GOES image: parallel trains of clouds. What to make of them? Here is a GOES visible image from today, 2019-12-01 about local noon, around Nova Scotia. Note the parallel trains or streaks of clouds, running approximately northwest to southeast.

A few hours ago, the wind was from the NW at 30-40kph (at Halifax); for the past 3 hours it's been from the NNW at about 25kph.

What's the physics behind the streaking? Is it simply cumulus clouds from convection being blown downwind?

The species is Stratocumuls undulatus Sc un.

They can form for example when cold, dry air moves over a warmer ground layer. A sharp wind shear at the boundary layer blows these waves. (Wikipedia on Sc).

They are not to be confused with Sc radiatus or yet another form, the so-called "cloud streets", which form along the wind direction.


Does Xenon really covalently bond to oxygen within quartz? Wikipedia's Xenon; occurrence and production says

  Within the Solar System, the nucleon fraction of xenon is $\small\mathsf{1.56 \times 10^{-8}}$, for an abundance of approximately one part in 630 thousand of the total mass. Xenon is relatively rare in the Sun's atmosphere, on Earth, and in asteroids and comets. The abundance of xenon in the atmosphere of planet Jupiter is unusually high, about 2.6 times that of the Sun. This abundance remains unexplained, but may have been caused by an early and rapid buildup of planetesimals—small, subplanetary bodies—before the heating of the presolar disk. (Otherwise, xenon would not have been trapped in the planetesimal ices.) The problem of the low terrestrial xenon may be explained by covalent bonding of xenon to oxygen within quartz, reducing the outgassing of xenon into the atmosphere.

I know that crystals can provide unusual amounts of local pressure. For example, this answer explains that ice VII has been discovered at room temperature as inclusions in diamonds.

Question: But I'm still surprised to read about covalent bonding of xenon with oxygen within quartz. How/where has this been observed in naturally occurring mineral or rock, and what is the evidence of covalent bonding?

Not sure this is appropriate for Earth Science SE (Chemistry SE would be a better fit), but the answer is "maybe".  quoting from the same Wikipedia article:

Three oxides of xenon are known: xenon trioxide ($\small\mathsf{XeO_3)}$ and xenon
tetroxide $\small\mathsf{(XeO_4)}$, both of which are dangerously explosive and powerful
oxidizing agents, and xenon dioxide $\small\mathsf{(XeO_2)}$, which was reported in
2011 with a coordination number of four.[97] $\small\mathsf{XeO_2}$ forms when xenon
tetrafluoride is poured over ice. Its crystal structure may allow it
to replace silicon in silicate minerals.[98] The $\small\mathsf{XeOO^+}$ cation has
been identified by infrared spectroscopy in solid argon.[99]

Cited references
97.
Bell, C.F. (2013). Syntheses and Physical Studies of Inorganic Compounds. Elsevier Science. p. 143. ISBN 9781483280608.
98.
Cockett, A.H.; Smith, K.C.; Bartlett, N. (2013). The Chemistry of the Monatomic Gases: Pergamon Texts in Inorganic Chemistry. Elsevier Science. p. 292. ISBN 9781483157368.
99.
Brock, D.S.; Schrobilgen, G.J. (2011). "Synthesis of the missing oxide of xenon, XeO2, and its implications for earth's missing xenon". Journal of the American Chemical Society. 133 (16): 6265–9. doi:10.1021/ja110618g. PMID 21341650.
Evidence is given in Crepisson et al (2019) for xenon (as $\small\mathsf{XeO_2}$) incorporation into silica at high pressure.  XRD measurements show changes in the lattice consistent with xenon substituting for silicon in the oxide structure.


What is the average cholorphyll concentration for the ocean? For chlorophyll-a, measured in mg/m3, what are the average values for:

Open ocean in general (global)
Northen latitudes (N. Atlantic Ocean)
Coastal waters around the UK (North sea, Irish Sea, etc)
equatorial waters

Is there any pattern regarding plankton productivity and ocean climate that would help answer this? I.e. warmer waters with higher levels of sunshine (Mediterranean) have higher productivity, than colder waters (North Atlantic). Or are there too many factors involved (stratification, eutrophication) to generalise for the oceans?

Behrenfeld and Falkowski, 1997 have maps of cholorphyll concentration for the entire world on pages 11-13 of the linked paper. The maps are divided by into yearly concentration and seasonal concentration, with the maps filled out from experimental data by two different modeling methods.

These maps are in mg C / m$^2$ / year, but they offer the normalization of $$\frac{4.6 \text{mg C / hour}}{1\text{ mg Chlorophyll}}.$$ Chlorophyll production varies by optical depth, which is the distance that light can penetrate into the water. Optical depth depends on various characteristics of the seawater like sediment node, so it doesn't have an exact analogue to water depth. However, Fig 1A supports a conclusion that plankton production is reduced by an order of magnitude at depth of 20 meters, and by 2 orders of magnitude by 60 meters.

If we confine the chlorophyll to entirely the top 60m of the ocean, then we can convert $$\frac{1 \text{ mg C}}{\text{m}^2\cdot\text{year}}\cdot\frac{1 \text{ mg Chlorophyll}}{4.6\text{ mg C / hour}}\cdot \frac{1 \text{year}}{8760 \text{ hours}} \cdot \frac{1}{60 \text{m}}= \frac{0.41 \text{ ng Chlorophyll}}{\text{m}^3}.$$

Using this convertion specifically on map A on page 11 of the linked paper, I get for your answers:

Open ocean in general: 75-150 g C/m$^2$/year $\rightarrow$ 30-60 $\mu$g/m$^3$
N. Atlantic Ocean: 150-250 g C/m$^2$/year $\rightarrow$ 60-100 $\mu$g/m$^3$
Coastal waters around the UK: 300-450 g C/m$^2$/year $\rightarrow$ 125-185 $\mu$g/m$^3$
Equatorial waters: 100-200 g C/m$^2$/year $\rightarrow$ 40-80 $\mu$g/m$^3$


Why do Euler poles for plate motions not stay fixed in time? Surely if a plate motion is a straight line across a sphere, this can be described by a fixed Euler pole, however I've been reading about a problem which I confess I don't fully understand which is titled the "Three Plate Problem" and talks about if three plates are moving relative to eachother, one of these relative motions will be described by an Euler pole that wanders. Why is this?

I think I can do an OK job explaining, but I could not find a proper diagram to illustrate this. Perhaps, if you could locate a professor at your university to draw this out and explain it would be best, as doing an illustration on computer is a bit time consuming.
Lets start out with a two plate system, plate $A$ and $B$.

${}_{A}E_B$ is the relative plate motion of $B$ with respect to $A$, meaning that $A's$ motion is fixed while $B$ is free to rotate.

Since this is only a two plate mode, $A$ and $B's$ relative plate motions are always the same, no matter where they are in time, you can always go back and forawrd in time, as nothing changes the relationship between  $A$ and $B$. IE, there is nothing to interfere with their relative plate motions.

Only 1 Euler pole is needed to fully describe the motions of two plates, in general. Lets now add a 3rd plate, plate C:

${}_AE_B$ is the plate motion of $B$ with respect to $A$

${}_BE_C$ is the plate motion of $C$ with respect to $B$

${}_CE_A$ is the plate motion of $A$ with respect to $C$

These three motions describe the 3 plate system.  So now lets imagine we are standing on $A$ looking at $B$ and $C$, what happens? Since we are on $A$, we move relative to $C$, and $B$ moves relative to us. But wait, a problem occurs, because $C's$ motion is dependent on $B$ being relatively fixed, and $A's$ motion is dependent on $C$ being relatively fixed, meaning if two poles are fixed, the third and final pole must wander to accommodate the reference frame. IE, because All of the plates are moving relative to each other (depending on the reference frame), the Euler poles are changing over time. This gets more complex as we keep on adding plates into the system.


Does Antarctica have a lot of aquifers? I got to thinking about freshwater on Antarctica. Obviously, there is a lot of freshwater ice. However, the deeper you go underground, eventually the dirt will be warmed geothermically. So does the geothermal heat melt the ice and create a lot of underground water? Or does surface ice have zero correlation with underground water?

I have no idea how aquifers are technically made. This is just idle curiosity/speculation from your average Joe.

Yes. So far as aquifers are concerned, Antarctica is just like any other continent. The Ice is 4 kilometres thick in places, but at the bottom there is water. If there is any place where water is not found at the base of the ice sheet, there will be an aquifer within a few miles. There are about 400 sub-glacial lakes in Antarctica, the most well known being Lake Vostok in Russian Antarctic Territory.

Lake Vostok is very large and deep, covered by 4 Km of ice, and Russian scientists have recently drilled down to it in the hope of finding living organisms. Although it is completely dark down there they were not disappointed, and many micro-organisms were found, but no vertebrates. There is a large, dry valley deep in Antarctica where precipitation is negligible and bare ground is everywhere, but how this affects underground water resources I don't think anyone could say.


How do glaciers move? Could Antarctica be separated? Consider the example of the Larsen Ice Shelf. Ice platforms are attached to glaciers such that they prevent surrounding warm air from directly melting the glaciers.  This is an important aspect of ice platforms.

What are the mechanisms of glacier movement?

When we talk about glacier movement, do we consider advance and retreat due to melting and snow deposition, or is the study of glacier movement more about the fluid sheet underneath the glacier that comes in contact with the rocks, which allows the glacier to move downhill?

With this second type of movement, glaciers can separate.  So is it possible for Antarctica to separate and disappear?

Glaciology is a large field of research, and I cannot include all aspects in a short answer. I'll try to give some concepts that can help you in your understanding of the cryosphere.

Glaciers are, per definition, moving due to gravity towards lower altitudes. There are some exceptions, e.g. rock glaciers are the stagnant remain of a moving glacier.

Large bodies of ice are called either ice caps (if smaller than 50,000 km$^2$) or ice sheets (if larger). Today, we only have the Antarctic ice sheet and Greenland, but during times of larger glaciation, large parts of the Northern Hemisphere were covered. Within the ice sheets, fast flowing areas are referred to as glaciers. Where those areas are formed depends on many parameters such as the mass balance, the basal melting, the topography, etc.

If the glacier or ice sheet reaches the ocean, it becomes buoyant. For larger glaciers, the section near the coast remains bulky enough to remain in contact with the ground.  The point of extent where the ocean reaches under the ice is called the grounding line - a subglacial beach, if you like.
As it's floating, tidal variations moving the ice sheets help it to break up, but in some cases, depending on thickness and topography, it can float in a rather uniform shape which we call an ice-shelf.

The same way as rivers and lakes are formed as rainwater floats towards the oceans, ice sheets and ice caps are formed as snow falls in cold areas, where it doesn't get warm enough to melt during the summer. As the snow accumulates it forms firn and later ice. The ice starts moving as the gravity and shear forces make it unstable.

Eventually the ice will melt, either on the surface due to warm air, e.g. during summer months, or in the oceans as it calves off into icebergs and is warmed by the ocean. Glaciers can also melt on the base due to heat flux from the Earth beneath or due to pressure. In this way, subglacial lakes are formed under the ice.

Large parts of Antarctica are situated below sea level. Partly this is due to the intensive erosion of fast moving ice, but the main reason is that the weight of the ice pushes down the crust into the mantle. If the ice sheet melts, the mass decreases and the land under it will rebound. This happens almost on a human timeline. Some areas, such as Hudson Bay, Scandinavia, and the Antarctic Peninsula, have a fast uplift making sea into land.

Maps from Quantarctica. 1: Ice flow velocity. 2: The topography under the ice. 3: Geoid height (not so relevant for your question). 4: Snow accumulation and blue (=old, hard) ice.

As I've suggested before, I recommend you to download the Quantarctica package. It's rather big but free and easy to use. You can investigate how the ice flows are forming the ice sheet and how the bed map looks under.

The large chunk of Larsen C Ice Shelf that just broke off, doesn't directly reshape the Antarctic continent or cause any change in global sea level, as it was already floating. However, if the ice shelf becomes more unstable, it can affect the ice sheet left trailing it and the flow pattern of the glaciers, and that would have a large impact on most human activities - and beyond.


Differences between linear airy wave theory and Stokes' 5 wave theory? and it's application What is the difference between linear airy wave theory and 5th order Stokes wave theory? What is the differences in terms of application. I am looking more on offshore structure analysis aspects.

Thanks.

You should find what you're after within the following:

https://rules.dnvgl.com/docs/pdf/DNV/codes/docs/2014-04/RP-C205.pdf

If not, one of their other documents should contain the information.
I hope this finds you well.


does silt form from sand ; does clay form from silt I believe that sand, silt, clay are defined by size. But are they also generated by different processes and from different materials? Alternatively do sand particles ultimately weather to make silt, and do silt particles ultimately weather to make clay?

Sand to silt is a physical process, silt to clay is most often a chemical process.

Sand and larger rocks are physically weathered to form silt, everything from frost wedging to simple abrasion.

Clay is a different creature entirely, for a start there is a disagreement about the definition of clay across disciplines. Several disciplines of geology use different size based definitions.  Clays can for from physical or chemical processes depending on the type of clay. Most often clay form from the hydrolysis of tiny mineral particles.


What are the implications of the recent discovery that huge oceans exist close to the mantle of the Earth? I was of the notion that as we get deeper into the Earth, it gets hotter and hotter. If so, how can there be huge oceans (they seem bigger than our Pacific) exist at such a place? If so, what are the possible implications of this discovery in shaping our understanding of the planet? I'm very curious to find out.

I am going to assume that you are referring to recent new stories with titles like "Rare Diamond Confirms That Earth's Mantle Holds an Ocean's Worth of Water" (Scientific America).

These articles are referring to research published in Nature: Pearson, D. G. et al. (2014).  The researchers found an inclusion of ringwoodite inside a diamond.  Here is a quote from the Nature article about the paper...

  Using infrared spectroscopy, Pearson’s team found that its tiny fleck
  of ringwoodite contained about 1% water by weight.  “That may not
  sound like much,” Pearson says, “but when you realize how much
  ringwoodite there is, the transition zone could hold as much water as
  all the Earth’s oceans put together.”

This doesn't mean that there is a liquid ocean of water within the transition zone.  There are minerals that are considered "hydrated" because they contain hydroxide ions.  Examples of these are the serpentine group and micas.

Ringwoodite can contain hydroxide ions within its structure, and these ions are the "water" that was measured.  If you were to lower the pressure, and increase the temperature, the water would be liberated from the mineral.  The point is that there are not huge oceans of liquid water within the mantle of the Earth; the water is locked up in the structure of certain minerals.

There are interesting implications from this research discussed in the Nature News article about the research.

Nature News Article


Time relativity relating to Carbon dating? Theoretically if in early years the earth was moving at an astronomically different pace (whether in orbit or rotation, whatever sounds better) wouldn't that alter the science of carbon dating? As I understand time relativity, If the speed at which the earth was moving changes, the elements and organisms there-in would experience time at a different rate.  Would we not expect that carbon would decay faster?  I know it's just theory but I'd like to know if this theory could be proven false. And is there any existing research that you are aware of that would support or debunk this theory?

Earth travels along its orbit at about 30km/s. If you plug that number into a time dilation calculator, you'll find that one second on Earth passes every 1.0000000050069 seconds in a Sun-centric reference frame.

Carbon-14 dating is good only to about 40,000 years into the past; Earth's time dilation would reduce that 40,000 years by a little under two hours, or far below the precision of the technique.

Edit: I'd like to address three more issues. First, the rotation of the Earth's surface only results in about 0.5km/s at the equator, and so is insignificant compared to the orbital velocity. Second, nothing has changed the Earth's orbit for many millions of years, probably for billions of years, so that would also have no effect on the dating.

Third, and more important, we're all traveling along on the Earth at (approximately) the same speed. So you, I, and a group of C-14 atoms in a fossil will all experience the same time dilation.


How accurately can a tsunami be predicted? Have there been any successful evacuations? With the current instruments in hand, how accurately can we predict tsunamis? Please consider me as a novice with only basic information how tsunamis are formed.

Has there ever been a successful evacuation in history in regards to incoming death waves?

The ability to predict depends on the cause of the tsunami. Earthquakes can't be predicted, so a tsunami caused by an earthquake can't be predicted. A meteor can be tracked for a considerable time in space before sticking earth so a tsunami caused by an meteor strike can be predicted.

There is also the possibility of a tsunami early warning system. There are currently sensors in some parts of the ocean which can detect a tsunami before "landfall" and provide an early warning system. Think of it somewhat like tracking a hurricane which generally takes a lot longer to reach land.

In a webpage it was reported that "in 1933 HVO [Hawaiian Volcano Observatory] used seismograms to predict (accurately) the arrival of a tsunami from a distant earthquake, and people in low-lying areas of Hawaii were for the first time successfully warned in advance." The word predict here is somewhat ambiguous. the scientists didn't know the earthquake would happen, but recognized that the earthquake would likely cause a tsunami.

Looking at the map below. Where tectonic plates connect, or where there are underwater volcanoes are prime locations to generate tsunamis.


Deuterium-less oceans Current fusion reactor schemes require deuterium and the plan is to extract it from the ocean where it can be found in small abundance. Does deuterium serve some purpose in the oceans? What would happen if there was none left?

Replacing 20% or more of the normal water in ones body with heavy water results is toxic (Kushner 1999). Then again, a number of vitamins are toxic in high doses, but vitamins are essential to human life. Could deuterium in small doses be essential to life? That's exactly what Somlyai et al. argue in their paper (Somlyai 1993).

However, it's a bit premature to start shouting "peak deuterium." We don't even know if ITER will prove to be successful, let alone point the way to commercially successful fusion. Even if it does prove to be successful, the deuterium consumption rate will be tiny. By the time our children's children's ... children would have to shout peak deuterium, we'll have gone on to even bigger and better things (if humanity lives that long).

Kushner, et al. (1999), "Pharmacological uses and perspectives of heavy water and deuterated compounds," Canadian Journal of Physiology and Pharmacology, 77.2:79-88.

Somlyai, et al (1993), "Naturally occurring deuterium is essential for the normal growth rate of cells," FEBS letters, 317.1:1-4.


How much earth has to be moved to get one tonne of copper I am trying to make sense of the mining process of minerals or metals.

I found two measures related to waste: the stripping ratio (which is usually larger than 3:1 for copper, i.e. 3 tonnes of waste for one tonne of copper ore) and the ore grade (which is <5% for copper, i.e. out of a tonne of copper, you can extract only 50kg copper). Is my interpretation correct?
How do they stack up in the mining process? Using a 1% ore grade and 3:1 stripping ratio, does that mean that to get 1 tonne of copper, we need to move 400 tonnes of earth, as we need 100 copper ore that comes along with 300 tonnes of waste?
Does the same logic apply to rare earth mining as well? I found the following numbers for the Bayan Obo mining district in China (see [1]):

Neodymium content: 18.5%
REO(rare earth oxide) grade: 4.1%
Recovery rate: 50%
Tonne mined/tonne REO: 49

So according to my understanding, to get one tonne of neodymium, we need 49/(18.5%*4.1%*50%) = 12920 tonnes. Is that correct? That would be a lot of mining for a tonne of neodymium.
Ultimately, I am interested in the amount of earth that has to be moved/mined to get one tonne of copper/other metals (which of course depend of course on the mine and the ore grade).
Thanks a lot :-). I am trying to make sense of the numbers to get a better understanding of the footprint of certain technologies (e.g. given that there are 2 tonnes of neodymium in a modern wind generator, we need to remove 26,000 tonnes of earth to get the neodymium for this (if my numbers are correct).
Best regards,
ProGeologist.
[1] Rare Earth mining: https://ui.adsabs.harvard.edu/abs/2013JOM....65j1327T/abstract - tables on page 1329 and 1331

Your questions regarding stripping ratio only apply to open pit mines. They produce much more waste rock than underground mines. Typically they mine more waste rock than ore.
Underground mines are more surgical and depending on circumstances some of the waste rock they produce is used as backfill in mined out stopes.

the stripping ratio (which is usually larger than 3:1 for copper, i.e. 3 tonnes of waste for one tonne of copper ore) and the ore grade (which is <5% for copper, i.e. out of a tonne of copper, you can extract only 50kg copper). Is my interpretation correct?

You are partially correct. In this scenario the amount of copper that would be delivered to the processing plant (also known as a mill or concentrator) in mined ore is 50 kg, i.e the amount of metal in the mill feed is 50 kg.
To get usable copper metal from the ore, after mining, it needs to treated in a processing plant to concentrate the copper bearing minerals and to remove the gangue minerals. The copper concentrate is then sent to a smelter to produce copper metal. The waste from the concentrator is sent to the tailings dam/pond/storage-facility.
If you account for the recoveries of these two processes, typically 80% for concentrating and 90% for smelting, the amount of copper metal produced from 50 kg of copper in mill feed would be 36 kg (50 x 0.8 x 0.9).

How do they stack up in the mining process? Using a 1% ore grade and 3:1 stripping ratio, does that mean that to get 1 tonne of copper, we need to move 400 tonnes of earth, as we need 100 tonnes copper ore that comes along with 300 tonnes of waste?

Yes. Such a scenario would give you 1 tonne of copper in mill feed.
Unfortunately, the paper you refer to was most likely written by primary metallurgists, or possibly chemical engineers, and not mining engineers. The emphasis of the authors is on the amount of metal recovered from mining and the amount of energy required to produce usable metal from various mining projects, not the overall quantities of material mined.
Regarding your question about the Bayan Obo mining district in China your calculations are not correct. Also, from the paper you refer to you cannot obtain the total amount of earth mined, ore and waste, because there is no reference to stripping ratio.
As you state, from Table I of your reference, the proportion of neodymium in REM (REM being rare earth metal)is 18.5%. Table II states Tonnes mined/Tonnes REM is 59. This usually refers to the tonnes of ore mined and supplied to the mill, not the total tonnes of earth mined (ore and waste). Additionally, as stated in Table II and reiterated in Table IX, the recovery from the primary processing plant is 50%.
Now, 1 tonne of REM supplied to the mill contains 0.185 t (185 kg) of neodymium. With 59 tonnes of ore mined per tonne of REM, the amount of ore mined and supplied to the mill to get 1 tonne of neodymium is 59/0.185 = 318.9 tonnes.
The mill only recovers 50% of the metal supplied to it. Therefore, for the mill to recover 1 tonne of neodymium 637.8 (318.9/0.5) tonnes of ore must be supplied to the mill.


Glowing Orange lakes seen from airplane at night I recently observed a phenomenon during a nighttime flight over upper Midwest of USA-specifically over Marquette, MI.  In what is a lightly populated area, I observed several very large rectangular regions glowing bright orange yellow, as if they were illuminated.  I believe they were drainage ponds from iron mines.  I theorize that the moon was at a critical angle and I saw a speculat reflection from these orange ponds that can be seen on google earth at 46°24'22"N 87°31'01"W · 1,244 ft.  Have you ever observed or heard of such a thing?  It was approx 01hr on Jan 11, 2019.

The orange lakes are most likely tailing dams, also known as tailings storing facilities given that they located near an open pit iron ore mine.

Once iron ore has been mined it is usually sent to a processing plant to increase the grade (amount) of iron in the product the mine exports. It does this by removing as much waste material as possible. Sometimes the waste is low grade iron ore (very low concentration of iron);.

Usually the ore is crushed, ground and treated chemically. What is deemed as waste (tailings) is sent/dumped to a tailings dam. There will always be an amount of unrecoverable iron in the tailings which will give the tailings a reddish color. Low Moon angles may accentuate the red or orange coloring.


How high can a mountain possibly get? Mount Everest is 8,848 metres (29,028 feet) above sea level and is the result of a continental plate smashing into another continental plate. Can a tectonic process build a mountain that's even higher? (Volcanoes excluded!)

Found an article that used a simple analytical modelling to determine how high a mountain can be. Reference

Based on simple physics, tallest a mountain will be on Earth is ~10 km.
This is based on:

Simple cone shape for the mountain. Vol ≈ $r^2 h$
Based on weight of the mountain:  Weight W ≈ $\rho g r^2 h$
Stress σ the mountain exerts on the ground underneath it is:

σ ≈ Weight/Area ≈ $(\rho g r^2 h)/r^2$ ≈ $\rho g h$
The limiting factor is the compressive strength of the rock:
Assume granite with an average density $ρ$ = 3 g/cm$^3$.
Compressive strength is $\sigma_C$ = 200 MPa = $2 \times 10^8\, N/m^2$
Stress = Compressive strength of rock  σ = $\sigma_C$ or $\rho g h_{max} = \sigma_C$.
Calculate max height:

$h_{max}$ ≈ $\sigma_C/(\rho g)$

$h_{max}$ ≈ $\frac{2 \times 10^8\, N/m^2}{3 \times 10^3 kg/m^3 \times 10\, m/s^2)}$≈ $10^4\, m$ = 10 km


What's with this anomaly in this sounding (the CAPE and CIN readings)? This sounding is from 2 hours after the 2.6 mile wide El Reno tornado on May 31 2013.

Your screenshot lists the raob as station 72357 on 2013-06-01 00Z.  Station 72357 is OUN and the sounding for that day time is available at the SPC sounding archive.

The SPC sounding analysis shows 3351 J kg$^{-1}$ CAPE and -76 J kg$^{-1}$ CIN for surface parcels.

My speculation for your anomolous non-physical values of CAPE and CIN is that the algorithm used in that software perhaps doesn't handle the lack of stratopheric data well.  The calculation of CAPE is the parcel buoyancy integrated from the level of free convection (LFC) to the equilibrium level (EL).  This sounding has no EL because the temperature data stops before the tropopause and never increases to equal the temperature of the lifted parcel.  A naive algorithm that does not take this into account would have issues calculating the CAPE and potentially produce undefined output.  I think that is the case in the software in your screenshot.


How much worse is the typical subway air, compared to street-level air pollution, in a typical city? An excerpt from a section about the capital of Taiwan, in an article I wrote about Air pollution in Taiwan:

  Further more, in greater Taipei, the outdoor PM2.5 concentration in
  the air at ground-level up until the height of three-stories is around
  ten to twenty times higher than the concentration in the air at the
  height of four-story buildings and above. Levels of other hazardous
  suspended particles such as silicon and iron were equally found to be
  significantly lower when increasing altitude. Professor Chang-Fu Wu
  (吳章甫) of the same university attributed this to dust and traffic
  pollution.

So, my question is, can this increasing pollution, when decreasing in altitude, be extrapolated to a negative (as compared to street-level) altitude as well, in a typical city? Intuitively, I would assume that parkings (don't forget about traffic tunnels) can be pretty bad, when thinking of sub-terrain places in a typical city, with regards to pollution? But what I am really interested in here, is finding out more about the increase in pollution in subways (underground transportation), as compared to the street-level.

Is this problem perhaps being mitigated partly by sucking in air from a high altitude? (this shouldn't be seen as the question, it's just a remark)

P.S. (this is also not part of the question, so please don't close this question because I wrote a remark): I think finding higher ground is actually one of the best ways to escape from pollution in cities. But of course many cities will not give this advice to its citizens ... it might be unpopular and sound bad.

Depends on what type of pollution you are talking about

Moreno et al., 2015 studied this problem in Barcelona, and compared Metro (subway) to trams, buses, and walking in various parts of the city. There is a massive overabundance of data in this paper that mostly speaks for itself, but let me summarize.

The subway was in first place or last place in most measures; it was the only system that didn't occupy the environment of the city streets. So these comparisons are probably exactly what you are looking for. Subway air had the lowest count of particulate matter, and the highest modal particle size; both of these are good. However, at the same time, the PM$_{2.5}$ (fine particulates which are particularly dangerous carcinogens) for subway and bus were notably higher than for tram and walking.

The black carbon levels were in the middle of the road; lower than for pedestrians but higher than bus or tram. However, the authors note that black carbon may have been overestimated for the subways; so these levels could have been lower.

Carbon monoxide is largely related to combustion engine usage; CO levels were lowest on the electric trams, and higher on the other modes of transportation. Carbon Dioxide, on the other hand, is largely related to other passengers breathing; CO$_2$ was highest on the crowded vehicles and much lower for pedestrians. CO$_2$, unlike the others, I don't think is a chronic health risk at the observed concentrations.

Conclusion

There is a lot of information in that paper, and I am not really qualified to judge the health risks from one factor against another. I can note that in no health measures does the subway have the worst air quality between the four transportation modes; and there is no other mode that has better air quality than the subway in all measures.

I suppose it is safest to say that, in a statistical sense across multiple measures, the subway air is not significantly more unhealthy than street level air.


Why do the earth sciences use mega-annum instead of mega-year? I've noticed that geology and related fields use mega-annum (Ma) instead of mega-year (Myr) as the unit for 1 million years.  Why is that?  Is an "annum" different from a "year" in geology?

Both mega-annum(Ma) and mega-year(Myr) designate one million years.  The distinction is that Ma is used to designate the time before present or geohistoric dates and Myr to designate a duration or span of time.  So if you want to say a rock is dated to 10 million years before the present you would use 10 Ma, and if you want to say that a rock is 10 million years old you would use 10 Myr.

There has been debate among scientific disciplines to simply adopt Ma as the standard unit.  However, the distinction that geologists have been using to distinguish between dates and durations for decades can best be illustrated as such:

  No one objects to the storming of the Bastille on 14 July 1789 (a
  date) or to the construction of Stonehenge from 2600–1600 BC (an
  interval specified by two dates). In the case of the latter, we say
  that the job took 1000 years, not 1000 BC. The distinction between
  geohistorical dates and spans of geological time is conceptually
  analogous. There is no internal inconsistency, and the International
  System of Units (SI) rules don’t apply to dates in either case because
  points in time are not units, even if they are specified in years
  (Aubry et al., 2009). The year, moreover, is not a part of the SI. It
  cannot be a “derived unit of time,” the designation proposed by the
  task group, because under SI conventions “derived units are products
  of powers of base units” (BIPM, 2006). The base unit for time is the
  second. The task group is thus intent on fixing a problem that doesn’t
  exist and in a manner that is at odds with their stated goal of
  “adherence to SI rules.”

The above quote is from the Geological Time Conventions and Symbols manuscript from 2011.  More detailed discussion can be found at this source.  This Science Blogs article from 2009 has some interesting discussions regarding this issue.


are laccolith, lobolith, dikes and sills formed of porphyritic texture? Laccolith, lobolith and batholith are shapes of igneous rocks which exist below the surface of the earth, dikes and sills too. And the way they formed by makes me think that they have a porphyritic texture, is that right? Or they have a coarse-grained texture? Because they have crystalled below the earth surface anyway?

Laccoliths, lopoliths, dikes and sills are all characteristic modes of occurrence of hypabyssal rocks, generally small in scale compared to most magma chambers. They are magmas which have cooled in a near-surface environment. None of these terms necessarily implies a particular petrologic texture. So, for example a dike or sill may be aphanitic, porphyritic, aplitic, pegmatitic or even glassy obsidian - and other less common textures. Nevertheless, many hypabyssal rocks are porphyritic. All this means is that the magma crystallized in two stages. The first stage was deeper and slower cooling, allowing some crystals to grow, sometimes to much larger size than the rest of the crystalline matrix. The second stage is when the magma is intruded at shallow depth, resulting in much more rapid crystallization of the remaining melt. Hence the porphyritic texture of large crystalls within a fine-grained matrix.


How to properly distinguish a transversal valley from a longitudinal valley? I'm confused about how to distinguish the two. Prior to making this question. I've read the wikipedia entry on the subject but it mentions that for example a transverse valley makes 90 degrees with that of the main mountain chain.
I'm not savvy with terrain profiles, so this clue about angles makes me confused. So could someone help me with an adequate diagram or picture on how to distinguish it from a longitudinal valley?
The same entry mentions about Val de Travers which it warns that despite of its name is a longitudinal valley. But I don't know why does it make this claim.
Because none of the articles do properly explain this with some sort of picture other than a photo I can't exactly tell at which difference is being talked about. Thus an arrow or some sort of marker or indicator over the photo or a diagram would be of much help for better identification.

I think that the simplest way is to just look at the map for these two valleys in the Switzerland:
Longitudinal valley:

You can see that this is perfect example on the map: we can easily see the direction of the ridges and the valley is pointed in the same direction. This type of valley was not made by river, but it was made with compressing of tectonic plates.
Transversal valley:

You can see here that some river got through the ridge (then they built the road because the river made all work). It doesn't go parallel ridges like the longitudinal valley. This type of valley requires a lot of work for the river so transversal valley are typically pretty short.


Winter in the Northern Hemisphere in July? Can anyone explain it? The July 2007 issue of the National Geographic Magazine dedicates several pages to "Climate Change" and "Global Warming".  The author explains in detail the Earth's movements and how they provoke great climate shifts.  "Wobble" is one of the four movements listed and is described as follows:

  "Earth slowly wobbles like a top as it spins on its axis, which shifts back and forth about every 20,000 years. The result: About 11,000 years from now, winter solstice in the Northern Hemisphere will be in July.

Although I know exactly what a top is, and how it spins, I find it hard to understand how wobbling is expected to bring about that forecast.

Can anyone explain more didatically how such a shift is expected to happen? How the wobble movement is doing it?
Is such an astronomic phenomenon accepted by scientists unquestionably?
If winter is expected to be in July 11,000 years from now and such a shift is under way right now, does it mean that winter in the NH is slowly moving towards July and that, perhaps, 5,000 years from now winter solstice will be in March?

Thank you.

Can anyone explain more didatically how such a shift is expected to
  happen? How the wobble movement is doing it?

First, it's probably a bad approach to think of it as a shift.  It's a rotation.  similar to a spinning top.   It's called precession.  It's always been there - (so to speak).  It's part of Earth's motion.

The Earth is sufficiently massive and space, sufficiently empty that there's effectively zero resistance and the Earth's precession is permanent and largely consistent.  (unlike a top that slows down due to friction from the ground and air resistance).

Earth's precession shifts a tiny bit due to the sun, moon and gravity from other planets but those adjustments are very slow and not relevant to your question.

As Earth's precession completes one rotation every 22,000 years (give or take), over a human lifetime that's about 1.5 degrees or 1.5 days, which is pretty small and easily missed by anyone not taking very careful measurements. That doesn't affect calendars however.

Calendars are a little complicated, and I'm not sure it's necessary to go into that in detail for your question.   Calendars also can be adjusted to match Earth's orbit.   Any un-adjusted calendar will eventually mess things up like putting July in winter, but that has nothing to do with the 22,000 year precession.   365.25 days (a leap year every 4 years), was inaccurate enough to lead to the year that lost 11 days in the UK in 1752.

365.25 days (Julian calendar) is much more accurate than 365 days (which loses a day every 4 years (in effect, a 365 day year would put July in winter in 720 years, not 11,000).  Any movement of winter across the calendar depends on how good the calendar is, NOT earth's precession.

365.242 days (Gregorian calendar), or 97 leap years every 400 years is better than the Julian (1 every 4).  Having an accurate accounting of leap years and being able to add or remove one as needed, will keep winter in the winter months for as long as we need to, much longer than 11,000 years.

What changes with Earths precession is the position of the stars.  The sky will shift depending on where Earth is in it's 22,000 year wobble.  Similarly, the North star won't always be the North star.   The night sky will look shifted by about 46 degrees in 11,000 years (some of the stars will have moved over that time-frame as well, but lets ignore that for now).

You've herd the term "Age of Aquarius".   The astrological ages each last about 1,800-2,000 years, and the cycle of 12 ages corresponds to Earth's 22,000 year wobble.  Note, that article says 25,860 years and your quoted 22,000 years.  The solar system also wobbles, so how those wobbles add up can give different estimates.   If you use 22,000 or 25,860 or 25,771 or 26,000 or 23,000 on average, the different numbers don't change the answer to this question.   This explains the variation in the numbers used.

  Is such an astronomic phenomenon accepted by scientists
  unquestionably?

Absolutely, 100%, unquestionably yes.  This is accepted, measured, confirmed and can be modeled and explained.  It's 100% accepted science.  Even the ancients were able to observe this with careful measurement, though they couldn't accurately explain it.

  If winter is expected to be in July 11,000 years from now and such a
  shift is under way right now, does it mean that winter in the NH is
  slowly moving towards July and that, perhaps, 5,000 years from now
  winter solstice will be in March

As the assumption is flawed, then both no and yes.  With an imperfect calendar, then this would happen and the rate would depend on the accuracy of the calendar as noted above (not precession).

Because we use a very accurate calendar that allows for adding and removing a leap year as needed, no "drifting" of the solstices across the months will happen.   There will be some yearly variation as the solstice is a precise point in Earth's orbit, so it happens not only on a day but at a precise time, it might be December 21 one year and December 22 the next year, but every year our calendar gets "messed up" by about 6 hours, and every 4 years, that 6 hour error is mostly corrected.   Jupiter also accelerates or decelerates the Earth in it's orbit and Earth's orbital speed varies depending on how close to perihelion and aphelion, so there's some variation year to year, but there's no movement across the calendar over 11,000 years.


Is it possible to form a diamond-sapphire hybrid? I've been looking into diamonds recently and was made aware of diamond hybrids where diamond is grown on either a seed diamond or cubic zirconia. I was wondering if it would be possible to do something similar with sapphire. Sapphire core surrounded by diamond might be pretty cool...

Sapphires and ruby's are both aluminium oxide. sapphire melts at 2000 degrees and diamond synthesis can happen at 600 degrees. To coat around the sapphire, you would have to use multiple diamond seeds, which would make a polycrystal. it's probably humanly acheivable.

The scientists would have to study the adhesion of a transition layer, because the sapphire is trigonal, and makes 6 sided crystals, whereas the diamond is cubic.

They do use vapor deposition already to dope crystals with very colorful metals, for example you can build a home kit for titanium quartz.

Perhaps if they used some kind of force to grow the diamond in a given direction, like a carbon-cannon in the vapor chamber, they can control the diamond and have one structure around the other mineral.


Regional and Relative Sea level I am a little confused by the terms "regional" and "relative" in the sea level change context.

Do the two words have the same meaning? Does the "regional MSL trend" in https://www.aviso.altimetry.fr/index.php?id=1599 have the same meaning with relative sea level in https://tidesandcurrents.noaa.gov/sltrends/sltrends.html?
Can we measure Relative Sea Level (RSL) with altimetry satellite data?

Assessing sea levels is a complicated business, as there are a number of factors which can affect sea level relative to a fixed point on land. For a start, land levels rise and fall; in some places land is lifted up by plate movements or volcanism, in other places  it may fall. Rising and falling atmospheric pressure makes very temporary local changes. The factor which causes the most concern these days is the rise in mean sea level caused by melting ice on land increasing the amount of water in the ocean. This has been going on since the end of the last ice age some 12,000 years ago, and is caused by global warming. This mean sea level is the one from which the height of mountains is calculated and the altitude of aeroplanes. Melting of sea ice causes no rise in mean sea level. Another factor is that, relieved of the burden of thousands of cubic km of ice at the end of the ice age, places like Scotland gradually rise up, and this rising of the land can persist for many thousands of years after the ice has vanished. In some places there is a seesaw movement where the rising of one part of a plate causes another part hundreds of miles away to descend.


What, if any, paleoclimate data can be derived from igneous rocks? Paleoclimate data often derives from sedimentary rocks. Metamorphic rocks can also contribute to paleoclimate information in a wide variety of ways.

What about igneous rocks? I guess that this can question be divided into two, about intrusive and extrusive rocks.

Extrusive rocks will have direct contact with the climate. They may exchange geochemical signals with the atmosphere or water they've erupted to. The cooling rate may be dependent on ambient temperature. Lava flows may fossilise the soil.

Intrusive rocks may be harder to interpret in that manner, if at all. The time resolution will obviously not be as good as dating individual beds from the lake floor, but I still think something can be gained from it. Maybe some igneous rocks can form only after a special sedimentary rock (derived from a specific climate) has been buried and remelted? What about isotopes? Sedimentay systems often fractionate various isotopic systems. Can this variability be later traced in igneous rocks?

Stable isotope signatures in igneous rock (primarily $\delta$18O) can be affected by climate, but the effect is complicated and unreliable enough that I doubt it can really be used to say much about palaeoclimate. You might be interested in my friend Lara Owens' dissertation in which she considers the influence of climate on $\delta$18O in lava from Mt Erebus, Antarctica. Oxygen isotopes in Erebus precipitation are some of the lightest in the world, and she suggests that this water, after incorporation into a hydrothermal system whose rocks were later assimilated into magma, caused the anomalous $\delta$18O in some of the samples.

It would be interesting to see if there is a global geographic trend in similar anomalies, but I haven't heard of anyone trying that.

A more direct way that igneous rocks can record paleoclimate is through the effects that the atmosphere can have on pyroclastic deposits. Isopleth maps often can reveal the direction the wind was blowing during the eruption. Clast morphologies might even tell you the weather -- I'm thinking of accretionary lapilli, which form when an ash-rich eruption plume encounters a rain storm.

In conclusion, you might be able to glean a few data points here and there, but nothing comparable to the amazing records available in sedimentary rocks.

Edit to add: I just went to a lecture by Jay Quade about figuring out the timing of uplift in the Andes, and whether it came before or after the Atacama became hyperarid. Among many other geochemical tools, he used $\delta$2H in hydration waters on tephra, primarily to figure out palaeoaltitudes. He said he thinks the relationship between $\delta$2H and altitude has been fairly constant over the period of investigation (back to 50 mya).

Edit to add: I had forgotten to point out that subglacial eruption deposits are often distinctive (tuyas, hyaloclastites, pillow basalts). Wherever these deposits are found, you know a glacier or ice sheet was present and if you can date the rock then you know when there was a glacier there. Some recent work has suggested that you can even figure out the thickness of the glacier using the concentration of dissolved gasses in melt inclusions in the subglacially erupted lava flow.


Artefacts in PERSIANN-CCS data I downloaded PERSIANN-CCS for the region of Pawlowdar, Kazakhstan and this has stripes all over my downloaded data.
For another AOI in Kazakhstan I do not have this problem.

Does anyone of you have any idea where these artefacts are coming from?
I did not process the data at all.

The Further reading link brings you to The PERSIANN System Fine Resolution Precipitation Estimates Using PERSIANN-Cloud Classification System which shows that the data is merged with signals coming from both geostationary and polar/near polar satellites. My guess is that it's just banding in one of these datasets (probably from that second group of satelites).

I tried to look at raw image data from these satellites (to illustrate my assumption), but I bump into sites that are affected by the current US government shutdown, resulting in e.g. incorrect and expired CSS certificates.

If you can dig up these raw images in a later stage, you'll probably be able to map the width of those bands to the aperture of the satellite.


How old is the Earth? According to most articles I've read online, the estimated age of Earth is 4.5 billion years.

Question: How old is the Earth?

So I actually want to confirm that this is the case. Maybe there are other famous theories saying it is 3 billion years old or 6, therefore my question.

Yes, the age of the Earth is about 4.5 billion years (4,500 million years). Your linked articles describes well how it was formed and how we know about it. The uncertainty is less than 1% and depends partly on the radiometric dating methods and partly on the definitions. Sometimes the age is said to be 4.567 Ga, that might be a little too exact number to claim, but at least it's easy to remember.

I haven't heard any different age constraints that are scientifically founded, but before we had access to the methods and data we have today, there was a broader range of estimates.

Early estimates were based on the supposed increased salinity of the oceans, but those estimates fail to recognize that salt is also removed from the seawater in subduction zones and to form evaporites.

Noteworthy is Lord Kelvin's very sensible estimate of 20–40 million years, published first in 1863. The estimate was based on the heat lost since formation and Earth's capacity to withhold its energy. Unfortunately, Lord Kelvin worked too early to know that $E=mc^2$, so energy is also generated within Earth and that is the main source of heat. He also didn't understand the Sun's source of energy and convection and therefore miscalculated the solar age constraint and Earth's heat flux.

Radioactive decay is not only the source of heat but also the process we use to measure the age by radiometric methods. These methods became known decades later and quickly provided age constraints sin the right magnitude.

Earth scientists have assumed the deep time age of Earth since the antiques. It must have been frustrating for the early geologists to not be able to put a number of the Earth's age. As a rudiment of that time, we still use their relative terminology to describe the development.

Our present estimate is based on a range of agreeing models and data. The Earth science community has, in general, moved on to new and more challenging questions.


Could dust blown up by a comet impact render the air unbreathable? In the docudrama Super Comet After the Impact, the impact is shown to have made the air within a few miles of it unbreathable, and humans need gas masks to breath in this area.
How realistic is this?

I was told to come here after originally posting on the space stack.

That doesnt seem realistic since eventually all the dust from all the volcanic activity, as well as that caused by our doing, eventually makes its way back down to earth. Most dust particles end up being soaked up by earths cloud layer coming down in rain. I have to agree with Gimelist but volcanism can and has produced conditions you mentioned by expelling caustic and poisonous gases and for what I understand nuclear detonations and the radioactive dust they send into the air is far worse in the long run.


In radiometric isochron dating why is at t=0 D*/Dref=const but P/Dref not? I am a physics graduate and trying to understand one of the assumptions made for isochron dating of rocks: at crystallization time of the rock, $t=0$, the ratio of the parent isotope to a stable reference daughter isotope was variable for different parts/minerals of the rock ($P/D_{ref}\neq const$), but the ratio of the radiogenic daughter isotope to the stable reference daughter isotope was constant ($D*/D_{ref}=const$). See for that the figure below taken from here :

My question: Why is the one ratio constant, but the other not? I taught $D*/D_{ref}=const$ holds, because just before $t=0$ the rock is still molten and components are well mixed, but then why shouldn't $P$ and $D_{ref}$ be also homogeneously mixed and uniformly distributed.

Additional question: In the figure below, taken from here, I get that the linear function is the isochron, but what is the logarithmic function and how does it help in the dating process/what is its contribution? Thanks

1) D* (radiogenic isotope) and Dref (stable reference isotope) are two isotopes of the same element. P is the radioactive parent of D*, and is a different element. Chemical fractionation between P and Dref occurs as the rock solidifies because different elements are preferentially incorporated in different minerals depending on how well their ionic radii and valences are compatible with the mineral's crystalline lattice.

Although there can be some mass-fractionation of isotopes of a same element, it is usually very small (IE negligible) relative to the chemical fractionation.
Often, for making such isochrons, geologists choose different mineral species with very different P concentrations (and thus varying P/Dref) to provide spread along the isochron line; this allows for more precise regression and determination of the slope / age.

2) The second diagram you show is a concordia plot, not an isochron. There is no common isotope on the ratio denominator. Rather, this plot shows two different isotope systems each with their own decay chain (238U->206Pb and 235U->207Pb), these two Uranium decay chains have different half lives. The curved line is the "concordia" curve, which is the expected result if the sample exhibits closed-system behaviour (IE Pb has not diffused out of the crystal).

In this case a mineral (probably a zircon) was formed at 2.6 Ga and had open system behaviour at around 0.4 Ga. (IE the radiometric clock was partially reset). The straight line is called a "discordia line" and is a mixing line between the two time points on the concordia curve.


Over what distance can weather be assumed to be constant? Good afternoon,
I'm working on an application makes calls to a weather API for different coordinates across the United States.
Instead of getting the weather at each and every point, I'm planning on clustering coordinates together based on how close they are to each other. That way, I can take an average of coordinates and get a single weather forecast that is representative for the group.
This raises the question, how close do these points need to be? Would a cluster of radius 50 Miles be sufficient? What about 250?
I'm really only gathering these features from my Weather source:

Temperature
Category (Rain, Cloudy, Hail, etc.)
Visibility

I don't really need a high degree of precision. In fact, the coordinates I'm using are going to have a  25-50 mile variation from their "true position."
I'm not a climate scientist, so I apologize if this question is a little rudimentary. I just wanted a second opinion on the topic so I can balance the trade-off between number of API Calls and fidelity to regional weather.

Weather is subject to Tobler's First Law of Geography: Everything is related to everything else, but near things are more related than distant things.
Temperature- this changes not only by the feature, but also the day of the year. The winter months, as well as the fall and spring, will have much more drastic temperature changes. This may be due to things like fronts, but is ultimately caused by heating differences from the sun. However, a few miles can yield quite a drastic change. Things become even more complicated when elevation is involved.
Precipitation- This is even more variable. Snow can be happening on a mountain, but have rain in a valley. Even the side of a mountain can influence how much rain is seen. I have seen it rain on one side of a building, but not the other. Precipitation is a tricky thing to forecast.
Visibility There are several factors that influence visibility. Fog and precipitation are probably the most common meteorological factors. Elevation can really influence your line of sight. Obviously, visibility is also influenced by the presence of smoke as well as dust.The smaller the particle, the more likely it will obscure vision. And snow tends to be more reflective than rain. Something else that may influence visibility is wind speed, as aforementioned particles can be kicked up from the surface. So visibility will change depending on how all of these change. It may even change depending on the direction you look.

All of this to say is that it really depends and there is rule of thumb.


Why do (some) silicic bodies behave effusively instead behaving explosively as in common? We encounter dacitic/rhyolitic melts generally in explosive volcanic events. But some of them behave as effusive dome flow. Why do some silicic bodies behave effusively?

Explosive volcanic events happen mostly because of saturation in gases, and increase in pressure above the strength of the top of the magma chamber. As the magma decompresses or cools, H2O (mostly), CO2 (also important), and other gases such as H2S, SO2, HCl, etc, form bubbles and increase in volume. If the magma chamber is confined, there is also an increase in pressure.

An obvious corollary is that gases have to be present. If the magma is mostly dry and volatile-free, there are no volatile species to form bubbles and the magma cannot explode.

Another factor is the viscosity of the magma. The less viscous it is, the easier it is for the magma to flow (and not build up pressure) and also the easier it is for bubbles to escape the magma. Viscosity of magma depends on temperature (hotter = less viscous), composition (more alkalis = less viscous), crystal content (less crystals = less viscous).

Taken together, a hot alkali magma without crystals and no volatile species will flow, whereas a cold partly crystallised wet sub-alkali magma will probably explode, even if they have exactly the same SiO2 contents.


Change in vertical wind intensity in atmospheric modeling I am a beginner to atmospheric modeling. I want to know about the change in vertical wind intensity in modeling studies.

In general, if I initiate a simulation,I will get the real vertical wind velocity of that place, or winds with weaker intensity calculated as per the model equations intensifying with each timestep? What are the factors which control it?

I am asking this because I made several setups to study a real time event and I am getting the winds with different intensity. I want to know which of them is right. if I am wrong anywhere, what could be the associated factor that caused it.

It really depends on whether you're model is hydrostatic or not.

If your model is hydrostatic, then the vertical velocity is found diagnostically. The diagnostic algorithm is called the Richardson Equation.

If your model is nonhydrostatic, often it is presumed that the vertical velocity is 0. The vertical velocity is presumed to be 0 (unless you do some spin-up or model restart, or some other special initialization), and the prognostic equation for vertical velocity is found.


How was the onset of the Cambrian period dated? What dating method was used to determine the beginning of the Cambrian, and what was its margin of error? Was only one fossil dated, or were a number of similar fossils used?

Fossils are only in very rare cases dated directly, because they do not contain sufficient radioactive isotopes for dating.
Most geological periods are first and foremost defined by biostratigraphy- fossil assemblages, typically.
The Cambrian period starts with the Fortunian stage - this stage is defined by the appearance of a certain trace fossil in Fortuna peninsula, eastern Canada, but is correlable with similar formations world wide. The whole discussion on how this stage is defined is available here.
As outlined in this paper, in addition to fossils, the Fortunian stage hosts various volcanic rocks which contain zircons, which can be dated by U-Pb. The age of the actual boundary is then interpolated from these data.


Why is the inside of the Earth so hot? I have heard that the Earth is made up of four layers, being the crust, the mantle, the outer core and the inner core.  I have also heard that the Earth's temperature increases as you move from the crust to the inner core, with the inner core having a temperature of 4700 degrees.

Why is it that the inside of the Earth is so hot compared to the outside of the Earth?

This is a very good question. There a few main heat sources: Heat(and work) left over from the formation of the earth, work (potential energy) generated by dense iron sinking into the center of the earth and forming a core, and radioactive energy. Since the Thermal diffusivity of the materials that make up the earth is low, heat transport is very slow and thus the planet retains a significant amount of its heat.

Another reason why the earth is so hot, is that mantle convection is a very inefficient way to transport said heat, and thus the earth loses energy very slowly.

We know how hot the interior of the earth might be because of laboratory experiments, and also volcanic eruptions. How much energy(temperature) does it take to melt gabbro (mantle rock)?

Interestingly enough, the earth is cooling. And the inner core / outer core boundary is a freezing front (meaning turning from a liquid outer core to a solid inner core). Though, it is a very hot freezing front.


How to de-stagger (or unstagger) WRF wind fields? I am trying to calculate wind speed from the U and V wind components of a Weather Research and Forecasting (WRF) simulation. However, I came to realize that some variables of the model (including wind components) are staggered. This makes it really difficult to analyze the model output as is, since the dimensions of staggered variables differ from those of non-staggered variables .

Does anybody have any hints on how to de-stagger these fields in a netcdf file produced by the WRF model?

The simplest way I've found in Python is to use the getvar function with the 'ua,' 'va,' or 'wa' variables from the WRF-Python module. Alternatively, you can take the midpoint between the staggers.
Edit: For example, using the WRF-Python module, you can get the destaggered wind variables with the following code

import netcdf4 as nc
import wrf
f=nc.Dataset('example.nc')
u=wrf.getvar(f,'ua')
v=wrf.getvar(f,'va')
w=wrf.getvar(f,'wa')


Can overshooting tops enter the stratosphere, or will they rather push the tropopause upward? Convective overshooting tops
reach above the normally horizontal flat layer of the convective system, a layer that should coincide with the tropopause.  If we have such an overshooting top, does this mean we actually have the cloud reaching into the stratosphere, or does it mean that the convective system locally pushes the tropopause upward, while the convection is still limited to the (temporarily extended) troposphere?  Both alternatives are given as unsourced answers to this identical Yahoo! Answers question, so I would like to see a referenced answer that specifically addresses the distinction between "air parcel reaches stratosphere" or "air parcel pushes tropopause upward".

(Note that this is not merely a matter of terminology, but should affect troposphere-stratosphere interaction in general)

Source: NOAA

This is an interesting question and I feel the best answer is "a little bit of both".  Consider your picture without the overshooting top and just the anvil.  The tropopause is clearly defined as the anvil spreads out horizontally against the static stability of the stratosphere.

Now let us consider a single parcel in the updraft, accelerating upward due to CAPE and hitting the tropopause with significant vertical momentum.  This parcel is full of tropospheric air but makes an excursion into the stratosphere until the negative buoyancy it experiences reduces its vertical velocity to 0 (the top of the overshooting top) and then continues to accelerate downward to eventually oscillate about its equilibrium level (level of neutral buoyancy).  For this single parcel I would argue that it is in the stratosphere.

Now consider all of the updraft parcels doing this.  They are all transporting tropospheric air upward into the stratosphere -- inside that cloud it is all tropospheric air and toward the edges it is a mix of tropospheric and stratospheric air due to entrainment.  The tropospheric air transported upward that mixes with the stratospheric air will reduce the static stability locally and may eventually modify the temperature gradient such that you consider the tropopause lifted.

I may run a simulation later with many grid levels around the tropopause and see what a model has to say.  I'll edit with my results.


Why does the meandering pattern of the jet stream itself propagate? It is well known that the jet stream follows an overall meandering pattern, but what is less well known is that this meandering pattern itself moves as a wave with a velocity much slower than the velocity of the jet stream itself.  So why does this meandering wave propagate, and what causes the meandering pattern in the first place?

I wouldn't characterize the movement of the jetstream as a "less well known" problem, at least not to anyone who has sat through a synoptic meteorology class.  The jetstream from a dynamic point of view is just an enhanced gradient in the heights on a constant pressure surface (or pressures on a constant height surface) and there are many factors the influence this gradient.

First, lets take a look at the northern hemisphere 500 mb heights and surface pressure:

What we see here is in the mid-latitude storm track we have a series of highs and lows on the 500 mb surface (blues are low anomalies, red high anomalies).  This particular pattern look to be wavenumber 7,  This is a planetary rossby wave. If the weather was frozen in place and all external factors eliminated, the wavenumber is going to dictate how fast this pattern rotates around the globe.  For low wavenumbers, this pattern will even move retrograde, but that is not something you see often (if memory serves, this is wavenumber 3 and lower).

You might wonder why I'm talking about waves at 500 mb when the polar jetstream is up a bit higher between 250 and 300 mb, varying seasonally.  The pattern of highs and lows is evident throughout the troposphere.  You can see it reflected in the surface pressure and in the image below you can see it in the 300 mb pattern.

So far we've mentioned that the wavenumber of the planetary wave has an influence on movement of the pattern, but what about how the pattern evolves?  There are a lot of factors here:

Oceans
Mountains
Surface heating
Convection

And perhaps the biggest:

mid-latitude cyclones.

Part of cyclone self development is a positive feedback between surface temperature advection and pressure changes at the tropospheric mid levels.  As the cyclone matures the advancing surface cold front will correlate with low 500 mb heights and lower 300 mb heights.  This response will perturb where the jetstream lies and indeed, the jetstream tends to lie over the fronts extending from a mid-latitude cyclone.  If you conceptualize the fronts from one cyclone extending back and forward to the cyclones next to it, this is the "polar front" and gives you a rough idea of where the jetstream is.

An additional factor in how the jetstream propagates is the particular shape of the jetstream.  There are a number of blocking patterns (e.g. Omega block, Rex block) that tend to persist as a stationary feature once setup.

Finally, remember that in an atmospheric column, pressure is just the weight of all the air above a height, and anything that can modify the column (e.g. surface heating, cooling, mid-level changes) can modify the 300mb heights and subsequently affect the positioning of the jetstream.


Is oxygen the most abundant element on Earth? When I was in school, I was taught that we need oxygen to breathe, but it actually constitutes only a small fraction of the atmospheric composition, and that nitrogen constituted the largest fraction of the atmosphere's composition.

This quick Google search mentions oxygen as the most abundant element.

How can this be reconciled?

Both of them.

The composition of the atmosphere, crust, mantle, core and bulk earth are all notably different.

The atmosphere is composed of ~78% nitrogen and ~21% oxygen, with small amounts of other gases.

The bulk composition of the earth by weight is mostly, iron, oxygen, silicon and magnesium, in that order, with all the other elements making up only about 5% of the earth's weight. Most of the earth's iron is in the core, which is about 85% iron. The rest of the earth is dominated by oxygen and silicon, primarily in the form of silicate minerals, which consist of $\ce{SiO4^{4-}}$ tetrahedra linked in different ways and with different cations filling in the gaps.


How to find/calculate the yearly evaporation of a given area? What I am asking, is exactly the opposite of the yearly rain. It is well measured and it has century long databases.

Consider a given, generally dry area. What I am trying to know: if this area wouldn't be dry, but it would be an open water surface (for example, a sea), but without any water resupply (i.e. rain), what would be the yearly level loss by evaporation?

I think, this information would be useful to calculate the irrigation need of not arable territories because of the lack of rain.

Additional difficulty: in case of larger areas, this evaporation rate would be probably smaller, because the winds in the central regions get moisture on the borders.

I suspect, calculating this would require a relative complex weather simulation, which is not available on the enthusiast level. But maybe some fist rule, estimation or already existing databases can exist.

What you are asking is one of the most difficult issues in hydrology. The evaporation from open water is a function of air temperature, water temperature, humidity, wind speed and fetch, water depth, water salinity,  degree of thermal stratification, and boundary effects (as you correctly point out). It is certainly not a trivial calculation!
As a first approximation you can apply an empirical coefficient to class-A pan evaporation data, but don't expect any great accuracy.

But then you progress towards a further aim of calculating a potential irrigation need. For this purpose I would say that calculating open water evaporation is completely the wrong approach. Rather, calculate the potential evapotranspiration ('ET0'), and then apply appropriate crop factors, as explained in the FAO documentation:
http://www.fao.org/docrep/s2022e/s2022e07.htm
Calculating ET0 is best done using the Penmann-Monteith equation, which is horribly complicated, but there are web sites where you can do the calculations on line. You will need monthly or dekad climate data for the crop(s) you envisage growing. This will be max and min temperature, humidity, average wind speed and average daily hours of bright sunshine. You will also need latitude, longitude and altitude to estimate the solar radiation. Even with all this data, it is a fairly lengthy calculation, but it is your best bet at realistic crop water requirements.


Can a cosmic impact break Earth's crust in large area exposing the magma ocean? Can a cosmic impact event break the Earth's surface in such a way so it expose liquid magma over large areas with solid rocks floating in it as "icebergs"?

I wonder, will such magma ocean experience tides and storms so that onybody survived on the "icebergs" to be in danger due to their constant move.

Let me first correct a small misconception. Where you are talking about 'the magma ocean', you are implying that one exists. This is in fact false. There is no 'magma ocean' in the Earth at the moment (and it has been like that for several billions years). The lavas you see erupting in volcanoes are not coming from a magma ocean. They are coming from either the crust or the mantle, both of which are solid. Magma generation is a localised anomaly in what would otherwise be a solid mass.

That said, the upper mantle has a section called 'the asthenosphere' which is slightly more ductile than the rest. Think about chocolate in a hot day. Still solid - but it can flow given enough pressure. The modern lithospheric plates (of plate tectonics fame) sort of float on the asthenosphere already now, and that's why you have plate movement and earthquakes and everything.

The asthenosphere is quite deep - some 100 to 200 km deep below the surface. If a cosmic impact is going to create a crater 100 km deep in the Earth, no one will be left around to care about whether they will survive on the 'iceberg'-like lithospheric plates. Again - this is irrelevant. The asthenosphere is ductile in timescales of hunderds of years (at least). If you were to pick up a piece of it now, it will just be like any other rock (albeit quite warm).

A magma ocean event probably occurred very early in the Earth's history (which is not going to happen again since Earth is already here), and the moon forming event also likely liquified quite a lot of the Earth. But this is not going to happen since there is no other big enough body that seems like it's going to collide with us at the moment.


Ice Age/Interglacial Period Cycle What happens if an Ice Age or Interglacial Period Cycle starts? I don't know what exactly what happened then.

I'm guessing this has been answered before, but in a nutshell, the primary mechanism over the last 3 million years or so is nothing more than colder summers in the Northern Hemisphere.  Now, one cold summer won't do it, you need hundreds, which usually requires an orbital variation or perhaps, ocean current change or perhaps an extended solar minimum, but the effect needs to last for at least for a few to several centuries, or something radical like a dinosaur killing meteor or a once in a million years volcano, but that's more of an extreme event and not relevant to your question.

There's places in the far north that are snow covered year round.  Some of the time it gets warm enough for snow and ice to melt, but where it doesn't stay warm enough for all the ice to melt, you get ice cover 365 days a year.

When you get an extended period of colder summers, then the ice cover can move south, covering more land in the Northern Hemisphere.   (The South pole isn't as important because the land near the south pole is already ice covered and that pretty much never changes).   As the ice moves south and covers more land, a few things happen, often referred to as feedback mechanisms.

1) more sunlight reflects off ice, less heat stays on the Earth to warm the atmosphere, this has a global cooling effect.

2) Oceans begin to fall as ice builds up on land.  Oceans absorb the most heat from the sun per square meter out of any surface on earth.  Ocean heat absorption also evaporates water vapor into the atmosphere, and water vapor acts as a greenhouse gas.  As oceans fall, they also cover less area and while the size change is a relatively small percentage, that also works to cool the earth.

3) as the ice grows higher, this has a cooling effect on high altitude air, which blows off the ice and cools surrounding areas and tends to keep the ice frozen longer.

4) as the oceans grow cooler, they absorb CO2 from the air, this lowers the amount of greenhouse gas in the air which has a cooling effect.

The cooler northern summers are thought to be driven by orbital changes such as low orbital eccentricity.

Interestingly, the effects such as orbital variations, milder summers and even CO2 are by themselves, quite small, but when taken together with the feedback mechanisms in place, the temperature change of the planet between ice age and inter-glacial period is quite large.  As much as 10 degrees c globally, corresponding with mile high glaciers covering most of Canada, half the United States, half of Russia and Europe, as well as 300 foot sea level drops and ecosystem changes around the globe.   Not all bad.  Some deserts will arguably get improved ecosystems, but the change is felt globally.

The inter-ice age period is the same thing just in reverse.  Orbital changes can lead to warmer summers which melts ice, and beings to reverse the 4 feedback mechanisms mentioned above.   Melting ice isn't all harmless though.  You get enormous lake sized pockets of water trapped in ice, waiting to give way, and floods like we've never seen.


Which is worse, plastic or styrofoam cups? Which disposable cup between plastic and styrofoam harm the environment the most?
Which is the most unhealthy to use for the Earth for humans and animals?

I suppose the answer depends on total lifecycle emissions as well as landfill environmental cost.
For plastic I assume PP or PETE.
For styrofoam production is based on polystyrene so some styrene emissions.

For lifecycle costs, emissions for manufacturing as well as energy (coal or gas power plant) need to be considered. Also are either recycled and in what proportion and does that impact lifestyle costs. Not an easy question, or one I can quantify. For simplicity l would look at two questions- production emissions of the actual cup and or feedstocks and recyclability of each cup.  According to this link styrofoam is not recyclable so I would guess plastic is not as bad.
https://sciencing.com/styrofoam-vs-plastic-cups-12400119.html
Here it says polystyrene is usually not recyclable locally. https://science.howstuffworks.com/environmental/green-science/polystyrene-recycling.htm
Here is a different perspective whose author suggests styrofoam lifecycle cost could be lower compared to some other options:
https://daily.jstor.org/is-the-30-year-long-styrofoam-war-nearing-its-end/

Not exactly an answer but at least a start


Conversion of BUFR format into grib I am looking for Upper Air Observations (UAO) for Bay of Bengal region. I found NCEP ADP UAO dataset available in BUFR format. I am supposed to use UAO data in grib format only for the purpose of data assimilaion.

Is there any way, one can convert BUFR data into grib format?

Thanks in advance

Here is how I would do this. ECMWF's ECCODES has a tool called bufr_ls and you can use that to  write the contents of that output to a text file. Then I would read that file into a scripting language such as Python and write out the contents as a GRIB file using PyGrib. You can also explore the output of bufr_dump and convert that also to GRIB if you wish. The full list of all BUFR format tools from ecCodes is given in this link BUFR tools
For more information regarding either of those softwares you can reach out to their support network and then get your doubts resolved.

UPDATE

If you want a 100 % Pythonic solution then you can try  Python-Bufr which basically wraps ECMWF BUFR or use this python BUFR library - bufrpy


How to map (survey) the structure of crust Mapping the bottom of the ocean is called seafloor mapping.  I was wondering what mapping underground is called, such as when locating caves and caverns.

I have seen it in movies, and I'm interested to know what is it called so that I can start searching for more info about it.

What you have probably seen in the movies, as used by the oil and gas industry is reflection seismology. This is where you shoot off a sound source (explosives, airguns, etc) and track the reflections of the sound waves from the various rock layers below the surface.

At a smaller scale, there is Ground Penetrating Radar, good for a few 10s of meters at best, which is higher resolution and good for detecting voids.


What is the strength of the Earth's magnetic field at McMurdo Station, Antarctica? Based on this map,

Below are images showing more specific detail.

I assume the field strength is between 0.6 gauss and 0.65 gauss, but I cannot tell between which ios-flux lines (if that is a legitimate term) McMurdo Station is located.  Are there precise measurements of the magnetic field strength at that location, within 0.01 gauss?

According to the current World Magnetic Model 2015 v2 (new one to be released on 10 December 2019!),

Longitude: 166.6863° E
Latitude: 77.8419° S
Elevation: 10 m

Date: 2019-11-25
Declination (+E | -W):   141.5232°    (-0.1829°/yr)
Inclination (+D | -U):   -80.3929°    (0.0399°/yr)
Horizontal Intensity:     10,396.8 nT (34.7 nT/yr)
North Comp (+N | -S):     -8,139.2 nT (-6.5 nT/yr)
East Comp (+E | -W):       6,468.8 nT (47.6 nT/yr)
Vertical Comp (+D | -U): -61,423.3 nT (54.8 nT/yr)
Total Field:              62,297.0 nT (-48.3 nT/yr)

Uncertainties:  0.57°   0.22°   133 nT  138 nT  89 nT   165 nT  152 nT


How are deposits of metals like tantalum located? I am curious of how metal deposits are located in general, but to keep my question focused I wanted to just ask about tantalum for example.

Are there people who traverse their own country drilling core samples here and there? What indicators would they be looking for tantalum in particular?

Metal oxide minerals like tantalite (tantalum) and columbite (niobium) often form placer deposits within basins and drainages. The placer deposits are a secondary ore deposits created by the weathering of tantalite/columbite bearing granite and the transport of heavy sands by water and gravity.

Based on this information, a good approach to prospecting for tantalum / niobium would be collect dark/black sand samples from stream beds within a granite mountain range and to collect samples from riverbeds flowing out of mountain ranges with exposed granite. Larger rivers with steep terrain can carry heavy sediment further away from its source area.

Example: Sawtooth Mountains in Central Idaho are a large granite batholith complex..  Salmon river and its tributaries would excellent areas to look for placer deposits (except of course most of this area is designated as National Forest land.)


How to perform regridding (1.0d to 0.5d) using bilinear interpolation for an irregular area? I need to regrid temperature dataset from 1 degree to 0.5 degree. In case we have data available for all grids falling in a square, as shown below, we can simply regrid it using bilinear/bicubic interpolation method in MATLAB.

But, the data grids which I have forms an irregular shape i.e., there are no values outsie the given grids as shown below.

How to do regriding in this case ?

Try something like this:

[x_grid,y_grid] = meshgrid(1:100,1:100);
z_grid=griddata(x_data,y_data,z_data,x_grid(:),y_grid(:),'v4');

You can change the method of interpolation if you prefer something else.

See:
http://www.mathworks.com/help/matlab/ref/griddata.html


What are these Gizmos at Izaña Atmospheric Research Center in Spain? This tweet from the account of the Centro de Investigación Atmosférica de Izaña (AEMET) http://izana.aemet.es  Izaña Atmospheric Research Center (AEMET) shows images of meteorological instruments pointing at the Sun. I recognize the small glass domed instruments in several images and in detail in the first image as Pyranometers based on this excellent and thorough answer.

But what are the long, thin telescope-like cylindrical objects, each on its own articulated pointer to track the Sun? There seems to be a whole series of them in the background in the fourth image.

Those are Sun/Moon multispectral photometers and ski radiometers. These are instruments that can scan the sky or track the Sun/Moon for direct measurements. They measure light intensity at multiple narrow wavelength bands, and are designed to measure atmospheric aerosols content and characteristics.

The ones in the third image seem to be a CIMEL CE-138 Sun Sky Lunar Multispectral Photometer (specs).

There is just a few brands that make these instruments. Others are Prede and Kipp & Zonen. I don't know why they have so many at the AEMET. Perhaps it is some sort of instrumentation investigation, where they are testing different types of photometers or different wavelengths. Or perhaps, as these instruments have a filter wheel inside, each one may have a different set of filters to have higher multispectral resolution.


It is possible to send a probe deep within the Earth? The deepest borehole ever drilled is just 12km.
Consider this as a possibility. A small self-propelled probe is created, its approximately the size of a football, and is very strong, made of materials with a melting point of a few thousand K. If this was dropped into one of the planet's various volcanic lava lakes, how far down could it travel? Or does the viscosity of the molten rock increase with depth limiting it to a few 100m only?

First, read these three very relevant questions and answers:
Why the "Mission to Earth’s core" proposal suggests using liquid iron instead of lead?
Can we really travel through earth's core?
Hypothetically, what would happen to the earth if a large hole was drilled through the center?

It is possible to send a probe deep within the Earth?

No.
Here's why:
First, there is a very common misconception that there's some sort of magma ocean underneath the crust. No - there isn't. The Earth's mantle is overwhelmingly solid rock. There are very small and localised places where you have melting, and that's where you have volcanoes (if it reaches the surface - most often it doesn't).
Second, even if you go to a volcano and drop your probe there, there is no simple tube that goes down. A volcano "plumbing" system is more like a maze with bifurcations, bends, kinks, and all of that. Not only that, you are going against the flow. You've probably seen videos of erupting lava flows (one, two). These things are massive and fast. Your probe will have to go against the flow in that thing. It will be worse than trying to go upstream in river rapids.
Third, even if you somehow manage to make a probe that autonomously navigates upstream in thin underground lava corridors with surprise bends, you have to remember the underground magma chambers are not 100% liquid. They are what we call "crystal mushes", which is a pile of small crystals (i.e., bits of rock) with liquid in between. Think more like wet sand, than pure liquid. So you're not swimming in something with no resistance, you also actively have more solids out of your way.
Fourth, molten rocks are extremely corrosive. You were talking about materials with high melting points. That's not your problem. Even the hottest lavas only get to about 1400 °C. We have relatively cheap materials that will melt at much higher temperatures. The issue is the reaction between the magma and the materials into making new materials, or dissolving completely in the magma. As an illustration, consider sodium chloride. Salt. The point at which it melts, if you stick it into a furnace is around 800 °C. Surely, that's much above the temperature of let's say an ocean, and it might be a good idea to make submarines out of salt! Clearly, bad idea. Because the salt will just dissolve into the ocean. Whether it melts or not is irrelevant. So that's the big problem with your probes - the magma will simply dissolve it.

So to sum up, you need your probe to be able to navigate in the dark and propel itself upstream in magma, be able to dig and clear space up front so it can move forward, and made of a material which is inert to the magma. Sorry - not happening. But a fun thought experiment nonetheless.


How do the different densities of the oceanic and continental crust affect earth's outer shape? I am currently reading a textbook and I am slightly confused at a paragraph that deals with some general facts about earth's outer shape.

It mentions that the density of the continental crust is less than the density of the oceanic crust. Then it concludes (somehow?) that the continental lithospheres weigh less than the oceanic lithospheres. Using this then, it says that the continental lithospheres are "floating more up" on the asthenosphere  than the oceanic lithospheres. And then it continues with other facts.

I feel like there's something missing here. I understand that the denser material will sink in more. But how does this affect earth's outer shape? I mean sure, it means that the continental crust will appear more higher than the oceanic, but I fail to see this. All pictures I have seen don't show this clearly. Could someone maybe explain this in more detail with an appropriate image or animation?

The two confusions have everything to do with Isostasy as mentioned by Gimelist. I advise you to read the Wikipedia page because it will explain everything to you! But maybe this helps:

The continental crust is made up of relatively light-weight material compared to oceanic crust. That's really all that the authors of your book should have said.

The fundamental idea of isostasy is that from a certain depth onwards to the center of the earth, the pressure is identical no matter where you are. This 'compensation point' is usually taken at about 100 km depth. This is an assumption about the physical state of the Earth -- it is thus an assumed reality!

This means that you can take any single column from 100 km depth (say, a cylinder, or a square meter) and extend it all the way to the surface, and all the columns that you could choose must weigh exactly the same (such that they cause the same pressure at 100 km depth). Mathematically, this is an integral over the densities(!) that you encounter as you move towards the Earth's surface: $\text{Pressure}=\text{mass}/\text{area}=\int_{100 \text{km depth}}^{\text{surface}(x)}\rho(x,z)\Delta z=\text{constant}$. It is the density that varies with $x$, i.e. your location on the earth, that makes the exact location of the $\text{surface}$ variable with $x$ also!

So you're moving up in your column and summing all the densities you encounter every meter. Density is always positive, so your sum is always growing. You also know that the solution has a fixed, constant, solution. We could thus just keep integrating from 100 km depth towards the surface, and when our integral reaches the constant, we know that we are at the earth's surface! That's a useful bit of information, because...

If the material in your column is relatively dense, the distance from 100 km depth until the $\text{surface}$ must then also be relatively small, because you're reaching the integrated constant faster! And vice versa, if the material in your column is relatively light you know that the surface extends out relatively far. It then follows that the oceanic crust has its surface at a lower level than the continental crust, because it is about 20% denser.

Effects of buoyancy only make the matters worse, as continental crust tends to be much thicker than the oceanic crust, and correspondingly it 'floats' higher on the fluid-y astenosphere below it. This is much like an iceberg floating on the sea: a larger iceberg both sticks into the sea more and sticks out of the sea more. The continental crust does the same: it has a deeper base and higher surface than the continental crust, because it 'floats' on the more dense 'fluid' underneath.

There are thus roughly two effects (although of very similar physical principles) that make the continental crust rise above the ocean crust: it is less dense and it is thicker! Therefore, continental crust rises above continental crust to produce the same pressure at depth, and its base lies below the oceanic crust because it is thicker (and floating like an iceberg).
So the missing piece of information in your book was the perspective of a constant pressure. I hope that helps :-)


"Impression and pseudomorphism" in fossils In a book on invertebrate paleontology I have (Treatise on Invertebrate Palaeontology, A) there is a diagram showing possible fates of a shell after the death of the organism.

One of the possible fates is "true fossilization". Another is "impression and pseudomorphism". What's the difference between these two?

Impression are just that, an impression, an imprint of the fossil but the fossil that created it is gone (or just separate) such as this impression of a ammonite.
Pseudomorphism is just a new term for a natural casting it can be a cast of the fossil or a cast of the fossils impression, again the shape is preserved the the original fossil is seperate or has dissolved and been replaced, for instance the natural casting of the braincase of hominids can be used to reconstruct missing parts of the skull. This snail shell is also a pseudomorph, the entire thing has been replaced with agate.
In true fossilization some component of the original material is still present this can preserve internal structure. With bone for instance a ture fossil of a bone often has some of the original calcium/phosphate with pore spaces around it filled in with other minerals.  Of course like anything in nature pseudomorph and true fossil are not completely discrete but ends on a spectrum, partial replacement is the norm.


Why is McMurdo Station in Antartica more hostile than Longyearbyen (Norway), while Longyearbyen is closer to the pole? McMurdo Station in Antartica (operated by the USA) is 77.85 degrees south (and 166.69 east), Longyearbyen (Norway) is the northernmost settlement with scheduled flights all year at 78.24 degrees north (and 15.47 east).
Longyearbyen is further north than McMurdo is south, but McMurdo rarely receives flights in winter, and seems to be a much more hostile environment overall.
Why is that?

The lack of oceanic and atmospheric currents going into and around Antarctica from equatorial latitudes means that much less heat is transported from the tropical latitudes to Antarctica compared to Svalbard. Therefore, at equal latitude (i.e. equal solar isolation), temperatures in the south are much colder.

In Antarctica, at 75°S latitude most of the land has permanent snow cover.

As for the flights, in addition to the fact regarding the distances mentioned by Erik, also consider that the only landing strip in McMurdo that can be used by planes with wheels is over an ice shelf (a floating platform of ice). Therefore, installing proper airport instrumentation is impossible, and landing is performed mostly by visual navigation. This is something that can not be done safely in the permanent darkness of winter months or in bad Weather.

There are scheduled commercial flights in summer from Punta Arenas to Union Glacier (latitude 80°S and more hostile than McMurdo). But they are extremely weather dependent. Most flights gets delayed, and waiting a week to fly is not unusual (it was even more common when the landing strip was some kilometers south in Patriot Hills).
Therefore, an Ilyushin 76 plane is waiting in Punta Arenas the whole summer just to fly once a week at most. All that added to many other logistical complications makes the round trip ticket to Union Glacier about USD$22,000. It wouldn't be much cheaper to McMurdo, so you can imagine that few people will be able to afford it. Therefore it is kind of a niche business that is not attractive for commercial airlines.

The only landing strip that is on solid ground in Antarctica and is large enough to receive commercial planes (medium size, nothing big) is on King George Island (latitude 62°S). DAP airlines also has scheduled commercial flights there, but they are also extremely expensive.  Tourist flow in winter is minimal; Auroras generally aren't seen there, and  therefore there is little draw for tourists to visit during the winter.


Guinea Current existence in the Atlantic Why does the Guinea Current exist at all?  There are no similar currents in the Pacific or Indian Oceans and the Guinea Current also disappear during northern summers.  Why?

The Guinea Current is in geostrophic balance with isopycnals sloping upwards towards the north. The current is not directly related to wind direction and magnitude and that makes rather especial. As many other eastern boundary currents, it is characterized by the presence of coastal upwelling (Bakun, 1978), which delivers nutrients to the surface waters and results in increased primary production.

 Source: RSMAS

The Guinea Current is connected with the North Equatorial Counter Current (NECC) and in fact it can be considered the eastern continuation of the NECC. The seasonal variations in the position of the Intertropical Convergence Zone affect the connection between NECC and Guinea Currents. The Guinea Current is also connected to the Canary Current flowing southward along the African coast. In this sense, the Guinea Current is at least partially related to the Indian and Pacific Equatorial Counter Currents. The difference is that there is no long stretch of coast parallel to the Equator in those oceans.

RSMAS ocean currents project provides a complete description of the main characteristics of the Guinea Current with references.

Also, the Guinea Current does not disappear during the northern summer. In fact, there is a tendency for the current to intensify (check Figure 3 in Bakun, 1978 for instance).

Bakun, A., 1978. Guinea current upwelling. Nature, 271(5641), pp.147-150.