Quotient farthest mouths/nearest sources Much googling has not left me any the wiser, so here goes. Let FM be the distance between the mouths of two rivers X and Y. Let NS be the distance between the sources of the same two rivers X and Y. What pair of two rivers X and Y on Earth will produce the biggest quotient FM/NS? Or the smallest?

Two candidates for the biggest might be Indus and Brahmaputra but I am sure there are others.

Tbb is correct. The 'Congo and Nile' is by far the winner. Their mouths are 4600 km apart, whereas if you trek into the Rwenzori mountains, Western Uganda, there is s small highland swamp in a saddle point on the Congo-Uganda watershed. On either side there are several points where you can claim to be 'at the source', where you can stand with one foot in the Congo basin and the other foot in the Nile basin. The Indus and Brahmaputra are less than half this distance apart.

As for the other extreme, it's impossible to say. There are several rivers which end at more or less the same place. One then has to argue, 'Is one river a tributary of the other, or not?'


How can we calculate the temperature of the atmosphere, including the greenhouse effect? I've been struggling to find equations that express how many degrees of warming greenhouse gases contribute, given the composition of an atmosphere (and solar insolation).

What I did find was the Stefan–Boltzmann Law, and that wiki article has good equations about black body radiation. It shows how to get a value of $279 K = 6 °C = 43 F$ for the plain Earth with no atmosphere. Then to account for the albedo of Earth, the effective temperature is calculated at $255 K = −18 °C = -0.4 F$.

Then the article basically states what the real values are without presenting any more equations or explaining how to calculate it.

  However, long-wave radiation from the surface of the earth is partially absorbed and re-radiated back down by greenhouse gases, namely water vapor, carbon dioxide and methane. Since the emissivity with greenhouse effect (weighted more in the longer wavelengths where the Earth radiates) is reduced more than the absorptivity (weighted more in the shorter wavelengths of the Sun's radiation) is reduced, the equilibrium temperature is higher than the simple black-body calculation estimates. As a result, the Earth's actual average surface temperature is about 288 K (15 °C), which is higher than the 255 K effective temperature, and even higher than the 279 K temperature that a black body would have.

And there were only 2 cites that only cited the fact that H2O, CO2, and CH4 are greenhouse gases.

I've been searching for how to calculate the warming due to GHGs, but no luck. I'm really hoping someone can shed some light on this. I'm looking for an equation that takes into account atmospheric composition and probably the rotation rate of Earth (or whatever body), and of course the solar insolation.

Please note I'm not really asking about climate change calculations. Climate change is more about how the atmospheric composition is changing (namely GHG increases). I'm simply looking for equations that dictate the temperature based on a given/constant composition of the atmosphere.

One can account for greenhouse gas effect for Earth's temperature in simple energy balance model in following manner.
Assume that fraction $f$ of longwave radiation emitted by Earth's surface is captured by green house gases in the atmosphere. Suppose Earth's surface temperature is $T_e$ and temperature of the atmosphere is $T_a$. The energy received from Sun should balance as follows
$$\pi {r_e}^2 F_0 (1 - A) = 4 \pi r_e^2 (1-f) \sigma {T_e}^4 + 4 \pi r_e^2  \sigma {T_a}^4 $$
where $F_0$ is solar constant (Energy received from sun per unit area per unit time), A is Earth's albedo, $\sigma$ is StephenBotlzmann constant and $r_e$ is Earth's radius.
Since the black body radiation are isotropic, 50% of radiation emitted by atmosphere travels toward Earth's surface and remaining 50% of radiation travels toward the space. Also, assuming that atmosphere receives all of its energy from Earth's surface through longwave radiation, it gives following energy balance equation
$$f \sigma {T_e}^4 = 2  \sigma {T_a}^4. $$
which leads to
$$ T_a = \sqrt{\sqrt\frac{f}{2}} T_e $$
Nearly 80% of the radiation emitted from Earth's surface is absorbed by greenhouse gases (including water vapour) and clouds. Substituting value of $f$ 0.8 and solving it for $T_e$ will get you the answer you are looking for.
Reference
Chapter 7 The Greeenhouse Effect in Introduction to Atmospheric Chemistry by Daniel Jacob
http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap7.html


Why are most cirrus clouds present over the equator and over tropical continents? As quoted from the AR5 IPCC report (chapter 7) here.

  Most high cloud (mainly cirrus and deep cumulus
  outflows) occurs near the equator and over tropical continents, but can
  also be seen in the mid-latitude storm track regions and over mid-lati-
  tude continents in summer (Figure 7.6a, e)

Clouds require moisture and therefore high clouds will exist in regions with upper-level moisture.  Synoptic scale ascent is on the order of cm/s and this is not an efficient way to bring moisture from the surface to the upper levels.

Consider this water vapor imagery:

Source: College of Dupage NEXLAB

In this image, the color represents the humidity of the mid and upper levels of the troposphere.  Brighter colors represent moisture at higher levels.  Darker colors represent moisture at mid levels.  Black represents dry mid and upper levels.

The brightest whites (highest level moisture) at this time are along the ITCZ and associated a mid-latitude cyclone in the northeastern US.  These are areas associated with convection, which unlike the synoptic scale flows is an efficient transport of moisture into the upper troposphere.  This convective outflow will first be associated with the "anvil" top of the thunderstorm, but as it is advected at the upper levels can manifest as cirrus clouds.  The ITCZ is driven by equatorial convergence and the upward branch of the Hadley cells.
Mid-latitude cyclones have a so-called "wet conveyor belt" that transports near-surface moisture into the mid and upper levels which can then manifest as upper level clouds (or lots of rain/snow).

To answer "why are most cirrus clouds in the tropics?" I would associate that with the large transport of water vapor into the upper levels by the persistent convection in the ITCZ.


Nonlinear Stokes equations for glacier modeling What is the difference between

$$\operatorname{div}(-\mu(u)\nabla u+pI)=f\tag{1}$$

and

$$\operatorname{div}(-\mu(u)(\nabla u\color{red}{+(\nabla u)^\mathsf{T}})+pI)=f\tag{2}$$

from the physical point of view, in the glacier modeling context?

Does it make sense to model a glacier with the first one?

To explain the notation, $u$ and $p$ denote the velocity and pressure fields, respectively; $\mu(u)$ denotes a velocity-dependent viscosity coefficient (for example, Glen's power flow law). The gradient of $u$ is

$$\nabla u=\left(\begin{array}{cc}\dfrac{\partial u_1}{\partial x}&\dfrac{\partial u_1}{\partial y}\\ \dfrac{\partial u_2}{\partial x}&\dfrac{\partial u_2}{\partial y}\end{array}\right)$$

and $(\nabla u)^\mathsf{T}$ denotes the transpose matrix of $\nabla u$. (If $u$ has 3 variables its gradient is analogous to the 2-variable case). Frequently, $f$ is $f=(0,0,-\rho g)$, where $g$ is the gravitational acceleration constant and $\rho$ the ice density. $I$ denotes the identity matrix and $div$ the divergence of a matrix is the divergence by rows, for example,

$$\operatorname{div}\left(\begin{array}{cc}w_1&w_2\\ s_1& s_2\end{array}\right)=\left(\begin{array}{cc}\dfrac{\partial w_1}{\partial x}+\dfrac{\partial w_2}{\partial y}\\ \dfrac{\partial s_1}{\partial x}+\dfrac{\partial s_2}{\partial y}\end{array}\right).$$

This way, we may rewrote (1) and (2), respectively, as follows:

$$-\operatorname{div}(\mu(u)\nabla u)+\nabla p=f$$

and

$$-\operatorname{div}(\mu(u)(\nabla u\color{red}{+(\nabla u)^\mathsf{T}})+\nabla p=f$$

If your viscosity $\mu(u)$ is constant, then there is no difference between the two formulations because
$$
  \text{div} (\mu \nabla u^t) = \mu \nabla (\text{div} u)
$$
and for incompressible materials $\text{div} u=0$. So the two formulations are identical for constant viscosities. For variable viscosities, this is a bit more complicated and may in fact not be correct.

In general, the second form you show (with the addition of the transpose of the gradient) is the physically correct form because it involves the strain rate $\varepsilon  = \frac 12(\nabla u + \nabla u^t)$ which is the physically correct quantity where the gradient $\nabla u$ has no physical reality. (This is because the invariants of $\varepsilon$ are independent of the choice of coordinate system, but the invariants of $\nabla u$ depend on the choice of coordinate system.)

The first form you show is a simplification one can work with if you know that (i) you have an incompressible fluid, and (ii) you have no Neumann type boundary conditions (as the "natural" boundary conditions for the two formulations are different).


Was Zealandia above water during the last Ice age? Was Zealandia above sea level during the last ice age? Like how Sahul or Sundaland were?

Was Zealandia above water during the last Ice age?

For the most part, no.
New Zealand's North and South Islands likely would have been connected, New Caledonia and other currently existing islands would have been larger, and some now-submerged areas would have been isolated islands that barely poked above the lower sea level at the time of peak glaciation. However, the vast majority of Zealandia is currently over a kilometer beneath the current sea level, which means that it was over 800 meters below sea level during the peak of the most recent glaciation.


How does NASA get a 360 degrees texture map of Earth? How does NASA get a 360 degrees texture map of Earth and separates it into specularity map, bump map etc? And how do they get the texture map of clouds separate?

If you're asking about how they are able to distinguish different layers of information on the Earth, your answer is found in the field of Remote Sensing. Using sensors running on several satellite systems (e.g. MODIS, ETM) that are isolated to pick up specific radiative bands (IR, NIR, Visible, etc.) you can derive some pretty amazing information.

Using map algebra on these bands, you can figure things out like cloud cover, vegetation health, elevation, temperature and land cover of the surface, etc. Many of these data sets can be found directly through NASA or USGS. Creating masks of different information using these techniques can lead to really amazing visualizations.

The really fascinating thing is that a lot of this information can be calculated on the fly using raw data and any GIS infrastructure or scripts. That's likely how NASA is able to visualize these data products the moment they collect them.


Does iron in core have chance to come out to crust? Is the iron in the inner core of Earth trapped forever? Are there any mechanisms that allow some iron to leave the core and come to the surface (eg: magma convention)?

No, we occasionally get fragments of upper mantle overthrust onto the Earth's crust, but then the specific gravity (density) contrast is not so great, roughly 2.7 to 3.0 for crust, about 3.2 for mantle. But the core is another matter. The density contrast is huge - the liquid outer core is between 9.9 and 12.2, whilst the solid core is estimated to be 12.6 to 13.0! (High pressure iron-nickel with some denser metals mixed in). Not only that, but the mantle is quite close to the surface, only tens of kilometres deep, whereas the Earth's core is 3000 kilometres below the surface.
Sadly, there is no volcanic process that comes from even remotely that depth.

Alas - many geologists, myself included, would dearly love to sample the core and compare the composition to iron meteorites (assumed similar). There are many other questions of geochemistry and isotopic composition which might be answered if only we could sample that deep. Unfortunately it is way beyond even the most optimistic advances in technology, so we just have to theorize.


How are biological oxygen demand and depth related? What is the relation between biological oxygen demand (BOD) and depth? I need to calculate the BOD of a drinking water tank and I have ultimate BOD at the surface of water, but I need to calculate it when depth varies. My calculations need an equation of de-oxygenation constant rate and BOD.

Biological Oxygen demand increases with accumulation of decaying organic matter in a water system. This means that BOD is highest where there is high concentration of decomposing organic matter in that system.

  What is the relation between biological oxygen demand (BOD) and depth?

The answer may vary as in some cases organic matter floats on upper columns of water and can be decomposed readily by aerobic microorganisms manifesting an increased BOD.

However, this study   which was conducted using waste water from stabilization ponds (depths ranging from 0-5m) shows that there is an increase in the Biological Oxygen Demand with increasing depth and this can be attributed to the settling down of organic matter in these ponds.


Are the polar vortexes main cause of ozone hole? I read some articles and news from various sources that the Arctic ozone hole has recovered. Some people claim that less emission of harmful gases due to covid-19 made this happen. AFAIK, the past few decades regulating and banning emission of CFCs and other harmful gases should have contributed to this.
But Some articles says that polar vortexes contribute to the change of the Ozone layer. It is a fact that CFCs and other ozone-depleting gases react with the Ozone layer and damage it.
My question is for the arctic/antarctic Ozone holes, do polar vortexes contribute more?
PS: This article in the Sinhala language made me ask this question. If you like, translate and read.

To blame ozone destruction on the polar vortex would be like blaming trees for surface ozone production downwind of cities. Yes, nature is involved in the process, but nature is not the source of the catalytic pollutant that caused large change in ozone concentrations.
The polar vortex is a naturally occurring meteorological phenomena that has occurred for millions of years, and the ozone layer was fine.  The issue is man-made halogenated compounds that catalytically destroy ozone (e.g. CFCs) when polar stratospheric clouds (PSCs) form.  The stronger the polar vortex, the colder it is and the longer the PSCs stick around, allowing more destruction of ozone.  The continental ice sheet over the south pole allows extremely cold temperatures, and so PSCs have been more prevalent there. Typically the Antarctic circle is much colder than the Arctic, so ozone destruction has been more prevalent in the southern hemisphere.  However, polar stratospheric clouds are occurring with increasing frequency in the Arctic.
I suppose you could argue that if there were no polar vortices, the ozone layer would not be so susceptible to CFCs.  However, the polar vortex and associated PSCs is a natural phenomena we cannot avoid.


How to calculate water vapor flux divergence from temperature, relative humidity, u wind and v wind? I have temperature, u wind, v wind and relative humidity. I am wondering to calculate water vapor flux divergence and convergence.

Would anybody kindly help to find our a solution for this?

The formula for moisture flux is $$q\vec{V} $$
where $q$ is the water vapor mixing ratio, which can be found using mixhum_ptr and $\vec{V}$ is the velocity.

Therefore the divergence of the moisture flux must be
$$\nabla{\dot{}q\vec{V}}=\frac{\partial(qu)}{\partial x}+\frac{\partial(qv)}{\partial y}+\frac{\partial(qw)}{\partial z} $$
$$\approx\frac{\delta(qu)}{\delta x}+\frac{\delta(qv)}{\delta y}+\frac{\delta(qw)}{\delta z}$$

which is computable if you have gridded data.

For example, you could compute this by setting
$$qu=q\ast u$$ $$qv=q\ast v$$ $$qfluxDiv=uv2dv\_cfd(qu,qv,lat,lon,opt) $$
Use uv2dv_cfd per http://www.ncl.ucar.edu/Document/Functions/Built-in/uv2dv_cfd.shtml

Note: If you wanted the turbulent moisture flux, you would need to subtract $\nabla{\dot{}\bar{\vec{V}}\bar{q}}$ from your answer.


What does strata mean here? What does strata mean here ?

  These consolidated layered strata are known as stratified rocks. The
  strata vary in thickness and may be tilted or horizontal. The
  sediments consist of loose particles of gravel, sand, silt in various
  proportions hence are porous and permeable.

It comes from a chapter called Materials of The Earth Crust-Rocks from Frank Morden's Geography Class IX Part 1

Strata always mean a collection of layers. A single layer is called a stratum. The plural of stratum is strata.


What factor(s) could cause this sort of temperature increase, mid-night/early morning? I am new to having a PWS (Personal Weather Station). I have not found any answers explaining why this sometimes occurs aside from explanations given factors that were not variables in my case (winds, cloud cover etc). While I had a minor gust (< 1 mph), no change in direction from what it's been all week (directly north). No change in cloud cover, fog, mist etc. Steady barometric pressure rise (overall slight) all night at 30.12 In to 30.26. Every once in a while I see a massive spike in temperature like this with no easily discernable factors and would like to understand why. Furthermore, I checked 5 other weather stations in the valley floor. It looks identical/exact same affects in a 30 mile range. However, as soon as we rise below the valley floor maybe 500 - 1000 ft, we see a steady decrease all night with a slight flattening during this time, but no increase.
Details of my location:
Northwest Montana, mountain surround valley, river bottom, low/lowest point in the valley 1/2 mile from river edge. Station is 6ft above ground, clear from any buildings, trees, structures by at least 200ft in all directions.

Temperature swings opposite from those expected by the diurnal radiation pattern (warming during the day, cooling at night) are typically due to air coming in from other locations.  Synoptic (large-scale) fronts can bring such rapid shifts, but often tend to be more sharp (rather than gradual) and in one direction (as the front passes).  However occasionally there can be interesting oscillations near more stationary fronts, such as this event from Oklahoma in February 2018:

More often, smaller nighttime fluctuations have to do with more mesoscale (local) features.  Different regions cool differently, and the pressure differences caused by the resulting differences in density move the air around... two common causes of such shifts can be circulations around oceans or other large water bodies (probably not pertinent to you!) and terrain-induced circulations (probably much more pertinent!).  The ones that are probably most impactful at night are downslope winds, which are caused by more rapid cooling on the mountain than the air around it, and downvalley winds, caused when enough air builds up from downsloping.  This lecture from Stephan De Wekker gives some more details on some of these features and other terrain flows.
Often slight shifts in larger-scale wind direction and the varying temperatures over different degrees of mountains and valleys can lead to quite a complicated set of rises and falls in temperature through the night.
It's also not impossible that are some issues with your station, I was initially concerned with a few things:

The winds in particular seemed odd -- due north the entire time is always suspicious, and less than 1 mph for an entire night and early morning, while certainly not impossible, makes it a bit more questionable as to whether significant temperature advection could occur.
Plus it's also rare to see temperature and dewpoint changing almost 100% exactly in step over long periods of changes -- moisture tends to be slower to alter except around sharper fronts (and on nights when the temperature nudges lower while the air is saturated [$T=T_d$]).

But a look at observations across the region for the time period:

does show perhaps your data isn't impossible.  The meteograms from Libby [KS59] and Missoula [KMSO] below do show very weak/calm winds and fairly similar temperature/dewpoints movement.

Still, there's no north winds (except when calm, which is a placeholder when there is no wind), and a slight bit more fluctuation between temperature and dewpoint, so it wouldn't hurt to check whether the station is properly observing.
I believe typically flows down a local mountain tend to be cooling at night, as the densest air (coldest) collects along the river.  Other features driven by forced air movement can bring warm air to valleys, like foehns and large-scale downsloping, but those tend to bring drier air in.
So assuming it's a valid feature, it appears to be something complex.  It can take years of observations to really understand the flows around complex topographic areas.  But I would posit a guess that maybe a slight wind shift gradually pushed the pooled dense valley air away from you far enough to get you into slightly warmer air away from the river valley bottom.  Or maybe winds become enough to mix down warmer air above.  Differences in snowcover/melting effects or clouds/precipitation might also play a part in what you experienced.  But in that part of the world, I'd expect you'll see many more peculiar local temperature fluctuations over your time observing!


What is the geochemical source for the helium detected in deep Arctic explosive eruptions? Recently, there has been explosive deep-ocean volcanism detected along the slowly-spreading Gakkel Ridge in the Arctic Ocean (see map below), according the National Geographic news article Arctic Volcanoes Found Active at Unprecedented Depths, specifically, the article reports that

  Powerful eruptions sent a plume of carbon dioxide, helium, and liquid lava up into the Arctic waters.

Image source

What is the geochemical source for the helium detected in deep Arctic explosive eruptions?

Helium is formed through the radioactive decay of uranium 238, uranium 235  and Thorium 232. A helium atom is an alpha particle that has collected electrons. The only way that helium is produced on Earth is by such radioactive decay deep underground.

Generally, the helium travels along cracks until it reaches a subterranean cavern where it accumulates.

Yellowstone National Park in the US is leaking helium.

Quoting from the website http://www.yellowstonepark.com/2014/02/helium/

  the gas is gurgling up from a store that’s been trapped in the Earth’s core for up to 2 billion years. Scientists believe that the
  helium began its exodus up from the depths roughly 2 million years
  ago.

  The helium was initially released when a “hotspot” of collected magma
  fought its way to the Earth’s surface and caused a series of volcanic
  eruptions, the most recent of which occurred 640,000 years ago.

The helium being release at Gakkel Ridge would be of a similar origin and it appears to be released in a manner similar to what is happening at Yellowstone NP. The article you provided a link for also states that carbon dioxide is being release at Gakkel Ridge, which is not inconsistent with the volcanic activity of the ridge.

From the website http://www.helium-corp.com/facts/heliumfound.html

  Carbon Dioxide is also found in some helium-bearing formations but the
  presence of this gas is primarily due to its proximity to ancient
  volcanic activity.

Other website that may be of interest are:
http://www.pa.msu.edu/sciencet/ask_st/051095.html

http://www.anl.gov/articles/underground-helium-travels-earth-s-surface-aquifers-new-study-says


How do seismic charges help to investigate the subsurface? In the film Kong: Skull Island, scientists investigate an island's structure by dropping explosive charges from helicopters:

Source: YouTube trailer

In reality, geophysicists do something similar using buried explosives.

Source: fondasol.fr

In simple terms, how does detonating explosives in the ground help us to understand the subsurface structure?

Explosives are just one way we can produce seismic waves in the ground. By placing geophones on the surface, which measure the rate of change of displacement of the surface, we can actually guess where there are boundaries between different rock types in the subsurface. When we detonate our chosen 'seismic wave generator' the geophones begin recording this change in displacement. As the seismic waves propagate and hit boundaries between rocks of different acoustic impedances (resistance to propagation of seismic waves) some of that wave energy will reflect back to the surface and some will be transmitted downward (http://petrowiki.org/Seismic_wave_propagation#Reflection_coefficients). The amplitude and sign (positive/negative) of those recorded wiggles tell us about how big the contrast in acoustic impedance is as well as if acoustic impedance is increasing/decreasing downwards. This allows us to produce a picture of the subsurface where the x-axis is offset of the geophones from the wave source and the y-axis is the time it takes for the wave to travel down and back up as shown in this picture:

However it is never that simple. A lot of processing has to be done to make sure our initial image is the most accurate picture of the subsurface we can make and even then there is still uncertainty. It must also be stressed that we don't actually know about the properties of the rocks themselves just that boundaries exist between these rocks. If we want to estimate that we can use processes such as seismic inversion.


Why doesn't Wolfram Alpha show low gravitational acceleration for the Hudson Bay? I thought I would be clever and add a new answer to Hudson Bay Has Low Gravity? by using Wolfram Alpha to report gravitational acceleration for different locations, but it looks like my cleverness backfired.

From this answer I found this view, a subsection of which is cropped and shown below.

I chose three points, the lowest, purple area near the West shore of the Hudson bay, a medium green-orange in lake Michigan near Chicago, and a high area just north of Iceland.

I was surprised to see Wolfram report such a high gravitational acceleration for the Hudson Bay area at 9.85 m/s^2! I was expecting something substantially lower than 9.81 m/s^2

Question(s):

Why is the gravitational acceleration for the west coast of the Hudson Bay so high from Wolfram Alpha?
Roughly what acceleration should I be getting there?
Could it be related to Wolfram Alpha's use of EMG2008 12th order for a model?
Why would it be reporting such large deviations in altitude for locations on water?

Here is the data:

                              lat   lon    Total   vert dev  down     west    south    elev
Western Hudson Bay    'low'  60.9N 94.1W  9.85176  0.00302  9.85172  0.00967  0.02816   -22
Lake Mich. (~Chicago) 'med'  41.7N 87.3W  9.8188   0.00352  9.81874  0.01119  0.03274  +175
North of Iceland      'high' 66.6N 18.8W  9.86107  0.00259  9.86104  0.00845  0.02406  -445

Wolfram Alpha links and raw data screen captures:

60.9N 94.1W, West Hudson Bay (low)
41.7N 87.3W, Lake Mich. (~Chicago) (med)
66.6N 18.8W, North of Iceland (high)

Wolfram Alpha reports values between 9.78 and 9.88 m/s^2 depending on the location, which is odd because it should stay within the range 9.76 - 9.83 all over the world. It also seems to be using the ocean floor as a reference elevation if the point falls in water.

Using Natural Resources Canada's tool, it reports a gravity of 981933.3 mGal (9.819333 m/s^2) for Hudson Bay at 60.9N, 94.1W at sea level, which seems more likely for that location.

Keep in mind that while the area near Hudson Bay has a negative gravity anomaly, this does not imply that it should have weaker gravity than Chicago (9.8026 m/s^2), which is much closer to the equator. It means that Hudson Bay's gravity is lower than what it should be at that latitude.  Gravity is even weaker near the equator (around 9.78) because as you get closer to the equator, the centrifugal force is stronger and slightly counteracts the force of gravity, also the mass of the Earth is slightly further away from you, thus has less gravitational pull on you. These 2 effects alone create gravity variations up to 0.5% (around 0.05 m/s^2)

Gravity anomalies are relative to a theoretical normal gravity based on an idealized ellipsoidal rotating Earth, and these anomalies are small compared to the variation caused by cetrifugal forces and the oblateness of the Earth. Anomalies range between -50 and +50 mGal (+-0.0005 m/s^2). Normal gravity at the Equator for sea level is about 9.78 m/s^2, and near the poles, around 9.83 m/s^2. Altitude also has a significant effect, at 5000 meters, gravity is about 0.01 m/s^2 weaker than at sea level.


How can the 'abiogenic oil' hypothesis be disproven? We do know that complex hydrocarbons (e.g., tholins) exist in the outer Solar System. Some geologists maintain that at least some oil on Earth is of non-biological origin. The mainstream, though, tends to discount their views. Is it possible to verify the hypothesis empirically and what should we look for in geodata to have it substantiated or disproven?

One possible key is isotopic fractionation via biological processes - see dating the development of the C4 photosynthetic pathway, and specifically isotopic fractionation between carbon-13 and carbon-14. δ13C from volcanic degassing is markedly different to that from biological sources; the arguments for human involvement in climate change (see e.g. the IPCC) rely on the changes in δ13C since the beginning of the Industrial Revolution: the value has shifted markedly towards that of the hydrocarbons we've been burning from its pre-Industrial value. (As for how we know atmospheric δ13C for CO2 prior to the Industrial Revolution - the answer is polar ice cores!)

Thus the arguments for/against abiogenic oil rest on (1) isotopic ratios, and (2) other geochemical indicator ratios; see e.g. Jenden et al. (1993).

Höök et al. (2010), in a review of the arguments for biogenic and abiogenic formation processes, say:

  However, theoretical studies, laboratory verification and discoveries of trace amounts of abiotic oil do not imply the existence of commercially significant deposits. [...] The lack of a clear and irrefutable success in locating abiotic petroleum in commercial quantities is problematic.

This year, Ahmed et al. (2014) advances the argument that Siljan Crater oil is unambiguously of biogenic origin due to the copresence of molecules of "known" organic origin (specifically terpane and sterane biomarkers). As for a definitive answer, [Wang et al. (2014)7 say:

  Whether abiotic (inorganic) process can form oil and gas resource is a difficult question that has been explored continuously by scientific community for more than a century but has not yet been solved.


Relative world carbon footprints by nation? Are there studies showing the relative positions carbon footprints of various countries? which one produce how much greenhouse gases?

I'm interested in comparing developing and developed countries and continents, and prefer university studies wherever possible.

The answer is no.

The search for a single and simple measure for each country’s contribution to global warming is unlikely to succeed, new research has warned.
The question of how to fairly quantify national contributions to global warming historically, and inform future policy on sharing the burden of reducing greenhouse gas emissions, has long been part of international discussions on global warming.
Researchers from the Center for International Climate and Environmental Research Oslo (CICERO) and the University of Oxford, UK, assessed if finding an answer to this question was possible or likely.
Dr Steffen Kallbekken, from CICERO, said: “There are vast differences in income, population, resources, technologies and capacity across countries. Because of this, the idea of distributive fairness has played a crucial role in the international climate policy debate.
“However, trying to find a single common formula for policymakers to decide the distribution of national efforts in a climate agreement was never likely to succeed.
“Although it references equality principles, the United Nations Framework Convention on Climate Change 2016 Paris Agreement tacitly recognises this fact, as in practice the differentiation is left to each country to decide for itself.”
Dr Jan Fuglestvedt said: “Our results indicate there is no simple and single correct answer to the question of how much each country has contributed to global warming. There are too many fundamental value-related and ethical questions remaining, to which it is impossible to find a single answer.
“A more useful approach would be for scientific studies to present not just one set of calculated contributions – based on some of many choices – instead present a spectrum of results showing how the contributions vary according to a broad set of choices.”


Will carbon tax be applicable to other emissions? Will Carbon tax be applied to other emissions or only carbon emissions like Carbon dioxide & Carbon monoxide ? Can non-warming pollutant emissions like Chaff(Chemtrail) also be taxed under the Carbon tax ?

For reference, see Why is carbon pollution given more importance than Sulfur pollution or Nitrogen pollution ?

The recent Canadian carbon tax law is just CO2.

CO, which you asked about, is bad for people and considered a pollutant.   Efforts to reduce CO have been underway for decades including carbon monoxide detectors in homes and garages and catalytic converters in cars.  The target behind CO is elimination as much as possible.   Being a pollutant, there's a different approach.  The tax is only meant to discourage CO2 production, which isn't a pollutant, but it is a problem due to gradual build up.

Likewise, sulfur pollution, coal being a primary source, is dealt with by strict limits (in the US), and scrubbers which catch sulfur emissions have been installed in coal plants since the 1980s.

Additional greenhouse gas taxes like CH4 might eventually come to pass, but, like CO, the effort with the greehouse gas CH4 should be elimination, not taxation.  It's also harder to put a number on CH4 released, which can be released by fracking seepage or cow burps primarily or by escape from thawing tundra (are we going to tax teh ground?).    CO2 is easier, for example because we know how much CO2 is produced per gallon of gasoline, for example, so a tax is straight forward, but cow burps or fracking seepage could be estimated so a tax there might be possible.

But the general idea, is that, if it's preventable and a pollutant of some form, then regulation should aspire to reduce output, even strive towards elimination.   CO2 is an inevitable byproduct of burning fossil fuels, so it can't be eliminated and it would be problematic to try, but it can be financially discouraged by taxation.


Time standard for IERS Bulletin A IERS Bulletin A and Bulletin B contains Earth orientation parameters. These include the time difference between UT1 and UTC and pole position. The values for these parameters are listed once per day, keyed by "MJD" (Modified Julian Date).

The documentation does not say which time scale these MJD values reference. Without qualification, MJD is typically taken to mean some flavor of Universal Time. If that is the case, which flavor of universal time is it: UTC, UT1, or some other flavor? If that's not the case, which is it?

I'm using the data in an interpolative fashion (Lagrange interpolation) to estimate the Earth orientation parameters at arbitrary points in time, so not having the correct time standard will lead to small errors in the interpolated values.

Short answer: UT1

Long answer:

The Julian Day (JD) is just a consistent day count since the beginning of the Julian period, that is January 12th 4713 BC. As the numbers tend to be large (today is day 2,458,557.5), in the 80's and motivated by computer memory limitations, the reduced JD was created which is just $JD-2400000$. Then, to remove the annoyance that the Julian Day starts at midday instead of midnight, the Modified JD (MDJ) was created, which is just $JD-2400000.5$.

By definition the MJD zeroes at solar noon at the 0° meridian. Therefore, it is not a regular time measure, it is tied to Earth's rotation and accelerates or decelerates depending on minute variations of Earth's rotating speed.

You can use basically any solar time including all flavors of UT time to define your MJD, but the most precise is UT1.

But UT1 is not a regular measure of time either, and is also affected by variations on Earth rotation speed. The only really regular time standard among the ones you mention is UTC, which is based on atomic clocks. Being regular, the solar noon drift off UTC and doesn't happen at 12:00 h UTC, therefore, leap seconds are added to keep UTC reasonably close to solar time. But a record of leap seconds is kept so you can use UTC to precisely measure time intervals independently of the variations of Earth's rotation.

In that sense UT1 and UTC are not two flavors of the same thing as you suggest, they actually measure two completely differing things. The first measure Earth's rotation and the second measures time. Due to the same reason, MJD cannot or should not really be referenced to UTC (otherwise it would not zero solar noon).

Said this, in those bulletins the MJD conveys exactly the same information than the date. So "2019 1 2" meaning January 2nd 2019, conveys exactly the same information than MDJ 58485, it is just a more machine friendly way to refer to a specific day. And it also removes the need to account for missing calendar days if you work with dates relatively far in the past.

Now if you want to know how much time have elapsed between two entries in the table, you need to know how to transform whatever version of solar time they use (UT1 in this case), to a regular time reference like UTC or TAI. That's why the "UT1-UTC" value is included. In any case, in doing such calculation you need to take in account any leap seconds added to UTC between the time of the two entries.

Does that makes sense?


Molten salt seas on the future Earth As the sun gets brighter, the oceans are expected to evaporate by the next billion years or so (the vapor slowly gets stripped off into space). The salt, which is less dense than most rocks, will be left behind. Then wait another couple of billion years. Most rocks melt at a higher temperature than sea salt: basalt melts at around 1000C, quartz melts at 1713C, but NaCl melts at only 801C (adding other salts will lower this). So will a tangerine sun loom large over red-hot waves softly breaking on abyssal beaches?

So will a tangerine sun loom large over red-hot waves softly breaking on abyssal beaches?

Probably not. Interesting question, and one might think that yes - you could melt the evaporite deposits that will be left after all the water is gone.

The problem is that molten salts are extremely reactive materials. They will corrode any rock they get into contact with. As most rocks on the ocean floor are silicates (basalts etc) you will just get chloride-silicate minerals. For example, the reaction between halite and nepheline (a fairly common silicate mineral) will lead to the formation of sodalite (another fairly common mineral):

$\ce{6NaAlSiO4 + 2NaCl = Na8(SiAl)6O24Cl2}$

There's a long list of known chloride-silicate minerals, and for a more realistic salt–basalt reaction the products can be things like scapolite, adrianite, or wadalite.

You will most likely end up with no salt, overlying a somewhat thin (metres?) layer of these silicate-chlorides. It could be that in some points you might have ephemeral pools of liquid salt, or in places where the chloride-silicate layer is thick enough to effectively isolate the liquid salt from the silicate rocks below, but those will probably be negligible features on the scale of the planet.

One final comment:

  quartz melts at 1713C

In isolation. When quartz is mixed with other things (like feldspars in a granite), it melts at a lower, eutectic, temperature.  See related question one and two.


Does grade of metamorphism apply to igneous and sedimentary rocks? Does grade of metamorphism apply to igneous and sedimentary rocks?

I know that grade of metamorphism applies to the scale in which a rock becomes crystallized. Or is it?

Please also define grade of metamorphism as a clarification.

I'm not sure I entirely understand your questions but I'll have a go.

  Does grade of metamorphism apply to igneous and sedimentary rocks?

Yes. Both igneous and sedimentary rocks can be metamorphosed. For example, a high grade metamorphic rock of the amphibolite facies could have been originally either a sedimentary rock or an igneous rock. It's not always straightforward to figure out if it was one or the other. Note that because igneous rocks already consist of "high-grade" minerals such as pyroxenes, amphiboles, feldspars, etc., and their grain size is already occasionally coarse, it may not be obvious than an igneous rock have been metamorphosed. Sometimes it takes a closer look to distinguish a metamorphic igneous rock and just an igneous rock. Sedimentary rocks, on the other hand, are originally composed of clays and other "low-grade" minerals so it's obvious when one is metamorphosed. A metamorphic fabric (foliation and the likes) is also much easier to develop in originally sedimentary rocks than in igneous rocks.

  I know that grade of metamorphism applies to the scale in which a rock becomes crystallized. Or is it?

I'm not sure what the question is. Usually higher grade metamorphic rocks have larger grain size. For example, greenschist facies rocks are commonly fine grained (for example phyllites or schists) whereas eclogite facies rocks are usually composed of big beautiful crystals, sometimes in the cm scale.

  Please also define grade of metamorphism as a clarification.

Start here:

Metamorphic grades


Are all natural diamonds made of organic carbon material? I've read that diamonds are created at a depth of about 180 km. By volcanic activity it comes above. But did plants and trees of 300 million years ago sink so deep? Or is it possible that  inorganic carbon, what was already in the Earth, is the source of diamonds?

I've heard also that there could be other exo-planets in the galaxy that are made of diamonds so it looks like it should be possible, or isn't that true?

Diamond isn't made of organic C at all. Organic matter would rather become oil, gas, coal or dissolve entirely.

C itself isn't very common in earth's mantle, but subducted eclogites and peridotites can lead to the needed C-accumulation.

But also meteorite impacts can lead to the genesis of so called micro-diamonds due to the very short lasting but extreme conditions.

Diamond's genesis takes place in depths from 150 up to 700km and at temperatures about 1200-1400°C.
Those conditions were present in the upper mantle during the archaeum and hadeum, that's why mining takes places mainly in older crustal zones.

You are right that volcanic activity brings diamond up to the crust and surface of the earth. This process is thought to take only some minutes... This is a very quick process so that the diamond crystal structure won't change back to graphite and it's also the reason many diamond deposits can be found in sediments.

I think that should answer your question.
I don't know about the diamond exoplanets, though I've heard of it.. I'd say the process that leads to this is pretty unclear, but perhaps someone has clearer thoughts or information on this.


Why does Morocco have so much phosphate? I read that Morocco/Western Sahara has 75% of the world's known phosphate reserves, but I couldn't find an explanation of what mineral is responsible for it and how it all ended up there

The Earth's crust contains an average of 0.27 percent P2O5. Most of it in the mineral apatite Ca10(PO4)6(OH,F,Cl)2.

  Apatite is slowly soluble in neutral or alkaline waters, and its solubility increases with increasing acidity.

  The PO4 content of most river and lake waters ranges from about 0.01 to 0.5 part per million (ppm), but may be much higher in soft acid waters and highly saline alkaline lakes. About one-sixth of the phosphate carried to the sea by runoff is in dissolved form. The ocean as a whole is nearly saturated with phosphate, but its distribution within the ocean is not uniform; deep cold waters contain nearly 0.3 ppm PO*, but warm surface waters contain only 0.01 ppm or less. Oceanic circulation brings phosphate- rich water to the surface in several environments, and phosphate may be precipitated either inorganically or biochemically, as the pH and temperature increase near the surface.

  Most of the world's phosphate production comes from marine phosphorites, many of which are associated with black shale and chert. Secondary processes including diagenetic phosphatization of calcium carbonate and .interstitial precipitation, reworking by waves and currents, and weathering have often played a prominent part in forming deposits of mineable quality.

  Common igneous rocks, such as granite, diorite, gabbro, and peridotite, contain only from about 0.005 to 0.4 percent P205 ,  but some of the less common alkalic rocks, such as ijolite and turjaite, can contain more than 1  percent. Variations in phosphate content of igneous rocks generally parallel those of ilmenite and magnetite.Apatite is slowly soluble in neutral or alkaline waters, and its solubility increases with increasing acidity, decreasing hardness, and decreasing temperature.

  Most phosphorus is carried to the sea as phosphate minerals or adsorbed on iron or aluminum hydroxides or clay.

  Most of the world's phosphate production comes from marine phosphorites. The richest and largest of these form at low latitudes in areas of upwelling associated with divergence, chiefly along the west coasts of the continents or, in large mediterranean seas, along the equatorial side of the basin. Lesser but significant concentrations form along the west sides of poleward-moving warm currents along the eastern coasts of continents.

In the Moroccan phosphate deposits however,

  The unconsolidated sediments on the continental shelf and uppermost continental slope off Morocco and the Spanish Sahara are sands, silty sands, and silts. Their sand fraction is carbonate-rich and considered to be mainly relict from Pleistocene times when sea level was lower. This relict sand is mixed with, and locally buried by, Holocene detrital silts which are concentrated on the slope and the middle shelf. Phosphate is locally abundant in the form of sand-sized detrital grains. These were derived from Cretaceous and Tertiary phosphatic rocks cropping out on the shelf, by erosion during the Pleistocene. The sand-sized phosphatic detritus is concentrated in relict placer-type deposits near parent-rock outcrops. Longshore transport during the Pleistocene has contributed further concentrations of phosphatic sand along the shelf edge. These deposits are of low grade (< 8% P 2O 5) and are of no economic interest at present. No signs of Recent phosphate mineral formation were noted. Thus, the hypothesis that this phenomenon is linked with the upwelling of nutrient-rich water does not appear to apply, at this time, to the region studied.


Does evaporated hand sanitizer pollute the environment? With all the COVID-19 stuff going on, I feel the usage of alcohol-based hand sanitizers has increased many fold.
I wonder what happens to all that evaporated alcohol in the atmosphere.
How soon does alcohol react in environment and what other substances are formed?

Assuming you are talking about ethanol: it is a common chemical substance, generated naturally from e.g. rotting fruits. So any pollution from hand sanitizers should be negligible.
What happens to the alcohol in the atmosphere is an interesting sequence of reactions. I took the info below from an article (see link below).
In the air, ethanol is oxidized quickly (half-life is a few days) into acetaldehyde $CH_3CHO$, which is further oxidized into other compounds, most of which are harmless. However, if the air contains nitrogen dioxide $NO_2$, it can form peroxyacetyl nitrate $CH_3C(O)OONO_2$, which is dangerous.
Source


Geomorphological feature identification I was studying a satellite map of Iceland and came across an interesting, but unnamed feature located between Vatnajökull glacier and Trölladyngja volcano (between 64°50'35"N, 17°11'21"W and 64°48'33"N, 17°04'25"W ; link to google maps). It is a distinct, bright patch of land, around 6.5km across with an indentation in the center. Its color and texture are different than these of the lava field next to it and the indentation looks (to my untrained eye) more like a collapsed lava bubble than a caldera.

Is it a volcano or something else?

The place is called Urðarháls. I could not find much information about it in the scientific literature... It is mentioned in Sigmarsson & Halldórsson (2015): they say it's an interglacial basaltic shield volcano, possibly associated with the Askja volcanic system. The fact that the volcano was eroded by glaciers probably explains the colour difference with the surrounding "fresh", postglacial lavas.

The crater looks like a pit crater to me: it probably collapsed when lava was drained somewhere else, leaving an empty chamber beneath it. Another good example of pit crater is the Dolomieu, on Piton de la Fournaise, which collapsed in 2007. Look at Staudacher et al. (2009): compare figure 3, before the collapse, and figure 11, after.

Note that the authors use the term "caldera", which is loosely defined... What Wikipedia calls a non-explosive caldera would be referred to as a pit crater by some. I guess the two terms kind of overlap.


Using an accelerometer as a geophone to conduct a seismic survey I am doing a capstone project for a sensor systems course and I would like to write  a python program to acquire, process and present seismic data like that of seismic surveys. Is it possible using just an Arduino and an accelerometer?

I have access to the following accelerometer:

SparkFun Triple Axis Accelerometer Breakout - MMA8452Q

Accelerometers have already been used for acquiring seismic data in a lot of studies: see this review, and references therein.

As for the code part, there is a Python framework for seismology: ObsPy.


Why is heavy precipitation from atmospheric rivers more likely to hit the West Coasts than the East Coasts? As an example of an atmospheric river, see http://www.wired.com/2014/03/california-atmospheric-river-rain/.

These events have been known to hit areas like California and Bergen, Norway.

Extratropical cyclones in the Northern Hemisphere rotate around the earth in the mid-latitudes in a mean westerly flow.  This means that, on average, the track of a storm between 30°-60°N moves from west to east.  Ahead of these extratropical cyclones is a strong frontal boundary with very powerful winds, sometimes up to hurricane strength near the boundary layer.  Moisture is advected (transported by wind) from the tropics (a very wet place, relatively speaking) by these powerful winds ahead of the extratropical cyclone. The moisture then creates a narrow channel of extremely moist air along the frontal boundary. Finally, the atmospheric river moves with the mean westerly flow as the frontal boundary/extratropical cyclone shifts east. Therefore, to answer your question, it is because extratropical cyclones on average move from west to east that ARs impact west coasts in the Northern Hemisphere.

Atmospheric River preceding Upper low in Mid-latitudes off of US West Coast

Another way to think of this is that tropical systems (those that develop between 0°-30°N) initially move from east to west in the easterlies.  Now ask yourself how often do the mid-latitude west coast's of northern hemisphere continents fall victim to category 3-4-5 hurricanes?  Caveat: remnants from weakening tropical depressions often move into the mid-latitudes before impacting these regions.

Track of tropical cyclones in the opposite direction of Atmospheric Rivers


How does Antarctica stay frozen? Antarctica receives heat from the Sun every day, so how does it stay frozen?

I have some thoughts about the answer but I'm unsure of whether it is correct; I hope people here can clarify.

My idea: the heat that Antarctica receives from the Sun is always 'travelling' from one spot to another, but the heat does not stay in a spot long enough to melt the ice.

Please correct me if I'm wrong, thanks.

It doesn't stay frozen.  Ice evaporates (or sublimates is the correct term) under direct sunlight, but that's at a molecular level, it doesn't melt, it goes from solid to gas under sunlight and in the cold, some of this newly formed water vapor goes back being to ice.

In an absolutely dry climate, well below freezing, ice would slowly sublimate and disappear.  In a warm dry climate, ice would melt (much faster), then it would evaporate.   The sun does sublimate ice off the antarctic ice sheet every day, but quite a bit less than is added by snow and condensation from moisture due to temperature change and brought over by wind.   The antarctic ice sheet is also, always moving.   Mostly Antarctica loses ice by pushing it into the ocean - over long periods of time and it gains ice by (see above) snow and condensation.   The ice has been on Antarctica for over 30 million years, but as far as I know, the oldest ice core we've found there is about 1.5 million years old.    Everything moves.


How do the various types of clouds affect the atmosphere below them in a polluted environment? I am working through this problem on my own as well, but am feeling that some perspective is in order. So, ignoring the obvious effects where precipitation will wash stuff out of the air, and blocking sunlight will prevent chemical reactions from occurring that depend on photon energy - in fact, we'll just assume a chemically inert atmosphere with no significant deposition and emission of pollutants. We'll also go ahead and use the most common height and shape-based cloud type categorization system (http://scied.ucar.edu/webweather/clouds/cloud-types). Also, to simplify, lets generally assume particulate pollution.

How does the presence of a cloud impact pollutant levels in the air underneath it and how does this vary by cloud type?

An ideal answer will consider at least one of the below:

Synoptic scale determinants of cloud type such as pressure systems
Thermodynamic changes in stability/mixing and/or boundary layer height
Humidity - can include quibbling over whether the meaning of pollutant levels means measurement of dry mass, visibility reduction, or measurement under ground conditions (But, unless you want to get into this mess, lets assume dry mass).
Cloud height (low, middle, high)
Cloud shape (stratus, cumulus, nimbus, cirrus, etc.)

I haven't found proper references yet, but this hasn't gotten an answer yet. To speculation!

Long-lived (non-precipitating) clouds can decrease solar insolation at the surface, reducing convection and mixing below the cloud and increasing pollutant concentrations. If clouds are just a symptom of a high-humidity environment, that can promote the condensation of semi-volatile species into particulates (nitrate, ammonia, some organics) if you don't count phase change as a reaction. Convective storms are associated with a lot of mixing, both within the boundary layer and between the boundary layer and the free troposphere, reducing concentrations.

Without the photolysis or rainout processes, I don't know enough about different cloud types and environments to speculate further. I'm hoping this at least sparks more discussion.


What causes a rainbow, its colours and its shape? What is the cause of rainbows? Do they appear due to rainfall or any other natural phenomenon. What makes it form a semi-circle in the atmosphere and its colours?

Short answer: A rainbow is formed when light enters a drop of water or an ice crystal and gets refracted and reflected back into an observer's eye.

Longer Answer: Light travels at different velocities depending on the media involved; it travels slower through water than it does through air, for instance. As light enters a raindrop or ice crystal, it first gets refracted. However, not all the frequencies of light get refracted at the same angle. The colors with the shorter wavelengths (e.g. blue, indigo, and violet) get refracted less than the longer wavelengths (red). This spreads the colors out just like passing through a prism. The light then gets reflected off of the back of the raindrop, gets refracted again as it passes out of the raindrop, and travels to the observer's eye.

The reason it is circular is because the light that got refracted and reflected back to the observer, does so at a specific range of angles, 40 to 42 degrees.

In order to see a rainbow, the sun (or other light source) must be directly behind the observer. A straight line is formed from the light source, the observers eyes, and the center of the rainbow. All rainbows are actually circles. We usually see it as an arc because the earth intercepts the circle. (BTW, because of this, no two people, even standing shoulder to shoulder, can see the same exact rainbow. Each rainbow is being created by different raindrops.) If you're ever in an airplane passing over a cloud with the sun above you (as opposed to near the horizon), you may see a complete rainbow. It's pretty awesome.  Here's an illustration:


Would climate change result in an increase in seismic activities? Would climate change result in an increase in seismic activities?
I can see two potential forces acting:

Temperature dilation of the Earth's surface.
A change in the distribution of water mass, fewer glaciers, stronger precipitation.

Is any of this possible?

Dilation of the Earth's surface due to atmospheric temperature changes will be negligible due to the amount of temperature increase.
Stronger precipitation will not directly lead to an increase in seismic activity. The force of the raindrops will be too small, even over a prolonged periods of time. If stronger precipitation were to occur, the most likely result will be an increase in soil erosion and landslides.
The reduction in glacial mass and the increase in water depth will change ground surface stresses. Where there will be an increase in the depth of water there will an increase in the overburden pressure produced by the water. This may cause an increase in localized seismic activity in some areas.
The loss of glacial mass will lead to post-glacial rebound in affected areas, predominantly: Antarctica, Greenland, Canada, Alaska. As the affected areas adjust to the lack, or reduction, of overbearing (overburden) pressure previously supplied by the glacial ice there will be an increase in seismic activity in those regions.


How can we have "floating" and convection currents in a non-liquid mantle? I've always thought the earth's layers were as follows:

Crust, a few dozen KM think in most places
Mantle, completely composed of liquid rock and molten metals, a few thousand KM thick
Outer Core, molten iron
Inner core, solid iron

The mantle being composed of a liquid made a lot of sense. The idea of plate tectonics floating on top of magma and bumping against each other made sense.

However, I've been told by Michael that the mantle is completely solid, which seems to not work as well with the ideas of

Floating/moving plate tectonics
Convection currents

If the earth's mantle is solid, why don't we say the plate tectonics are "resting on" the mantle instead of "floating on"?

How can we have convection currents through something that doesn't flow? Even if the solid rock in the mantle can why doesn't the heat just distribute itself evenly through conduction, and negate any convection tendencies?

I realize that entire books can be written on this topic, so a generalized answer is fine.

Is the mantle solid?
It's all a matter of timescales. The mantle is undoubtedly solid (except locally in the uppermost regions where melting can occur) but on a long enough timescale it can display plastic behaviour under high temperatures and pressures, with a viscosity on the order of $\text{~}\mathrm{10^{21}~Pa~s}$ (based on estimates from isostatic rebound after melting of ice sheets). Think of plasticine - it is obviously solid but it deforms easily under stress. This is how the mantle behaves on long timescales at high temperatures and pressures. On short timescales the mantle is a brittle solid and this is what allows it to transmit seismic S-waves.

Why does the crust 'float' on top of the mantle?
The answer to this is quite simple - the crust is less dense than the mantle and so on the long timescales, where the mantle is ductile, the crust does not sink into the mantle (except at subduction zones but that's another story). Granitic continental crust has an average density of around $\mathrm{2.6~g~cm^{-3}}$, basaltic oceanic crust is around $\mathrm{3~g~cm^{-3}}$, and the upper mantle is around $\mathrm{3.5~g~cm^{-3}}$.

How does convection work in the mantle?
The details of mantle convection are a subject of active research but all geologists agree that the mantle does convect vigorously and that this is the major form of heat transport from the core to the crust. If you calculate the Rayleigh number for the mantle you come out with $R_a~\text{~}~10^6$ which indicates that convection should be vigorous. On the other hand, the thermal diffusivity of the mantle is very low ($\text{~} \mathrm{10^{-6}~m^2~s^{-1}}$) and so conduction is not the dominant form of heat transport.


Melting basalt on the lunar surface - what would the resulting material be like? The idea is to melt the fine-grain portion of basalt regolith using a large Fresnel lens, and let it cool to a solid. The lens would track along a tamped bed of material leaving a molten puddle something like 2 cm thick. This would be done on top of more regolith with the same characteristics - which means some of the material would sink into the stuff below and get mixed. Then it is left to cool to a solid.

The conjecture is that Fresnel lenses, and the equipment needed to create flat beds of tamped powder regolith and track such lenses across it, is so light that it could be a good way of creating construction materials. If they aren't very good materials they could make up for that in the simplicity of making them and the possibility of making enough that the fact they have weaknesses doesn't matter - just use more.

What might the material yielded by such a process be like?

Edit: Since someone asked, this could yield thin basalt objects of any 2D shape, or objects built up of various layers into 3D shapes. Such objects can be joined with more molten basalt and parged to form continuous rock walls, floors, and arches. An approach to excavation also based largely on the use of lenses (for trenching, and boring for the placement of explosive micro-charges) is used to create voids that are then lined with rock this way.

It is explained more here, and here is the current model of the equipment:

Melting lunar dust of basaltic composition will result (unsurprisingly) in basalt lava. There might be some volatile loss - if for some reason the basalt had some H2O or CO2 trapped in the solid you will most likely lose it. It's probably not going to change its chemical properties much though.

On Earth, as lava cools down fast, for example when it's erupted underwater, or when it's the top of a lava flow in contact with air, it quenches to volcanic glass. When it cools down slower, there is enough time for small crystalline material to form in it. These are usually tiny crystals in the μm size. On the Moon, I reckon the lava would cool down slightly slower than on Earth (since there is no air to conduct away heat), but since you're talking about a lava layer which is only 2 cm thick I'm pretty sure it will cool down fast enough for the formation of glass, and any crystalline portion of it will be negligible. I am not sure whether it will crack or not. From my own experience of melting rocks, when you have a similar amount cooling down in Earth's atmosphere, they crack. But then, silicate glass does not crack when cooled down in air. I guess it comes down to the composition of the rock/glass.

The lava will not percolate down to the regolith. Lavas hardly penetrate soils on Earth, so it is probably not going to happen on the Moon where the gravity is much weaker.

If I were looking for construction materials on the Moon, I would just build a quarry. Seems easier than melting down dust.


How do oases form in the middle of the desert? I am wondering if there are any theories about the formation of oases, and I am also curious about why an oasis can even last for a very long period of time.

I have heard that fresh water exists on the surface of the desert because of a difference in elevation of the desert, causing the underground water to pop up. Is it the reason why oases exists?

Oasis are places where aquifers are connected to the surface. The source of the water in the aquifer however can be hundreds of miles away in areas that do get significant rainfall.

The trick is geologic strat have different properties; some allow water to flow easily, others are very water tight, a water accessible layer covered by a water proof layer creates a aquifer. Faults or erosion can breach this water seal allowing to water to the surface, as can human wells. Recharge areas are places at higher elevation where water can enter the aquifer and flow downhill, they can be hundreds of miles away and are often in the mountains which often get much higher rainfall.  A picture is worth a thousand words.


At what point does plate tectonics stop? As the core and mantle of the earth cools, it will reach a point where new crust cannot be produced.

How can this point be calculated?

If we can, has anyone done such calculations?

Thanks!

One permanent threat to plate tectonics is the oceans vanishing. The scientific jury may still be out on this matter, but most geologists and geophysicists consider water to be the lubricant that makes plate tectonics possible. In a billion years or so, the Sun will have become 10% more luminous. This is conjectured to make the Earth to undergo an unstoppable moist greenhouse / runaway greenhouse, and the oceans will vanish.

The core is still emitting residual heat from the formation of the Earth. As the core cools, iron in the outer core freezes onto the inner core. This is freezing is an additional source of heat. The solidification of the Earth's core thus represents another permanent threat to plate tectonics. The liquid outer core is conjectured to have frozen solid less than three billion years from now.

A nearer term threat is the formation of the next supercontinent. Plate tectonics may operate in fits and starts. What makes subduction zones form is not known. What is known is that a major subduction zone vanished when India collided with Asia, and no new subduction zones formed elsewhere to take its place. If this conjecture is true, plate tectonics will temporarily stop in a few hundred million years when the next supercontinent forms, only to restart later when too much heat stress builds up inside the planet.

This is all highly conjectural. No scientist will live to see their conjectures falsified.

References:

Kasting (1988), "Runaway and moist greenhouse atmospheres and the evolution of Earth and Venus," Icarus 74.3 : 472-494

McDonough (2003), "Compositional model for the Earth's core." In Treatise on geochemistry 2 547-568.

Silver & Behn (2008), "Intermittent plate tectonics?" Science 319.5859.


Sedimentology (Particle size distribution parameters) The Inclusive graphic standard deviation (sorting) value of this claystone sample is negative (-1.29). Is this right to be considered as very well sorting ? However, the bivariate plots of depositional environment do not include negative values on the axis of the standard deviation.

Note: The granulometric data was obtained by laser diffraction technique.
The formula of the inclusive graphic standard deviation after Folk 1974:
$\sigma_1 = \frac{\phi_{84} - \phi_{16}}{4} + \frac{\phi_{95} - \phi_{5}}{6.6}$

Folk and Ward (1957) were the ones who created a measure of sorting using graphical moments of particle size distribution based upon φ values obtained graphically from the cumulative frequency curve at specific percentile levels.

I wasn't aware that negative values were possible based on the equation, but I am not up on my sedimentology..

Assuming your value is correct, it would signify extremely well sorted material:  the Inclusive Graphic Standard Deviation (Folk and Ward, 1957) has a phi range of <0.3 (extremely well sorted) to >3.0 (extremely poorly sorted).

Folk, Robert L., and William C. Ward. "Brazos River bar: a study in the significance of grain size parameters." Journal of Sedimentary Research 27.1 (1957).


What is this "crystal ball" located at a meteorological station? I found what looks like a "crystal ball" in a meteorological station in the Vlădeasa mountains (Romania). What is its purpose?

It's a Campbell-Stokes sunshine recorder, used to record the times at which the sun is shining. It acts as a lens, focusing the sunlight onto a piece of card. If the sun is shining, the focused beam will burn a hole through the card at that point.

Here's a closer view of a sunshine recorder in Wendelstein, Bavaria:

Source: Wikimedia Commons

And here's a used recording card with holes burned through it:

Source: Wikimedia Commons


Can the formation of gypsum evaporites (sand roses) be simulated in the lab? Has the process of formation of sand roses been simulated in laboratory conditions, or does it take too long?

Yes, it has.

Cody & Cody (1998), Journal of Sedimentary Research.

http://archives.datapages.com/data/sepm/journals/v55-58/data/058/058002/0247.htm

Abstract:

  Gypsum crystals were grown in experimental conditions analogous to
  saline terrestrial environments within bentonite clay gels by
  diffusion control at three different temperatures, four brine
  salinities, and four tannic acid (a model terrestrial humic substance)
  concentrations. The resulting crystals correspond to natural gypsum
  formed in terrestrial environments. Prismatic gypsum typically grew at
  both high and low temperatures in the absence of the organic additive.
  With increasing organic acid concentrations, the prismatic crystals
  progressively became flattened perpendicular to [001], and two
  temperature-dependent trends developed. At low temperatures, a
  hemi-bipyramidal habit dominated by 1111 faces developed, whereas the
  lenticular e103 dominated habit forme at higher temperatures. With
  progressively greater concentrations of organic material a(100)
  penetration twinning developed, secondary complex nucleation occurred
  near the twin interfaces, and finally, rosette and rosette-like
  aggregates formed. Higher temperatures generally favored better-formed
  and larger rosettes. The presence of 5% and 15% NaCl greatly decreased
  nucleation density and resulted in larger single crystals and crystal
  aggregates. The a(100) penetation twins appear to be diagnostic of
  gypsum growth in natural terrestrial sediments at a pH greater than
  7.5.

Relevant bit about gypsum roses is in bold.


Could glacial melt alter plate tectonic movement? Let's say some event caused runaway glacial melt, and removed half of the ice currently locked away in specific areas of the planet. Would the significant weight changes on various plates and fault lines be enough to dramatically shift how current plates were biased against one another?

Yes, it's called glacial rebound. Some areas of the globe are still responding to the disappearance of the ice of the last ice age. A well known example of this are the raised beaches in the northern Baltic, where the crust is rising due the melting of the ice sheet that covered Scandinavia.


Is Antarctic sea ice at record levels? Every time I read a news article about Antarctic ice extent, I don't seem to have a clear answer as to what the deal is. If I look at the February sea ice extent from the National Snow and Ice Data Center (NSIDC), I get no trend that I can see:
.

If I look at the September data from NSIDC, then I get a clear increase.. NSIDC even tells you what the trend is.

  Monthly Antarctic September ice extent for 1979 to 2014 shows an increase of 1.3% per decade relative to the 1981 to 2010 average.

Finally, if I look at the monthly values it is even trickier:

What I can tell is that the minimum extent seems to be unchanged, while there is an increase in the maximum extent. If I where to analyze the trend using all the data, I wonder if any significant trend would be extracted.

I don't want to create any controversies, as I realize that the gains in the Antarctic (small increase of ~100,000 km2 per decade) are much smaller than the loss in the Arctic (decrease of ~500,000 km2 per decade) (NSIDC).

My questions are: Considering the level of variability in coverage, can the Antarctic sea ice extent be considered at "record levels"? If so, what is the consensus on the causes of  this increase?

There have been a number of studies based on observations and modelling of the Antarctic Sea Ice trends.  One major observation is that since continuous satellite coverage began in late 1978 (3), there has been an increase in annual Antarctic sea ice extent (1)(2)(3)(4), that reach ~28% of the Arctic sea ice loss (1).

Critically, according to Simmonds (2015) (1) (and Fan et al. 2014 (3)), that despite interannual, sub-decadal and multidecadal variations, there is a statistically significant increasing trend in sea ice extent for all seasons since late 1978 (As shown in the image below).

Caption (from the NSIDC): Arctic and Antarctic Sea Ice Extent Anomalies, 1979-2012: Arctic sea ice extent underwent a strong decline from 1979 to 2012, but Antarctic sea ice underwent a slight increase, although some regions of the Antarctic experienced strong declining trends in sea ice extent. Thick lines indicate 12-month running means, and thin lines indicate monthly anomalies.

Essentially, the sea ice extent annual trend is at record-levels since records began with continuous satellite coverage (from late 1978).

As to why this trend is occurring, there is a considerable amount of uncertainty (1)(2)(3)(4), particularly in reconciling modeled sea ice with the extent observed (1).  Simmonds (2015) (1) suggest that this could just be a consequence of the different dynamics between the Arctic and Antarctic - i.e. one model does not fit both ice caps.

Observations documented by Fan et al (2014)(3) indicate that since 1979, there has been a decrease in sea surface temperatures (SST) and surface air temperatures around Antarctica, with the exception of the Antarctic Peninsula and surrounding seas. The trends indicate that in the southern summer (December-February) there is a trend of SST dropping by 0.6°C corresponding to a 9% increasing trend in sea ice extent during the same time - this is also noted by Simmonds (2015) (1) as being the greatest trend in sea ice extent.  This is accompanied by intensified westerly winds and a strengthened meridional sea level pressure gradient, both in the southern summer and in the annual mean.

Fan et al. (2014) (3) suggest that there is evidence for a multidecadal climate variability regime occurring in the region - this stands to reason considering that the time of observations of sea ice extent has only been ~35 years.

There have been several theories suggested in the literature, below are a few of them:

Fan et al. (2014) (3) describe an earlier idea that the increase in greenhouse gases and ozone depletion may cause an increase in the increased westerly winds, there is considerable uncertainty in the interaction between these factors (4).
Models from Holland et al. (2014) (4) suggest a link between Antarctic-wide ice thickness and area trends contributing to overall sea ice trends.
Related to the models above, several papers suggest that the mechanism is related to increases in meltwater fluxes from the Antarctic continent itself (2)(3).  The meltwater flux is modelled to have increased during the southern summer, depositing greater amounts of cool freshwater into the surface layers of the surrounding Southern Ocean, resulting in cooler SSTs in the southern summer, potentially causing the increase in summer sea ice extent trend.
However, most critically, Holland et al. (2014) (4) note that the freshwater 'extraction' by sea ice is a small percentage of the actual fresh meltwater flux. Instead they model that instead of freshwater flux, the driver is based on trends of Antarctic ice thickness and area.

This means that the increase in sea ice is not a 'counter balance' for the ice melted from the continental ice sheets, but rather, according to the models, the increasing sea ice extent appears to be a symptom of the continental ice sheet melting.

References

(1) Simmonds 2015 Comparing and contrasting the behaviour of Arctic and Antarctic
sea ice over the 35 year period 1979–2013 Annals of Glaciology

(2) Bitanja et al. 2015 The effect of increased fresh water from Antarctic ice shelves on
future trends in Antarctic sea ice Annals of Glaciology

(3) Fan et al. 2014 Recent Antarctic sea ice trends in the context
of Southern Ocean surface climate
variations since 1950 Geophysical Research Letters

(4) Holland et al. 2014 Modeled Trends in Antarctic Sea Ice Thickness, Journal of Climate (Full text here)


What's the partition coefficient (D) of Nb for apatite? Was there any experimental study that determined $D$ for apatite and silicate liquid?

The GERM Kd database only lists one study with carbonatite liquid, but that's not what I'm looking for.

Yes, in the paper Trace element partitioning between apatite and silicate melts (Prowatke and Klemme, 2006), where they present experimental apatite/melt trace element partition coefficients for a large number of trace elements, including $\ce{Nb}$.  The experiments were performed at pressures of 1 GPa and at a temperature of 1250 C.

What the experiments revealed were:

An average of $D$ = 0.0018 for $\ce{Nb}$ (this value is an average of Table 5: Trace element partition coefficients between apatite and different silicate melt of the linked document).
$D_{Nb} \approx D_{Ta}$
The partition coefficient was not significantly affected by changing melt compositions.


Why were both the sun and the moon red today? Today was a normal day, except the sun and moon colors were strange. After 5pm, the sky was covered with cirrostratus-like translucent clouds and the sky was a blend of blue and grey.

Everything would be fine, except that the sun was orange between 4-5pm. Then by around 5-6pm, the sun was completely red like blood even though it was still high up, and it was 1+ more hour to sunset.

Then, I didn't look at the sky until 8pm when it was already dark. When I went out, the moon was red just like the sun couple hours before.

The whole thing I saw from around south side od Chicago on US Labor Day (4 Sep, 2017). I didn't take pictures of the sun unfortunately because I disregarded its color, but I took pictures of the moon.

Here's how the moon looked through my phone camera, through binoculars:

Here is a similar picture but edited so that the moon looks exactly like I saw it with naked eye:

What can thia be caused by? (As of writing this at 10:06pm the moon is still red, and it is 6 hours since both the sun and the moon were red/orange)

EDIT: I also didn't see anything about this phenomenon in the media which is strange, and once again, this was seen from Chicago.

Smoke.  There was significant smoke across the USA, which attenuated the light from the sun/moon due to increased scattering.  The smoke particles effectively cause the light to reflect in different directions, so you see more colors.

See below for the HMS Smoke Polygons for the day, which clearly shows smoke over your region from the intense smoke/wildfire activity in the Pacific Northwest.  You can also see the NASA Worldview composite of VIIRS visible imagery for the day, with fire locations in red.


"steep slope" when cold fronts encounter warm fronts: Confusing sentence in textbook I'm currently reading a university textbook on processes that result in rainfall events. In the current processes, I'm reading there is a cold front that basically pushes warm air upwards which results in pretty heavy rain. A little before that, the process that a warm front basically moves above cold air which results in winter rain with a long duration. In the textbook I find the following sentences:

  Typically, cold fronts have relatively steep slopes, about 1 in 30 to 40, while warm fronts have slopes of 1 in 60 to 120; thus precipitation is usually more intense and areally more concentrated at cold fronts than at warm fronts.

What means "1 in 30"? Could it be 1/30 = 0.0333 = 3.3% ? 1 in 60 = 1/60 = 0.016666 = 1.7%.

That would result in a steeper slope for cold fronts. Is my understanding correct? Is a 2-3% slope for warm air pushed by cold fronts realistic?

The slope is the ratio of the vertical to horizontal distance.

From here

  "Warm fronts have a gentler slope and generally move more slowly than cold fronts, so the rising motion along warm fronts is much more gradual."

You can see the steep slope of a cold front visualized,

and a more gradual slope for the warm front:

But depending on the source, there seems to be varying definitions of what the slope value actually is.  It makes sense, given that the answer would be different depending on how deep you go into the front and there would be seasonal variability.

This site has a nice example:

  "The cold front is steepest in the lowest several hundred meters of the atmosphere with a slope of about 1/100, meaning that elevation increases about 1 kilometer for every 100 kilometers of horizontal distance from the surface front. Then the upward slant relaxes into a much more gentle slope (e.g. 1/300). All along the upward slant of the cold wedge, cold air abuts with warmer air, creating an upward-slanting boundary characterized by large temperature contrasts."


Sea cave vs Sea arch How do you distinguish sea cave from sea arch?
If I want to classify a crack of sea cliff as sea cave, has it to have a dead end? Would you call a geological formation as a sea cave even a kayak can pass through?

Cheers!

I don't know if there is a definition of the difference.  Sea caves are typically erosional features not solutional and do not have much length like typical limestone caves so to restrict them to only being a cave based on a totally dark section would force the reclassification of many sea caves to something else.

Typically an arch has an opening diameter greater than its length.  In our parts, Pacific Northwest North America, a sea cave can be just about any opening in the cliff where there is a section that is continuously shaded.  The cave can have multiple entrances.


Why do diamond mines seem to always appear conical? Are the above-ground mines all that way? All at about the same angle? From the BBC's Russia: Eight missing in flooded diamond mine:

The main hard rock sources of diamonds are either kimberlites or lamproites.

Many kimberlite and lamproite deposits occur as:

  carrot-shaped, vertical intrusions termed 'pipes'

As the term "carrot-shaped" suggests, the general shape of the pipes is conical and when viewed in horizontal cross-sections they are generally quasi-circular.

When such structures are mined by open cut methods, as with open cut mines of tabular orebodies it is impossible to mine any open pit to any great depth with vertical walls for ground stability reasons. The mine walls are stepped and the parts of the walls between the horizontal steps are sloped. Because of this, open pit mines start out wide at the top, on the surface, and they get narrower with depth.

If the deposit being mined has a quasi-circular horizontal cross-section and is shaped something like a carrot then the open cut mine will also be conical or quasi-conical in shape.


Ocean air reaching maximum humidity How many miles (or how many hours/days) does air have to travel over the ocean to reach maximum humidity or carry the maximum amount of water it would hold at typical humidity assuming a wind speed of roughly 10 miles per hour?

I understand the typical humidity to be roughly 80% over the oceans. I have a fantasy world with its own landmasses and I'm trying to be able to figure out the climate based on temperature, wind direction and rainfall at different latitudes.

Take North Africa versus the same Latitude in China. At 30 degrees latitude you don't always get a desert climate. If the wind can travel over water it will bring in some rainfall but I'm trying to understand how much depending on the answer to the above question.

https://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html

The amount of evaporated water can be expressed as:

gs = Θ A (xs - x) / 3600                                 (1)

or

gh = Θ A (xs - x)

where

gs = amount of evaporated water per second (kg/s)

gh = amount of evaporated water per hour (kg/h)

Θ = (25 + 19 v) = evaporation coefficient (kg/m2h)

v = velocity of air above the water surface (m/s)

A = water surface area (m2)

xs = maximum humidity ratio of saturated air at the same temperature as the water surface (kg/kg)  (kg H2O in kg Dry Air)

x = humidity ratio air (kg/kg) (kg H2O in kg Dry Air)

Note! The units for Θ don't match since the this is an empirical equation - a result of experience and experiments.

Found the answer to my question.


What do the little flags on these martian wind speed data points mean? According to this answer the weather at the InSight lander on Mars can now be seen online at https://mars.nasa.gov/insight/weather/ This includes the wind speed and I believe the direction (if that's what those little flags mean).

Question: But I'm not sure so I'd like to ask; what do the little flags on these martian wind speed data points mean?

A bit of history...

From the question Was the telltale on the Mars Phoenix Lander used for meteorology? Why not a hot wire anemometer instead?

above: GIF from images transmitted from Mars. From the The Telltale project page on the Mars Simulation Laboratory. Also archived here.

They indicate wind direction (given by the long line or "barb") and speed (given by the shorter flags extending from each barb). In the same linked page you can read:

  The barbs extending from each wind speed data point indicate the
  compass direction of the wind (e.g., a wind blowing from the north
  will have a barb straight up above the point; a wind blowing from the
  west will have a barb off to the left). Full and half flags extending
  from the barbs indicate the wind speed, with each half flag
  representing approximately 2.5 meters per second. A circle in place of
  a barb indicates a wind speed less than 2.5 meters per second.


What is "small layer thickness" defined as in terms of bulk Richardson number approaching gradient Richardson number? In many sources (https://glossary.ametsoc.org/wiki/Bulk_richardson_number), bulk Richardson number is defined as an approximation to gradient Richardson number. The prior only approaches the ladder when layer thickness, $\Delta z$ becomes "small". What is small defined as? For example, comparison of simulation domain to $\Delta z$, overall length $\Delta z$ approaches 0, or etc?

Strictly speaking, $\lim_{\Delta z \to 0} Ri=Ri_b$. This is because the gradient Richardson number: $$Ri=\frac{\frac{g}{T_v}\frac{\partial \theta_v}{\partial z}}{\left(\frac{\partial U}{\partial z}\right)^2++\left(\frac{\partial V}{\partial z}\right)^2}$$ can be approximated as $$Ri \approx\frac{\frac{g}{T_v}\frac{\Delta \theta_e}{\Delta z}}{\left(\frac{\Delta U}{\Delta z}\right)^2++\left(\frac{\Delta V}{\Delta z}\right)^2} \tag{1}$$
which can be rewritten as the Bulk Richardson Number: $$Ri_b=\frac{\frac{g\Delta z \Delta \theta_v}{T_v}}{(\Delta U)^2+(\Delta V)^2} \tag{2}$$. The derivation of (2) from (1) is left as an exercise for the reader.


Do you have any informations about fossil-rich cherts from Scandinavia? Me and some of my friends have found many rocks similar to these in central Europe - we believe that it is fossil-rich chert that originally comes from Scandinavia.

There are many interesting fossils like brachiopods and sea urchins.

We find many of them in southern Moravia - there are many sandpits with quartenary sediments (mostly sands and gravel) that were deposited by river Svitava. We think that these stones must had been transported by glaciers from Scandinavia and then deposited by rivers.

I have searched for this material on the internet and could not find any informations about its formation or deposition. Do you have any informations please ? Could you provide me some links, pdf-thesis or an explanation  ?

Thank you.

What you are looking for is information about the "Oslofeltet" (Oslo-field) in Norway (dated to be from the Ordovicium period, 443 - 488 million years old). This is a concentrated field of of fossils. There is a Sement museum ('cement') in a small place called Slemmestad where it is possible to view fossils from what was formerly an ocean bed. Geologicaly speaking, the entire area around Slemmestad is very interesting.


The axis of rotation of the earth passes through the geographical poles or is there a true axis? The general idea that has been taught to people is that there is an imaginary axis that crosses the earth from the north pole to the south pole (or vice versa).And that is the axis of rotation.

But I have always thought that idea is not so accurate and that there are other poles that are the true and the geographics don't coincide with the true poles.

If I am correct with that idea, I can affirm that there is also a true equatorial line that doesn't coincide with the geographical equatorial line.

Am I right?

[Update]

I asked that question because I live in Ecuador and here there is a commemorative monument of the French geodesic mission (between 1736 and 1744) and besides being a tourist center in which visitors are shown experiments as a container full of water with a siphon in which no swirl occurs because they are in exactly the equatorial line, in addition to other tricks.

Here you can see a video of different experiments:

https://www.facebook.com/nasdaily/videos/923542644464555/

I have reasoned and I think that the effects caused by being on the equatorial line would happen if the axis of the earth did not have wobbles and according to what it says here:

https://en.wikipedia.org/wiki/Equator

"Precise location
The precise location of the Equator is not truly fixed; the true equatorial plane is perpendicular to the Earth's spin axis, which drifts about 9 metres (30 ft) during a year. This effect must be accounted for in detailed geophysical measurements"

Then the true equatorial line would change in a range of +/- 9 meters each year and the effects shown to tourists on the equatorial line may have been for the following reasons:

They are false tricks since the effects of the equatorial line move throughout the year in an area of approximately 9 meters and for such "experiments" to happen they should move the devices to find the effects of the equatorial line constantly throughout the year.
The tricks are true, but they do not happen exactly on the geographical equatorial line, but within a range of 9 meters.

Geographic axis is NOT fixed.

North and south poles are NOT fixed.

Ideology is reverse of what you are thinking.

First suppose that Earth is rotating about some arbitrary axis => Then this axis intersects on Earth's surface at two points => Now, if you see earth from above and observe earth rotating in counter-clockwise direction then this point is defined as North pole and hence other will be south pole.

In short, first we see earth rotating about an axis and then north and south poles are defined according to it.

Also, the axis of rotation wobbles and as a result north and south pole wanders a bit. This is known as Chandler wobble.

Note: It is very important to realize that according to chandler wobble axis of rotation wobbles with respect to Earth. Earth itself is NOT wobbling due to chandler wobble, it is only changing the axis of rotation.

So, there is no concept of true axis here, but only one axis -> geographic axis which wobbles.


What are baroclinic and barotropic waves? I have a basic understanding of what baroclinic and barotropic mean but cannot seem to get my head around baroclinic waves and barotropic waves.

Barotropic flows are those for which the fluid density $\rho$ depends on pressure $p$ only, i.e. $\rho = \rho(p)$. For example, constant density, isothermal, and isentropic flows are barotropic. Baroclinic flows are flows that are not barotropic. In this case the fluid density depends on pressure AND temperature, salinity, constituent concentration. Heavy fluid sitting adjacent to lighter fluid will sink and rise, respectively.

  These flows are said to be baroclinic, meaning pressure breaking.

Consider the two fluid elements below. In the barotropic case, lines of constant $p$ are parallel to lines of constant $\rho$  so there is no mechanism to generate vorticity. On the other hand, in the baroclinic case, the lines of constant $p$ and $\rho$ are not parallel. The latter arrangement give rise to changes in vorticity $\vec{\omega}$ and circulation because the net pressure force no longer passes through the center of mass of the fluid element.

Seen another way, take a look at the vorticity equation with density variation:

$$\frac{D\vec{\omega}}{Dt} = (\vec{\omega}\cdot \nabla)\vec{u} + \frac{1}{\rho^2}(\nabla \rho \times \nabla p)$$

The cross term on the right hand side is the baroclinic torque. When it is zero the flow is barotropic whereas if it is nonzero the flow is baroclinic.

When applied to waves in the Ocean the result is that barotropic relates to waves propagating at the ocean surface. Baroclinic relates to waves propagating along density surfaces in the interior of the ocean (or internal waves).

One good example is the surface tide and the internal tide. As the surface tide (regular tide) sweeps around the main oceanic basins, it rubs against the ocean floor giving rise to internal tides. The former are called barotropic tides, whereas the latter are called baroclinic tides.

References:

P. Kundu, Fluid Mechanics

B. Sutherland, Internal Gravity waves


Are certain isobar temperatures higher in mountainous regions? So we know that the air temperature at higher elevations is lower. But is the air temperature at a certain isobar over, say Vail, Colorado, higher than the air temperature of the same isobar over, say, New York City?

And more importantly, do these differences in air temperature along the same isobar affect the large-scale atmospheric circulation?

Well, if there were no other factors, the temperature at the same isobar should be the same all over the Earth. But there are other factors, like winds, air mixing, albedo, ocean currents etc.

The temperature in atmosphere is lower at higher altitudes. That's because the air is gas, and it compresses. So the air at ocean level is denser than the air at 10km height. The air heats from the ground, and when it's getting warmer, it goes up. But because there is lower pressure, it expands, and while it's expanding, it cools down. That's why the higher you go - the colder it is. But if the pressure is not changing, the temperature shouldn't change too.


Where can I find detailed historical breakdowns of U.S. lightning fatalities on a year-by-year basis? e.g. Something like this, but for historical years (preferably covering 1980-2007, since the NWS detailed lists only start from 2008). Location of strike, victim name, where the victim was at (under tree, out on open water, at beach), etc.

If such a resource does not exist, then what's the next best thing? All the archived meteoroepidemiology (yes I know that's not a word) data I've been able to find is limited to overall numbers of lightning deaths by state/on a national basis.

For a comprehensive literature review of sources of lightning fatalities data you can check the paper "Striking Back: An Assessment of Lightning related Fatality and Injury Risk in Canada", it covers US and Canadian sources. But if you want to know which one is the largest and arguably the best. That would be NOAA's Storm Database. The data you can access trough the online interface is quite limited, so I would recommend to go to the Bulk Data Download area, and get the original spreadsheets. You will see 3 files per year: Locations, Fatalities and Details, from 1950 to 2017. I would recommend to download the "Details" files, as it also have information about the location (Lat/Lon) and number of deaths and injuries, and a short narrative of the event.
It is a large table, as an example, I took the following screenshot of the most important data columns for all the lightning events with casualties in 2009:

You can download the Fatalities file if you want more info abut the age, gender and location of the victim. The relevant fields look like this: