What are these lake-like blue patches in the desert, visible in satellite image? I found some blue patches in the Arabian desert in Google Earth.  It looks like as if they were lakes with sand dunes rising out of the water.  But there isn't water in the desert, at least not this much, or is there?  So what do we see on the image?  I realize that the colour we see in the image may not be accurate.

Link to Google Maps

In response to Fred's comment about whether it might show water after a rain

I took some time to browse Landsat archives and see if things are changing.  Here's a comparison of the same region on two different days (note the different dates, about 1.5 months apart).  The comparison shows that things are changing, i.e. it doesn't permanently look like this.  Most of the time it's like the first image.  This is not the exact same area as above, but it's "nearby".

Are there satellite images freely available taken at wavelengths that can clearly show water?

Update 2  Here's some daily MODIS images from the same time as the two photos above, I'm not really sure what to make of them though.  See the clouds passing through 2013 Aug 3-4.  The precipitation layers in the same tool do confirm rain during those two days.

Update 3  Yet another image showing more clearly what looks like lakes.  Click for description and full-size image showing larger area.  This is the eastern part of Rub' al Khali.

Update 4  These are likely old and dried up lake beds.  Mention on Wikipedia.  Quote from article:

  All that remains of the lakes are their eroded basins, standing up in forlorn little buttes a meter or so high, in stark white or gray against the Rub' al-Khali's infinity of rusty-red sand.

It doesn't explain the bluish colour, but it's likely these dried up lake beds that I see on the images.

Some ground-level photos here.

The 'bluish' areas are exposed gypsum and gravel across which the sand dunes are moving. The colour is likely an artifact of the 'natural' colour palette used when processing the SPOT image. To understand just how arbitrary and variable the results of that processing can be, consider the following image captured at a fairly high zoom level in one of your 'blue' areas:

Meanwhile just to the south-west, there is at least one identifiable lake (at 20.896022N ,54.007201E, perhaps an up-welling of ground water, possibly transient and apparently highly saline, judging from the lack of vegetation around it) and, as you can see here.... it has an entirely different appearance to the blueish areas you've identified.


What causes the earth to be a good grounding system? When working with electricity, rubber shoes are recommended because they prevent current from running through your body.
But I've read that usually the earth is more negative charged than positive. So how is it possible that contacting the earth is dangerous in some situations as it is also negative charged, and when you touch an electrical wire you also get a lot of negative charges (electrons). So in theory, they should repel each other, but apparently, they attract each other to cause a current in a body. How is this possible? Isn't the earth negative charged (most of the times)?

The electricity you're talking about is the man-made kind, which is completely independent of any charge the Earth has relative to its atmosphere. Man-made power sources are almost all referenced to the Earth as zero volts, as established by connecting the "ground" to a conductive rod driven into the ground. Each house's electrical system is also grounded in this way. Since earth (lower-case "e") is at least somewhat conductive (except for perhaps dry sand), if you grab a conductor while standing barefoot on the ground then current will flow through you, through the ground, and then back to the source of electricity and/or your house's local grounding rod. Enough volts, and good enough conduction, and you get hurt or killed. Rubber shoes, rubber gloves, and just plain common sense can prevent this.

Again, this has nothing to do with the charge the Earth has relative to its atmosphere, as man-made power is generated referenced to Earth ground; plus, since it's almost always alternating current, the polarity changes 50 to 60 times a second, so any purported existing voltage wouldn't protect you.


Geology: What's make a group of bedrock a formation? Geology: What's make a group of bed a formation?

Basically a formation is just a layer or group of layers of rock that is both distinct enough to be identifiable in the field and large enough to show up on a geological map. Usually it is many nearly identical layers grouped together or just one large layer. Its not a hugely precise definition but it is a lot like the term "species" in biology, it's a working definition, created more for usability than precision.


Interpolating world data to a local grid in Python I have an NC file that has global data with a high resolution (about 25 minutes) so a lot of coordinates.
I have some measured values of some region with irregularly spaced coordinates.
In order to mathematically operate between the two, I am aiming to interpolate the global data to the local irregular grid, instead of the opposite, to minimize the uncertainty.
How do I achieve this? I was thinking of Scipy's griddata module but cannot seem to initiate the process. Thanks a lot.

EDIT:

I tried the following, a little heavy on resources but I think it works.

from scipy.interpolate import interp2d
f = interp2d(longw,latw,Zw)

where longw,latw,Zw are the world coordinates of the NETCDF file and the 2D variable respectively.

Then I applied f(lon,lat) to all my irregular observations y iteration to interpolate. The lon and lat are the observed coordinates of the local region.

As @gansub implicitly suggested, you may have a better outcome by defining the output grid as well.
Check this very similar question:
How to interpolate scattered data to a regular grid in Python?

After comments, I realize I missed the irregular target grid. Maybe this answer helps:
https://stackoverflow.com/questions/3242382/interpolation-over-an-irregular-grid


GIMMS NDVI3g grid cells not entirely square-shaped? The official data description of the recently updated GIMMS NDVI3g record describes the grid parameters of the dataset as follows.

grid-name: Geographic Lat/Lon
pixel-size: 1/12=0.0833 degrees

size-x: 4320
size-y: 2160

upper-left-lat: 90.0-1/24
upper-left-lon: -180.0+1/24
lower-right-lat: -90.0+1/24
lower-right-lon: 180.0-1/24

This means (at least to my understanding) that in x-direction, the cell size equals

> (180-1/24) * 2 / 4320
[1] 0.08331404

whereas in y-direction, the cell size equals

> (90-1/24) * 2 / 2160
[1] 0.08329475

I.e., the single grid cells are not entirely square-shaped. Am I missing something in my calculation or does the officially described pixel size of "1/12=0.0833 degrees" simply result from rounding effects of the manually calculated edge lengths in x- and y-direction?

Your understanding is inaccurate. The shifts by $\frac{1^\circ}{24}$ are only relevant for figuring out, where the pixel centers are located and where to start when you are looking to find the right grid index for a certain point. As for the resolution, it is much simpler. We have $4320$ pixels covering $360^\circ$ in longitude direction, i.e. a resolution of $\frac{1^\circ}{12}$ and similarly for the latitudinal resolution.

As for the square-nature of these pixels, they are only squares in lat-lon coordinates, not in terms of length on the ground.


Calcareous deposits in arid soil? I read this line in my textbook:

  Lower Horizons of arid soil are occupied by calcareous deposits called kankar because of the increasing calcium content downwards.

My question is that why only in arid soil? Increase of calcium content will led to formation of kankars in other types of soil also, then why it happens only in arid soil?

Karkar is made of calcium carbonate.

then why it happens only in arid soil?

Because this is what happens to calcium carbonate in wet environments:

It dissolves away, forming a cave. Calcium carbonate, or calcite, is soluble in mildly acidic solutions. Rainwater is mildly acidic because of CO2 from the atmosphere dissolving in it, so it never allows for the formation of calcium carbonate deposits in the soil to begin with.
As for why it forms in arid soils, the Wikipedia page for Caliche explains it well:

Caliche generally forms when minerals leach from the upper layer of the soil (the A horizon) and accumulate in the next layer (the B horizon), at depths around 3 to 10 feet under the surface. It generally consists of carbonates in semiarid regions—in arid regions, less-soluble minerals form caliche layers after all the carbonates have been leached from the soil. The deposited calcium carbonate accumulates—first forming grains, then small clumps, then a discernible layer, and finally, a thicker, solid bed. As the caliche layer forms, the layer gradually becomes deeper, and eventually moves into the parent material, which lies under the upper soil horizons.
However, caliche also forms in other ways. It can form when water rises through capillary action. In an arid region, rainwater sinks into the ground very quickly. Later, as the surface dries out, the water below the surface rises, carrying up dissolved minerals from lower layers. This water movement forms a caliche that tends to grow thinner and branch out as it nears the surface. Plants can contribute to the formation of caliche, as well. Plant roots take up water through transpiration, and leave behind the dissolved calcium carbonate, which precipitates to form caliche. It can also form on outcrops of porous rocks or in rock fissures where water is trapped and evaporates. In general, caliche deposition is a slow process, but if enough moisture is present in an otherwise arid site, it can accumulate fast enough to block a drain pipe.

(photo from http://www.naturephoto-cz.com/karst-cave-photo-24442.html)


Literature on atmospheric modelling I need to understand some basics about atmospheric modelling, since I am working with data from the COSMO model for my thesis. My questions mainly concern model validation, like learning about the most common metrics to evaluate model accuracy. Therefore, does anybody have suggestions concerning good introductory textbooks for atmospheric modelling?

To clarify where I am coming from:

I am looking at regional climate data for the Antarctic as simulated by COSMO in Climate Mode driven by ERA-Interim. Observations in the region and for the period of interest are naturally sparse, so I wondered how I can validate the model data against the few observations there are. This led me to the question whether there are some general practices and statistical methods to validate output of an atmospheric model and hence the idea to ask for pointers to introductory textbooks.

"Atmospheric modeling, data_assimilation and predictability" by Euginia Kalnay, is an introductory book, which is good to get an overall overview of the subject.

If you are more interested in the numerics I would recommend "Numerical Methods for Fluid Dynamics" by Dale R. Durran.


Can aerostats be used for fine-grained control of the weather Most of the discussed geoengineering ideas aim to change the average temperature of the earth instead of trying to control local weather.

Aerostats can be used to change the local temperature in several ways:

if covered with reflective material they can create shadow;
if covered with dark material they can significantly increase the temperature above the cloud potentially dispersing the cloud;
if combined into a structure similar to a solar updraft tower, they can transport dust and humidity to the height where they would not be transported by natural winds and by that either condensate the water or create new clouds.

With a large enough number of devices like this it should be possible to guide humid air to deserts, or to prevent hurricanes by removing convective available potential energy on their path.

Is there any research about the possibility of controlling the weather with devices like these, or is there some obvious flaw that would make this completely impossible? (Lack of helium is not a good argument, as these aerostats are not meant to lift any additional weight, and are meant to be as large as possible, so could use air heated by the sun).

If this is possible, what percentage of earth surface would we need to cover with these devices to counteract CO2 effects? From a rough assessment of incoming radiation vs radiation trapped by human released CO2 it seems to be much smaller than 1%.

No, the idea is quite impractical. Lack of helium is no obstacle because unmanned balloons, whether tethered or remote controlled could be filled with hydrogen, but to affect the climate you would need millions of them, which is too expensive and impractical. Geo-engineering projects are generally the stuff of science fiction and not practical in the real world. One way climate could be modified on a local scale is to refill places like the dried up Aral Sea with water from the ocean. Apart from other beneficial effects, this would probably produce enough evaporation to affect local rainfall. Rainfall is also locally affected by the presence or absence of trees, so if you want to increase rainfall in arid areas, one way to achieve it is large scale tree planting. That might be difficult in semi-desert environments, but nevertheless it has been done. Sometimes tree roots can reach down to a water table, which is how enormous cypress trees are in some places  able to grow in the sand seas of the Sahara Desert.


Sea breeze - magnitude of horizontal pressure gradient? What is the range of horizontal pressure gradients typically caused by the differential heating of land and water under sea breeze conditions?

In his book, Simpson (Simpson, J. E. (1994). Sea breeze and local winds. Cambridge University Press) shows a figure that includes the pressure difference between Jersey in the Channel Islands and Paris. It gives an idea of the magnitude of the pressure difference. As was mentioned in the comments, sea breeze tends to be perceived as a density current on constant pressure surfaces.


What Caused The Sea Levels to Drop During the Maastrichtian Epoch? Anyone who has studied ice ages would know that during the last two-and-a-half million years of Earth's history, there have been periods where there was enough ice to suck up a lot of water. As a result, sea levels fell by an average of 100 meters. Among the most famous examples of this sort of drop is Beringia, the landmass that connected North America to Asia.

However, that doesn't seem to be the only way to reduce sea levels.  On the image below is how much North America changed in only less than ten million years.

On the left is what North America looked like 75 million years ago.  On the right is North America at the time the dinosaur empire fell nine million years later.  It's not just North America that experienced this drop.  As a matter of fact, the whole world was undergoing the same process (it's just that I couldn't find one compatible enough to post in this SE.)

The big deal with that is that unlike in the Ordovician, Carboniferous, Permian or Quaternary periods, this marine regression was not because of ice, as its extent (therefore its influence) was barely minimal--alpine at the very best.  There was no massive pileup of polar ice as was the case in the other periods listed last sentence.

So if ice weren't the cause of the sea levels dropping during the latest Cretaceous age, then what else could cause the same thing to happen?

Tectonic activity can change the volume of oceanic basins and hence, modify the sea level, ice not involved.

Firstly let's explain the left picture.

At Cretaceous the tectonic activity was high. The flux of material from mantle to ocean ridges and plateaux reduced the volume of ocean basins, wich produced a global high sea-level observed in differents parts of the globe.

During Campanian and Mastrichtian global transgressions are recognized in several stratigraphic sections of the Earth.

Z. Dubicka and D. Peryt (2012) studied a stratigraphic sequence in Poland wich also showed transgression phases on Mastrichtian. They correlated them with other strata of the age.

  This sea-level rise, recorded in south-eastern Poland, can be
  correlated with the transgressive peak recognized by Hancock (1993);
  this corresponds to the Craise Graise (¼ Vijlen Member) exposed in the
  CPL quarry at Halembaye in Belgium, which in turn corresponds to the
  lower Belemnitella junior Zone, i.e., earliest Late Maastrichtian.
  Hancock (1993) suggested that this peak may occur globally. He
  correlated it with the Prairie Bluff Chalk on the northern margin of
  the Gulf of Mexico and with strata that lie a little above the base of
  the Tinton Greensand on the Atlantic coastal plain. The transgressive
  peak in the earliest Late Maastrichtian was also documented in the
  Sopelana section in the Basque Arc Domain in Spain (Gómez-Alday et
  al., 2004), which coincides with the inoceramid extinction, the
  informal definition of the Lower/Upper Maastrichtian boundary.
  Moreover, a marked transgression in the middle Maastrichtian was
  reported from the Southern Hemisphere by Huber and Watkins (1992) who
  noted a higher diversity of keeled foraminifera, which they
  interpreted as reflecting a possible transgression.

Then let's focus in your question about the sea level drop. It is pretty obvious a regression happened, at least at North America.

The sea level drop appears to be global too, according to Matsumoto (2002) and associated to a slowing down of global tectonic activity.

  Tectono-eustasy may have been the main cause of the phenomena of
  transgression-regression, but certain kinds of other tectonic
  movements which affected even the so-called stable platforms were also
  responsible for the phenomena. The combined effects of various causes
  may have been unusual in the Cretaceous, since it was a period of
  global tectonic activity. The slowing down of this activity followed
  by readjustments may have been the cause of the global regression at
  the end of the Cretaceous.

Zofia Dubicka, Danuta Peryt (2012): "Latest Campanian and Maastrichtian palaeoenvironmental changes: Implications from an epicontinental sea (SE Poland and western Ukraine)", Cretaceous Research
Volume 37, October 2012, Pages 272-284.
https://doi.org/10.1016/j.cretres.2012.04.009

T.Matsumoto (2002): "Inter-regional correlation of transgressions and regressions in the Cretaceous period", Palaeogeography, Palaeoclimatology, Palaeoecology. Volume 187, Issues 1–2, 1 November 2002, Pages 35-60
https://doi.org/10.1016/S0031-0182(02)00504-7


Where do aurorae australis begin and in which direction do they move? During a polar night is there any pattern or consistency to where aurorae australis begin?  I'm assuming they become visible first in the exosphere and descend down to thermosphere.  Do they tend to begin and move from east to west, or west to east or is it entirely random?

Auroras start at a distance of 80-200 km above the Earth's surface.

The color of the aurora will be blue/purple if the air molecules in the area below 120 km are excited.

If the air molecules in the area from 120-180 km are the ones that gets excited the colour will be yellow/green.

Above 180 km gives the red light in the aurora.

The most powerful aurora will in general be 180 degree from the Sun's position and it will move from east to west at the opposite side to where the Sun is.

During powerful auroras the aurora arch can easily cover 270 degrees or more if close to the magnetic poles, if the aurora covers the area away from the magnetic poles the aurora arch will get smaller.

When the charged particles from the Sun interact with Earth's magnetic field a powerful ground current will be induced, this can induce DC power in power lines and severely damage the AC power transformers. Should an event like the one that happened on September the first, 1859 (the Carrington event) hit us today we would have major problems with power supply and satellite communication.

You can read more about all of this here, Aurora and please take a look in the sources there too.


Maximum temperature possible on earth on a day What is maximum temperature that can we have on earth on a single day?

I assume that after a certain limit, radiation and convection would start working strongly to have equilibrium of surroundings.

According to thermodynamics principles how high temp in theory can go before equalization process restrict any further increase?

Highest I found till now was 58 ℃
in Libya.

This is theoretical question lets say an Air mass stays over an area and sun radiation is also highest how hot it can get

Maximum temperature over what area? There are of course local hot spots at hydrothermal and volcanic centers which far exceed the generally excepted maximum recorded temperature, of 58 deg C in Libya (as you correctly state). Many other high temperature anomalous areas exist in areas where there are no met sites to record them. For example, in the Afar triangle depression in the horn of Africa, or in the foothills of the Jebel Akhdar in Oman. In the latter case the steep slopes of black harzburgite rock re-radiates high summer insolation to well into the 50s, but as far as I know, the maximum temperature has never been investigated. Then there is the time-scale. Global warming will almost certainly increase the maximum recorded temperatures over the coming decades and centuries.

On the geological time scale, the sun's radiance is very slowly increasing, so it is only a matter of time (billions of years) before the planet gets so hot that photosynthesis will cease - in which case whatever humanity evolves into will eventually fry.


How do 'greenhouse gases' let heat in, but not let it out? That honestly doesn't make any sense to me. How could heat pass through a gas one way but not the other? Its not like our upper atmostphere has a bunch of doors that can only open one way. To me, that seems to fly in the face of everything I've been taught about how the physical universe works.

If heat can pass through a substance one way, there's no reason why it can't go through the other way. Except for 'greenhouse gases' apparently.

The closest thing I know of that works this way is one-way mirrors. But that doesn't have the same effect. The reason you can see through one side and not the other is because most light is reflected, but not all. Thus if you're in a dark room, the light coming in from the outside will overwhelm what little light is being reflected from within the room. But if you're on the outside, virtually no light is coming through from the dark side and thus you can only see what is being reflected.

In short, it makes no sense to me and flies in the face of everything I've been taught. Now, I'm not a climate change denier. Actually, this is something I just now thought about. I've never really bothered to question it before.

In a nutshell:

The radiation that enters is shortwave radiation from the sun.  Solar radiation is dominated by visible (as well as UV and near infrared) radiation with a wavelength mostly between 0.2 µm and 2 µm.  This wavelength is determined by the temperature of the Sun, in the order of 6000 K.  For visible radiation (roughly between 0.4 µm and 0.7 µm), all the gases in the atmosphere are (almost completely) transparent.  Clouds do scatter this radiation so you can't see the Sun directly when it's cloudy, but they still let plenty of light through, so it's still light on a cloudy day (just less bright), although it does feel cooler.

The radiation that leaves is longwave radiation, also known as terrestrial radiation or (incorrectly) as thermal radiation.  For Earth, this is dominated by radiation with a wavelength of mostly between 4 µm and 40 µm.  This wavelength is determined by the temperature of the Earth, at around 290 K.  At these wavelengths, greenhouse gases are mostly opaque.  They absorb the radiation.  The greenhouse gases reradiate the absorbed heat, but in both directions (back to Earth AND up to higher layers in the atmosphere), and at a lower temperature.  The upward longwave radiation gets in turn absorbed by higher-up layers of greenhouse gases, et cetera, such that ultimately the layers of greenhouse gases that do radiate into space tend to be high up in the air (say at 240 K).  Thus, their overall effect is to radiate less heat into space than the Earth surface would in the absence of those gases.

The most important greenhouse gases are water vapour, carbon dioxide, and methane.

Source: gisgeography.com

Source: science of doom


What temperature do small meteorites have on impact A question which has haunted me for years. What temperature do small meteorites (which don't evaporate on impact) have if you find them immediately after they hit the surface. I understand that the outer parts are heated by atmospheric friction, but what about the inside? Can the inside keep its low temperature that it inherits from space?

There are some stories on the internet about meteorites that were so cold, that the moisture of the air froze on the surface of the meteorite. Can this really happen?

Subquestion:

Are there numerical simulations that can prove this?

Some of the rumours are summed up here:
"Frosty" meteorite (Wikipedia).

Love & Brownlee (1991) put together numerical models for the experiences of micrometeorites entering the atmosphere. They say:

  The peak temperatures experienced by submillimeter micrometeoroids rarely exceed 1700°C. Maximum temperature and mass loss rate generally occur at altitudes between 85 and 90 km during ∼1 sec of peak heating. A typical melted particle spends ∼2 sec at temperatures above the melting point.

Flynn (1989) discusses interplanetary dust, with figures for peak temperatures given in the abstract.

But I think that what you really want is Sears (1975), Temperature gradients in meteorites produced by atmospheric passage:

  Temperatures in the order of 200°C have usually penetrated no further than 5-10mm, which is consistent with a luminous flight time of the order of 10s.

Using the geologists' rule of thumb for timescales of cooling (I believe $\tau^2 = \ell/\kappa$, where $\tau$ is the timescale, $\ell$ is the thickness of the cooling body, and $\kappa$ is the thermal conductivity - though it's a while since I've had to do this so I may be misremembering...), the information above about the height above the surface at which peak temperature is commonly reached, and an estimate of particle velocity, you can probably back-of-envelope a temperature for a meteorite on impact!


Concept of artesian aquifers and pressure is not clear. I do not understand how the Artesian aquifer is causing the water in the flowing well to reach a level higher than the ground surface? And what role does the piezometric surface play in it?

The red line or piezometric line is the level to which the water wants to rise - if it were allowed to reach hydrostatic equilibrium. Artesian conditions are anywhere where a confined aquifer sits below the hydraulic head level (the level to which the water wants to rise).
In this case the water is confined and cannot reach the water table even though it wants to - this means it is not at hydrostatic equilibrium. This aquifer is described as having a confining pressure or hydrostatic head. If you put a well into anywhere along this confined aquifer, the water will rise out of the aquifer to the level of red line.

I think in your case its a bit confusing as the piezometric line sitting above the whole of the confined aquifer suggests the whole area is artesian but the 'flowing' conditions are only where the piezometric line sits above the actual surface, meaning the water will actually rise above the surface. Another example is that if you were to dig a well, to the left or right of the highlighted area, the water would rise to that level but would still be below the surface so conditions wouldn't be described as 'flowing'.

(http://www.env.gov.bc.ca/wsd/plan_protect_sustain/groundwater/flowing_artesian_wells.pdf)


How is relative humidity determined from a wet and dry bulb readings? The question What is the second thermometer in the image from the Esperanza Antarctic temperature record? shows what might be a wet/dry bulb setup.

I've given one to a friend to measure humidity for fun (it's me who thinks it's fun). I'd learned about them in Earth Science class a zillion years ago, so when I happened to see one recently I grabbed it.

I understand the very basics of how it can indicate humidity; the drier the air, the faster water will evaporate into it and so the colder the wet bulb will be with respect to the dry bulb.

To get a numerical value for humidity with this set up you use the coarse table on the front (there's a finer table on the back of the box) and look up the dry bulb temperature and the dry minus wet difference to find an approximate humidity. For example If I look up 19 and 2 °C for those respectively (roughly what's shown in the image) I get about 81% relative humidity.

But suppose I hooked up a camera to a Raspberry Pi and imaged the two thermometers, processed the image and determined the two temperatures and wanted to calculate the relative humidity without interpolating the table.

Question: How is relative humidity determined from a wet and dry bulb readings? What are the steps and where's a good source for the equations and parameters involved?

Click for full size

Edit: 1 May 2021
The following procedure uses the less accurate method from page 455 onward from the scanned sections of the book pictured below, from the original answer.
The procedure is a multistage process ideally suited to either a spreadsheet or programming code.
The equations use SI units.
1. Calculate the saturated vapor pressure at the dry bulb temperature
This is done using the equation:
$P''_{ws} \ = \ 0.61078\ e\ ^{17.27T_{dry}/(273.3+T_{dry})} \ \ kPa$
Where $T_{dry}$ is the dry bulb temperature.
2. Calculate the saturated vapor pressure at the wet bulb temperature
This is done using the equation:
$P'_{ws} \ = \ 0.61078\ e\ ^{17.27T_{wet}/(273.3+T_{wet})} \ \ kPa$
Where $T_{wet}$ is the wet bulb temperature.
3. Calculate the moisture content of saturated air at the wet bulb temperature
Use the equation: $r_o \ = \ \frac{18.016 \ (1.0048)P'_{ws}} {28.9664 \ (P_{atm}-1.0048)P'_{ws}} \ \ kg/kg$
Where $P_{atm}$ is atmospheric pressure
4. Calculate the enthalpy of water vapor pressure at the wet bulb temperature
$H'_{wo} \ = \ -0.00000662 \ t_{wet}^3-0.000194 \ t_{wet}^2+1.8375 \ t_{wet}+2500.83 \ \ kJ/kg$
5. Calculate the enthalpy of liquid water at the wet bulb temperature
$H'_{wl} \ = \ 0.0000063 \ t_{wet}^3-0.000727 \ t_{wet}^2+4.2058 \ t_{wet}+0.03 \ \ kJ/kg$
6. Calculate the enthalpy of water vapor pressure at the dry bulb temperature
$H'_{wi} \ = \ -0.00000662 \ t_{dry}^3-0.000194 \ t_{dry}^2+1.8375 \ t_{dry}+2500.83 \ \ kJ/kg$
7. Calculate the moisture content of saturated air at the wet bulb temperature
$r \ = \ \frac{r_o*(H'_{wo}-H'_{wl})-(1.005 \ t_{dry}-1.005 \ t_{wet})}{(H'_{wi}-H'_{wl})} \ \ kg/kg$
8. Calculate the vapor pressure
$P_w \ = \ \frac{r \ P_{atm}} {1.0048 \ (18.016/28.9664+r)} \ \ kPa$
9. Calculate the relative humidity
$\phi \ = \ P_w/P''_{ws}$

Previous Answer - scans from relevant pages from reference book
I'm going to go old school with this one.
The following pictures are the relevant pages from: Environmental Engineering in South African Mines, The Mine Ventilation Society of South Africa, 1989, pp 451-455. They give the psychometric equations that are required to calculate relative humidity from wet & dry bulb temperatures.

For simplicity, I use the less accurate equations on p455, section 9.2.
As a slight diversion, the other way to measure wet & dry bulb temperatures is to use a whirling hygrometer. The wet bulb temperature is always read first because it will start to warm as soon as the hygrometer stops whirling.


How has and how does the lithosphere affect climate change? The climatic system can be divided into five main components: the atmosphere, the hydrosphere, the lithosphere, the cryosphere and the biosphere.

All these physical systems operate at different time and spatial scales. The lithosphere, that makes the uppermost, rigid layer of the earth, is formed by a few dozens of tectonic plates that move laterally while resting on the Earth's fluid mantle (plate tectonics). The collision between lithospheric plates builds mountains, and their separation forms ocean basins where sediment is accumulated, on timescales of tens to hundreds of millions of years. Hence, it is considered that its effect on climate change is not on the same timescale as the other components of the system and is not given as much attention.

Despite its low effect on the historical time-scales, undoubtedly, it poses a load on the system. Note that I am not interested on events that can in fact interact with the timescales of other climatic components. For example when land masses ocupied positions near the poles and the effect of the resulting increase in glaciation can be on the same time scale as other non-lithospheric physical phenomena. Nor am I interested in singular volcanic eruptions or activity of that sort.

I am interested in how the processes such as continental drift, mountain growth, and erosion, affect climate evolution.

This is a huge and interesting topic.
Certainly there are many ways the climate is affected by the lithosphere (and also what is going on in the asthenosphere). The lithosphere is naturally also affected by the climate. I find it difficult to distinguish the 'components' as matter and energy can flow from biosphere to lithosphere and from hydrosphere to atmosphere etc. Somehow it might be appealing to think about lithosphere as a slow 'component' but keep in mind that the atmospheric circulation have been much more stable than the locations of the continents. Deserts have been in the same latitudes, even as continents have been moving.

A few areas of influence to consider:

Location of landmasses affects ocean currents and climate e.g. closing of Isthmus of Panama.
Supercontinents certainly had a very different climate than what we experience today.
Uplifts and orogenies can have local, regional and global effects.
Carbonates in the lithosphere plays an important role the carbon cycle. See e.g. this.
Rate of vulcanism also follows tectonic conditions.


Does the diameter of the earth decrease because of soil subsiding due to irrigation and rainfall over the years? I am taking a course on coursera where the instructor talks of a soil subsidence concrete post that was put there in Everglades southern Florida in 1920s. He goes on to describe the level of earth that has decreased over the years due to soil subsidence.

Now there have been rains on the earth for years and in past couple of centuries, the area for agriculture has increased significantly which in my opinion leads to increased soil subsidence due to irrigation.

Doesn't this continuous rainfall and irrigation lead to higher subsidence and hence decrease in the diameter of the earth?

Disclaimer: this is probably TLWR, but you can absolutely apply some physical reasoning to arrive at the answer.

Changes in surface height of the earth are governed by the conservation of mass, i.e. that if mass ($M$) is removed in one location (everglades soil erosion), then an equal amount of mass must be gained at another location (perhaps accretion on the seafloor).The total change in the earths mass is zero $$\Delta M = M_1-M_2=0$$
$$-M_1=M_2$$.

Mass may be broken up into the volume ($V=\Delta x \Delta y \Delta z$) multiplied by density ($\rho$), so $M=\rho V$. In terms of the conservation of mass equation from above, then:
$$-\rho_{1} \Delta x_1 \Delta y_1 \Delta z_1 = \rho_{2} \Delta x_2 \Delta y_2 \Delta z_{2}$$

The place where erosion occurs is described by the left side (with subscript 1). The place where accretion occurs is described by the right side (with subscript 2). This equation says the total mass lost by area 1, must equal the total mass gained by area 2. Now consider the following two situations.

1) The transported sediment does not undergo any change in density. If the density does not change, you have $\rho_1=\rho_2$. Let's also say the eroding area ($\Delta x_1 \Delta y_1$) equals the accreting area ($\Delta x_2 \Delta y_2$) for simplicity. Then all equal terms in the conservation of mass cancel out and you're left with
$$-\Delta z_{1} = \Delta z_{2}$$

2) The transported sediment does undergo a change in density. There's a host of reasons why density can change. If the density changes then we can't let the density terms cancel in the conservation of mass. Lets still say the eroding area and accreting area are equal. The conservation of mass becomes
$$-\rho_1 \Delta z_1 = \rho_2 \Delta z_2$$
or conversely
$$-\Delta z_1=\frac{\rho_2}{\rho_1}\Delta z_2$$
This says that the amount of change in height at location 1 is not equal to the amount of change at location 2 (sure they're proportional, but not definitely not exactly equal).

Putting it all together to answer the question, the average earth radius (r)  is the average of all heights (z) with respect to the center of the earth $$r=\frac{z_1+z_2+...+z_n}{n}$$

Try this all out with arbitrary numbers to convince yourself. Add the changes $\Delta z_1$ to $z_1$, and $\Delta z_2$ to $z_2$
$$r_{before}=\frac{z_1 + z_2 + z_3}{3}$$
$$r_{after}=\frac{(z_1+\Delta z_1)+(z_2+\Delta z_2)+z_3}{3}$$
Rearrange $r_{after}$ to be
$$r_{after}=\frac{z_1+z_2+z_3 + (\Delta z_1+\Delta z_2)}{3}$$

Case 1 If density doesn't change (i.e. $-\Delta z_1=\Delta z_2$), then $$r_{after}=\frac{z_1+z_2+z_3 + (\Delta z_1-\Delta z_1)}{3}$$
The changes cancel out and $r_{before}=r_{after}$. The earths radius does not at all change.

Case 2 If the density changes, $r_{after}$ becomes
$$r_{after}=\frac{z_1+z_2+z_3 + (\Delta z_1-\frac{\rho_2}{\rho_1}\Delta z_1)}{3}$$
and you can see that $r_{after}$ does not equal $r_{before}$.


Why do clouds have areas of darkness instead of scattering light to produce a rainbow? I suspect it has to do with the difference in size of a rain drop and that of the water particles in the cloud.

It really depends on the cloud. Actually, it depends on its density and thickness which is related to concentrations and type of hydro-meteors in it, the size distribution of water droplets and ice crystals, and shape of ice crystals.

Rainbows are formed by the refraction and internal reflection of light in water drops (usually rain).

But cirrostratus clouds can form a halo by refraction on ice crystals in shape of hexagonal prisms. These halos have angular radius of about 22 degrees.

Another optical phenomena that you might find interesting is a corona around the Sun or the Moon which is caused by diffraction of light on water droplets and tiny ice crystals. Angular size of a corona depends on the size of water droplets.

'Areas of darkness' are due to the density and optical thickness of a cloud. More ice crystals and water droplets cause more scattering which results in less light reaching your eyes making a cloud appear darker.


Can a sonar used to graph the ocean floors detect through polluted and highly populated waters? So graphing the ocean floors using sonar is not anything new. But what are the limits to sonar?

Would it be possible for a regular sonar device to emit sounds that are strong enough to penetrate through polluted waters? And if they can, how much pollution is needed to block the sonar completely? And by pollution I mean plastic waste (bottles, bags, etc).

Also, would highly populated waters be a problem? I'm talking about corals, fish, algae, and others. I'm pretty sure just one fish wouldn't do much, but what about a whale? Or a swarm of fish?

Using sonar to map the ocean floor is not usually affected by pollution or by the occasional fish, if it's a normal herring or cod sized fish. Plastic pollution usually floats or sinks so it isn't a problem. A fish the size of a basking shark would show up on the sonar, but it wouldn't be a problem. Large shoals of fish also show up, but it would have to be a very large shoal indeed to interfere with mapping the ocean floor. There are seasonal shoals large and continuous enough to do this, but only at certain times of the year in a very few locations where they are on migration in their billions. I have never heard of one causing problems for a vessel whose mission was to map the ocean floor or search for a sunken ship. Sonar is sometimes used by trawlers to search for shoals of fish.


Independent sources of information on radiation pollution in Europe Bear with me if this is a wrong place to ask this question. I aksed this question on Physics at StackExchange and was told it will be more on topic here.

Recent news show a fire has started close to the former nuclear plant in Chernobyl because someone was burning grass. Ukrainian State Scientific and Technical Center for Nuclear and Radiation Safety explained:

  the fire in the exclusion zone has been extinguished. [...] The updated modeling results indicate that the potential maximum concentrations of Cs-137 in the surface layer in Kyiv were lower than 0.1 mBq/m3. The forecasted concentrations are less than those observed previously and more than 1000 times lower than the acceptable levels established by NRBU-97. They do not pose any harm to the health of the population.

The information has been confirmed (translation mine) by Polish National Atomic Energy Agency:

  With regard to false information appearing in public space about the alleged occurrence of radioactive contamination in Poland, the National Atomic Energy Agency strongly denies this type of information. The radiation situation in the territory of the Republic of Poland remains normal. There is no threat to the health and life of the population in the country.

On the other hand, we have received contradicting information from several friends, family and "trusted" sources that there was a threat to our safety and we should stay at home for two days and close the doors and windows to avoid contamination. I consider this fake news, but I am also aware that sometimes governmental agencies delay notifying the public because of political or other reasons. For instance, when there was Chernobyl disaster in 1986, some scientist at one of Polish physics institute had access to Geiger counter. They started to carry over their own measurements of contamination but they were told to stop doing that by the institute authorities that there connected to the Communist Party at that time.

There used to be a similar problem with smog air pollution in my and other European countries. There were some governmental measurements of air pollution but there was also some controversy how they measured air pollution, how frequently they reported it and how they defined safety thresholds. In a response to that problem multiple companies started to produce low-cost devices that you can install at your home to measure air pollution. This provides a source of information independent from governmental agencies.

Is there similar initiative, agencies, companies, etc. that measure radiation pollution in Europe?

Two websites I've come across that might be of interest are:

Radioactivity Environmental Monitoring Joint Research Centre, for Europe.
Radmon.org which provides radiation information from number of
global station.


Forest rings shape regularity In the answer to "Why is ground water rising on these forest rings?" it is written:

  these rings are too numerous and too regular in shape to be related to either kimberlites or (even more bizarrely) Oklo-type natural nuclear reactors

How is the regularity of forest rings assessed? How many near-rings and other shapes have been found?

From my correspondence with Dr. Hamilton, who is one of the leading researchers on forest rings (emphasis mine):

They can be irregular (see figure below) but it is not very common. You
are right, the circularity is why we notice them and there are
probably lots that we don’t notice because they are not round.
However, the mechanism of formation that we have postulated ought to
produce circular shapes. All point-source force fields in an isotropic
medium will produce a circle if the area of influence is large enough.
We argue that the source of energy is the electrochemical potential
(redox) difference between the inside and outside of the ring; and the
force is an electrical field. The groundwater and glacial overburden
have fairly isotropic electrical conductivity (the inverse of
resistance) and therefore circularity is a requirement if the current
density is sufficient.

This photo was taken near from northeastern Ontario north of Kapuskasing. The circular ring is  ~150m across.


About the actual radiative impact of greenhouse gas emission over time Say we will emit a certain amount of greenhouse gas over the next 50 years (e.g. 100 billion tons CO2-eq in total). What would happen if I implement a certain GHG mitigation effort to cut the same amount of GHG (say sequester 20 billion tons CO2-eq) in the early years (e.g. year 0-10) vs in later years (year 40-50)?

I would imagine that cutting the gas earlier would be better since overall global warming is a cascade of positive feedbacks? A bunch of other similar questions can be asked like cutting the same amount of GHG over first 10 years (but no cutting thereafter) vs spread out the cutting to the entire 50 years. What are some major consideration to look at? Is it generally better to cut GHG as early as possible?

There is no doubt that the sooner the mitigation effort happens, the greater will be its impact.

In other words, the impact on year 2100 climate of the sequestration of 20 billion tons $\ce{CO2}$-eq right now, is much bigger than the impact that the same action will have in 30 years from now. Therefore, a mitigation action today is much cheaper than one done in the future but with equal impact on year 2100 climate (assuming no dramatic changes in the sequestration technology).

This is due to the long lifetime of $\ce{CO2}$ in the atmosphere, that is usually estimated to be longer than a few centuries. Although, some sources place the lower limit at around 30 years, its lifetime is most likely longer than 50 years.

This means that any $\ce{CO2}$ that is not captured today (or emitted), will remain in the atmosphere trapping heat and rising Earth's temperature until year 2100 and beyond.


What is the current status of geophysical global cooling theory? Plate tectonics effectively rubbished the theory of geophysical global cooling as a means of explaining many surface features on the Earth. However, this wiki says that the same process is responsible for certain surface features on the surfaces of Mercury and the Moon.

Do such processes play no role in Earth's Geology? Or are they only effective on smaller bodies? Why?

The effects one can see on other planets (and many of the icy moons in the solar system) are typically faults and scarps due to the fact that during cooling, these bodies contracted. Since the surface was solid, the only way to accommodate the contraction is through faults.

But Earth's surface is not solid on long time scales. We have plates that move, scrape, and subduct. If you shrink the perimeter of Earth slowly, you don't get compression faults. Rather, you're just going to accelerate subduction a little bit and maybe slow down mid-ocean ridges a bit.

In the end, the point is that the system of plates that covers Earth can accommodate slow shrinkage of Earth without producing visible faults.


Changes in Real Solar size around 1979? Has been observed any changes in the real sun´s size on ocassion of the 1979 solar storm event ? (after and before)

No, no such changes have been observed. Laclare et al. (1996) summarize various published solar diameter data from observations made between 1970 and 1995. Here's Figure 6 from their paper.

As you can see (and as Laclare et al. point out), solar semi-diameter has shown no significant variation during the measurement periods. Given their deviation from the other data sets, the Wittmann data seem rather suspect, but even they show absolutely no change between the 1972 and 1981 data points. In short, none of these data are consistent with the notion that solar diameter changed in 1979.

References

Laclare, F., Delmas, C., Coin, J. P., & Irbah, A. (1996). Measurements and variations of the solar diameter. Solar Physics, 166(2), 211-229.


Would it be possible, from the earth’s creation or during its various geomorphological changes, for all the following hypotheses to be probable? I’m designing a fictional world setting for a game, and I would like to know whether it has a relative coherence based on science. (Don’t mind if it is an almost improbable scenario).
Would it be possible, from the earth’s creation or during its various geomorphological changes, for all the following hypotheses to be probable?

Earth has multiple natural satellites which create new natural phenomena (ex. extreme tides and tidal currents)
Earth temperature is higher enough to melt the ice so that humans can sail through the north and south pole, but also low enough for people to survive.

My thoughts: I was thinking maybe multiple asteroids colliding and some of them (big enough) entered the earth’s orbit and became natural satellites, while others crashed into the earth’s surface to reshape the landscape etc.
Alternatively, if there could be a whole different planet similar to earth which had multiple moons since it's creation.

The second part of the question is easy to answer - given that the Arctic has been ice free in relatively recent geological history, e.g. in the Mesozoic, and it is expected to be ice free in summer within a few decades as a result of global warming, positing a habitable planet where polar oceans are navigable, at least in summer seems fairly safe.


How accurate are climate proxies in giving us a clear picture of global average temperatures throughout Earth history? Since reliable modern records of climate only began in the 1880s, proxies provide a means for scientists to determine climatic patterns before record-keeping began, though it appears that the the distribution of proxy records for global average temperatures, just like the instrumental record, is strongly non-uniform, with more records in the northern hemisphere.

How accurate are climate proxies in giving us a clear picture of global average temperatures throughout Earth history?

Overall, any individual proxy is not a reliable indicator.  It's the combination of multiple proxies that provides a clearer picture.

For example, tree ring growth has been correlated with temperatures.  However, it's not without it's anomalies:

  ...from the middle of the 20th century tree ring growth was less than might have been expected from the temperature record... ([source]

(http://www.climatedata.info/Proxy/Proxy/treerings_introduction.html))

If we were to only look at tree-rings, we could not possibly trust on them as a reliable source, since they have known problems.

We can also use coral as a indicator of past climate.  However, it's also somewhat questionable:

  However, long (multi-centure) records are rare, and the possible influence of non-climatic influences has not yet been confidently established.
  source

Ice-cores are not immune to skepticism:

  An indisputable interpretation of ice-core oxygen isotopes in terms of
  atmospheric temperature variability, moreover, remains elusive, and
  precise annual dating can be difficult.

However, if we can combine these three indicates along with other indicators (pollen, earth bores, etc), we can increase the reliability of our understanding.  For example, if most indicators show a cold year, we can more reliability say it was a cold year.

Combining these proxies together helps us to gain a clearer picture of the past environment.

Overall Reliability

However, with that said, the amount of uncertainty with the multi-proxy method is not small.

At the Workshop on Mathematics in the Geosciences, Blake McShane presented a new algorithm for estimating paleoclimate.  This algorithm provided a more reliable estimate by increasing the uncertainty of the predictions.  That's an important point that I will restate:

Through his talk, he showed that his method was more reliable because it was less certain.

Even that wide uncertainty level, he questioned:

  Indeed, this should make us increase our level of uncertainty (indeed perhaps
  our wide intervals are in fact optimistically too narrow)!

  source

In the end, we can look at proxies for guidelines and trends, but they cannot be used for reliable readings.


How to distinguish an explosion crater from an impact crater? (How) Is it possible to tell the difference between a man made explosive crater and an impact crater?

A manmade crater would leave behind traces of the chemical(s) used to create it (C4, TNT, ANFO, etc.). Assuming the impactor were large enough, there would be traces of shocked quartz or other shocked stone in and around the crater. If the impactor landed in limestone, then there would be significant quantities of quicklime. (I'm purposely omitting thermonuclear devices here.)


Why does the moon orbit the earth and not the sun instead? The planets orbit the sun by the sun's gravity,and earth's gravity is weaker than the sun's gravitational pull.

The moon does orbit the sun but it also orbits the earth.  But your assertion that the earth's gravity is weaker than the sun's is not universally true.  If the sun's gravitational pull were greater than the earth's HERE on the earth, the sun would literally suck everything not attached to the earth's surface into itself.  Clearly that's not happening.
Remember that Newton's Law of Gravitation says that the force is inversely proportional to the SQUARE of the distance.  So while the sun does have a stronger gravitational pull, the distance that both we and the moon are at makes the earth's field dominate.


In hydrology, what's the difference between specific and total catchment area? I am getting stuck on the concepts of Total Catchment Area (TCA) and Specific Catchment Area (SCA) as I try to learn more about TOPMODEL and hydrology modeling. What do these metrics mean in hydrology? The context I encounter these in is in calculating Topographic Wetness Index (TWI) values.

My understanding so far is that: TCA is basically equivalent to a watershed for any given pour point; SCA helps determine saturation and saturation excess flow and it is the ratio of a local catchment area for a pour point divided by the width of the contour where that pour point is. I'm especially uncertain about SCA because it's unclear to me how the width of the contour is involved in a catchment area (based on my conceptual framework of a watershed a/k/a catchment area being defined by a single pour point). So, maybe I also need "Flow Width" (a term I think I've seen used to describe that contour width used in SCA) to be explained in order to understand SCA.

To give some context to what I'm referring to, here's a passage which references both TCA and SCA:

  "Upslope area is the total catchment area above a point or length of contour and the specific catchment area is the upslope area per width of contour or cell size, L (Moore et al., 1991). Specific catchment area is used to calculate saturation and saturation excess overland flow in hydrological models such as TOPMODEL (Beven and Kirkby, 1979) and, along with other topographic indices, to calculate erosion and landsliding in many other models. Upslope area is commonly used for mapping channels on the basis of threshold upslope areas for channel initiation.

J. Wainwright & M. Mulligan. Environmental Modelling: Finding Simplicity in Complexity. Oxford: Wiley. 2012. Ebook.

This was originally posted in GIS.SE where it was suggested it be moved here.

I will try to bring you some insights. In my opinion, SCA is poorly named.

Actually, the width is not involved in the catchment area which is given by TCA. SCA introduces a diffusive flow factor by considering flow width. It is a one dimensional value so it is not representative of an area and that's why it might be confusing. It gives us an idea of how concentrated are the incoming flow.

Besides this, I think you are also confused by the outlet concept which is often defined in GIS or in some conceptual definitions by a point. But actually, in order to compute a flow at an outlet you need flow velocity and a cross section. If this cross section area is assumed to be rectangular, it can be defined by the width and the height will vary according to the incoming flow. So when the outlet is considered as a point, it is more like a targeter of the outlet that has some dimensional characteristics.

So, for studies at the plot scale or the hillslope scale, the outlet is often defined by a line which is representative of the flow width at the downslope.

For grid based data, a pour point targets a representative area defined by the spatial resolution of your terrain data. If a point has no flow width, this area has one and the flow width is generally assumed to be the cell size as mentionned in your quote.

If you understand that, you may understand that the broader the width, the more diffuse will be the overland flow and therefore the less wet regarding the TWI or the less erosive. Of course, it remains resolution dependent.


What fraction of Earth's crustal material survives the supercontinent cycle? I know that things are not as simple, but for the sake of argument I'll assume a supercontinent cycle of $\sim$400 Myr periodicity is active on Earth.

If that is the case, then my naive understanding was that roughly all of Earth's crust is reformed on this timescale, and information about the past is forgotten due to melting in the subducted zones.

However I stumbled upon a research article that cites "Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 2.5 billion years ago) comprises of..." as summary of another article.

So there is a fraction of crust that survives this process and is several cycles old. Do we know the fraction of material in the crust that survived this process?

There is two parts to this answer, first continental crust tends to persist and oceanic tends to be recycled. This is largely due to density, continental crust is less dense and tends to "float" compared to the mantle and is very difficult to push back into the mantle for remelting. Only a tiny fraction of continental crust ever gets subducted mostly as sediment on oceanic crust, so basically by piggybacking on subducting oceanic crust. This is why continent to continent convergent boundaries form mountains with no subduction, they can only push down by pushing even more material up, in effect packing together like wads of compressing clay.

Second continental crust is reworked by other processes, erosion, faulting, rifting, mountain building, metamorphic processes, etc. These are regional effects and thus more random, so how much they alter can vary quite a bit from continent to continent. Exposed un-reworked continental crust is rare but this is due to the accumulation of events reworking smaller regions and the tendency of sediment covering it up. There is much more unexposed old continental crust buried under the sediment, often referred to as the shield portion of the craton, Shield is the portion of the continental crust that is not sediment and is not tectonically active (even some shield is partially metaphorically altered, but this is where you find unaltered material) There is quite of bit of ancient shield (brown in this picture) although it still makes up a small percentage of the overall continental crust. Even then only a fraction of it has survived all the continental cycles and is completely unaltered since the first continents formed.

This image illustrates how much of the oldest continental crust is still around(purple).

Basically oceanic crust is guaranteed to be reworked eventually, check the age of oceanic crust, while continental crust has a more random factor involved meaning some in the more stable regions of some continents has not been reworked. That is why they are only small scattered areas.


Is salt accumulating over time? The rainfall leaches salts (Mg,Na,Ca,K,.., Cl) from weathering rocks, where those ions were freed from chemical bonds by sunlight, acidic water etc. The runoff eventually goes into the oceans, where evaporation of water leads to accumulation of salts. Over geological timeframes the oceans fall dry and the salts deposit as huge layers.

My question: Is there a net accumulation of salts, or do subduction or other effects reintroduce these ions into mineralic (and non-salt) chemical bonds? -my question is about whether this is a primarily one-way street from minerals to salts, or whether the salts get 'recycled' by, e.g. being subducted and then re-bound in the heat of the mantle.

There is a limit to how much of a given salt can be dissolved into water, this is known as it's solubility and it's dynamic based upon how much of any particular ion is already present. Once concentrations exceed the local solubility of a given compound precipitation occurs, this can be seen in the modern Mediterranean basin with the precipitation of calcium carbonate onto the seabed. There are also older examples of this response such as chemically precipitated chert in New Zealand.

That's one way in which dissolved chemicals can be re-integrated into the rock cycle, biological processes can also play an important role. Plankton take up many elements from sea water during their life cycle, notably silica and calcite for forming rigid structures these are then deposited in the deep ocean when they and the creatures that predate them die and form the basis for many sedimentary rocks.

So while there is a steady input of mineral salts into the ocean there's only so much of it that can accumulate and in fact a lot of them are removed at far lower concentrations due to biological use and subsequent deposition.

A measure of any deposited material may eventually be subducted with the oceanic crust on which it has settled, at which point it will be integrated into any subductive-melt sourced minerals. There is a trend towards the chemical depletion  of the mantle when it comes to certain elements which appears to be a one way street but the ocean does eventually give back a large percentage of what is dissolved into it.


Is there an estimate for the length of the American Cordillera? There was no geography site on Stack Exchange, so I thought the best place to ask about this was in Earth Science: Do we have an estimate for the length of the American Cordillera (the chain of mountain ranges in the west of the Americas, reaching from Alaska down to Antarctica)?

I tried calculating it by using the lengths of the mountain ranges listed on the Wikipedia page, but some mountain ranges don't have a length recorded anywhere. The best I could get was a rough estimate of about 8500 miles, the length of the Alaska Range, the Coast Mountains in British Columbia, the Cascade Range, the Sierra Nevada, the Sierra Madre Occidental, the Baja California peninsula, and the Andes. The Sierra Madre de Chiapas, COrdillera Central, and Graham Land had no length to add, and maps were no help.

Does a record exist for this lengthy range, or did no one ever bother?

A difficulty in finding a resource that provides an estimate of the length of the entire American Cordillera is as, @fre0n states in the comments

  there is very few standard mention regarding this unit as a whole, instead it is more often localized

As can be read in the Wikipedia article American Cordillera, where they state that

  The American Cordillera is a chain of mountain ranges (cordillera) that consists of an almost continuous sequence of mountain ranges that form the western "backbone" of North America, Central America, South America and Antarctica. It is also the backbone of the volcanic arc that forms the eastern half of the Pacific Ring of Fire.

The Wikipedia article lists the constituent mountain ranges as being a line of overlapping mountain ranges from the Alaska and Brooks Range right through the Andes to the southern tip of South America, also suggesting that the Cordillera could

  possibly be followed through the arcuate South Georgia Ridge across the Southern Ocean to the mountains of Graham Land on the Antarctic Peninsula.

Given the earlier definition of the Cordillera being

  an almost continuous sequence of mountain ranges that form the western "backbone" of North America, Central America, South America and Antarctica.

according to Google Maps, where I used this definition and traced the distance (right-click on map -> Measure distance -> select points along the 'spine' of the Americas and Antarctica), I determined an estimate of the total length as being approximately 17,000 km (or about 21,500 km if the South Georgia Ridge and Graham Land Mountains are included).


Why are inversion layers so important in meteorology? I keep hearing the term "inversion layer" when reading about pollution and meteorology.

I know it vaguely amounts to "some place where the gradient of temperature is inverted".
But why are inversion layers so important in meteorology ? Why do they matter ? Air is colder here ... Big deal ! ?

Farrenthope is correct, but I would like to add some detail.

An inversion occurs when the air is warmer than the ground. It is called an inversion because it is the opposite of what occurs during the day. During the day, the ground is heated by the sun and the air near the ground rises.

However, during clear and calm nights, the ground will cool faster than the air. This means that at a certain time, the air will be warmer than the ground. With nothing to move pollutants upward, the air just stagnates. People will still keep pumping pollutants out, with the pollution just accumulating. During the day, however, the pollutants are lifted upwards, and do not stagnate.

For those mathematically affluent, the equation for a concentration of a pollutant can be written as $$\frac{\partial c}{\partial t}=-\vec{v}\cdot\nabla_h c-w\frac{\partial c}{\partial z}+\nabla \cdot (K\nabla c) +S_c(t)+C$$

where $c$ is the concentration of the pollutant, $\vec{v}$ is the wind vector, $w$ is the vertical velocity, $K$ is the Fick's law constant, and $C$ is the chemistry term.

If we consider the following assumptions which are common, regardless of an inversion:

Diffusion is a small process ($K\approx0$)
The pollutant undergoes no chemical change ($C\approx0$)
The equation boils down to
$$\frac{\partial c}{\partial t}=-\vec{v}\cdot\nabla_h c-w\frac{\partial c}{\partial z}+S_c(t)$$

During an inversion, because air at the surface is not going up, there is no air going down. This means $w\approx0$. With no vertical velocity, the air near the ground is slowed by the drag the ground has on the air, making $\vec{v}\approx0$. This boils the equation down to $$\frac{\partial c}{\partial t}=S_c$$.
Since $S_c \ge0$, $c$ will just keep increasing.

A good example of a dangerous inversion is the Donora event.


Why are oceanic plates denser than continental plates? In the theory of tectonic plates, at a convergent boundary between a continental plate and an oceanic plate, the denser plate usually subducts underneath the less dense plate.  It is well known that oceanic plates subduct under continental plates, and therefore oceanic plates are more dense than continental plates.

My question is why are the oceanic plates always denser than the continental plates.  I'm aware that the difference in density can be attributed to the plates differing compositions, but what I'm interested in is why these plates have different composition in the first place giving rise to their relative difference in densities.

Ocean lithosphere (geophysical definition of crust + upper mantle that acts as a 'plate') is primarily of basaltic composition - the upper levels are basalt and the lower levels are gabbro. The top levels have been proven with boreholes, whilst the lower levels have been inferred from transform fault sampling and comparisons with ophiolites. This sequence is produced by partial melting of mantle peridotite at a fairly controlled rate. So much so that basalts formed in this way even have a specific composition "MORB" (Mid Ocean Ridge Basalt).

In contrast, continent lithosphere is more complex and tends to be of a 'granitic' composition. This includes granites but can also include a lot of metamorphic rocks (eg. gneiss) and sediments. Sediments are lower density anyway (high pore space), but so are quartz-rich rocks such as granites. The various processes that build continents tend to favour silica rich compositions, resulting in this bulk "granitic" composition. For example, limited partial melting will initially produce high silica, high alkali melts. Erosion will tend to break down most common minerals before quartz - leaving quartz-rich sediments (hence sandstone is primarily quartz). Metamorphism of pelites (rocks rich in Al and Si) will tend from the initial mudstones & basalts through to gneisses & migmatites (which have a lot of quartz and feldspar). Migmatites are partially melted - and the melted bits are essentially granite.

Basalt is denser than granite. On gravity surveys, basalts and gabbros will appear as positive anomalies, whilst granites and sedimentary basins will appear as negative anomalies.


Unstable North Polar Vortex? What would cause a polar vortex to become unstable a split into 3 smaller ones? How rare is this and what long term effects could this cause if the vortex stays unstable?

http://www.severe-weather.eu/long-range-2/update-on-the-splitting-polar-vortex-and-winter-trends-across-the-european-continent-through-mid-january/

There are two key intermittent mid latitude circulation patterns during boreal winter.

One is blocking flows, leading to the formation of blocking anticyclones.  One can gauge the location of blocking events through the CPC blocking index.

The other one is sudden stratospheric warming, where the winds cause a disturbance such that the temperature in the stratosphere (the layer above the typical weather layer, the troposphere) warms significantly.  To view this one needs to look at the temperature change over the poles, typically by looking at the 10 hPa isobaric surface. If the temperature change is around 50 to 70 degrees Kelvin over an area of synoptic scale and the temperature change is rapid, over a period of 3-4 days, then you have the possibility the weather can be impacted by a sudden stratospheric warming event.

The possibility is that a sudden stratospheric warming in January 2019 could cause the stratospheric polar vortex to split. Based on the peer reviewed reference The Influence of Stratospheric Vortex Displacements and Splits on Surface Climate it is actually the troposphere that causes polar stratospheric variability through vertically propagating Rossby waves. The math behind that is quite complex but it also feeds off linear theory (which can be seen in the quasi-geostrophic Potential Vorticity equation). Some of these vertically propagating waves can travel all the way up into the mesosphere. These lecture notes on Rossby waves mention that Rossby waves cannot propagate vertically if the mean zonal winds are easterly or if they are westerly and exceed a certain speed. It is only the wintertime atmosphere that permits Rossby waves to reach the stratosphere and deposit energy and hence sudden stratospheric warmings are only observed after boreal fall.

In the northern hemisphere most vertically propagating Rossby waves arise due to the topography.  In the southern hemisphere the sudden stratospheric warmings are a rarity due to lack of such topographical features. The last sudden stratospheric warming over the southern hemisphere was in 2002.

The resulting stratospheric anomalies can in return influence surface climate but the mechanism on how exactly this occurs is the still the matter of scientific research.  One of the theories that is currently popular is the wave mean flow interactions. This can be easily summarized as concerning how planetary scale Rossby waves influence the circulating zonal flows around a planet.  The other main theory is wave reflections at the tropopause.

So what is the net result of either of the above two possibilities? Either way they affect mid-latitude storms. Storms could either become more intense, shift equatorward, or there could be extremely cold air advection spells as the stratospheric air gets mixed into the troposheric air.

As to the rarity of polar vortex splits - they are coupled to those sudden stratospheric warmings. If you look towards the climatology of SSWs, observations show that they occur more during El Niños and La Niñas than during neutral conditions. Sudden stratospheric warmings happen almost every other year in the NH. However sometimes the polar vortex isn't split during these events but is merely pushed equatorward.

The long term effect a polar vortex split could be extended spells of extremely cold weather in the affected areas, and when the vortex reforms on into summer it would be shrunk in size from the dispersed energy giving rise to greater easterly wind circulation near the poles.

UPDATE

Now that the reanalysis data is available from January 2019 I want to add some visuals for the Dec-2018/Jan 2019 polar vortex split and ongoing cold wave.

The OP's link, plus this SlashGear article on the polar vortex split provide GEFS and GFS forecast data, pointing to a three-way split of the polar vortex. I went through reanalysis data from the period of Dec 18th 2018 through Jan 30th 2019 and there appears to be two separate candidate dates for a three-way split of the stratospheric polar vortex; it really depends on whether one considers the small vortex over the North Pacific as one of the split vortices or not on Jan 5th 2019. The 5th January event is the one that most closely resembles that GFS forecast data. In saying this, the reanalysis data is averaged over a full day as opposed to the single point in time of the GFS data. In the geopotential height anomaly there is a clear three way split but one must remember that the anomalies are calculated vis-a-vis the climatological period 1981-2010. Either way this will require more detailed research before the three-way split is confirmed or not.

Finally from the reanalysis data it appears that, in contrast to the 2018 event, this year's event points to significant instability in the dynamics of the polar vortex. There are clear suggestions that the polar vortex is breaking and reforming again over short time scales, which is interesting.


Where does the 2015 Nepal earthquake rank amongst earthquakes since 1900? Wikipedia provides a list of deadly earthquakes since 1900. Where would the April 2015 Nepal earthquake (magnitude currently estimated as 7.8 or 8.1) rank in this list, in terms of magnitude?

About 80th.

I counted the earthquakes of each magnitude on the List of deadly earthquakes... article. If the Nepal earthquake is about M7.8, then it's in the range 69th to 86th on that list:

Note that there are more earthquakes than this in recent history, the list has already selected for deadliness. Also note the point in the comments about different magnitude measures in the list, and the fact that the list is a few years out of date. I don't think these things change the answer.


What kind of cloud is this? I would like to know if anybody knows the name of this cloud formation.

The picture was taken in Bern Switzerland, just before a cold front moved in. I am thinking about roll clouds or Asperatus undulatus... It was wavy but the clouds formed rolls.

I think it is stratocumulus. Sometimes it rolls like that. Nice picture


Hyperspectral Detection of Ore How can I use hyperspectral satellite imagery to remotely detect copper or any prespecified mineral deposit in general?

Where can I find a database of the absorption and reflection bands of various ores, and what satellite imagery source could give reliable data?

Hyperspectral analysis is being used in mining and exploration extensively as a cheaper and quicker alternative to the likes of x-ray fluorescence, x-ray diffraction and others. Hyperspectral is even being used on an active mining faces with scanners installed on excavators and processed image being fed to a computer display that operator can use to direct digging of ores.

Now, as to the crux of your question - no, or at least very difficult. The problem with hyperspectral for ranged resource detection is that it primarily uses visual and near-infrared parts of spectrum. These wavelengths are very easily absorbed/scattered by everything and, therefore, they lack any penetration.

In most cases Earth's surface on satellite imagery will be covered by vegetation and various recent sedimentary formations which will make it nigh impossible to 'see' the bedrock potentially containing ore-bearing rock types and mineralogies.


How to identify a predator's coprolite from an herbivore's? I have a coprolite that is 8" by 5" and weighs 8 lbs. The shape is similar to a lumpy brain, the colors below outer crust are deep red and the crust is pastel green and grey. It has a strong density and can't be chipped with a hammer. It came from the Grand Canyon.

Here are some pics:

If it is a predator's coprolite you should expect to see bone fragments. Coprolites from herbivores? I would expect them to be pretty rare as there is almost nothing likely to fossilize.
As for meteorites, they come in many forms: stones, irons, palasites, chondrites. The candidates need a good description. A weathered heat ablation surface is the most obvious characteristic to look for. In all cases the rock identification is best achieved with a polarizing microscope, unless it is something very obvious like an iron meteorite.


Potassum-Argon Dating and Proportions of Daughter Products in Potassium 40 Decay Channel So Potassium 40 decays in such a way that roughly 89% of it becomes Calcium 40 and 11% of it becomes Argon 40. When they list these figures are they implying that after 1 half-life, of the 50% of the material that decayed to daughter products, 89% of that 50% is Calcium 40 and 11% is Argon 40?

Furthermore, does this mean that those will be the proportions of the daughter products in any given number of half lives?  Is the partitioning of the decay probability to 89% Calcium and 11% Argon  only observed at half-life intervals? Or is this constant throughout the decay chain, such as in between half-lives as well?  It should be constant (89% and 11%) throughout? Right? I had recently read some confusing literature on the subject and began to doubt my own understanding.

Potassium 40 has a half life of 1,300,000,000 years,  which means that within that time half of the 11 percent which you refer to will have decayed to form Argon 40. Potassium 40 has two modes of decay, which is unusual for a radioactive isotope. Only 11 percent of it becomes argon 40, the remaining 89 percent decays by a different mode and becomes Calcium 40. but there is no need for you to worry about Calcium 40, it is the 11 percent of K40 which becomes Argon 40 which is useful in dating ancient rocks. Fortunately geologists don't have to wait until it has completed one full half life for it to be useful. By assessing the amount of Argon which has accumulated within the material since it was ejected by volcanoes in pristine condition and had no Argon at all in it, geologists can get a rough idea of the age of the rocks. The potassium/argon method is very tricky to carry out and error can easily creep in.


How do we detect floods? How do we know that there was a flood at a certain place at a certain time.

For example if there was a flood in place A 200 years ago. How could we detect it?

Floods are associated with considerable sediment transport and higher than normal water levels.
Therefore, the study of sediment layers in river banks, lake bottoms or the ocean floor can reveal large sediment deposition events, that could be associated with floods or landslides. The characteristics of the sediments can be used to identify the process that generated it, and the organic matter trapped within the sediments can be used to date the time of the flood.

Here is an example of how a sediment layer from a flood looks like in a sediment core

It is taken for a paper that might be interesting to you: Lake Sediments as Archives of Recurrence Rates and Intensities of Past Flood Events. The image in the left is a picture of the sediment core (with a overlay showing the changes in reflectance along it).


Do seismic travel times from one location to another differ based on factors other than distance? Bit puzzled why it appears that seismic travel times from one location to another appears to just be a function of the distance, and not any other factors.

Do seismic travel times from one location to another differ based on factors other than distance?

Yes

The biggest controlling factors are:

Distance
Velocity Model
Composition (though velocity model and composition are related)

I believe you understand the first factor, so I will focus on the other two. The most common GLOBAL velocity model is PREM, which is depicted below(Image Source):

Velocity models basically assume the internal P and S velocity structure of Earth. If the crust is thinner than average in the area where the source is, the arrival times will be faster than if the crust is thicker than average, though depending on the distance this could be negligible. This is because seismic waves travel faster in than they do in the crust, so the least time tends to involve travel through the mantle.

The other controlling factor is composition, or in other words, heterogeneities within the earth. Depending on the composition the wave travels through, arrival times could be slower or faster. For example, imagine an interplate earthquake traveling through a subducting slab and into a seismometer: the arrival times are slower because the wave speed of lithosphere is slower than the wave speed of mantle. In fact, its these deviations from our velocity model predictions that help us find heterogeneity in the earth to begin with! This is essentially how we find our natural resources, though instead of using earthquakes as the source we use man made active seismic waves.


Is it ever possible for an continental plate to subduct under an oceanic plate? It is well known that oceanic plates subduct under continental plates. This may be attributed to the plate's age and density, plus the water on top of it.
So I was wondering if it is ever possible for a continental plate to subduct under an oceanic plate, perhaps if the oceanic plate is covered with shallow water? I've tried to search up on this question on many search engines and sites but to no avail. Thanks for your answer!

No it is not possible because the continental crust's density is lower.
Conversely, oceanic plates can subduce under continental ones because they are heavier. This is because continental crusts are formed by granites and sedimentary materials. Their density rounds $2,7g/cm^3$, granites ones, while oceanic crust rounds $3g/cm^3$, basalts and gabbros ones.
Oceanic plates start to subduce at a certain age. Presently there are not pre-Jurassic oceanic plates that do it. This is related with the stack of hidrated sediments over the igneous materials.

An exception to this are ophiolites, where oceanic plate obduce continental one. This is not happening presently at any place on Earth, but there are fossilized examples as Semail Ophiolite at Oman.


When sea level rises, does the increased ocean area cause the earth to cool down somewhat? When the sea level rises, more of the planet's area is watery and less of it is land.  Does this change in surface condition result in a change in global warming, such as a decrease in the net radiation watts that we expect for the globe?  How does this change affect other "forcings" like radiative and water vapor?

As you say, land and water albedos are very different. Meaning that a square meter of water, in average, absorbs more energy from the sun than a square meter of land. Also water transfers heat vertically more efficiently than land due to convection and it also affects climate by providing a ready moisture source.

That said, changes in the surface of land vs water do have an impact on climate. However, the change in water surface area due to sea level rise is very small compared with other changes in land/water surfaces. Let's crunch some numbers to see it more clearly...

Lets consider a good approximate of the length of the global shoreline of 620,000 km (a precise number is impossible to get due to the coastline paradox). Now, at current sea level rise of 3.2 mm/year, 30 years would mean about 10 cm of sea level rise. If we assume that the typical slope is such that this moves the shoreline also 10 cm forward, the associated area increase would be:

$620000\, \text{km} \times 0.0001\, \text{km} = 62\, \text{km}^2$

And this is negligible compared with other effects like the drying of the Aral sea (~28,000 km$^2$), the construction of the Three Gorges Dam (1,084 km$^2$), or even the construction of the Palm Islands in Dubai (80 km$^2$).

Even if our very rough calculation above is multiplied by ten or even one hundred, the contribution of sea level rise would remain small compared with other changes.

At a global scale over the last 30 years there was a net increase of 58,000 km$^2$ of water surface, but mostly due to natural processes or large infrastructure projects. Sea level rise played just a very minor role in those changes.  Indeed the following figure from the paper Earth's surface water change over the past 30 years shows changes from land to water in blue and changes from water to land in green:

Now, what's the effect of this increased water surface area (even if it is not due to sea level rise), that's another question that I won't get into in detail. But in general it will be a warming effect, both because of the lower albedo of water, and because of the warming effect of low clouds. However, the actual effect will depend on where the new water bodies are located; some extra water near the sea wouldn't have the same impact as some extra water in the middle of a desert.


Uncertainty In ERA-Interim data Greeting,
What is the estimated uncertainty value in Temperature, relative humidity, U and V winds of ERA-Interim data?

There is no traceable uncertainty associated with each datum in the ERA-Interim reanalysis.

However, in ERA-5 there is an ensemble.  This multiplies the data volume, but it means you can use the spread between the ensemble members to get an estimate.  See ERA-5 page.  ECMWF want us to use ERA-5 now anyway.


What is this strange feature on Mars in Valles Marineris While I was browsing Mars on Google Earth, I stumbled upon an interesting feature on one of the slopes of Valles Marineris. The feature seems unique in the sense that I couldn't find any similar element on the valley.

It made me think of sand that just fell from the clifftop or the veins of water that have already been observed on Mars (such as http://www.wired.com/2011/03/happy-birthday-mro/#slideid-591036). But it doesn't seems to match completely with this explanation.

Does any of you have seen this before from current Mars research or from similar phenomenon on Earth?

Coordinates :

14°32'25.35"S 54°15'12.43"O

Google GMail direct link :
https://www.google.ch/maps/space/mars/@-14.5528401,-54.2675885,41353a,20y,4.75h,0.44t/data=!3m1!1e3

Looking at the 2nd image in your question, namely of the vertical profile, the feature inhabits what appears to be an erosion channel to the valley floor (a very rough estimate of the erosion channel is shown below).

(Please excuse the rough-MS Paint style arrow)

The feature has the appearance of being an example of a small slope failure, a similar, but much smaller example of other much larger landslides have been observed in the Valles Marineris according to the article Long-runout landslides and the long-lasting effects of early water activity on Mars (Watkins et al. 2014).

According to research based on observations of similar larger scale features, the article Mechanisms of slope failure in Valles Marineris, Mars (Neuffer and Schultz, 2006) slope failures on Mars have been found to occur due to gravitational, fluid or seismic (i.e. 'marsquakes') influences.

The other influence as to why these landslides occur in the area is explained by Watkins et al. (2014) from observations and models based on spectral imaging and satellite image analyses, a significant amount of hydrated silicate clays contained within the stratigraphy of the Valles Marineris facilitate geomorphic processes, including landslides - the process is aptly used as the title of the Red Planet Report web-article Clays greased long landslides in Valles Marineris.


How quickly do landslides occur? When a landslide occurs, how long does the ordeal typically last?

Obviously the answer is that they vary a lot, however, I'm talking about some specific examples such as the one in Sierra Leone in 2017, or even the landslides in the Philippines going on right now. How quickly did these (or anything similar) landslides move, or how long does it take for them to occur from start to finish?

A historic yet well observed landslide in the East Kootenays of British Columbia took approximately 100 seconds to settle, Frank Slide.  The slides at Sierra Leone and the Philippines that you mentioned are a different type of slide made of mud and other unconsolidated materials.  I cannot find any information on them but I have witness a few slides in my previous forestry work.  From my observations a slide can occur in 10s of seconds, quick slump flowing fast enough that one cannot escape if you were to be in the path, the one I witnessed took a truck off the road and about 150 meters down a shallow bank the people in the truck escaped but we lost the truck.  They also can occur very slowly, we had an area that due to changes in the drainage up slope started slumping.  The slumping started in March but didn't stop until September.  In the case of the slow slide/slump it took a hectare of forest and slowly moved it down slope and across a road very slowly.  Often the speed of the slide seems to be affected by the amount of water in the soil.  The fastest being the closest to be categorized as a debris flow rather than a slide, the other factor is the steepness of the slope, the steeper falling faster.


The effect of buildings on frost I have see this morning this curious garden where one part was covered with frost while the other was frost free.

Question 1:
What are the factor that play a role in this configuration?

My guess is radiation from the building and the wind (the frost free part being more protected from the wind by the building) but then I wonder : Will there still be these two zones after a night without any wind? (Question 2)

The left house is heated, the middle one isn't but it's inhabited, the shed is closed but not insulated and without heating source inside.
There isn't any other surrounding structures that could create shade.

The open side of the garden is facing south.

I observed the frost after sunrise, but before the sun rays were reaching the garden.

I would say the most relevant factor involved would be Radiative cooling, with ground areas closer to the buildings not losing as much heat energy as the buildings act to reflect some of the radiation back keeping those areas frost free, while open exposed areas lose more energy and experience frost.


Why is Earth not a sphere? We've all learned at school that the Earth was a sphere. Actually, it is more nearly a slightly flattened sphere - an oblate ellipsoid of revolution, also called an oblate spheroid. This is an ellipse rotated about its shorter axis.  What are the physical reasons for that phenomenon?

Normally in the absence of rotation, the natural tenancy of gravity is to pull the Earth together in the shape of a sphere.

However the Earth in fact bulges at the equator, and the diameter across the equatorial plane is 42.72 km more than the diameter from pole to pole.

This is due to the rotation of the Earth.

As we can see in the image above, the spinning disk appears to bulge at the points on the disk furthest from the axis of rotation.

This is because in order for the particles of the disk to remain in orbit, there must be an inward force, known as the centripetal force, given by:

$$F = \frac{mv^2}{r},$$

where $F$ is the force, $m$ is the mass of rotating body, $v$ is the velocity and $r$ is the radius of particle from the axis of rotation.

If the disk is rotating at a given angular velocity, say $\omega$, then the tangential velocity $v$, is given by $v = \omega r$.

Therefore,

$$F = m\omega^2r$$

Therefore the greater the radius of the particle, the more force is required to maintain such an orbit.

Therefore particles on the Earth near the equator, which are farthest from the axis of rotation, will buldge outwards because they require a greater inward force to maintain their orbit.

Additional details for more mathematically literate now that mathjax is enabled:

The net force on an object rotating around the equator with a radius $r$ around a planet with a gravitational force of $\frac{Gm_1m_2}{r^2}$ is the centripetal force given by,

$$F_{net} = \frac{Gm_1m_2}{r^2} - N = m\omega^2r,$$ where $N$ is the normal force.

Re-arranging the above equation gives:

$$N = \frac{Gm_1m_2}{r^2} - m\omega^2r$$

The normal force here is the perceived downward force that a rotating body observers.  The equation shows that the perceived downward force is lessened due to the centripetal motion.  The typical example to illustrate this is there is an appearance of 0 gravity in a satellite orbiting the Earth, because in this situation the centripetal force is exactly balanced by the gravitational force.  On Earth however, the centripetal force is much less than the gravitational force, so we perceive almost the whole contribution of $mg$.

Now we will examine how the perceived gravitational force differs at different angles of latitude.  Let $\theta$ represent the angle of latitude.  Let $F_G$ be the force of gravity.

In vector notation we will take the $j$-direction to be parallel with the axis of rotation and the $i$-direction to be perpendicular with the axis of rotation.

In the absence of the Earth's rotation,

$$F_G = N = (-\frac{Gm_1m_2}{r^2}\cos\theta)\tilde{i} + (-\frac{Gm_1m_2}{r^2}\sin\theta)\tilde{j}$$

It is easily seen that the above equation represents the perceived force of gravity in the absence of rotation.  Now the centripetal force acts only in the i-direction, since it acts perpendicular to the axis of rotation.

If we let $R_{rot}$ be the radius of rotation, then the centripetal force is $m_1\omega^2R_{rot}$, which for an angle of latitude of $\theta$ corresponds to $m_1\omega^2r\cos{\theta}$

$$N = (-\frac{Gm_1m_2}{r^2} + m_1\omega^2r)\cos{\theta}\tilde{i} + (-\frac{Gm_1m_2}{r^2})\sin{\theta}\tilde{j}$$

By comparing this equation to the case shown earlier in the absence of rotation, it is apparent that as $\theta$ is increased (angle of latitude), the effect of rotation on perceived gravity becomes negligible, since the only difference lies in the $x$-component and $\cos\theta$ approaches 0 as $\theta$ approaches 90 degrees latitude.  However it can also be seen that as theta approaches 0, near the equator, the $x$-component of gravity is reduced as a result of the Earth's rotation.  Therefore, we can see that the magnitude of $N$ is slightly less at the equator than at the poles.  The reduced apparent gravitational pull here is what gives rise to the slight bulging of the Earth at the equator, given that the Earth was not originally as rigid as it is today (see other answer).


What definition of "seamount" is used by the largest utilised databases of seamounts? Appears that answering what seamounts are is a non-trivial question. My take is what matters is data, since authoritative opinions on the topic are at best subjective. As such, my position is the definition used by the largest (utilized) database of seamounts would be the best source understanding what seamounts are and are not.

What is the largest utilised database of seamounts?
What definition is used by the largest utilised databases of seamounts to define seamounts?
Does it include formations that are above water?

The largest database of seamounts contains over 33,000 seamounts and was created by Yesson, Chris; Clark, MR; Taylor, M; Rogers, AD.  Link

For their list, they defined seamounts and knolls as

  Seamounts and knolls are 'undersea mountains', the former rising more than 1000 m from the sea floor
  Yesson, C et al. (2011): Lists of seamounts and knolls in different formats. doi:10.1594/PANGAEA.757564

In their paper, they set the definition of a seamount as a sub-surface feature, not breaking the water.  This puts the highest elevation in their dataset is 2m below sea level.  The pulled their definition from Morato, et al (2008), which states: "seamounts are defined as any topographically distinct seafloor feature that is at least 200 m higher than the surrounding seafloor, but which does not break the sea surface."  Then, they subdivided the features into knolls and seamounts at an heigh of 1km (with knolls being between 200m and 1km in height).

So, specifically answering the question, that databases uses the Morato, et al (2008) definition, which excludes super-surface seamounts.


Yellow and brown spots on leaf tip On a barley farm, there are yellow and brown spots on leaf tips.
Possible causes:

Some kind of parasite
Weather condition
Bad seed

Looks like some farms using the same seed are affected

What might be the actual cause? What could be the solution?

I would suggest you contact your local government agricultural authority.
It looks like the barley crop might be infected with a pathogen, such as a fungus.
It could be a form of barley rust.
Different regions of the world have different forms of rust.
Your local agricultural authority should be notified in case the outbreak poses a bio security risk in your region.