ago was the very first limestone formed? It could be approximately dated by its fossils, but what if it was in the Precambrian and contained no fossils - how could it be accurately dated then?

Probably at the Hadean or at the beginning of the Archean, but there is no geological registry.

The mechanism that can lead to inorganic limestone formation is weathering of magmatic carbonatite rocks. I found Siilinjärvi carbonatite complex in Fennoscandia is dated 2.6Ga (Tichomirowa et al, 2013), so Archean. It is the oldest one I found.

Another mechanism that could produce limestones in ancient eons is described by user @BillDOe in this related answer:

  Once life evolved in the world's oceans, the vast majority of
  limestone formation has been through the organic process. However,
  before life did evolve, limestone formed through an inorganic process
  where rain water falling through a CO2-rich atmosphere reacted to form
  a weak carbonic acid solution that then reacted with
  calcium-containing minerals to form calcites. This then washed into
  the world's oceans to form limestone deposits.

The premise comes from this stanford.edu work and is a bit controversial because there are no proofs limestones formed by this mechanism.

International Stratigraphic Chart image

M. Tichomirowa, M.J. Whitehouse, A. Gerdes, J. Götze, B. Schulz, B.V. Belyatsky (2013): "Different zircon recrystallization types in carbonatites caused by magma mixing: Evidence from U–Pb dating, trace element and isotope composition (Hf and O) of zircons from two Precambrian carbonatites from Fennoscandia", Chemical Geology, Volume 353, Pages 173-198, ISSN 0009-2541.
https://doi.org/10.1016/j.chemgeo.2012.11.004.


How can we have groundwater depletion when the Earth is 78% covered with oceans? Why does depletion of underground water levels happening, if the Earth is covered by nearly 78% water, and there is also water in rivers and lakes?

How can we still lack groundwater?

How can we still lack groundwater?

That 71% of the Earth's surface is covered by oceans is completely irrelevant to the issue of fresh groundwater depletion. Salty groundwater is useless for drinking or irrigating crops.

The issue at hand is the depletion of those underground reserves of fresh water. This depletion can result from natural or human causes. The Sahara is an example of natural depletion. The Sahara was significantly wetter than it is now several thousands of years ago. Rains over the course of a few thousand years created a number of underground reservoirs of fresh water in the Sahara. Rain stopped falling on the Sahara about 7000 years ago. The few remaining oases in the Sahara are places where groundwater still comes close to the surface as a result of that roughly 3000 year long wet spell.

Humans can also cause groundwater depletion. It takes several centuries for rainfall to percolate down to the water table. The replenishment of aquifers is very slow. This is balanced by a very slow trickle from a natural spring here, another one there. The end result is a more or less steady state where the slow replenishment balances the slow outflow. It's very easy to disrupt that balance. Climate change (both natural and anthropogenic) can change the replenishment rate, while artificial wells can drastically increase the depletion rate.


Can El Niño and La Niña occur at the same time? We often read that El Nino and La Niña occur alternatively. Are they the exact opposite of each other? Or, in other words, can they happen at the same time? (i.e. the whole Pacific Ocean has a higher temperature than normal).

If so, what is the common name of them?

By definition, El Niño and La Niña cannot occur at the same time. They are instead opposite extreme phases of the El Niño Southern Oscillation.

El Niño conditions occur when the average temperature of the Niño 3.4 region is a half degree or more over the average for three consecutive months or more. La Niña conditions occur when the average temperature is a half degree or more below the average for three consecutive months or more. The reason for looking at a rather narrow band of the equatorial Pacific rather than looking at the Pacific as a whole is because of teleconnections. Whether El Niño, neutral, or La Niña conditions apply has wide ranging impacts across the globe.


How is carbon distributed among the atmosphere, the oceans, the biomass and the unburnt fossil fuels? In relation to my other question about carbon cycle and climate change, i would like to know some estimates of the carbon distribution among the atmosphere, the oceans, the biomass and the unburnt fossil fuels.

Here are more specific parts of this question.

How much carbon is there on Earth?
How much carbon is there in the atmosphere (in the form of CO2 and other gases)?
How much carbon is there in the oceans in the form of CO2 and gases?
How much carbon is there currently in the biomass?
How much carbon is there left in the form of fossil fuels?

If possible, i would also like to know how this distribution has changed, for example, over the last 100 years (in particular, how much carbon from the fossil fuels has been burnt over the last 100 years).

1.How much carbon is there on Earth?

Taken as whole, the Earth is estimated to be 730 parts per million carbon by mass.

So $4.4 \times 10^{21} kg$

http://quake.mit.edu/hilstgroup/CoreMantle/EarthCompo.pdf

  How much carbon is there in the atmosphere (in the form of CO2 and CO)?

$3.1 \times 10^{15} kg$ CO2 and insignificant CO, so $8 \times 10^{14}$ kg of C.

  How much carbon is there in the oceans in the form of CO2 and CO?

Carbon of all forms in the the ocean is $4 \times 10^{16} kg$

http://ioc-goos-oopc.org/documents/oosdp/oosdp_br5.pdf

  How much carbon is there currently in the biomass?

$8 \times 10^{14}$ kg (not including soil)

$2 \times 10^{15}$ kg (if soil is included)

  How much carbon is there left in the form of fossil fuels?

$5 \times 10^{15} kg$

http://www.gcrio.org/CONSEQUENCES/vol4no1/carbcycle.html

(This could be an underestimate, depending upon what you consider to be "fossil fuel"; methane clathrates are estimated to hold $10^{16}$ kg of carbon)

  If possible, i would also like to know how this distribution has changed, for example, over the last 100 years (in particular, how much carbon from the fossil fuels has been burnt over the last 100 years).

The amount of carbon in the atmosphere has increased about 30% since pre-industrial times, and the amount in biomass, not including soil, has decreased about 10%.  Amount in the oceans has not changed significantly.


What causes lava eruptions (and shutoffs)? I understand the process of volcanism and the reason for magma deposition on the surface of the earth.

What is not clear to me, or what seems to be less well explained is why eruptions occur and then stop. What is the operative cause or causes of a flow to start or stop?

As far as my understanding goes there would seem to be two possible obvious explanations:

(1) The magma rises in bubbles, like a lava lamp, through the earth, so the flow begins when the bubble reaches the surface and stops when the bubble is exhausted.

(2) The magma rises as a constant stream, but causes earth to build up around the stream, eventually snuffing it out by mass accumulation. In this explanation, the lava constantly searches for thin spots where it erupts until it blocks itself off, then the pressure forces its way through some new location.

Are either or both of these explanations correct or incorrect? Is there a mechanism I have not considered?

Lava eruption in Iceland the size of Manhatten that began in 2014.

Basaltic magma (pictured above) rises for several basic reasons: 1) High temperature, low density liquid mass that is buoyant relative to surrounding rock and 2) Low crustal overburden stresses that allow upward movement of the underlying buoyant magma.

Many magmas fail to break the surface if overburden keeps them "capped", but they can flow horizontally (ie between sedimentary bedding planes) if that's where the zone of weakness lies. Many may also simply lose their heat to surrounding rock and solidify on their upward migration. In many cases, buoyancy of rising magma may meet a layer of similarly dense material, effectively stopping it in its upward track.

Heat loss is important as magmas can stop flowing once relieved reservoir pressures slow upward flow to the point that rising magma cools faster than it can be replenished from below; as the flow trickles down, what's left just cools down, solidifies in place and flow stops.

On the other hand, a large reservoir contains both enormous buoyancy and, importantly, heat. That heat, constantly replenished by a large supply below, will prevent excessive conductive heat loss to surrounding rock and solidification of magma pathways, ensuring the path to the surface stays open. It's also worth noting that the local stress field changes as a magma body is emptied and can also work, along with heat loss, to cap flow.


Why air do not suffer density stratification of its gaseous components? The different gases that make up the air have different densities. So, naively, one would expect the heavier gasses to pool in the lower atmosphere and the light ones at the top.

I asked myself this question a long time ago and I found the answer to be that the mixing produced by atmospheric circulation was more than enough to keep the whole mix homogeneous, and I was happy with that answer until I considered the case of caves, or chambers within the Earth that have been discovered in underground mines, and that have been isolated for millions of years. But despite of that, there is no reports of miners dying because on the top of the cavity the air was only nitrogen or oxygen at the bottom.

Is the mixing produced by molecular movement due its temperature enough to avoid stratification? Or is there another reason? Would air at very low temperature suffer from density stratification?

So, naively, one would expect the heavier gasses to pool in the lower atmosphere and the light ones at the top.

That's overly naive. That same naive expectation would lead one to think that uranium should be concentrated in the Earth's core, or that a mix of water and ethanol should be differentiated with water on the bottom and ethanol on top. Uranium is instead concentrated in the Earth's crust, and water and ethanol readily mix. Entropy and chemistry can lead to counterintuitive results.

That most certainly is the case with gases. The entropically-favored distribution is a thorough mix. Attaining this thorough mix can take a long time if only molecular diffusion is in play. Turbulent mixing makes the mixing proceed much more rapidly.

There are places where this entropically-favored distribution does not occur. Gases can be concentrated in mines and in basements. For example, mines have problems with concentrations of methane and carbon monoxide (both less dense than air), but also with concentrations of carbon dioxide and sulfur sulfide (both more dense than air). Basements in areas with lots of granite have problems with radon (significantly more dense than air). Gases can concentrate in mines and basements due to a diminished turbulent mixing. This enables processes that produce gases to overwhelm the slow molecular dispersion process, resulting in an entropically-disfavors distribution.

The Earth's upper atmosphere is also differentiated. Here, the extreme rarity of the upper atmosphere means that turbulent mixing is highly attenuated. Extreme solar radiation (high UV and x-rays) produces gases by splitting molecular oxygen, water vapor, and to a lesser extent, nitrogen, into constituent parts. The very long mean free path in the upper atmosphere means that the lighter components move higher than do the heavier components.


Why doesn't it snow even when it is below freezing? I know the temperature of a place is determined by various factors, a few of which I can think of are: Altitude, distance from sea, latitude, wind etc.

My question is basically regarding latitude. If a place is closer to the poles, the temperature would be very low. So if the temperature is low there is a chance that it snows (I do not know what other factors lead to snowfall). But even when the temperature is below 0 in places near poles (Finland) it doesn't snow. But it snows in Germany.

So why there isn't any snow in Finland but in Germany? Does a negative temperature indicate chances of snow?

Farrenthorpe is right, a little surfing the net for snow distribution would clarify the picture for you. However, I think you are referring to certain times when it rains further north and snows further south. There are several reasons for local anomalies, of which the most important is the dynamics of the polar jet streams. These are strong high-altitude wind that blow constantly in both hemispheres. These winds have meanders which migrate around the world, as depicted in:

https://www.google.com/search?q=jet+stream++image+OR+picture+OR+diagram&lr=&as_qdr=all&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiX44v3tbHJAhUEjywKHSncCP4Q7AkINA&biw=1352&bih=631#imgrc=LXFiBx8qaJg5xM%3A

Meanders in these polar jets pretty much control the mid- to high latitude weather within the troposphere, bringing bulges of Arctic air south, and counter bulges of warm mid-latitude air to further north. But then they move on, and the reverse conditions sometimes prevail. As a long-term average the latitudinal control on snow distribution dominates. Of course, there are other influences as well, mainly related to heat re-distribution by the great ocean currents.


Does the Earth receive a net charge from the aurorae? The sun radiates a lot of charged particles to the Earth. When the magnetic field of the Earth lines up to the poles, we get the beautiful polar lights.

But are there as many negative charged as positive charged particles or vice versa, such that the Earth gets charged by the Sun?

No. If that were the case, the Sun would eventually develop a net charge. Let's imagine that's the case and the Sun develops a net  positive charge. That charge would eventually stop negative particles from flying away and facilitate the ejection of positive ones. This regime would then restore the neutral charge of the Sun.
This negative feedback makes sure the Sun remains neutral and that Solar winds carry no net charge.

See this Q&A for more details:Does the solar wind correspond to a net electrical current?


How does the lifetime of methane vary in the atmosphere? When reading about methane and its effect on climate, it is clear that its lifetime in the atmosphere is important to the global warming potential.  However, the lifetime does vary from 9 to 15 years, depending on conditions.  What are those conditions that would affect the lifetime of methane?  How does the lifetime of methane vary in the atmosphere?

This wikipedia article, says that the hydroxical radical is the most important sink of atmospheric methane:

In addition to being the largest known sink for atmospheric methane, this reaction is one of the most important sources of water vapor in the upper atmosphere.
$$\ce{CH4 + ·OH -> ·CH3 + H2O}$$
This reaction in the troposphere gives a methane lifetime of 9.6 years. Two more minor sinks are soil sinks (160 year lifetime) and stratospheric loss by reaction with ·OH, ·Cl and ·O1D in the stratosphere (120 year lifetime), giving a net lifetime of 8.4 years.

However, it goes on to say:

increasing emissions of methane over time reduce the concentration of the hydroxyl radical in the atmosphere. With less OH˚ to react with, the lifespan of methane could also increase, resulting in greater concentrations of atmospheric methane.


How is the total area of the world's oceans 361 million sq km? How is the total area of the world's oceans 361 million square kilometres? I can't see how the five individuals ones add to that.

When I Google how many squared km is this/that ocean, I get

When add the areas of those five oceans,  106.5+161.8+70.56+14.06+20.33

I get 373.25 million sq km.

Yet the world ocean, which should be the sum of the 5 oceans, is 361 million sq km.

If I try this site  https://www.infoplease.com/world/world-geography/oceans-and-seas

It says Pacific = 155.557,  Atlantic = 76.76,  Indian = 68.556, Southern =2 0.327, Arctic = 14.056

155.557 + 76.76 + 68.556 + 20.327 + 14.056 = 335 sq km

So, also, not 361 million square km

Any idea why the figures differ and what are the correct figures?

Commenter Universal Learner points out "Currently NOAA says there is only one ocean"

https://oceanservice.noaa.gov/facts/howmanyoceans.html

and "At the comments of the question I linked you can read a great: "I once heard a lovely description of the world's seas (by a polar scientist) as "One ocean with three big estuaries" ;-) "

  While there is only one global ocean, the vast body of water that
  covers 71 percent of the Earth is geographically divided into distinct
  named regions. The boundaries between these regions have evolved over
  time for a variety of historical, cultural, geographical, and
  scientific reasons.

  Historically, there are four named oceans: the Atlantic, Pacific,
  Indian, and Arctic. However, most countries - including the United
  States - now recognize the Southern (Antarctic) as the fifth ocean.
  The Pacific, Atlantic, and Indian are known as the three major oceans.

  The Southern Ocean is the 'newest' named ocean. It is recognized by
  the U.S. Board on Geographic Names as the body of water extending from
  the coast of Antarctica to the line of latitude at 60 degrees South.
  The boundaries of this ocean were proposed to the International
  Hydrographic Organization in 2000. However, not all countries agree on
  the proposed boundaries, so this has yet to be ratified by members of
  the IHO. The U.S. is a member of the IHO, represented by the NOS
  Office of Coast Survey.

And they have a graphic saying 1 world ocean.  Historically 4 basins.  Now 5 basins. And that the boundaries aren't agreed upon by all countries. Though that text refers to a basin as an ocean, so their terminology doesn't quite match their graphic.


Where can I get historic hourly precipitation data for Italy? I am looking for a time-series of hourly precipitation for Naples, Italy. I'd like to learn how to find this sort of data for Italy in general, as well.

Ideally this data would cover a recent year with no gaps greater than a few days, and would come as a spreadsheet with time-stamps and precipitation measurements on the hour side-by-side. I'm not picky and will format as needed, but I haven't found anything close to this yet. Also, public-domain/open-data is much preferred (we all like free things right?) but is not a limiting factor in my search.

Research thus far:

I've searched and cannot find a text-based data source as I described. I think the closest source I've got is the following, which does not have observed hourly precip: https://weatherspark.com/history/32302/2014/Naples-Campania-Italy On that page it says:

  Precipitation

  This station provides hourly reports of significant weather events at and around the station, but does not report the quantity of precipitation at the station itself. This is common for weather stations located outside of the United States, and for a small subset of stations in the United States that are located at lesser used and smaller airports.

I'm familiar with the difficulty of getting hourly precipitation and certain other meteorological variables from most weather stations outside of the U.S. and major international airports. In many cases, locals have been able to help me, often by providing the data themselves (these locals tend to be experts) or sharing the right channel to reach out to in their country's national government or research institutions. I haven't had such success in Italy though, but I only know/have asked a couple of relevant scientists. In part I'm hoping this question will serve as me asking more Earth scientists who work in Italy.

I've searched the European Union Open Data Portal, which feels like it would be the right place but is not (yet) as far as I have seen.

In searching for digital elevation data (which I'll be using with the precip data in this project), a Cornell page pointed me to Italy's Military Geographical Institute. From what I can tell through a Google Translate lens, this site doesn't offer hourly precip data. I don't speak Italian and have only poked around a couple of pages, so I could be missing something.

I turn to you, ES:SE. Where can I find historic hourly precipitation data for Napoli, Italia?

The US NCDC has this link to surface hourly global data which I was indeed able to find Napoli on.

It appears, based upon this page describing the World Data Center For Meteorology, that there may be restrictions on using the data commercially outside of the United States.


How far would average sea level rise from a 25% increase in total ocean volume? What amount of average sea level rise (in meters above 2020 levels) would be associated with a 25% increase in total ocean volume?
The reason I ask is because of this study that indicates Earth has lost appx. 25% of its water to space via methanogenesis process splitting the hydrogen molecules off of H2O, then the hydrogen escaping into space.
Regardless of whether this study is accurate, it has made me wonder what the Earth would have looked like with 25% more water. How much of a sea-level rise would that represent?
Obviously this would be a fairly complex equation since terrain is not uniform in contour. Less land is displacing every new layer of water you ade, compared to a lower layer of water. So (in addition to any changes from the radius of the sphere increasing) there should be a decreasing amount of average sea level increase per unit of water volume, until all land is covered.
I've looked to FloodMap.net for an answer, but they don't seem to provide the amount of water volume, at least, not to free users.
Curious if there is an open source code library that can handle this kind of calculation, or if there is a simple formula that would get us within a reasonable margin of error (i.e. it would provide a sea level that could be plugged into FloodMap to show what shorelines would look like under 25% more water, given today's continents).

It is not hard to do this calculation if you have global topography. Using a version with $\frac{1}{6}$- degree resolution and a sea level rise of 1027 m, the result is @Erik's value of 445 million cubic km. Here's the bit of MATLAB code:
H = 1027;   % sea level rise (m)
topo(topo<0) = 0;   % change all ocean depths to zero
topo(topo>H) = H;   % level off all land at a height of H
topo = topo.*(cosd(lat')*ones(1,2160)); % land volume per grid cell
land = sum(topo(:))*18.5^2/1000; % total land volume in km^3
water = sum(cosd(lat))*2160*18.5^2*H/1000 - land; % added water volume

Greenland and Antarctica fare ok, but Europe and Australia are basically gone:


Are there sources that offer derivative climate change data? Meteorologists often say that it’s difficult to attribute any individual weather event to climate change, but I’m wondering, do meteorologists or weather services study or publish derivative climate data?

For example, “this is the first time temperatures have reached 30° C for seven consecutive days at this location” or maybe “this is the first eleven‑month period without snowfall at this location”.

Since you comment on statistics provided during sport events, I should point out that this method is not scientifically sound. The reason is that for any given data you will find something that will make this dataset unique or "the first of this kind in recorded history". For a light take on this, refer to this XKCD comic.

What is methodically required is that first the criteria are defined and only then the data are evaluated. Weather services will typically publish things such as

Ranking average temperature within a calendar month (e.g. this July was the third hottest in recorded history (example is purely fictional)) at a certain location
Ranking of daily minimum/maximum temperature at some location (e.g. this was the coldest day ever measured)

Details on this will vary from country to country. There is also a wide range of measurement data or derived data for experts to analyze. Also, weather services will engage in studies about the impact of climate change.


Can we extrapolate wind speed data to higher altitudes? I have some data (GRIB layers) about wind components u and v, which I would like to use to estimate wind magnitude and direction. But the model says it is for 10 m altitude.

Is there a way to extrapolate this value for higher altitudes? lets say 600 m. If yes, how? which other variables should I consider that can bias this calculation?

Thanks a lot!

Yes, but it may not be valid. The extrapolation will be valid for about 0.1 * PBL Height using the Log-Wind Profile

You will need:

PBL Height.
A second Wind speed (within 0.1*PBL Height)
Surface Sensible Heat Flux
Surface Latent Heat Flux
Potential Temperature

You can use the last three variables to calculate the Monin-Obukhov Length (MOL). Then use the MOL to calculate $\psi$:

If L>0 $\psi=\frac{z}{L}$

If L=0 $\psi=0$

If L<0 $\psi=2\ln(\frac{1+x}{2})+\ln(\frac{1+x^2}{2})-2\tan^{-1}(x)+\frac{\pi}{2}$

where $x=(1-15\frac{z}{L})^{\frac{1}{4}}$

Now that you have $\psi$, you can derive the friction velocity and surface roughness length using the log-wind profile  and $\psi(\frac{z}{L})$. Once you have those two, you can extrapolate wind speed 600 meters up, provided the surface layer is that high.


What's causing this high SO2 concentrations in Kazakhstan? I was using this website for weather conditions around the world called Ventusky (https://www.ventusky.com/) and one of its features allows you to view SO2 concentration. I stumbled upon this high concentration of SO2 near Zhezkazgan in Kazakhstan (https://www.ventusky.com/?p=47.47;65.97;6&l=so2). I googled it but couldn't find anything. Satellite images show desert and mountains. Any ideas what could this be?

Images:

The source of SO2 is the smelter associated with the Jezkazgan (Zhezkazgan, Жезказган) copper mine, mined by Kaz Minerals. The complex also produces sulfuric acid.

If you check for the other atmospheric pollutants with ventusky.com, you will see associated particulate matter - PM 2.5 and PM 10.


Successful Earthquake predictions Have there been any instances where seismologists have successfully predicted the occurrence of earthquakes?

If so, then why has the number of scientists working on this area has declined (as compared to topics like Hazard Assessment) ?

The Haicheng Earthquake is the only successful evacuation of a devastating earthquakes. It's notable that the Chinese scientists thought they had figured out ot predict earthquakes, but have subsequently failed to predict many catastrophic earthquakes and many people's lives have been ended, ruined, changed.

It is news to me that this research is in decline, but there has been recent scrutiny for failing to predict earthquakes. This type of research is very hard, and probably not answerable, here is a related question:Is earthquake prediction possible?

Hazard assessment is much easier because we can model many different types of known earthquakes and infer the damage from that. There aren't as many unknowns, it seems, for what happens after an earthquake as there is during the buildup. Plate Tectonics is complex as we live in on a dynamic planet.


A good book or source for climate science and meteorology basics? I have a mainly a hydro-geological and geo-statistical background, I would like to have a basic introduction to meteorological, climatic processes and modelling techniques related to these fields. Any good resources?

Cambridge University Earth Sciences Department's reading list particularly suggests:

Pierrehumbert, R.T. (2012), Principles of Planetary Climate. Cambridge University Press, Cambridge UK, ISBN:9780521865562.
IPPC assessment reports
Cronin, T.M., 2010. Paleoclimates: Understanding Climate Change Past and Present. Columbia University Press, ISBN 978-0-231-14494-0

... plus many others, with a range of focuses, all of which are made explicit.

Other books include:

Physics of the Climate System, Peixoto and Oort
An introduction to dynamic meteorology, James Holton


If I was to tunnel straight through a mountain, what kind of rock would I find? I'm developing a semi-realistic game involving stereotypical dwarves digging into mountainsides and carving out grand caverns for themselves, similar to those in Moria or the Lonely Mountain from Tolkien's works.

I'm attempting to research what kind of layers of rock (in layman's terms) you'd expect to find in a typical non-volcanic mountain range in say, northern Europe. So far though I'm at a loss so at this point anything would be a help!

As Gary mentioned, it really depends on particular context for your mountain. How did it form? Is it volcanic in nature? Or maybe just old rocks being uplifted by some episode of compression.

On average, Earth's crust is pretty much granite. So chances are that you will find that inside your mountain. That wouldn't be a bad assumption. Granites form by cooling magma slowly, so most volcanic-type mountains are made of granite or something similar. For example, the Andes (below) are made of fine-grained Andesite near the surface and Diorite (Andesite's coarse-grained version, which is similar to Granite, but not quite) at depth.

In the case of cooling magma to form rocks, the slower the cooling, the larger the crystals will be. So rocks that cooled near the surface, will be composed of tiny crystals while rocks that cooled deeper will have larger crystals.

You could argue for more exotic rock types but that would imply a slightly more complex geological history (which is totally possible). For example, you could have uplifted a huge package of sedimentary rocks without any volcanism involved. Or you could have simply eroded everything around leaving large rock packages like the Venezuelan Tepuis (below).

In general, the rocks deep inside a mountain (or simply super old rocks) have also undergone a lot of compression, so sedimentary rocks will be unlikely as you would have converted them into metamorphic rocks, e.g. limestones would be marble, sandstones would be quartzites (like the Tepuis), shales would be slates (or schists, etc.), etc.

Similarly, metamorphic rocks that have undergone a higher degree of compressional and thermal stress (i.e. deeper in the mountain) will grow larger crystals.

Of course, like anything in geology, other complex scenarios do exist where these rules of thumb don't work. But in general, this should get you started.

Anyway, hope that helps.


Could a massive flood have formed the Grand Canyon? I believe that the accepted theory for how Arizona's Grand Canyon was formed was that erosion caused by the Colorado River flowing through the area over millions of years was the force at work.

Yet accounts of a massive flood have been passed down to various peoples throughout the world, even in landlocked areas. Could the Grand Canyon actually have been formed by such a cataclysmic flood?

In either case, it is assumed that vast amounts of water formed the gigantic chasm; the main difference being: over how much time did the transformation occur?

If a global deluge were accepted as a possibility, is the condition and appearance of the Grand Canyon consistent with such an origin?

tl;dr: no.

Long answer:

First of all, like mentioned by others in the comments, you would need some physical mechanism to take a whole lot of water, evaporate it, and drop it at once at a place where the Grand Canyon is now. This is not something that's going to happen because of physics. If there was some extraordinary event which could have caused this, we would get so much more evidence from it other than the Grand Canyon.

But let's assume, that somehow, by some magic or act-of-higher-being, an enormously large amount of water fell on the Colorado plateau at once. How would that look?

The huge amount rock removed from the plateau to form the canyon would have to go somewhere. And it would go there very violently, as huge boulders, irregular conglomerates and just a whole mess of mixed up geology. However, when you look downstream along the Colorado river, you don't see this stuff anywhere. When you look in the Gulf of California (which we know very well because of oil exploration), you don't see this stuff in there. Instead you see very nice sandstones, shales, marls, clays, etc. Definitely stuff that should not be there if there was a huge flood. Furthermore, those sedimentary rocks are interbedded with volcanic rocks and limestones. If this was a sudden event, all of this could not be there.
The Colorado river is meandering. If it was a huge sudden flood you would not get this morphology.
So far I was talking about lack of evidence. There is also some direct evidence for the incision rate of the Grand Canyon. Using a plethora of of scientific methods, such as radioactive isotope dating, cosmogenic dating, thermoluminescence, etc., it's possible to directly get a time when a certain thing happened (depending on the method). This allows us to know exactly when a certain rock formed, exposed, eroded (again, depending on the method). Using these scientific methods allowed us to infer that the Grand Canyon formed in the last several few million years, at an incision rate of a few dozen to a few hundred metres per one million year. The value depends on the exact location in the Grand Canyon and also on which research group you're asking. But whether the argument is about if it's 100 or 200 metres per million years is irrelevant for this discussion - it invalidates any suggestion that it formed in one sudden magical act of flood.


What is the metamorphic field gradient useful for? As I understand it, the metamorphic field gradient is the PT line traced out by the maximum temperature points of a series of PTt paths of rocks from the same metamorphic event.

What exactly is this useful for? It seems that it doesn't really describe anything of physical significance since the $\mathrm{T_{max}}$ points can occur at different times so it doesn't represent a snapshot of the geothermal gradient at any fixed time.

You are entirely correct. Todd and Engi write:

  The mineral assemblages of rocks at the surface lie on a locus of
  P–T-conditions… It must be stressed…does not imply a P–T-distribution or geotherm realized at any one time during the orogenic evolution of this area. Even assuming the P–T-values
  reflect maximum metamorphic conditions, these were established at
  different times in different areas…show the integrated effect of all
  the tectonometamorphic processes…i.e. the sum of burial, heating,
  tectonic and erosional unroofing and cooling.

Notwithstanding, the metamorphic field gradient is still useful, particularly when comparing different sets of rocks.

Each of the samples in your figure (A, B and C) is a single rock and looking at it tells you the history of this rock and this rock alone. When studying a large area (a "field") there will be many rocks, that may differ from each other in their individual P–T-path. For example, in a rock suite that is now dipping 90°, one might argue that walking 3 kilometres on the surface equals 1 kbar of pressure, equals about 3 kilometres of depth. Because of that, each sample along the transect will have experienced different temperatures, with ideally the deeper ones also being the hotter ones.

By choosing a convenient reference point (maximum temperature of an individual sample), and connecting all samples along a transect, you can get an estimate of a P–T gradient, which can approximate a geotherm (under many assumptions). The same Todd and Engi paper has this figure:

Each of the lines is based on several dozens of individual samples. Based on this representation of the data, they go on to conclude:

  The metamorphic field gradients and age determinations and consistent
  with two stages of metamorphism. The first stage created the field
  gradients preserved in the northern part of the field area. The second
  thermal pulse affected only the south-eastern part of the field area.
  This occurred at a later time, under lower pressure conditions.

Reaching those conclusions is only possible when condensing the 100 or so individual samples they used (i.e. 100 individual P–T-path loops) to what turned out to be only two metamorphic field gradients.

Todd, C. S. and Engi, M. (1997), Metamorphic field gradients in the Central Alps. Journal of Metamorphic Geology, 15: 513-530. doi:10.1111/j.1525-1314.1997.00038.x


Why is more carbon in the atmosphere good, up to a certain level? According to Elon Musk, there's "an argument" stating that the current level of carbon in the atmosphere (more than 400 ppm) is better than it was some hundreds of years ago (200 ppm). He even calls these low carbon levels carbon starvation.

https://www.youtube.com/watch?v=kzlUyrccbos&t=45m4s

What is this argument based on? What harm would it do if the level fell again to 200 ppm?

If plants were growing poorly when atmospheric CO2 was 200ppm, it was probably because Earth was in the middle of an ice age and covered with glaciers, not because plants were starved of carbon dioxide.

All things being equal, increasing the amount of carbon dioxide available in the atmosphere can benefit some plants, but the problem is that all things do not remain equal.

CO2 is only a fertilizer in environments where CO2 is the limiting input for a plant; plants in the outdoors may receive too little moisture, too much warmth, or too little sun for additional CO2 to make much difference.
Adding CO2 to the atmosphere also changes global and regional climates, reducing precipitation and increasing temperatures in ways that offset benefits from CO2 fertilization.

The authors of Plant growth enhancement by elevated CO2 eliminated by joint water and nitrogen limitation in Nature Geoscience found that

  the presence of a CO2 fertilization effect depends on the amount of
  available nitrogen and water. Specifically, elevated CO2 levels led to
  an increase in plant biomass of more than 33% when summer rainfall,
  nitrogen supply, or both were at the higher levels (ambient for
  rainfall and elevated for soil nitrogen). But elevated CO2
  concentrations did not increase plant biomass when both rainfall and
  nitrogen were at their lower level. We conclude that given widespread,
  simultaneous limitation by water and nutrients, large stimulation of
  biomass by rising atmospheric CO2 concentrations may not be
  ubiquitous.

Scientific American tackled the question in Ask the Experts: Does Rising CO2 Benefit Plants?, concluding that "Climate change’s negative effects on plants will likely outweigh any gains from elevated atmospheric carbon dioxide levels."

Researchers cited in that article pointed out that added CO2 provides diminishing returns, with Samuel Myers, principal research scientist in environmental health at Harvard University, noting that “We know unequivocally that when you grow food at elevated CO2 levels in fields, it becomes less nutritious."

The second part of your question was what would happen if CO2 levels fell to 200 ppm. This is unlikely to happen on human timescales; the current CO2 level is about 410ppm, rising 3-5 ppm per year. CO2 levels were at about 280ppm for most of human civilization, only increasing substantially when fossil fuel use became widespread in the 1800s. CO2 has a residence time in the atmosphere of several centuries.


Are there any differences between the subalkali and alkali rock occuring tectonic environments? Here question ends. Beyond details exist

Do they occur on the same tectonic regime?
For a start to distinguish Subalkali rocks froms Alkali rocks,
my knowledge says that mantle is the source of Alkali rocks. Ocean Island Basalts are Hawaii, Reunion etc are all Alkali rocks. Large ignous provinces are also sourced from mantle by the mantle plumes. Such as Deccan, Siberian traps.

But in Robil Gill's ((Gill, R. (2010). Igneous rocks and processes: a practical guide. John Wiley & Sons.)) book on page 291, (chapter 9-Alkali rocks) says that Most of the large igneous provinces are subalkaline and they are much bigger and more frequent than the Alkaline Large igneous province. From this i derive that LIP's can be subalkaline.

So are there any difference between subalkali and alkali rock occuring tectonic environments ?

Yes, there are many differences and subdifferences and nuances.

I will try to keep it in simple terms which will satisfy your question.

Alkaline magmas form by low degree partial melting of the deep mantle. This is why you see them in hotspots. It's very hot down there, but you do not form a lot of melt. For example, the amounts of melts in Hawaii are negligible compared to what you have in large igneous provinces (think Deccan Traps) or mid ocean ridges. Another tectonic setting with common alkaline magmas are rift zones. The best example is the east African Rift (Ethiopia, Kenya, etc). Again - deep melting of the mantle leads to alkaline magmatism.

Subalkaline magmas form in shallower melting. For example, the voluminous mid ocean ridge basalts are not alkaline, and the melt forms within a few kilometres of the surface. Arc magmas (andesites etc) are also not too alkaline because they form by fluid-assisted melting of not too deep mantle above subduction zones.

Even though large igneous provinces form by mantle plumes, the melting so extensive that the melts are not alkaline any more. To get alkaline melts, it has to be low-degree partial melt.