what is a transverse isotropic rock? I know isotropic means equal properties in all directions , but the term "transverse" is not making it easy for me to understand.

You are correct. Isotropy means that the property at some specified point (X,Y,Z) is the same, whether the measurement is made along any direction.

If the property varies depending on which direction you make the measurement in, then that property is said to be "anisotropic". For example, the permeability of a material (i.e. its ability to conduct fluids) may be anisotropic if fluid can move preferentially in one direction and it would be difficult for it to move in a different direction (like the tubes below). This means, the permeability of this material at a given point (X,Y,Z) depends on which direction you make the measurement, i.e. high permeability parallel to the tubes, low permeability otherwise.

Transverse isotropy (also called hexagonal symmetry) is a special kind of anisotropy in which there exists a special "axis of symmetry" such that the property you are measuring appears to be the same as you make measurements perpendicular to this axis. Basically, rotating around this axis of symmetry, the property looks pretty much the same, i.e. it is isotropic in this transverse direction. However, once you go off axis, then the measured property will change.

In geology (especially in sedimentary geology), transverse isotropy is usually a good approximation to many phenomena (elasticity, permeability, heat conductivity, etc.) due to the fact rocks are deposited mostly horizontally. This means that things will look very similar laterally (in both N-S and E-W directions) but very different vertically.

Finally, transverse isotropy is just an approximation to the much more complex nature of real rocks. If you were to add multiple sets of fractures to a rock on top of its layered nature, you will need to use a "less symmetric" model to describe it: orthorhombic, monoclinic, or triclinic. But for most practical purposes, transverse isotropy does a pretty good job.

Hope this helps!


What are we seeing when we see the curvature of Earth? I don't know if this question's for here, physics, maths, or geometry.

I know that this or something similar has been asked a million times, but I've recently come to the concept that since the horizon is a circle centered at the viewer's position, the whole horizon is at the same level, hence why it's flat.

So what is it that we're seeing when we start seeing the curvature once we're high enough? I have a feeling that the answer to this has to do with the angle that the globe takes in your "camera", but the question still stands, what is this picture looking at? Why does it show a curve in the horizontal?

the horizon is a circle centered at the viewer's position

There are two things wrong with this. The first is the assumption that the Earth is entirely spherical - there are no hills, mountains or other bulges to block the view. But let's make that assumption, because there's a more fundemental misunderstanding in the geometry.

The horizon is a circle that is centered horizontally at your position, but not vertically, because by being above the surface you can see a little way around the curve of the planet.

If you're standing on the ground you are only looking from a couple of metres altitude, so you can't see very far around - this means that the circle of the horizon is centered only a small distance below your feet. Note that from this height you can't make out any curvature in the horizon.

If you're standing at the altitude from which your picture was taken, the horizon circle is centered some depth into the planet. So you are not looking out across a circle, as you imagine - you are looking down, onto a circle. Or if you like, you're looking down onto a disc that happens to have some portion of the planet piled on top of it. And when you look at a circle (or a disc) from above, it appears curved.


Is there any new water formed on, or brought to, Earth? I've found 2 sources stating that there is new water being formed on Earth.  The first site states that it is coming from hydrothermal vents in the sea floor.  The second site is basically saying that new water is being generated through biological processes.  However, to me, this just seems water that is already here coming up to the surface in the case of hydrothermal vents, or the rearranging of atoms into water molecules through biological processes that are already here on Earth.  Maybe this explanation is just semantics, but I'm also wondering if new water is coming here from meteors/meteorites.  To me that would be new water on Earth.  Is there any definitive proof of new water being formed on or brought to Earth?

Your explanation(s) sounds correct.

Your first article says as much.

  There is a water cycle on earth that takes wet sediments deep into the
  mantle to be re heated and circulated back up as new sea floor. This
  is where the water in hydrothermal vents originates - it is NOT new
  water. However, there remains a possibility that some of the water
  emerging from the mantle has been there since the formation of the
  earth so some of it MAY be 'new'.

And your 2nd article

This is at least partly semantics calling it "new" water.  When we burn gasoline for example, the hydrocarbon structure becomes Water and CO2 - is that new water, or just re-arranging molecules by chemical reaction and fire?

  I'm also wondering if new water is coming here from
  meteors/meteorites.

Water absolutely reaches the Earth by comets and meteors.   We're hit by comets and meteors all the time and comets especially are water-rich.   That is new water, though I wouldn't want to put an estimate on how much.  Too big a margin of error.

Earth also loses water by UV rays from the sun.   Most of the atmosphere the Earth loses is Hydrogen and most of that Hydrogen comes from Water.   Losing 90 tonnes of Hydrogen per day works out to nearly 800 tons of water per day, which sounds like a lot, but compared to the vastness of our oceans, it's a proverbial drop in the bucket, even over hundreds of millions of years.

So Earth adds water by comets and Earth loses water by photo-disintigration and atmospheric escape.   I've read that it's a net loss, not a net gain, but it's pretty insignificant either way.    Some articles suggest Earth has lost a pretty good share of it's water over billions of years.   I think there's a pretty big margin of error in those estimates, personally.

In 200 or 300 million years, as the sun grows a little larger and brighter, we might need to begin to worry about Earth losing too much water (maybe).  That's if we're still around, of-course.


USA and UK government report on plane emissions: 200% difference... which is right? The report's respective ratio of 1 passenger car vs one long haul plane are 40% versus 110%:

Image 1 (DEFRA):
car = 171 plane  = 195 (110%)

Image 2 (EPA):
car = 4096 plane = 1760 (40%)

If the us uses petrol, it should be the other way around if anything

A car exhaust is at 50cm altitude, versus a plane at 10km altitude. The atmospheric lifetimes of the heavy fumes should therefore be different in the EPA's 100 year atmospheric lifetime indices.

Why do the reports have a ratio of 40% vs 110 % GWP CO2 equivalent for a car vs a plane?

EPA source:

I've looked into this briefly and noticed a few things that are worth pointing out.  First, your EPA table looks like it was based on Table 8 of this EPA pdf:

https://www.epa.gov/sites/production/files/2018-03/documents/emission-factors_mar_2018_0.pdf

There’s a note in the table that,

  Air Travel factors from 2017 Guidelines to Defra / DECC's GHG
  Conversion Factors for Company Reporting. Version 1.0 August 2017.

So, with a lovely bit of irony, those EPA air travel numbers are taken from the UK/DECC/Defra, which are available here:

https://www.gov.uk/government/publications/greenhouse-gas-reporting-conversion-factors-2017

Note that they’ve translated the names of the air travel distance categories so they make sense in the US market:

US short-haul (< 300 mi) = UK domestic (UK to UK)
US medium-haul (300 - 2300 mi) = UK short-haul (< 3700 km)
US long-haul (> 2300 mi) = UK long-haul (> 3700 km)

Taking some numbers from US short-haul/UK domestic as an example, the CO2 emissions are,

0.14002 kgCO2e/pass km = 140.02 gCO2e/pass km = 225.3 gCO2e/pass mi

which is just basic units conversion and agrees with your EPA table and the EPA pdf.  The same is true for the CO2 emissions in the other distance categories.  Note that the EPA are using the numbers for the CO2e emissions without radiative forcing feedbacks from water vapor, contrails, NOx, etc., which is the dark blue portion of the bars in your plot from the BBC.  You should be comparing that portion of the emissions, not the full bar including the light blue.

There's a further problem with the CH4 and N2O values in your EPA table.  Taking the same example as above but for CH4 emissions,

0.00006 kgCO2e/pass km = 0.06 gCO2e/pass km = 0.097 gCO2e/pass mi = 0.0039 gCH4/pass mi

This is correct in the EPA pdf, but has been mis-transcribed in your EPA table as 3.9 gCH4/pass mi.  Oops! someone got confused between grams and kilograms, and they've made the same mistake in the CH4 and N2O entries for all modes of transport.  They’ve then used this to calculate the overall GWP column, so their values are oversensitive to CH4 and N2O:

GWP = 225*1 + 3.9*25 + 7.2*298 = 2468.1

The correct calculation is,

GWP = 225*1 + 3.9e-3*25 + 7.2e-3*298 = 227

The bottom line is that I think the GWP column in your EPA table is nonsense and the aircraft emissions factors have the same source (albeit the BBC are probably using more recent UK emission factors).  The respective CO2 emissions for cars in the sources I've linked to aren't wildly different (297 gCO2/mi in UK, 343 gCO2/mi in US) and for motorcycles are almost identical (183 gCO2/mi in UK, 189 gCO2/mi in US).


If the atmosphere is (very nearly) an ideal gas, how can it ever be barotropic? A barotropic fluid is a fluid whose density is a function of pressure only, i.e. $\rho=\rho(p)$. My understanding is that, in the atmosphere, in general, the tropics are barotropic whereas the extratropics are baroclinic.

If the atmosphere is an ideal gas, then $\rho =p/R T$. Therefore, density is a function of pressure and temperature. How, then, can the atmosphere ever be barotropic?

You are correct, the atmosphere cannot ever be barotropic. It is important to note that the ideal gas law is relevant only as a state equation; it does not describe the gas as a whole. The barotropic assumption effectively states $P=\rho RT_0$. Effectively, it says "hold temperature constant" You may note this is particularly important when discussing the hydrostatic and hypsometric/barometric equations.

On that note, the atmosphere is never entirely barotropic; the atmosphere cannot undergo entirely adiabatic motions; the wind can never stay geostrophic, etc. There are assumptions that are bad, and we know they are (take a class in micrometeorology dealing with similarity theory). But in the words of George Box, "All models are wrong, but some are useful." These simple models teach us about basic atmospheric behavior.

It is also worth noting that the ideal gas law is not the only equation of state. The Boussinesq and anelastic approximations can lead to interesting other formulations of the equation of state.


Is it hotter in different places with the same air temperature? I am from (and live in) Minnesota, USA. In the summer here it always reaches temperatures in the 90s (F) for periods of time but not every week. The humidity is often high and the dew point often tropical.

My wife is from Guangdong province in the south east region of China. The temperature there most closely resembles Florida, USA. It is usually in the 90s during the summer instead of sometimes. It is always humid and feels tropical.

My wife, her friends and family routinely comment on how incredibly hot it is in China. They say people often don't even go outside because it's so hot. They say it is not like Minnesota, but much worse.

My question then... how? Is this merely perception of growing up in a tropical environment without artificial climate control or is there science that backs up their claims? If our regions are the same air temperature with similar humidity and dew points, I don't understand how it can feel so much hotter there.

While perceptions about the climate can have an effect on how we react to our environment, Guangdong and Minnesota are fundamentally different climates altogether. Using the Koppen-Geiger climate classification system, Minnesota is mostly a Temperate Continental (Dfb/Dwb) climate, meaning that is has warm summers and long cold winters, while Guangdong is a Humid Subtropical (Cfa/Cwa) climate with hot and wet summers and a short dry winter. The classification is largely based on monthly average temperatures and precipitations based on climate normals (~30-year periods).

It might be the case that temperatures match up at some points, but based on the classifications/geography of both areas, it would seem that Guangdong experiences more humidity and much longer warm periods, which combined would raise the Humidex (https://en.wikipedia.org/wiki/Humidex) above that of Minnesota.

For more information on the Koppen-Geiger classification, https://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classification


What does the absence of passive margins between 1740-1600 million years ago tell us about the tectonic environment at that time? In the article Passive margins through earth history (Bradley, 2008), a passive margin is defined as:

  a synonym for the bulkier Atlantic-type
  margin, trailing-edge margin, rifted margin, or divergent margin. A
  passive margin is one formed by rifting followed by seafloor
  spreading, so that the resulting plate consists of both continental
  and oceanic lithosphere, welded across an igneous contact.

In the research, the author determined that in terms of the abundance of passive margins that the distribution varied with time, from the article:

  They were abundant at
  1900–1890, 610–520, and 150–0 Ma, scarce at ca. 2445–2300, 1600–1000, and 300–275 Ma, and absent
  before ca. 3000 Ma and at 1740–1600.

The absence of passive margins older than 3000 million years is uncertain, possibly due to lack of preservation; however the absence between 1740-1600 million years is described vaguely by the author as being the result of

  One by one, each of these margins collided
  with something, leaving no passive margins at all

possibly related to the coalescencing of the "supercontinent" Nuna - but the total absence is not noted in association with other supercontinents (Rodinia, Pangaea etc).

What does the absence of passive margins between 1740-1600 million years ago tell us about the tectonic environment at that time?

Good paper you reference there.  I think you are starting to answer some of your question by noting that Bradley associates the absence in passive margins with the Nuna supercontinent.  All "rifting" / spreading is taking place in the oceans - pretty much a requirement for supercontinents,  and in this case all continental margins (or at least for those with surviving geological record) were destructive margins.  Over time the duration of passive margins has changed.  For more recent supercontinents you mention, the shorter cycle of a passive margin may have made it very unlikely that tectonic events could cause a simultaneous gap in all passive margins.

As Bradley points out in his conclusions, tectonic activity when Nuna was around may have been globally more sluggish that today, or during the time of Rodinia and Pangea. It may also tie in with the formation of some mineral deposits.  For example, there is a peak in porphyry deposits at about this time.  Now taking into account that older porphyry deposits are less like to have survived (lost through erosion, buried or consumed in later tectonics) the peak at this time may reflect that it was a particularly good porphyry generation time for so many to have survived.  Porphyries do like convergent margins and there would have been lots of those.


How different can microclimates be than their surrounding areas? How much different in temperature and pressure can a microclimate be than the surrounding region?  In other words, if you had a dry region but then a valley within a ring of mountains that isolated the local environment could the valley have distinctly different humidity, temperature and pressure and how far much different could it get?

Elevation is often responsible for the biggest differences; you can have snow and glaciers on the top of mountains in warm climates. South America can show you how extreme the differences in precipitation can be: rain forest on one side of the Andes Mountains, world's driest (non-polar) desert on the other. So really it depends on how high and complete your mountain ring is.
Here is a decent book on the subject.


What is the difference between dew and rain? What is the main difference between dew and rain?

Would it be correct if we say that rain is done in the upper troposphere while dew done in the lower troposphere? Or there are better definitions for the main difference between them?

Dew is condensate that forms on the surface, usually by the surface cooling to a temperature below the dew point of the air. Thus the water vapr accumulates onto the surface.

Rain is formed by Collision-Coalescence or the Bergeron-Findelsen process. The cloud droplets are formed by the condensation of water vapor on aerosols, when the air reaches supersaturation via the Kelvin Effect and Raoult Effect (which makes up Kohler Theory).


How do scientists determine the absolute or 'chronometric' date of fossils? Absolute dating is the process of determining an approximate computed age of something like a fossil. How does that work?

Biostratigraphy - observing which fossils were present in which stratigraphic units, and using minimally-deformed sequences to determine age order - gives us relative ages of fossils.

Absolute ages, however, rely on geochemical chronometers: just like dating the reversals in the Earth's magnetic polarity by establishing how old the oceanic crust that records them, or working out when volcanic eruptions happened. Which chronometer you use depends on exactly what you're working with, but what they all have in common is that they use radiometric dating: the "ticking clock" is radioactive decay, which proceeds according to a radioactive isotope's half-life. Radiocarbon dating can be used for the most recent of these, but the example I'm going to use is uranium-series decay in corals - even though it's a weird one, because unlike most systems it doesn't measure parent-daughter ratios, but rather how closely the system has approached secular equilibrium.

Uranium is soluble in natural waters at conditions found on the Earth's surface; thorium, however, is not; so corals (predominantly calcium carbonate), while growing, continuously incorporate uranium but not thorium. Once they stop growing, this is no longer true - the amount of uranium incorporated in the coral is now fixed. Uranium-234 decays to give thorium-230, which is itself radioactive, with a significantly shorter half-life. At secular equilibrium, the rate of thorium-230 production (from uranium-234 decay) equals the rate of thorium-230 decay, so 230Th reaches steady state. Provided secular equilibrium has not been reached and the concentration of 238U (234U's parent) is also known, it is possible to calculate how long ago the coral stopped incorporating new uranium - became a "closed system". The mathematics of U-series secular equilibria are well understood but somewhat tedious, and are freely available.


How to calculate residence time for an element in a reservoir? The residence time for an element in a reservoir can be calculated by the reservoir size at steady state divided by the inflow or outflow rate. Given the following diagram, I need to calculate the mean residence times for nitrogen in the following stocks:

Atmosphere
Fixed Nitrogen on Land

But I am confused by this question, what exactly is its steady state? what exactly is the reservoir size and what it the inflow and outflow?

Thank you

EDIT: Problem-solved with the help of Camilo Rada. The way you calculate residence time is by using the formula:

$\text{Residence time} = \frac{\text{Reservoir size}}{\text{in-flow or outflow rate}}$

In the example I looked at the box in the diagram for atmosphere's content of residence, being $3 \times 10^{20}$ units, that will serve as our total reservoir size, then we can either choose the outgoing or incoming flow (as an approximation as the reservoir is not in steady state), I chose the outgoing, so we add them together: $7 \times 10^{12} + 7 \times 10^{12} = 14 \times 10^{12}$ units per year. Now plug that into the formula:

$RT_{ATMO} = \frac{3 \times 10^{20}}{14 \times 10^{12}} = 21,428,571 \, \text{years} = \, \backsim 21 \, \text{million years}$

It would be the same process for each box.

Steady state is when the size of the reservoirs doesn't change with time (because inflow=outflow). The size of each reservoir is the number inside the boxes and the flow rates are the numbers beside the arrows.
If you calculate the total inflow/outflow from each reservoir, you can use the relationship you did enunciate at the start of the question to easily calculate residence times.

However, according to the diagram those reservoirs are not in steady state. So either the question is ill posed, or you are supposed to make some approximations (or a more complex calculation, but I don't think that's the case).


Is Bowen ratio an absolute indicator of land surface type based on the amount of heat transfer from the surface? Bowen ratio (BR) is the ratio of sensible heat flux to latent heat flux, i.e.,

$$Q=Q_{s}/Q_{l}$$
where $Q_{s}$ is the sensible heat flux and $Q_{l}$ is the latent heat flux. It is an indicator of the amount of heat lost from the surface to the atmosphere. In water bodies, latent heat of vaporization is higher and hence the bowen ratio is less than one. In dry urban surfaces (e.g., buildings and asphalt roads), evaporation is lower and the bowen ratio is greater than one.
The bowen ratio over different surfaces have different values.

Can we then identify the underlying surface roughness type based on the bowen ratio alone?

I am thinking of the latitudinal and altitudinal dependence of the heat flux regime. For example, assume that there are the same vegetation distribution at 1km above sea level (a.s.l) and 4 km a.s.l at different but relatively closer latitudes, then can they have the same bowen ratio?

My idea is that BR is not the right way of quantifying the type of surface roughness because the lower pressure and temperature at 4 km in the example above favors more sensible heat flux than latent heat flux which increases the bowen ratio and gives wrong signal that the surface type is bare soil or sand.
Can someone explain why BR is used as a means of quantifying the surface roughness type?

A very simple answer is that it is related to the demands of the vegetation types and their ability to maximize the net radiation. A "perfect" plant that covered the entire surface would theoretically result in a BR of 0 as 100% of Rn is used for photosynthesis and released as ET, such that H=0 and LE=RN and B=H/L. It obviously doesn't work that way though.

Since $B=y\frac{\partial T}{\partial e}$ where y is the psych constant (~0.4 and really not a constant) it can be seen that the gradients of temperature and moisture, not the actual values, are the only two factors that matter in determining the Bowen ratio. Each plant essentially has a "specific Bowen Ratio" range where they are able to maximize their use of RN for the environment they are in. If the climate changes in that area the plant would not be able to survive.

That is a very very basic and highly simplified explanation, but hopefully it helps


Can earthquakes affect the atmosphere? Recently an earthquake of magnitude 6.9 shook the northeastern region of India, where I live. After the earthquake, the climate has changed dramatically resulting in excessive hail showers, thunderstorms and heavy rain, continuously for 11 days until now.

It is the time for the usual monsoon period, but the weather is quite unusual. Can an earthquake affect the weather; is this kind of behaviour a common after-effect?

Apparently there is no relation of earthquakes with the weather. But in a book, "Earthquakes- mitigation by Tatsch" there are several precursors associated with ponding earthquakes. One is unusual weather. Some of these precursors are pre- and some post-earthquakes. Your cited earthquake may have some relation with it.


hydrologic vs. hydrodynamic modelling of surface runoff In the description of a Software it says that it computes the net rainfall, runoff formation and runoffconcentration on a surface hydrologically. With an extra module, the runoff formation can also be computed hydrodynamically.

What is the difference? How does both work, roughly speaking?

The word "hydrological" is meant to indicate that the model only includes a sort of bulk description of the water: where it is, how much is there, and where it flows. It generally only includes length and time scales of interest to the system in question. So, for ground water models, this may be tens of meters and longer in horizontal direction, and hours and longer in time.

On the other hand, "hydrodynamic" is generally understood to resolve the governing equations for water flow, i.e., the Navier-Stokes equations (possibly posed in a porous medium). This must then deal with the length and time scales of eddies, which are substantially smaller and shorter than the ones above, and consequently requires a lot more computational power.


Polar Ice caps are melting? Questions on enviromental impact The polar ice caps are melting at a significant rate partly due to the albedo effect, releasing greenhouse gas-methane into earth’s atmosphere. At the same time we are logging our forests for agricultural expansion. Is year twenty -thirty an accurate prediction for polar ice extinction?

A.)  Is there a model to show just how much our forests absorbs green house gases?

B.)  Will an abundance of $CO_2$ & methane-gas over load the earths forests & oceans natural ability absorb such gases and start to kill them off.

C.)  Does our ocean's plankton act as a mechanism to recycle the atmospheres $CO_2$ Green house gases.

BBC Artical $CO_2$

I think you misinterpret the article you cited. In the article it is stated that:

  The melting of the polar ice-caps has
  an effect "the equivalent of about 20 years of additional CO$_2$ being
  added by man"

This is due to the energy in sunlight which is no longer reflected by the white ice and snow of the polar caps. This energy will be partly absorbed by the darker surface of the ocean or land which will be underneath the ice-caps. This absorption of energy (instead of reflection) has an effect which is equal to "the equivalent of about 20 years if additional CO$_2$ being added by mankind".

There probably are models that can tell how much CO$_2$ can be absorbed by trees. However, an ecosystem which is in balance (e.g. a full grown forest) doesn't absorb that much CO$_2$ anymore. This is because the growth of new trees is equal to the dying and decomposition of old trees (in balance). Only a little part might be stored in the soil.

An increase of CO$_2$ might increase the growth rate of trees due to in increase of effectiveness of photosynthesis. (Stomata will have to be open less longer to require the same amount of CO$_2$ and therefore trees will lose less water for example).

Our ocean does absorb CO$_2$ as well. Algea, phytoplankton, and chemical process all make this happen. What you mean with recycle -- as well I'm not sure.


Seismic dispersion: What does it really mean and what causes it? Body waves (to some extent) and especially surface waves show dispersive characteristics during propagation. In Dr. Christopher Liner's book [Elements of Seismic Dispersion (2012)], this phenomenon is quickly attributed to propagating seismic energy being frequency-dependent. I've heard this phrase for a long time, and I am still unsure how to visualize and/or quantify it for the sake of really understanding this phenomenon.

Indeed, why can't one phrase it as being wavelength-dependent as well? Also, for both surface and body waves, what are the primary factors that cause/generate seismic dispersion?

Frequency- or wavelength-dependent are indeed equally valid terms but frequency is in practice more measurable than wavelength, so much so that seismic wavelength is calculated not measured. Dispersion is caused by material density, the material the waves pass through will, depending on density, pass certain waves, and wavelengths of those waves, better than other waves and wavelengths.

Describing my visualisation of the effect is difficult, the best way to look at the effect is to find seismic traces of the same earthquake from various ranges. This will show the different wave fronts spreading out as they travel. This is largely due to their compatibility with the material they pass through. I find it comparable to structural resonance there are frequencies that interact well with the rock they're travelling through, they get a boost, and there are those that interact less well, they get held back by the material they're travelling through.


Calculating the displacement of a fault In the calculation of scalar moment magnitude of an earthquake we have the formula

$$M_0=\mu AD$$

where:

$\mu$ is the shear modulus of the rocks involved in the earthquake (in Pa)
$A$ is the area of the rupture along the geologic fault where the earthquake occurred (in m2), and
$D$ is the average displacement on $A$ (in m).

In many cases the displacement can occur in the subsurface.In order to predict the moment magnitude of such earthquakes the value of $D$ must be estimated. How is this process carried out ?

The process is carried out by solving an "inverse problem" and there are many ways to estimate the moment depending on the observable. For example if you have some measurements of ground deformation following the earthquake (using GPS/InSAR) then by combing a physics based model, with an optimizer, you can estimate the area/slip distribution that best explains the observations. Once you know the area/slip distribution then you can estimate the moment.

The physical models can be simple or complex (e.g., semi-analytical or fully numerical). Same goes for the optimizer (local or global). For computationally expensive numerical models global optimization is typically not feasible. For local optimization you need a 'reasonable' initial model.


Timeline of Himalayas/Tibetan plateau formation Note: edited based on helpful comments.

In Walking with Cavemen, Robert Winston claims an African rainforest existed 8 mya, but by 4 mya it was gone. He attributes this to newly Himalayas-triggered Indian monsoons, which prevented rainfall from reaching Africa. However, it's my understanding that India collided with the rest of Asia circa 50 mya. So why did the monsoons take so long?

Multiple comments have noted that Winston should have credited the monsoons to the Tibetan plateau. Either way my assumption is that, until the mountains had been pushed up far enough, they didn't threaten the forest's rain supply. On a linear approximation, by 8 mya the Himalayas' mean height would be approximately 85% of its present value, which bounds the "critical value" of the altitude as a percentage of its current one. A similar calculation applies for the Tibetan case.

Why did the motion of India lead to a multi-stage mountain formation? How did the timing of these effects influence Africa?

Drying out of North Africa is likely the result of something far more local. I've never heard of the either the Tibetan Plateau or the growing Himalaya as causing changes to Africa's monsoons and always understood the connection between Milankovich cycles and the consequences of glaciation. According to this study, which modelled weather patterns of the time:

Aridification of the Sahara desert caused by Tethys Sea shrinkage during the Late Miocene

The drying of Africa started much earlier and was likely related to orbital cycles of glaciation-induced drying of the Mediterranean region.

  Through a set of experiments, we demonstrate that the African summer monsoon was drastically weakened by Tethys Sea shrinkage, allowing arid, desert conditions to expand across north Africa. Not only did the Tethys shrinkage alter the mean climate of the region, it also enhanced the sensitivity of the African monsoon to orbital forcing, which subsequently became the major driver of Sahara extent fluctuations.


Why do cities at high altitude regions have high atmospheric pressures? Why do cities at high altitude regions, such as Lhasa, altitude 11995ft (3656 metre), have high atmospheric pressures such as 30.11inHg (101.97 kPa) in the weather report?

The reason for this is that the reported value is the relative pressure and not the absolute pressure. If meteorological stations reported the absolute pressure, dependent on elevation, it would been really confusing. So air pressure is always adjusted to sea level.

This is also why your home barometer has to be adjusted to show the correct pressure depending on the altitude where you are.

Here are a link to the weather close to where I live. It is at 150 m elevation,
https://www.yr.no/place/Norway/Buskerud/R%c3%b8yken/B%c3%b8dalen/hour_by_hour_detailed.html?spr=eng If you seek for Drammen you will see the green line showing the same pressure but the elevation there is close to sea level 10m or so.


Missing pages in Knauss' "Introduction to Physical Oceanography, 2nd edition"? "Introduction to Physical Oceanography, 2nd edition" by John Knauss is a popular oceanography textbook. I bought a copy. It ends at page 308, apparently in the middle of the index. (It seems unlikely that the index would end at "tidal," without having entries for such oceanography favorites as "water, "wind," and "waves.")

I sent an inquiry to the publisher. The publisher was not helpful. I sent the book back to the vendor, and requested a replacement. The replacement was identical.

Does anyone have a copy of the book with index pages beyond 308? Or are they all like that?

I own the Second edition, 2005 reissue of this textbook, purchased through Amazon in August 2009.

After p308, my copy has only one more page of content (p309), which is the last page of the Index. You indeed have a faulty copy. I recommend you send it back for replacement again and request them to inspect the copy before shipping.

If you are still unlucky with the second replacement, I would try e-mailing the publisher with your purchase invoice and request a pdf of the book which would complement your hardcopy with the missing page.


Did we find cinnabarit? We searched for cinnabarit in an abandoned mine (Google Maps, in Békásmegyer, Hungary). We collected these samples, but as we are not geologists, we are not sure what we found. Pictures about the samples:

Did we succeed, is this indeed cinnabarit?

Did we succeed, is this indeed cinnabarit?

Probably yes. Cinnabar has a very distinct brick-red colour, and some of your samples definitely have it. I'm not certain how much of this is actually cinnabar and how much is other stuff, but there is enough cinnabar in there to make it obvious just from the picture.

IMPORTANT

Cinnabar is toxic. It will release mercury metal on oxidation (that is, exposure to air), on exposure to water (so don't throw it in the river), and on exposure to strong light (that is, sunlight). On heating it will release mercury vapour. People die because of this.

Go to the mine, and put it back in there, never taking it back. In case you do want to keep one of them, make sure it is clearly labelled as TOXIC and DANGEROUS and POISON in both English and Hungarian, and keep it away from children and pets.


How long does a magnetic pole reversal take to complete? Geomagnetic pole reversal is a "regular" phenomenon on Earth. Although the interval pattern has been irregular at times (sometimes with millions of years of difference between change intervals), Earth has settled in the last 20 million years into a pattern of a pole reversal about every 200,000 - 300,000 years (source: NASA). Based on this pattern and the fact that the most recent pole-switch occurred ~780,000 years ago, the Earth is "overdue" for a pole switch.

My question: How quickly does a pole switch occur?

Is it instantaneous? Does it take years? Millennia?
Is the current movement of the pole part of a drawn-out switch, or is it just "normal" pole movement? Again, from NASA:

  The magnetic north pole has been creeping northward – by more than 600 miles (1,100 km) – since the early 19th century, when explorers first located it precisely. It is moving faster now, actually, as scientists estimate the pole is migrating northward about 40 miles per year, as opposed to about 10 miles per year in the early 20th century.

From some previous research, it seems like it doesn't always make a "clean" switch either, with multiple poles appearing globally -- would this multi-pole extravaganza increase the switching time, or is it also normal?

The entire process appears to take 3,000-4,000 years, according to Valet and Fournier's May 2016 review article "Deciphering records of geomagnetic reversals," which was published in AGU's Reviews of Geophysics.

  The complex dynamical structure of reversals is supported by
  sedimentary and volcanic records. Provided that resolution is
  adequate, the reversal process seems to incorporate one precursor and
  one rebound prior to and after the transition. However, the three
  phases are rarely observed in a single record. This is likely to be
  caused both by field geometry and recording limitations. The duration
  of each phase does not exceed 3–4 kyr. Therefore, precursors and
  rebounds can be seen as part of the whole process, and the expression
  of a continuum of behavior between secular variation, excursions, and
  reversals. Another possibility is that the dipole collapse is not
  large enough or that the nondipole/dipole ratio varies.

Better resolution of the process and the time involved will require at least a 10-fold improvement in paleomagnetic sampling resolution, the authors contend. And one of the challenges is finding suitable lava flows or sediment layers that were created during the transition(s) in question.

As for whether current fluctuations indicate the earth is about to have a reversal: We can't tell, because the recent paleomagnetic record includes similar changes (sometimes regional rather than global) that did not result in reversals, Valet and Fournier write.

  The present evolution falls within the normal range of field
  variability that prevailed for the past 2 Ma.


What is the history of atmospheric O₂ concentration? (This is about O₂, not CO₂)

How did the concentration of oxygen change?

Over geologic time frames since plants began to produce it,
and during the time since the carbon dioxide increase caused by humans began is most interesting.

It would be most interesting to have an abstract description, even if simplified.

Plots of the concentration over time are useful too, but not central.

Refer to the stratigraphic chart for timeline and stratigraphic units. And i tried to be as up to date as possible in the limited time. Which is also the reason why i omitted some details in favour of an overview.

It is assumed that during the early and middle Archaen only very sporadic oxygen production took place. This changes towards the end of the Archean, when a flow of oxygen from shallow ocean parts to the atmosphere began.

This article suggests that the following "great oxygenation event" (goe), at the early Proterozoic 2.33Gy just took up to 10 million years. During the goe, atmopsheric oxygen increased to 1 or 2 percent, the exact percentage seems unclear. But it seems that in some places, a fully oxygenated ocean existed slightly before the goe at the end of the Archean, at ~2.5Gy. These waters would have been able to produce excess oxygen for the atmosphere in a small or regional scale slightly earlier.

Atmospheric O2 stays low during the Proterozoic, probably because it is used up in weathering processes.

At the beginning of the Cambrian, O2 was still low (~5%). This article describes the development thorugh the Phanerozoic by combining data from modelling and proxies. See Figure 3 (there's your plot;-). It shows that not before the end of the Ordovician atmospheric O2 rises to above 10%, topping off at the end of the Permian at ~32%.

These days, oceanic as well as atmopsheric O2 levels are falling and will continue to do so because of fossil fuel combustion.


Slab-breakoff - always connected to continent/continent collision? The question came to me when pondering the Andes:
Is a slab-breakoff always connected to the transition from subduction of oceanic crust to a continent/continent collision?

Current understanding is that subduction, or quite general plate tectonics, is mainly driven by the pull caused by the negative buoyancy of cold, dense oceanic crust, with other factors playing a minor role.
Let's look at the destructive end: When the oceanic crust subducts under a continent it vanishes into the mantle, possibly dragging a less denser continental mass after it, until the ocean has closed and that dragged continent collides with the other one. We know that happened in the Himalayas, the European Alps and with the Appalachians (list not complete).
It has been theorized that under the unwillingness of continental crust to subduct in a continent/continent collision, the pull forces can cause the dangling oceanic crust to detach. Such detached slabs of long since subducted ocean floor may still reside in the mantle, e.g. under the Himalayas, in several stages in the Alps, where the 'sudden' gain in buoyancy caused by the detachment may be one of the drivers for the uplift and orogeny.
Though partly speculative and not good for an "ad-hoc" and general explanation for an orogeny, is that process assumed to be always connected to a continent/continent collision? I found no discussion or proposal in literature about the Andes (Nazca plate subduction), at least not when searching superficially.

Slab break off happens also during arc volcanic-continent collisions.
Andes is not an exception.


What is "sheltered site" (as opposed to "exposed site")? What is "sheltered site" (as opposed to "exposed site")?

It's used in context of location of trees in bumpy ground areas and weather damage.

Depends on the context. Examples can be: In depressions instead of lonely on the plain, inside of the forest instead of at the edge, along a river bank or lakeside instead of on dry ground.

Or, in short: exposed to wind & weather instead of sheltered from the rigour.

Also depends on the tree. Some pioneer trees can grow individually in adverse conditions, others like it in groups and warm and wet.


Global warming cycles Everyone is saying we are in a global warming, an unnatural one at that because of CO2.

Has there ever been a 'global warming' in Earth's history?  I know that global cooling is cyclical and 'looks' like global warming at the beginning of the cycle and luckily it is cyclical.  There was a good explanation that the 'great dying' was because of global warming.  If there is such a thing what would make global warming cyclical.

Venus is global warming for sure but what could have stopped the cycle of warming to go to cooler therms and stop the 'Venus' effect that can not be changed? There is a negative feedback for global cooling thus keeping that in check.  Is there a negative feedback for global warming?

Has Earth's climate ever changed? Sure.

[1]

There are many feedbacks within the climate system, some negative as you mention but some also positive. A well-known positive feedback is the greenhouse gas effect, which in the present age is caused by anthropogenic fossil fuel emissions. Increasing greenhouse gases (GHG) causes the atmosphere to trap more longwave radiation and increase the temperature. Negative feedbacks can occur in the climate, such as the "Planck" feedback which describes the T$^4$ dependence of radiation emission--so as the planet warms it emits an even larger amount of radiation.

Climate models already take into account many of these feedbacks, but one of the largest unknowns is the effects of clouds and aerosols on the climate. The distribution of phase of clouds may change as the climate changes, which could possibly counteract the warming (as made popular in the hotly-contested Iris hypothesis [2]) or further enhance the warming.

A forcing related to clouds that further complicates their feedback is the aerosols that they form on. Let's say the climate warms a lot and the planet goes into a major drought. That will cause more deserts which will increase the amount of dust in the air. That dust (for a given amount of water) could potentially suppress precipitation in the clouds, thereby extending their lifetime and increasing the amount of sunlight reflected. Without fully knowing the distribution and effects of aerosols (and their respective impacts on clouds), an accurate estimate of cloud feedbacks is difficult.

A runaway effect on Earth could technically be possible. You talk about feedbacks as a mechanism to prevent that, but some mechanisms are not easily reversible. Thinking about the ice coverage in Earth's polar regions, if all of that ice melts for a given increase in T, decreasing T does not necessarily allow that ice to grow back to the same coverage...and especially not at the same rate.

So a changing climate is a complex system with many different interrelated components that cannot simply be predicted by a $dT/dt = dGHG/dt$ relationship. There are numerous feedbacks that are all dependent not only on each other but also sometimes-irreversible processes.


Could the speed in which the plate is moving affect how quickly mountains rise? In an episode of History Channel's How the Earth Was Made, there was a remark when India left the rest of Gondwana 80 million years ago only to collide with mainland Asia 50.5 million years ago.  The remark was, "very fast in geological time."  Afterwards, it was said that "as with any smash, the faster the collision, the bigger the wreck."  In the episode, those remarks were written as an explanation for the Himalayas' "unique size".

But is this true?  Could the speed in which one plate collides with another REALLY affect the size of a mountain range?

The height of the Himalayas

Like Keith McClary says in his answer, there really are two factors in creating growing/shrinking mountains.

Mountains grow due to various reasons. In the case of the Himalayas it's like you must've seen in the documentary: the collision between the Indian and Eurasian continental plates. The material has to go somewhere and thus goes up (simplifying the geology a bit; I think that concepts like buoyancy these days also give some nuance to the subject, but the general picture stays the same). In the Himalayas, the two plates have moved into each other for at least 2500 km, so that's a lot of ground to move!

If that was the only process at play, there would be way higher mountains. I couldn't find a corresponding figure for the Himalayas, so consider instead the following present-day profile through Switzerland, running roughly north (left) to south (right).

You can see that the present-day Alps are at maximum 4 km high. Compare that against a reconstruction of the geology that should be present, running along basically the same profile:

You can see that the mountains could be as much as 20 km high! You can appreciate just how much mountain has disappeared, for another very young mountain range! So, the reason that mountains aren't as big as they could/should have been, is that they are cut down by erosion. Rain, snow, wind, temperature, all break down mountainous rocks into smaller broken pieces. Those pieces are transported away from the mountains as sediment in rivers (such as the Yangtze for the Himalayas).

So, the height of the Himalayas is very much controlled by the relative size of the two effects: how fast does the mountain range grow, and how fast does erosion break it down again. If the two are in equilibrium, the mountain doesn't shrink or grow. If erosion dominates, the mountain will slowly disappear over time. But in the case of the Himalayas, the mountain building generally outpaced the erosion, leading to the unique heights of the Himalayas. In this case, the speed of the collision is definitely the main factor!

The size of the Tibetan Plateau

Now if your question was also about why the Tibetan Plateau is so wide (rather than the Himalayas so high), I recommend you read https://oak.ucc.nau.edu/wittke/Tibet/Plateau.html , a very well-written summary of the three main hypotheses:

The speed of the collision has lead to a very step-wise straight faults toppling over each other, rather than folding over, which could lead to very long faulted sections. "Crust is thickened by the faulting and subsequent movement of large masses of rock, which are stacked one on top of another like cordwood."
When India hit the Eurasian plate it still had a heavy oceanic plate that was going under ('subducting') under the Eurasian plate. Now the oceanic plate has disappeared, and now the continental plate is being pulled underneath the Eurasian plate. "This process is reminiscent of taking a block of ice and pushing it beneath another ice slab, causing the latter to rise upwards. However, it is difficult to imagine how the buoyant Indian crust could be kept deep enough to get far beneath the plateau before bobbing to the surface. Perhaps the great speed at which India is colliding to Eurasia allowed this to happen."
The last hypothesis is simply that the continental collision puts a lot of heat below the plateau. "Like a hot-air balloon, the heated crust is buoyant and rises with the addition of light granitic material at the bottom of the Eurasian crust increasing the height of the Plateau."

This picture shows all those three hypotheses. 1=distributed shortening, 2=underthrusting, 3=lower crustal flow. In each case, a plateau is formed relatively far away from the actual collision between the two plates.

It is likely that, really, all three hypotheses together are at play. As explained on the website, at least the first two hypotheses are thought to be related to the speed of the collision.

So, yes, both the height and the width of the Himalayas are thought to be linked to the speed of the collision/relative plate movement!


What was the ocean circulation like during the time of Pangaea? So Enderton and Marshall (2009) wrote an interesting paper on the ocean circulation of various aquaplanets covered with certain terrain: e.g. an aquaplanet with a small ridge of land that ranged from North Pole to South Pole, and studied the effects it had on the ocean circulation.

I'm curious: Has anyone ever applied this type of analysis to a Pangaea-like planet?

Here is an estimate from Beauchamp and Baud (2002), for parts of the ocean around Pangea, for the latter parts of it's existence (~300-250mya). It is based on various previous papers that looked at deposits of carbonates and phosphate deposits, and made a few assumptions, including a sufficient supply of silica and nutrient inputs, and environments suitable for particular biota, including particularly siliceous sponges:

Beauchamp, B. & Baud, A., 2002. Growth and demise of Permian biogenic chert along northwest Pangea: evidence for end-Permian collapse of thermohaline circulation. Palaeogeography, Palaeoclimatology, Palaeoecology, 184(1–2), pp.37–63. https://www.sciencedirect.com/science/article/pii/S0031018202002456


Why do Volcanoes give out so much Sulphur Dioxide and Carbon Dioxide? From my understanding, the mantle is in a highly reduced state, so I can't understand why a volcano would give off a highly oxidised gas such as sulphur dioxide.

Carbon dioxide is too an oxidised gas which is emitted by volcanoes, however I justify it's emission because carbon dioxide is continually being fed into the mantle by the subduction of carbonate sediments, is this correct? If this is true, why is there still carbon dioxide emitted at mid ocean ridges?

Or is this all wrong, and the gases are being emitted because they are still being degassed from the solid mantle in the process if heterogenous seperation which separated the atmosphere from the mantle. If this is the case, why have all other gases been seperated but not the two I have mentioned?

the mantle is in a highly reduced state

This is not entirely correct. The core is in a highly reduced state, but the mantle is not necessarily reduced, and is quite oxidised in some places. The mantle is heterogeneous.

2.

  however I justify it's emission because carbon dioxide is continually being fed into the mantle by the subduction of carbonate sediments, is this correct?

The carbon dioxide in the mantle does not necessarily derive from subduction of carbonates.

3.

  Or is this all wrong, and the gases are being emitted because they are still being degassed from the solid mantle in the process if heterogenous seperation which separated the atmosphere from the mantle. If this is the case, why have all other gases been seperated but not the two I have mentioned?

Not entirely accurate. Although it is true that some of the gases in the atmosphere derived from the differentiation of the core-mantle-crust system, a popular theory suggests that many of the gases came after the differentiation through other planetary bodies such as comets and meteorites. You are also implying that carbon dioxide and sulphur dioxide are the only two gases that are emitted from volcanoes. No. Water vapour is also emitted (commonly much more than the other two) and also other gases. It's just that less people care about the water and it gets less publicity, because, well, it's just water. There are other gases that are emitted as well: nitrogen, the noble gases. But they are much less common than the other two. They are not the only gases.

The authors of Fluxes and sources of volatiles discharged from Kudryavy, a subduction zone volcano, Kurile Islands write:

  Several potential sources for CO2 can be identified: (1) hotspot-type mantle, (2) MORB-type mantle, (3) subducted oceanic crust (MORB), (4) marine carbonate, (5) organic C from crustal and subducted sediments

They also give a table which states that in island arc volcanoes, 12% of carbon is sourced from the mantle, 67% is sourced from carbonates and 21% is organic carbon. Note that this only gives the amount degassed from volcanoes in subduction zone arcs. This does not mean that all carbonate-hosted carbon is released from the rocks to be degassed. I read somewhere that only 50% is degassed, and the rest is lost to the deep mantle. I would also expect that MORB magmas will have significantly less carbonate-sourced carbon.

Also, The deep carbon cycle and melting in Earth's interior
may be of interest.


Regarding the theory of the origin of water on Earth through meteorites, why wouldn't the water evaporate on impact? Water on earth has been theorized to have come through comets trapped inside crystals. But why wouldn't that water evaporate on impact, and wouldn't the atmosphere at that time allow the vapours to escape Earth?

Also, what is the current scientific opinion of the validity of this theory ?

why wouldn't that water evaporate on impact, and wouldn't the atmosphere at that time allow the vapours to escape Earth?

The water would very likely evaporate on impact.

However, gravity would prevent the gas phase water molecules from leaving Earth.

The speed of a water molecule must be compared to the escape velocity of Earth (11 km/s) to determine whether or not the molecule can escape.

At a given temperature, the velocity of water molecules will be governed by a Boltzmann distribution.

The most probable velocity of a molecule will be:

$$V= \sqrt{\frac{2kT}{m}}$$

where $m$ is the mass of the molecule and $k$ is Boltzmann's constant.

For example, at a temperature of 300 K, a water molecule will have a most probable velocity of 520 m/s, about a factor of 20 below the escape velocity.

  what is the current scientific opinion of the validity of this theory?

Comets have a higher fraction of deuterium in their water compared to Earth.

According to "Earth's water probably didn't come from comets, Caltech researchers say", this refutes the hypothesis that a large fraction of Earth's water came from comets.


Continental collision – evidence left of river mouths and estuaries along the boundary? Are there any examples of now completely landlocked former river mouths or estuaries that became so after continental collision? As an example, consider the closure of the ocean between India and the Eurasian Plate – is there any evidence today, e.g. up in the Himalayas, of ancient river mouths or estuaries that are now stranded on the convergent boundary of the two continents?
As a corollary are there any rivers today which contain evidence of an opposite flow direction in the past, as a consequence of the above? Such cases, if they exist, would be interesting mirrors to the idea of continental rifting's contribution to river flow reversal (I'm thinking of the extraordinary discovery of the River Amazon's former east-to-west flow before South America rifted away from Africa: http://www.livescience.com/4253-amazon-river-flowed-ancient-times.html).

Reference:
Continental collision
Continental drift

There were certainly river mouths or estuaries in the rivers that drained off the proto-Himalayas into the last retreating stages of the Neo-Tethys Ocean. Such rivers comprised dozens of small rivers and the westward-flowing Proto-Ganges itself, which deposited the Siwalik formation which now forms the Lesser Himalayas. That is, the southernmost 'soft' 'salt and pepper' sandstones, up to about 2500 metres , which now abut the Indian plain. However, there is almost nothing left in terms of recognizable estuarine sedimentary structures. It has all been compressed, folded, imbricated, overthrust and subject to varying degrees of diagenesis and cataclasis. Most of this sediment was meandering mud flats, sandy outwash and restricted shallow marine sediments, with some similarities to the 'cuvette' environments of the European Old Red Sandstone.

As to the second question, your mention of the closure of the Tethyan Ocean  leading to the Indian-Tibetan collision suggests that you already suspect (correctly) that the Ganges is a case in point. It's headwaters were  originally in southwestern China, and it originally flowed westwards along the foot of the proto-Himalayas (what is now the high Himalayas)and out to the Indian Ocean somewhere in the vicinity of what is now the Indus basin in Pakistan. As continental collision progressed there was continental up-warping in what is now  the Himachal Pradesh area of India. This reversed the Ganges drainage so that it now flows eastwards.
This has important modern implications, as it was the originally westward-flowing Ganges that brought arsenic from the marine Tethyan sediments of western China, and which is now the source of the arsenic groundwater problem over much of Bangladesh and adjacent areas.
See also my paper: http://link.springer.com/article/10.1007%2Fs10653-005-7102-9   But don't pay the exorbitant price! - I can send you the original text for free! :-)


What is the motivation behind the choice of unglazed Porcelain as a Streak plate? What characteristics does Porcelain possess that makes it a good choice for the Streak test?
Additionally, are there any other materials that could also be used for designing a Streak plate?

It's white, so the streak colour is obvious.
It's hard. Porcelain is made from aluminosilicates like sillimanite and mullite. Mohs hardness is around 7. Not many geological materials are harder than it, and streak is not a diagnostic feature for those that are harder.
It's rough (i.e. unglazed) so it's really good in breaking tiny fragments from the tested material, thus producing the streak.
It's cheap and widely available.


What mechanism is used to measure ocean currents from cables? The volume transport of the Florida Current (one of the parts of the Gulf Stream) is measured using an underwater cable. What are the processes that allow for these measurements? How can we obtain measurements from a cable? Where else is this technique applied?

Image from http://oceancurrents.rsmas.miami.edu/atlantic/florida.html

The most likely explanation is that a device similar to a hot wire anemometer has been used; but one that has been designed to be used in oceans.

A hot wire anemometer is basically an electric heater that has been calibrated. The heating element radiates heat into a surrounding medium, depending on the design and  construction of the anemometer, either air or water. The greater the heat loss, the greater the flow of the cooling medium over the anemometer element.

By calibrating the anemometer it is possible to determine the velocity of the medium, in this case ocean current, over the anemometer and from that it is possible to determine the volume flow rate.

Solid state devices, using silicon transistor sensors have also been developed to measure ocean currents.


Fossil or Pseudofossil? I found these rocks in the Oregon Coast Range many years ago and have always wondered whether the interesting image was a pseudofossil or an actual fossil.  If it's a pseudofossil, any ideas on how it would form? If it's a fossil, what on earth is it? The image measures about 37 mm at its widest point.

Thanks for any insight you can provide!

It's been identified by a paleoichnologist as most probably a new species of Paleodictyon.


Is there a name for the great circle where latitude and longitude are equal? Is there a name for the great circle where latitude and longitude are equal? I have attempted a google search but only the equator and the prime meridian are defined in the sources I can find. ( It is of relevance in developing a map application which keeps track of latitude and longitude ).

The curve where latitude and longitude are equal is not a great circle.  But as joe khool writes in his excellent answer, it's called the curve of Viviani!  It's easy to see that the curve is not a great circle, because, using naïve spherical coordinates (in radians) $(\phi,\lambda)$ with $\lambda$ being longitude and $\phi$ being latitude (zero at equator), this curve passes through $(0,0)$, and also through $(\pi/2,\pi/2)$ which is the north pole ($(\pi/2,\lambda)$ is the north pole for any $\lambda$),  But it also passes through, say, $(1,1)$ which is not on the great circle the between previous two points.

In fact the curve you get looks like this:

Note. I plotted this by defining Cartesian coordinates in the obvious way:

$$
\begin{align}
 x &= R\cos\phi\cos\lambda\\
 y &= R\cos\phi\sin\lambda\\
 z &= R\sin\phi
\end{align}$$

and then plotting $(x,y,z)$ for $\phi = \lambda$ and $\lambda\in[-\pi/2,\pi/2]$.

An earlier version of this answer plotted $(x,y,z)$ for $\phi = \lambda$ and $\lambda\in[-\pi,\pi]$.  This means that $\phi$ takes values which are not in $[-\pi/2,\pi/2]$ of course.  I had assumed that these points would end up around the back of the planet: that you'd get a kind of 'S' which wraps around the planet, but in fact it ends up around the front of it again:

This surprised me!


Global Gridded Daily Temperature (at 2m): difference between GEFS Reforcast and NCEP Reanalysis I am looking for gridded/raster estimates of daily mean temperature (ideally ambient/at 2 meter) for a public health analysis. Specifically, I want to correlate daily mortality counts with daily mean ambient temperature (globally, between the years 1990-2016). I want to use gridded data rather than nearby temperature stations to allow for some extrapolation to areas without stations with long time series (e.g. large swaths of sub-Saharan Africa).

The accuracy of temperature in terms of degrees is somewhat less important relative to the accuracy of day-to-day variability for this project.

It seems like the GEFS Reforcast and NCEP Reanalysis products both provide daily mean temperature at a global extent, albeit at different spatial resolutions. I've looked at the documentation and underlying papers, but my earth science background is weak and I can't really suss out the difference between the two products.

Is one product substantially better than the other for global mean ambient temperature estimates? Is there a simple difference between the two products that I've missed?

Parameters I care about (roughly in order):

Daily measurement of mean temperature with global coverage
High spatial resolution
Accuracy of day to day variation (e.g. if day 1 was X degrees hotter than day 2, is that reflected?)
Accuracy of daily mean estimate

The fundamental difference is that you are comparing an ensemble reforecast with a reanalysis product. The assumption here is that the reanalysis provides the best possible information based on all available measurements using state of the art modelling.

The reforecast on the other hand simulates the forecast process based on current models and all available observations, i.e. it only utilizes observations up to the forecast base time, then runs a forecast just like a forecast system does in real life. This might still be good but you are looking at forecasts with a lead time of 0 to 24 hours if you are using the first day.

Also, GEFS is an ensemble system. That means that it performs several forecasts for the same days using different starting parameters. In this way, it is possible to estimate the uncertainty of the forecast system. E.g. if for a certain day the available forecasts deviate a lot, you can assume that there is higher forecast uncertainty.

As a summary, I'd say that using reforecast data would require some more justification than using reanalysis data. Using the ensemble information may be a good reason to use GEFS reforecast but would also add another layer of complexity.

Finally, allow me some general comments:

Have you considered using data from other services, most notably ECMWF? The ERA-Interim reanalysis is quite commonly used and has very good reputation. Or, as gansub pointed out, you can consider the reanalysis by JMA.
No matter which product you are using, do not take the results as "truth". You may find that interpolating down to an individual location requires more thought than people usually expect. For example, what happens if your location is a land location but falls into a sea pixel? This would greatly affect simulated 2m temperatures and the diurnal cycle. Using a neighbouring pixel in such cases may get you better results.
Speaking of the diurnal cycle, do you really care about daily means? In this kind of studies, I have seen people distinguish between day and night-time temperatures, which appeared to me as quite crucial.


Will the Mini Ice Age solve our Global Warming Heat problem There is news on the web saying that there will be Mini Ice Age in couple of decades.
The question is: Will this Mini Ice Age take away all the excessive heat and prevent Global Warming?

I'm going to try to answer this, though it's actually a very hard question depending on how close you look at it.

Lets start with the American Physical Society's statement on climate change - which, they've made an effort to balance out following their 2007 statement of "evidence is incontrovertible" that got some members upset and lead to a handful of high profile resignations.    More on that here

This is their more balanced statement.

http://www.aps.org/policy/reports/popa-reports/energy/climate.cfm

  The relationships between the atmospheric concentration of greenhouse
  gases and their radiative effects are well quantified. Forcing from
  the long-lived greenhouse gases: carbon dioxide, methane, and nitrous
  oxide, is presently about 2.5 Watts per meter squared (W/m2). Of this
  total, 1.6 W/m2 is from carbon dioxide alone. The total anthropogenic
  forcing is uncertain, particularly because the magnitude of the
  negative forcing associated with sulfate aerosols is unclear. While
  changes in solar irradiance may have affected global climate in the
  last century, a 0.15% change irradiance, the order of estimated
  changes, results in only a 0.36 W/m2 forcing.

and, numbers vary, but this seemed a pretty fair article on Solar Irradiance:   http://earthobservatory.nasa.gov/Features/SORCE/sorce_03.php

It says:

  The number of sunspots visible from the Earth not only changes from
  day to day, but also in cycles that can last from decades to centuries
  to millennia. The most well-known and well-analyzed of these cycles is
  the 11-year sunspot cycle. Over the course of 11 years, the yearly
  average number of sunspots and faculae slowly increases and then
  return to normal levels before rising again for the subsequent cycle.
  The change in the Sun’s yearly average total irradiance during an
  11-year cycle is on the order of 0.1 percent or 1.4 watts per square
  meter.

So, 1.6 watts per square meter from Co2 (2.5 watts total) and (up to) 1.4 watts per square meter low to peak solar irradiance, but there's a problem with that 1.4 number.    It's low to high, meaning low to average is 0.7 watts per square meter and that's how we should measure assuming the sun enters a grand minimum, we should measure against the average, so the real number is 0.7 watts per square meter drop - assuming the study is right and the sun does enter a new Maunder Minimum.

Skeptical Science posts a similar number:

Source:  https://www.skepticalscience.com/solar-activity-sunspots-global-warming.htm

The variation in their chart appears to be similar to the 0.7 variation we should expect from the NASA article, average to low range.

There's also the, all but guarantee that CO2 will continue to rise, at least, for several more years, so the APS estimate is likely to go up.   Also, the APS number doesn't include feedback mechanisms - and they say as much in the article linked above:

  The largest source of uncertainty lies in determining the magnitude of
  climate feedbacks. For example, an increase in trapped radiation and
  the associated warming is expected to increase the level of water
  vapor in the atmosphere, which would tend to further enhance the
  greenhouse effect ó a positive feedback. An example of a negative
  feedback would be an increase in clouds that reflected more sunlight
  back into space. The actual feedback from changes in clouds is
  uncertain since they also act to trap outgoing infrared radiation.

Now, the positive feedback from water vapor is a given and the negative feedback from clouds is more uncertain, so I think the APS article is a little bit more friendly to the skeptics than the actual science (IMHO).  Clouds reflect sunlight, but clouds also trap heat at night.  The total cloud effect is, well, a little more cloudy than APS' one line suggests.

Skeptical Science has an article on cloud feedback here:  http://www.skepticalscience.com/clouds-negative-feedback.htm

So, where does that leave us:

Well, first, the study that the sun is going to enter a grand minimum in the next few decades needs to be verified, lets start there.   A whole bunch of bad science has been published by those trying to disprove, discredit or cast doubt on climate change - so skeptisism of new studies first, especially on this topic, but, lets say they're right - which was the original question.   Would that be sufficient to stop man made global warming?

No.   I think it's pretty likely it would be insufficient.   0.7 is less than 2.5.   But, if they're right, it's still kind of good news, cause it would soften the blow - and that's a good thing.   I hope they are right.   But the sun's maximums and minimums have a pretty small effect on climate change.  Maybe a degree here or there.   Man made climate change should be 2 degrees by the end of the century, and perhaps more if left unaddressed in centuries that follow.

As Steve Emmerson points out, the effect of the Maunder Minimum isn't 100% accepted as the sole cause of the Mini ice age.   There's still some unknowns, but I feel, with pretty high confidence, that the sun entering a new grand minimum would be insufficient to stop the warming, but it might slow it down, a little.

Too long?   I can try to clean it up a bit later.


Why does the shoreline sometimes recede prior to a Tsunami? It is well known among regular beach goers that a sudden shoreline drawback is often a warning sign for an impending Tsunami.  My understanding of Tsunamis is they they form as a result of the seafloor abruptly changing, causing a local vertical displacement of water at the site of above the disruption, which initiates the wave.

How does this process ultimately result in the shoreline often receding prior to the Tsunami reaching the coast?

It has nothing to do with the geological cause of the tsunami. Instead, it's a result of the way waves propagate. You can see the same effect on ordinary wind-generated ocean waves — the waterline draws back before each wave peak arrives and washes up the beach. Tsunamis are much bigger waves, in terms of both amplitude and wavelength, so the effect is more dramatic.

The particles in some surface waves, including wind waves and Rayleigh waves (a component of what is often called ground roll), have in a circular or elliptical motion — in the case of a wind wave the motion is clockwise if the wave is traveling from left to right (see this animated comparison for Rayleigh waves). The 'backwards' motion in the trough results in the drawback you are asking about.


Which greenhouse gas has the most influence over global warming? Carbon dioxide is the gas everyone talks about because of how much we emit, but it is the most influential greenhouse gas ? I know there are a lot of other gasses are way more potent to retain heat within the atmosphere (water vapor, methane) but exist in smaller quantities.

Can we quantify the relative influence of each greenhouse gas over global warming  ?

The annual amount of CO2 we emit from using carbon that was in relatively long-term sequestration (coal, natural gas, petroleum) is on the order of 40 GT. To put this in perspective: the amount of food humans consume over the same period of time is on the order of 4 GT. Our CO2 production is an order of magnitude larger than worldwide food consumption. And the problem with it is that it takes weathering to remove it from the atmosphere - meaning it can stay around for millennia, and we're very definitely the ones extracting it from the ground.

H2O only stays in the atmosphere as long as the temperature allows. This means that it won't be the driving factor. There is a slight positive feedback with more H2O leading to a warming so it can hold more H2O, but there's also a negative feedback of about the same size with cloud formation reflecting the sunlight back to space.

Ozone in the upper atmosphere is responsible for the warming at the Stratopause. It's the reason why we have our atmosphere divided into layers with the Troposphere getting cooler with height, the Stratosphere getting warmer with increased height, and the Mesosphere getting cooler again with height. The Ozone absorbs the very energetic solar radiation that would otherwise destroy the DNA in your skin and cause cancers, but as it's a triatomic molecule, it's also very good at absorbing longwave radiation. In this case, a hole in the ozone above the Antarctic may be allowing slightly more longwave radiation to escape - and repairing the hole so we humans can survive might also be trapping additional heat. https://climate.nasa.gov/faq/15/is-the-ozone-hole-causing-climate-change/

CH4 stays in the atmosphere on the order of a decade before chemically reacting with oxygen molecules to become CO2 and H2O - but while it's present, the effect is about two orders of magnitude greater than that of CO2. But since the methane hydrates have been stable, they're not culpable in the warming. Although there are large quantities in tundra and ocean shelves, there's little point in making it the talking factor for anything except scare tactics.

This page https://www.epa.gov/ghgemissions/overview-greenhouse-gases discusses the relative sizes emitted, but temper this with the measurements of these gases. CH4 us currently less than 2 ppmv and CO2 is over 400 ppmv, making it easily the biggest factor in our warming, and in fact, the warming from CO2 is what's causing the tundra to melt and the East Siberian Arctic Shelf (the largest on the planet) to warm and release its methane.

This is why we concentrate on CO2 (it being the largest factor and also the only one we seem to have much control over).

Hopefully this puts it into perspective, and you can do your yandex.com searches for more details.


Gaussian wavelet generation with a given frequency How can I generate a Gaussian wavelet (time domain) with a given central frequency.

I mean if I take the Fourier Transform then its spectrum should be around that given central frequency instead of zero. For example the peak of spectrum is 20Hz and its side lobes becomes nearly zero around  $20\pm 10$.

I carried out a few coding exercise which I tried are here.
Link

If I understand the question, I don't think you can do what you want to do. The spectrum of a Gaussian time series must contain frequencies down to DC, i.e. very low frequencies (Python code from scipy.org):

A wavelet whose spectrum is a Gaussian is called a Ricker wavelet, or sometimes Mexican Hat wavelet. I often use this wavelet to model seismic reflection data. It has a central frequency, and is bandlimited. As such, the wavelet oscillates around zero amplitude — it does not have a DC component:


Why is the pressure on the poles higher in Summer and lower in Winter? Just to give context, this was not my original question but one that I ended up stuck with while trying to find a cause for the following observation (which is almost universally true for temperate climates):

Places on the WEST coast of continents tend to have a higher precipitation in WINTER, while places on the EAST coast of continents have a higher precipitation in SUMMER

To see this view the following maps
http://www.city-data.com/forum/weather/2895681-driest-wettest-months-year-world-maps.html

If the region between 30 degrees and 60 degrees from the equator is the one that comes under the the influence of Westerlies, this is the relevant region to be considered on the map.

To view just a couple examples of this phenomenon, see the precipitation pattern in

https://en.wikipedia.org/wiki/San_Francisco#Climate

https://en.wikipedia.org/wiki/Rabat#Climate

compared to

https://en.wikipedia.org/wiki/Tallahassee,_Florida#Climate

https://en.wikipedia.org/wiki/Shanghai#Climate

The flow of moisture laden air is the primary determinant of precipitation. Due to the coriolis force, the air in the Northern hemisphere moves clockwise, and the air in the Southern hemisphere moves counter-clockwise.

As the main prevailing winds causing rainfall on the WEST coast of continents is coming from the WEST , it must have been moving polewards, then bent East due to the coriolis force (Westerlies)

Thus, there must be some reason why the Westerlies are stronger in Winter. The only possible explanation I could  think of is that the pressure over the poles is higher in Summer (causing weaker pleward westerlies) and lower in Winter (causing stronger poleward westerlies)

This claim is in fact true, as is substantiated by Wikipedia.

https://en.wikipedia.org/wiki/Westerlies This page states that the pressure over the poles is lower during Winter causing stronger Westerlies:

"The westerlies are strongest in the winter hemisphere and times when the pressure is lower over the poles, while they are weakest in the summer hemisphere and when pressures are higher over the poles."

On the same wikipedia page, it states the claim I am asking an explanation for:
" This occurs when the Arctic oscillation is positive, and during winter low pressure near the poles is stronger than it would be during the summer

I would like an explanation of this phenomenon, ideally explaining why the polar pressure varies to such an extent...

Also, I would like to know if the logic I have used to reach these conclusion is valid

My answer will only relate to the question in the title: Why is pressure on the poles higher in summer and lower in winter?

Due to the axis tilt of the earth the winter hemisphere gets less heated by solar radiation. This leads to a high temperature gradient from equator to the winter hemisphere pole (strong baroclinicity). In contrast we have a low temperature gradient from equator to the summer hemisphere pole.
The missing solar heating in the winter hemisphere additionally leads to descending air at the pole leading to low pressure at jet stream level (around 300 hPa). On a non rotating planet the air would of course directly flow from the high pressure (equator) to the low pressure (pole) to remove the pressure gradient. As warm air would flow to the cold pole air, this would also weaken the temperature gradient. But due to the rotation of the earth, air flows around the area of low pressure. This flow gets increasingly stronger as the meridional temperature gradient strengthens.

This maybe seen from thermal wind balance, which tells us that the geostrophic wind $V_g$ is related to the temperature gradient $\nabla T$ by
$\frac{\partial V_g}{\partial \ln p} = -\frac{R}{f}k \times \nabla T$.
Here $p$ is pressure, $R$ is the gas constant for dry air, $f$ is the Coriolis parameter and $k$ is vertical unit vector. Assuming there is no zonal temperature gradient, we can conclude that a strong meridional temperature gradient leads to an increasing change of $V_g$ with height. We can observe this strong wind as the strong/weak jet stream in the winter/summer hemisphere. What does all of this have to with the pressure?

The jet stream acts as a barrier, dividing the warm and cold air masses. The Temperature will keep getting lower which will also increase the pressure and temperature gradient. In return the barrier (jet stream) gets stronger. This positive feedback mechanism remains until after winter solstice. Then the radiation reaching the pole will increase again, warming the air masses. Which will then lead to a weakening of the gradients.

So summarizing the above one could say, the missing radiation cools the air leading to a low pressure system at jet stream level. The jet stream itself gets stronger as the temperature gradient increases and acts as a barrier for warm and cold air masses and therefore maintains the pressure difference.


What is the consensus among geologists about climate change being caused by humans? I'm terribly frustrated with the way that climate change has been debated in Europe. I live in the Netherlands and members  of one of the biggest parties here, the Party for Freedom (PVV), frequently deny climate change and use terms like "climate hysteria" and "the religion of climate change". While I'm no climate scientist, geologist or meteorologist I do worry about the climate, simply for the reason that the large majority of experts does! I know that the exact percentage of consensus has been debated, consensus according to Bloomberg, consensus according to the Guardian explaining their methods, but it's pretty hard to argue that there is no consensus in general..
However, one of the arguments that climate change skeptics use is that the 97% (or whatever percentage you feel is right) consensus among climate scientists  is misleading. Misleading, because most climate scientists are meteorologists, and meteorologists tend to have a different view on climate, compared to geologists. The skeptics say that the consensus among geologists is way lower. From what I understand (again I'm  no geologist), is that some geologists support an alternative theory to explain climate change that involves plate tectonics.
Question: What is in fact the consensus among geologists about climate change being caused by humans?
Remark:
Please excuse me for the elaborate introduction to my question. I don't want to make this a concealed political statement, but it is something that's bothering me. Why would you, as a layman, choose to believe the small minority on such an important issue? I definitely don't think we should ignore or silence climate change skeptics, obviously accepted scientific beliefs have been proven wrong in the past, but it does feel rather strange to me that so many politicians are of an opinion that is backed by only 3% of the world's leading scientists.
Thanks in advance!

First, a correction. Most climate scientists are climatologists rather than meteorologists. Climatology and meteorology, while related, are quite distinct sciences. Meteorologists and climatologists don't see eye to eye. The consensus amongst meteorologists regarding climate change is not nearly as strong as it is amongst climatologists. Many meteorologists still doubt human-driven climate change.

One key issue is that meteorologists know that predicting the weather beyond a week or two is impossible thanks to the butterfly effect. This knowledge makes them rather skeptical of claims by climatologists regarding what will happen in 50 to 100 years. Climate is not weather, of course. That weather is not predictable beyond a week or two does not mean that climate is not predictable.

The same cannot be said regarding geologists. They take a long view of things, arguably longer even than that taken by climatologists. The consensus amongst geologists is quite strong. The Geology Society (British) issued a strong statement regarding climate change in 2010 (Climate change: evidence from the geological record) and made this even stronger with an adddendum in 2013. The Geological Society of America conducted informal surveys of its members at annual meetings in 2009 and 2011 (GSA members on climate change: Where, what, and ways forward?) The consensus was quite strong. Of the 181 members who were surveyed, only two "clearly stated they do not believe anything will occur because climate change is not happening". This is in line with the 97% consensus amongst climatologists.


How much and what kind of radiation passes through a cloud? I've read that 80% of sunlight is passing through clouds. Now there a small clouds and big clouds so it should be some average. Is this true or is the amount of sunlight passing throug a cloud really much more depending on the size of clouds. Is it for instance on a totally cloudy day that only 30% is passing and on a nice summerday when a cloud comes by it is 90%. Probably it depend on how high in length the clouds are.

But perhaps even a more interesting question is, are all wavelengths passing though on the same level? So is uv-light passing even easy as infrared light? In my experience though when walking in the sun it feels that much more than 20% of those warm IR-rays are being blocked by clouds (even if they are very tiny). So is it possible that even 70% of the IR rays are blocked or perhaps relatively moren than visible light or UV-light?

Here is not a detailed article, but one you might find some informative thoughts in:  http://www.americanscientist.org/issues/pub/sunshine-on-a-cloudy-day

On a basic note, any generalization starting with "clouds block x or x%" are far too general to compare actual percentages.  It assumes a cloud is a cloud is a cloud.   They are not.  What a cloud actually does to block or not block electro-magnetic radiation is not an absolute.  It varies by type of cloud, thickness, altitude, angle of the sun and likely many other factors.  As a generality, clouds block a part of visible, UV and IR light depending on a number of factors especially depth of the cloud.  Some of the EM waves are absorbed, some reflected and others pass through.  The UV end of the spectrum tends towards passing through while the IR end is more prone to being reflected which helps to create a greenhouse effect.  These are often presented as absolutes, but are actually generalities.


Cone of uncertainty in cyclones Whenever I look up the track of a cyclone on the map, I always notice that the cone of uncertainty bulges as it moves towards land/ target. I have inserted two images to show you what I mean, you could look up any other image but its always the same. Is there any specific reason for this phenomenon?

As the name suggests it is a region of uncertainty.
There are many uncertainties when modeling and predicting weather systems.
When meteorologists model the path of a cyclone/typhoon/hurricane they never know for certain where a cyclone will actually end up. At any point along its path a local variation may cause it speed up, slow down, rotate at a slightly different rate or slightly change its path, left or right.
Meteorologists run several models for such cyclone systems on computers. Each uses either a different algorithm and/or different weather parameters. The results of all the models are then used to determine a region where the cyclone is likely to be in with a given time frame.
The greatest certainty is closest to the cyclone. The further away the projected path is from a cyclone the greater is the uncertainty. This results in a larger spread of possible locations where the cyclone could eventually be. When drawn on a map this region looks like a cone.


Continentality/Oceanity Is there a specific temperature range that is considered to be the change from Continentality to Oceanity? Would this temperature change with latitude?

Would be nice if someone could point me to some literature on the subject.

Thank you!

The borders are fluent between continentality and maritimity. However, there are several indices, aiming to clarify this question. For instance, the probably earliest one is from Gorczynski (1920):
$$K_{Gorczynski} = 1.6 \cdot \frac{A}{\sin \varphi} - 14$$
where $A$ is the annual temperature amplitude of the location and $\varphi$ the latitude of the location. Another one, which is more often used, is from Iwanow (1956):
$$K_{Iwanow} = 260 \cdot \frac{\Delta T}{\varphi}$$
where $\varphi$ is the latitude again and
$$\Delta T=T_\mathrm{max} - T_\mathrm{min}$$
where $T_\mathrm{max}$ is the temperature maximum and $T_\mathrm{min}$ the temperature minimum. The results are characterized as following:

K < 100: maritime
100 < K < 200: continental
K > 200: strongly continental

To answer the second part of the question: as the indices show, the latitude needs to be considered. Currently I do not have the original publication by Gorczynski or Iwanow here, however there are some papers comparing different indices (there are several more), for example this one. Furthermore, the indices can be looked up in the most climatology basic literature and encyclopedia. At least, it is needed to mention that Gordon Stanger hits the point in his answer in the last sentence: The continentality is just one variable - there are several more. Look for climate classifications, like those from Köppen & Geiger or Schultz.

Edit: Original reference

Gorczynski, L. (1920): Sur le calcul du degre de continentalisme et son application dans la climatologie. In: Geografiska Annaler 2, p. 324-331.


Why is a layer of the subsoil so dark on this construction site? I have this construction site right outside my house, which I would like to give you some geographical background about before asking my question. Have a picture first though

There used to be industrial buildings of red clay bricks like the piece of wall still remaining. These walls, however, had a white stone facade around them so I'm not too sure the wall still standing was indeed part of the structure before demolition.

The city I live in is Dresden, Germany and the district I live in was a major bomb dropping zone during WWII. For some reason in my district they decided to just let some walls of otherwise vanished old structures be and use them to mark estate borders, or to just be there really, which looks quite beautiful in some cases.

Seeing this construction site I cannot help but notice this black layer of earth under what seems to be a layer of rubble. Even though its not that noticeable on the left side, its continuous throughout the hole and starts appearing at the same height.

As I said before, this area used to be exposed to heavy bombardment. So now I'm wondering if that might be the "fire layer" where the excessive heat hast left its mark in the ground.

Or is it, perhaps, a natural occurrence in slightly deeper depths, for the soil to turn that dark?

Regarding your question:

  So now I'm wondering if that might be the "fire layer" where the excessive heat hast left its mark in the ground.

The short answer is no. The layer seems to be about 1 meter thick. No bombardment related fire can cause blackening 1 meter deep.

Now, why is it "black"? First of all, it's not black. It's dark brown. I've seen black soils, and trust me - they are pitch black. There are several reasons for it. My best guess is that it's simply moist. You know how things appear darker when wet? Same here. My hint is the floor of the site. I'm guessing it's the same material, but it's drier so it looks lighter.

There are more reasons, some concerning the organic content of the soil (for example, peat - a highly organic black soil) or the mineral content of the soil (soil composed of high iron contents will also appear black).


Turbidity/clarity vs optical depth Are measurements for clarity (secchi disk) or turbidity (nephelometer) made for water quality related in any way to measurements made for optical or aerosol optical depth in meteorology?

A secchi disk is basically a measurement of optical depth, and is very similar in principle to the measurements of AOD made in meteorology.  Those measurements are quantified at a particular wavelength of light (or a few discrete wavelengths), related to the Beer-Lambert law of light extinction.  Light extinction occurs due to scattering and absorption and the total attenuation is integrated.  A nephelometer, in contrast, has it's own light source which is shining on the particles, and a detector measures the reflected light (absorption is not being measured).  The nephelometer is calibrated to measure particle density by volume of a particular type of particle, based on the reflected light signature.

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

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

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


How to interpret cloud coverage chart? The following page describes the historical cloud amount at various locations along the path of totality of Solar Eclipse 2017.

How do I interpret the cloud chart?

When it says the cloud amount is 50%, does it mean that half of the sky is visible?
In the following chart

how is the mean calculated? It's clearly not the mean of other numbers in that row.

In that chart, how should I interpret the terms "clear", "scattered", "broken", "overcast", and "obscured"? I understand what they mean in English, but what do they mean in terms of my ability to see the eclipse?

The mean is probably the average cloud cover in percentages: 41% cloud coverage on average over time. The categories you mentioned: 'clear', 'scattered', 'broken' and 'overcast' are defined in different ways sometimes. Basically there is a human observing the sky analyzing the coverage in oktas or tenths (e.g. 6/8), or more likely there is a sounding device looking through the sky and getting a value in percentages of the cloud cover (e.g. 75.0%). To get one of these categories from the device data, the percentages are turned into oktas or tenths. Some data is lost in this transformation and thus from the categorized data it is impossible to get calculate the actual mean.

Some use more the oktas (World Meteorological Organization) and others (I would guess often USA) tenths in the categorization. Also after quick googling the categorization bins seem to be differ from source to source at least for the ones who use tenths. The clear and overcast bins are for all the same less than 1/8 or 1/10 and more than 7/8 or 9/10 respectively. Obscured also always means basically that the value is undetermined: perhaps there is fog and the device doesn't get the responses it would've wanted. Some have also a category 'few', but since it was not present in the data they have used a categorization that doesn't include it.

Based on all above I would guess the categorization is the same as in this webpage. Categories are clear: less than 1/10, scattered: 1/10 to 5/10, broken: 6/10 to 9/10 and overcast: over 9/10. As the tabulated values are historical they give a climatological average of what are the possibilities of different cloud cover scenarios. I would suspect that clear and scattered scenarios are good enough for watching an eclipse so e.g. in Salem you would have a 32.2 + 19 = 51.2 percent chance to have a decent or better viewing conditions.