In geology, what is apparent dip and how is it related to true dip? How is apparent dip related to true dip?  How can true dip be calculated from apparent dip?

From https://en.wikipedia.org/wiki/Strike_and_dip

  Apparent dip is the name of any dip measured in a vertical plane that is not perpendicular to the strike line. True dip can be calculated from apparent dip using trigonometry if you know the strike. Geologic cross sections use apparent dip when they are drawn at some angle not perpendicular to strike.

see http://www.webpages.uidaho.edu/~simkat/geol345_files/2012lab2.html


Gelifluction vs Solifluction I'm currently studying cold environments, looking at periglacial processes.

I've been looking into gelifluction and solifluction as processes of periglaciation. The two terms seem to be used, mostly, without differentiation.

However, I am given to understand that there is a difference between the two processes. Apparently gelifluction is more distinct to periglaciation than solifluction.

Could anyone explain the difference between the two processes, if at all there is a difference?

Solifluction is not restricted to cold climates. Gelifluction on the other hand is, it requires by definition a permanent/seasonal layer of frozen soil. In periglazial environments the porewater above the frozen ground layer becomes easily saturated. Solifluction encompasses numerous processes, Gelifluction is one of them...

The wikipedia page for Solifluction provides more information.


Why don't spring tides occur at full/new moon (age of tide)? Tides observations everywhere show that spring tides occur not at full or new moon, at the time of maximum driving forces, but typically a day or two later.

What causes this delay?

The age of the tide (a.k.a, age of phase inequality, lunitidal interval) at a location is a term that denotes the interval between the time of a Full or New Moon (when the equilibrium semi-diurnal tide force is maximum), and the time of the local spring tide. In most cases, there is a delay between maximum forces and occurrence of maximum elevation.

The tidal forces generate waves of very long wavelength that travel all around the ocean with a velocity determined by the shallow water progressive wave velocity equation, $c=\sqrt(gH)$, where $H$ is water depth. The delay between the moon phases and their effect on the tide is the time that it takes for the wave to travel around the ocean.

There are two different mechanisms to consider: resonance and friction.

The fact that the age of the tide is analogous to the increase of the phase lag of a forced, linearly damped harmonic oscillator as the frequency increases was known since the XIX century. The damped oscillator analogy does not explain the phase magnitudes in the real ocean.

The inclusion of friction is necessary to explain the observed time lags. Proudman (1941) showed that by including frictional effects on coastal areas, a positive age of tide appear in the tidal solution. If there is some resonant frequency in an ocean basin close to the semi-diurnal frequencies ($M_2$, $S_2$...), friction enhances the age of the tide resulting in higher delay values. Garrett & Munk (1971) and Webb (1973) provided a methodology for the calculation and estimates around the oceans. The longest delays (longer than 60 hours) were estimated in areas with the largest continental shelf, as they represent areas of strong tidal dissipation: the North Sea, the Ross Sea, Hudson Strait, the shelf off Argentina, the Bering Sea, and the Sea of Okhotsk.

The age of tide can be obtained from the harmonic constants by dividing the difference in phases of the $S_2$ and $M_2$ constituents by frequency separation between both constituents:
$ Age\_of\_tide = {Phase\_of\_M_2 - Phase\_of\_S_2 \over 1.0163 }$, where the phases are measured in degrees and the age of tide is in hours.


How would this experiment's different particle types produce atmospheric reflectivity? The MIT Technology Review news item Harvard Scientists Moving Ahead on Plans for Atmospheric Geoengineering Experiments discusses a proposed experiment to study in a carefully controlled way the reflectivity induced by various kinds of particles released into the stratosphere. The underlying idea being explored is that increased atmospheric reflectance could partially offset warming effects due to greenhouse gases.

Sometime next year, Harvard professors David Keith and Frank Keutsch hope to launch a high-altitude balloon, tethered to a gondola equipped with propellers and sensors, from a site in Tucson, Arizona. After initial engineering tests, the “StratoCruiser” would spray a fine mist of materials such as sulfur dioxide, alumina, or calcium carbonate into the stratosphere. The sensors would then measure the reflectivity of the particles, the degree to which they disperse or coalesce, and the way they interact with other compounds in the atmosphere.
The researchers first proposed these balloon experiments in a 2014 paper. But at a geoengineering conference in Washington, D.C., on Friday, Keith said they have begun engineering design work with Arizona test balloon company World View Enterprises. They’ve also started discussions about the appropriate governance structure for such an experiment, and they plan to set up an independent body to review their proposals.

This is an effort to explore how best to do a small, controlled test and how to establish proper guidelines. This type of atmospheric experiment is very different than the long established practice of cloud seeding for rain, so this thoughtful approach is taken.
A short review of the background concept and associated issues can be found in the video shown in this article, after the first minute or so it gets more serious.
While Alumina (Al2O3) and calcium carbonate (CaCO3) might be in the form of solid particles for such an experiment, and particle size can be engineered to various controlled size distributions ahead of time, sulfur dioxide (SO2) is a gas at STP. At one atmosphere of pressure, it would become a liquid at about -10C. Would the plan be to spray or atomize liquid SO2 at the low ambient temperature at altitude?
If I understand correctly, SO2's mechanism would be to 'chemically scavenge'  water vapor from the air, forming reflective droplets of sulfuric acid. Would the alumina and calcium carbonate also seed water droplet formation as their reflective mechanism, or would only the particles themselves be reflective?

foreword: Particles and Droplets

Commonly, atmospheric particles can be considered as wet particles. E.g. when we talk about sulfate particles ($SO_4^{2-}$), these particles are actually droplets with dissolved sulfuric acid (or with a dissolved sulfate-cation compound).

Mechanism involving $SO_2$

$SO_2$ is released as gas and it reacts to $SO_4^{2-}$ (sulfate). Basically, there are different reaction pathways for the formation of sulfate from $SO_2$:

$SO_{2,g}$ --(gas phase reaction)--> $H_2SO_{4,g}$ --($H_2O$ accumulates)--> "sulfate particle"
$SO_{2,(g)}$ --(goes into solution)--> $SO_{2,solution}$ --(formation)--> $H_2SO_{4,solution}$ (deprotonizes directly)

Commonly, the second pathway is dominant. The relevant aspect is that it leads to the formation of ultra fine sulfate particles (sulfate droplets).

Sulfate particles are cloud condensation nuclei. That means that they support the formation of clouds. There are satellite pictures available, in which you can identify shipping lanes by lines of clouds. These clouds were formed because ships emit large amounts of $SO_2$ (at least outside of sulfur emission control areas).

Most clouds above the ocean reflect more solar radiation than the sea surface. In general, clouds above the ocean are considered as "good clouds" with respect to cooling the Earth. Since a large proportion of the Earth is covered by sea surface, one might wonder to generate clouds above it - e.g. by releasing $SO_2$. However, as far as I know, this process is relevant in the troposphere.

Releasing $SO_2$ into the stratosphere (as proposed in the linked article) is not meant to support cloud formation (correct me, if I am wrong). Nevertheless, the released $SO_2$ leads to ultra-fine sulfate particles. These sulfate particles themselves effectively scatter solar radiation and, thus, prevent it from reaching the Earth's surface. There is also a Wikipedia article available here.

Unfortunately, sulfate indirectly degrades the ozone layer: sulfate leads to the release of radicals that (and their successors) catalytically destroy ozone. See Keith et al. (2016) for a more detailed overview.

Why $CaCO_3$?

The basic idea is to add salts of alkali metals that neutralize sulfuric acid and nitric acid (generated in the presence of sulfuric acid) when we emit $SO_2$. This will reduce the negative impact on the ozone layer. $CaCO_3$ is such a salt (Keith et al., 2016).

Why $Al_2O_3$?

Foreword: I am not expert on this and just read some articles on this topic.

According to Weisenstein et al. (2015), fine aluminum particles (as well as diamonds) are an alternative to sulfate particles. According to them, aluminum is favourable. However, as studies on emissions from missiles and space crafts indicate, $Al_2O_3$ also has negative impacts on the ozone layer (SomeReport; DoD, 2004): $Cl$ radicals are released that degrade ozone. $CaCO_3$ also counteracts here, too.


Relationship between natural disaster and global warming, in the media Sorry in advance if this is too broad a question. Feel free to let me know if it is off-topic.

I don't know more than the next person around about climate change, but I am really not a climato-skeptic myself. Yet, I feel uneasy about the way the media reports about the relationship between natural disaster and climate change, and I am looking for an unbiased assessment of these reports.

At least in what some would describe as “mainstream” media, my impression is that the following pattern emerges:

When a natural disaster or nasty weather seems "intuitively" relatable to global warming (e.g., hurricanes, floods, etc., which a lay person like myself could believe would become more common with global warming), journalists go out of their way to find an expert who will tell them "yes, this is going to be more likely to happen as the planet warms up" and then headline things like "Flooding in Paris Maybe Due To Climate Change", to only cite the latest ( https://www.cbsnews.com/live/video/20180127140626-flooding-in-paris-maybe-due-to-climate-change/?ftag=CNM15cf32c).
On the other hand, when a natural disaster or nasty weather seems to "intuitively" contradict global warming (e.g., snowstorms, cold-wave, etc., which a lay person like myself has a harder time understanding how the phenomenon would become more common with global warming), journalists go out of their way to find an expert who will tell them "this really is consistent with global warming and does not debunk the predictions of climate models at all" and then headline things like "Why the winter cold snap doesn’t disprove climate change” to only cite the latest (this is the title under which an article once appeared on CBS, before the title seem to have changed to https://www.cbsnews.com/news/adam-sobel-president-trump-global-warming-tweet-climate-change/).

I am not interested in these two examples per se. In particular, I am not claiming these specific reports are biased (or unbiased for that matter, I am simply not qualified to make that call).

Rather, my question is:

On average, is the media doing a fair and balanced job as an educator of under-informed people (like myself) on that topic?
Are they providing an even and science-based account of the relationship between natural disaster and global warming, honestly explaining how global warming is a complex phenomenon which may have surprisingly different --- and sometimes maybe “counter-intuitive” for lay people --- impacts here and there (including cooling and increased likelihood of sever weather in some areas)?
Or are they inflating reports “in favor of” action against climate change (e.g., reports that natural disasters will be more frequent with climate change, and that some “counter-intuitive” event do not disprove climate change), while maybe minimizing other reports of situations in which climate change could impact some areas in ways that some would view as “positive”?
Following useful comments: if "averaging" makes the question too hard to answer, which media does a good job, and which doesn't?
Any empirical work done on that question? Did anyone try to text-mine information websites and assess biases (compared to the best scientific evidence) in the media’s presentation of the relationship between natural disaster and global warming?

First thing first: It is very hard, if not impossible, to attribute a single anomalous weather event to climate change. The weather exhibits a huge amount of natural variation.

The recent spate of cold weather that recently has hit the eastern part of North America is consistent with climate change and has even predicted to be a consequence of climate change. However, this spate of cold weather is also completely consistent with natural variations in the weather. As noted above, it's very hard to attribute a single weather anomaly to climate change. Winter weather is, by its nature, extremely variable.

It's also important to remember that this cold weather is a local event. Europe and Asia have been quite balmy this winter. Do not be surprised if December and January turn out to be considerably warmer than historical values when averaged over the entered planet. And even if it isn't, that does not falsify climate change. Climate change is about what happens after removing short term variations ("years" is short term) from the equation.

Note that I have been consistently using the term climate change rather than global warming. It's not that global warming is an incorrect term. People mistakenly take global warming to mean that every single day will be warmer than it was a year ago, everywhere on the planet. The science does not say this. As noted above, the recent spate of cold weather that has plagued and continues to plague eastern North America is completely consistent with and has been predicted by climate change (or global warming, if you will). But it's also consistent with natural variations.

That said, at least one event during the last year most likely was amplified by climate change, and that would be the huge amount of water dumped on southeast Texas by Hurricane Harvey. Tropical cyclones (e.g. hurricanes) and even very strong ones, are natural occurrences. Climate change does not predict that we will get more tropical cyclones. It does however predict that they will get more severe as the Earth warms up, on average. The huge amounts of water dumped by Harvey are consistent with and predicted by climate change, but not so much consistent with natural variations. While Harvey itself wasn't caused by climate change, a sizable portion of the 52 inches of the rain that it dumped most likely was a result of climate change.

Update, since I didn't directly address the questions raised

One reason I didn't address those questions is because the original post has too many questions (Martin: Please read up on how to write a good stackexchange question.) I'll focus on a couple of them.

  On average, is the media doing a fair and balanced job as an educator of under-informed people (like myself) on that topic?

The first of the cited reports in the question has the teaser headline "Flooding in Paris Maybe Due To Climate Change" -- but the link does not discuss that at all. The news report merely covers the fact that Paris is currently flooding. (Perhaps a once longer version did cover a potential link to climate change.) This is a disservice because a potential link between flooding in Paris and climate change does exist. In particular, climate change has roughly doubled the probability of severe flooding events in Paris.

The second cited article is much better. It does not attribute the late December / early January cold snap in the US to climate change. It merely states facts. One fact is that many people (including the president of the US) see a cold snap as falsifying climate change. Another fact is that this is not the case. Climate change, aka global warming, does not say that winter will vanish. (Okay, some alarmists do say that. You need to ignore them, along with the deniers.) The natural variations in winter weather in temperate climates is huge. Climate change has not overcome these huge swings. We will continue to see cold snaps.

  Are they providing an even and science-based account of the relationship between natural disaster and global warming, honestly explaining how global warming is a complex phenomenon which may have surprisingly different --- and sometimes maybe “counter-intuitive” for lay people --- impacts here and there (including cooling and increased likelihood of sever weather in some areas)?

This depends very much on where one gets ones news on climate change issues. Fox News? The odds are against it. According to one study, 72% of Fox News's reporting on climate change was inaccurate or downright false, with the inaccuracies veering toward denialism. This same study found MSNBC to do a much better job, with only 8% of its reporting on climate change being inaccurate or downright false (with the inaccuracies here being mostly overly alarmist).

That said, an 8% error rate is nothing to write home about, and the superficial nature of the reporting is even less to write home about. The news media is not where you should go if you want good reporting on climate change, or on science and technology in general. I have a rather low regard for news media journalism regarding science and technology. The reporting is rather awful. Keep in mind: Journalists in general avoided STEM classes from the ninth grade and up, and when they couldn't, they took classes like Physics for Poets.


How is the difference in crust and mantle composition explained? We know that the composition of the crust is SiAl and SiMa and the one of mantle is mostly ophiolites, but why? Which are the geological processes that make this difference exist?

Generally speaking , Earth interior is classified using two models , the mechanical and chemical model . the chemical model layers are crust , mantle and core. these layers organized while earth started to cool after formation at the stage known as planetary differentiation . heavier materials like Fe And Ni sunk to the core , while the lighter materials like Al and Si stayed at the outer surface of the ball .
Read more about Planetary differentiation if you are interested


How does remote sensing of ocean currents work? I am aware that techniques exist for measuring surface currents using HF radar, either from land-based installations or from space.

How do these work? I have assumed in the past that it's some sort of doppler system, but if I'm right about that, how are currents separated out from waves?

I'm not familiar with land-based methods, but for global measurements, one method is to use satellite altimetry (I'm more familiar with the geodesy side, but many of the same satellites are used).  I think many of the current methods interpolate global or regional currents from a sparse network of buoys.  As more radar satellites are launched, however, satellite measurements of sea surface currents will become more common.

Global-scale satellite-based radar altimetry measures the average elevation of the ocean's surface over a few kilometers (the exact amount depends on the wavelength of the radar band being used).  Over this distance, waves cancel out, so the measurement is accurate to within a few centimeters.  (This is aided by using the motion of the satellite to enhance the image, referred to as Synthetic Aperture Radar (SAR).)

Surface currents in the ocean are directly related to the slope of the ocean's surface. (Again, at the scales we're working with, wind-formed waves cancel out.)

Once you have an accurate snapshot of the elevation of the ocean, you can calculate the direction and magnitude of the surface currents.  (Note that this is only the surface currents! Deep ocean currents are different matter altogether.)

This is also how we coarsely map the ocean floor from space.  (For example, Sandwell & Smith's extensive work: http://topex.ucsd.edu/WWW_html/mar_topo.html)

The average elevation of the ocean's surface with respect to center of the Earth follows the geoid (by definition).

Seamounts on the ocean floor cause a preturbation in the geoid above them.  Water effectively "bunches up" around seamounts (or rather, the surface of gravitational equipotential "bunches up" above the seamount).

By repeatedly measuring the oceans surface (over several years) we can remove the effect of surface currents and get an accurate picture of what the geoid looks like over the ocean.  You can then use this to predict water depths over the oceans on a spatial scale of ~1 kilometer.

In fact, to calculate surface currents, you need this information to begin with.  The surface currents are calculated as deviations from this measurement of the geoid.


How to determine if this fault is normal, sinistral? Studying for an exam tomorrow and stumped on this question (parts d and e).

The region show in Map 2 consists of a series of sedimentary strata
that have been tilted and then eroded, producing an unconformity. Lava
flows covered the unconformity, and the region underwent further
tilting and then faulting before erosion transformed the region in to
a plain.  Using the data provided by Map 2 determine
a. amount of net slip
b. rake of net slip on the fault plan
c. plunge and trend of net slip
d. relative movement along the fault e. type of fault

The original answer for d & e was that the eastern block moved NW relative to the western block, and it was a sinistral reverse fault.  Can't remember why I chose reverse and not normal.
Lab TA appears to be saying not sinistral, just 'normal'.
So my questions are, how would you determine that it's a normal fault and not reverse?  Why not sinistral?
I can't see an indication of how the foot wall (western block) has moved relative to the hanging wall.  I know the TA is the person to ask but it's an online course and answers were slow to come at the best of times.

So, the basic geological history is given. From this, the units named Bed 1, were deposited, then tilted. Bed 2 was deposited and tilted (along with Bed 1). The entire sequence was then faulted.

So, how can we tell what the fault did?

First of all, notice that there was movement of the eastern block to the north-west. This can be deduced because all the contacts have been shifted in that direction.

So, let us undo that shift to the north-west:

Now, we can see that the contact between Bed 2 and Bed 1 does not line up. This means that we must have had movement up or down as well. The only way to work this one out is by knowing which way the contact dips. If it dips northwards, then the eastern block moved up. If it dipped south, then it would overlie all the sediments to the south. This suggests that Bed 2 dips northwards.

Upward movement of the eastern block would then reveal Bed 1 when the area was eroded.

My conclusion therefore, is that the fault moved the eastern block north-west and up, relative to the western block.

Did I miss anything? It is late, which I will claim as an excuse. If my logic is unclear, let me know and I can try add more pictures, or video of me waving hands about, which is my usual approach.


What is the earth's core temperature? What is the earth's core temperature and is it really directly related to the earth's mantle?

The inner core of the Earth is a large sphere of nickel-iron alloy. Surrounding this is the molten inner core which has a temperature of approximately 5400 ℃.

The source of heat that keeps the Earth's core hot and molten is the decay of radioactive elements, predominantly uranium, thorium and potassium.

The Mantle and Crust act as insulators for the Earth's Core.


What would a planet's sky look like with different chemical compositions, such as low nitrogen, high methane etc? What are the processes, chemicals and particles involved in creating colour in a planet's sky? Could you give some examples of sky colour processes different from what happens on Earth?

Except for Rayleigh scattering (Is the color of the sky the same everywhere on earth?) gases typically do not add any color to atmospheres, they are usually transparent in visible light. The Halogen gases (F$_2$, Cl$_2$,Br$_2$, I$_2$) have color though, and there are a few other colored molecular gases, but you would not expect them in planetary atmospheres.

The color in planetary atmospheres comes almost exclusively from particulates, such as hazes (smog basically), ice crystals (not just water), and mist with chemicals in solution. The atmosphere of Titan is colored by tholins: organic molecules of H, N, C, O and possibly S. The other planets' atmospheres are colored by particulates such as ammonia ices (NH3), sulfuric acid droplets (H2SO4), tholins, and other exotic stuff.

It is important to note the color reflected or scattered by an atmosphere can be quite different than the color transmitted through an atmosphere, which is why our sky is blue in the daytime but reddish at dusk or dawn. So the color of exotic clouds or haze on other planets may look completely different seen from below rather than above.


How to remove 'silk braid' noise in satellite data? Satellite remote sensing data is a powerful tool for researching the spatial distribution and temporal variation of atmospheric species.

Aura is one satellite owing to NASA which meaning atmosphere in Latin literally.

OMI which means Ozone Monitoring Instrument has the global observation data for $\ce{O3}$, $\ce{NO2}$, $\ce{BrO}$ etc.

Getting the $\ce{NO2}$ monthly mean data from TEMIS, the ESRI grid format file was plotted by me showing here:

I have noticed that the figure are covered by discrete silk braid (in my plot, they are plotted in green color liking raining top->down) like this:

IMHO, these braid must be not related to the anthropogenic emission but something related to the satellite orbit.

For quantify research of certain grid box, these braid would influence the finite column concentration.

Besides, from NASA Giovanni online visualization tools, the figure below is also the $\ce{NO2}$ tropospheric column in the same area.

There are no silk braid like my figure.

So, my question is here: How to remove these abnormal value for more precise data.

That would be nice if anyone familiar with this area give me some advice.

Update

Thanks for @deneil's attention. I presented two data source here for distinguishing.

TEMIS data was called Dutch OMI NO2 (DOMINO) data product v2.0.
In its official manual here, it said, I quoted:

DOMINO = Level 2 product
The DOMINO data contains geolocated column integrated $\ce{NO2}$ concentrations, or
$\ce{NO2}$ columns (in units of molecules/cm2). DOMINO data constitute a pure Level 2 product, i.e.
it provides geophysical information for each and every ground pixel observed by the instrument, without the additional binning, averaging or gridding typically applied for Level 3 data.

The Giovanni visualization tool use OMI/Aura $\ce{NO2}$ Cloud-Screened Total and Tropospheric Column Daily L3 Global 0.25deg Lat/Lon Grid which means it's level 3 data.

I think the difference sitting there. But I have also tried OMI $\ce{NO2}$ level2 data from NASA (OMI has two independent data source in Dutch and NASA), it has 15 candidate scenes which was plotted different from the TEMIS DUMNO2 data.

Here is an example. The figure below plot the level 2 data in tilted grid due to the satellite orbits. Level 3 data must resample the tilted grid data into regular grid network.  So, I think my first figure shows the right result as level 2 data's character.

Updated II

There are three different source for tropospheric $\ce{NO2}$ column. It seems that Berkely's dataset is the best choice.

You ask, How to remove these abnormal value for more precise data?

The short answer is that you might be able to make your data look more representative of the natural 'truth', but you will probably have to pay for this with some precision. The problem is that the measurement itself is imperfect: this looks like an artifact of the data collection method. The general name for unwanted energy that interferes with a signal you are interested in is noise.

In your case, there is some random noise, and there is this coherent (i.e. spatially organized) noise. It is likely impossible to substantially attack either type of noise without touching the signal. In other words, you will probably have to pay for the noise reduction with some loss of precision. This may be a trade-off you are willing to make.

Reducing noise

There are many, many ways to reduce noise in data. A very common way to reduce random noise is to apply a smoothing filter such as a simple mean in some small, moving window (often expressed as a convolution operation). The problem with this is that it just mixes the noise into the image.

You can also think of a smoothing high-cut filter in the spatial frequency (aka wavenumber) domain. A common approach to removing the sort of spatially organized noise you have is to use a 'notch' (narrow) cut filter in this domain, which has the effect of removing noise with that spatial frequency. In other words, you can remove stripes.

Filters that remove stripes can be found in various image processing software, or could be implemented with various scientific computing languages (e.g. MATLAB's Image Processing Toolbox or scikit-image for Python). Here are some options:

FFT in ImageJ/FIJI — I would start here, unless you're already into MATLAB or Python.
Destripe in GIMP — another good option.
Destriping in ISIS — an image processing package from USGS.


When do winds gets stronger? Do winds on Earth always gets stronger when the temperature is higher or are winds only increasing when the temperature gets higher.

So the difference is that when temperatures áre higher (with a constant level) that there is less difference in temperatures but in case of gétting a higher temperature the differences of temperatures are higher and that causes stronger winds?

So is a high temperature the most important factor or the increase of the temperature?

Your question is a bit confusing, but there is a strong connection between temperature and wind,in their spatial gradiant I would say, however, instead of temporal differences.

Imagine winds are only driven by changes in pressure (higher temperatures -> lower pressure and vice versa). Imagine there are two surface areas with different temperatures (say some frozen lake and a nice grass field in the sun nearby). Therefore the horizontal pressure gradient (due to horizontal temperature gradient) would force the existence of wind, blowing from the High to the Low pressure zones.

Now imagine another situation where there is no horizontal gradient (differences) of temperature nor pressure. The surface is homogeneous. Now imagine all the homogenous surface gets warmer at the same rate, but still remains homogeneous). There would be no reason, thus, for stronger winds (apart from molecular-scale phenomena due to warming, but I believe is not the focus here).

To summarize: winds driven by temperature differences do get stronger if temperature differences spatially increase. A high temperature, alone, does not say much and is way to vague to relate to what you ask.

You could also think of Antartica: very cold and high speed winds. Just to give a hint of how more complicated the relation between temperature and wind may be.


Is wave spectrum always positive and why? Is the 2-D elevation wave spectrum (as a function of wavenumber and direction, with units of $m^4$) always positive? If so, why would that be the case?

Yes, wave variance or energy spectrum, direcional or non-directional is positive-definite as @aretxabaleta said in the comment.

In linear water-wave theory, the surface elevation is described as a linear superposition of sinusoids:

$$
\eta(t) = \sum_{i-1}^{N}a_i \sin(f_i t + \phi_i)
$$

where $a_i$, $f_i$ and $\phi_i$ are the amplitude, frequency and phase, respectively, of each wave component $i$.

The most commonly used wave spectrum is the wave variance spectrum. Wave variance is:

$$
\langle\eta^2\rangle = \dfrac{1}{2N}\sum_{i=1}^{N}a_i^2 = \sigma^2
$$

and wave variance spectrum $F(f)$ is defined such that:

$$
F(f)\Delta{f}=\dfrac{a_i^2}{2}
$$

In the limit of $N \rightarrow \infty$ (continuous spectrum), the following holds:

$$
\int_{0}^{\infty}F(f)df = \sigma^2
$$

Being quadratic, both wave variance (spectrum integral) and individual discrete spectrum components are positive-definite.

Note that so far we implied non-directional frequency spectrum, i.e. spectrum defined in frequency space. It can be also defined in wavenumber $k$ space, and the following holds:

$$
\int_{0}^{\infty}F(k)dk = \int_{0}^{\infty}F(f)df = \sigma^2
$$

$$
F(k)\Delta{k} = F(f)\Delta{f}
$$

$$
F(k) = F(f)c_g
$$

where $c_g$ is group velocity of an individual component.

The non-directional spectrum is simply an integral of directional spectrum over all directions:

$$
\int_{0}^{\infty}F(k)dk = \int_{0}^{2\pi}\int_{0}^{\infty}F(k,\theta)dkd\theta
$$

Be careful about units here. All spectrum integrals must come up at $m^2$. Thus, $F(k)$ has units of $m^3$ and $F(k,\theta)$ has units of $m^3$ $rad^{-1}$.

If you are considering polar (spectral bins scaling with $k\theta$ instead of $\theta$) directional wavenumber spectrum such that:

$$
\int_{0}^{2\pi}\int_{0}^{\infty}F(k,\theta)k\ dk\ d\theta = \sigma^2
$$

then $F(k,\theta)$ has units of $m^4$ $rad^{-1}$.


Where to start with P190s Seismic Navigation Files? I have a few P190s navigation files from a 2D reflection seismic acquisition shoot and wondering what the best way was to extract UTM's (or latitude and longitude) and depth. I am reading through the headers and trying to make the best of it, but I am having a hard time making sense of it.

It should be easy to spot the lat and lon coordinates. Have you found the spec? http://www.seg.org/documents/10161/77915/ukooa_p1_90.pdf


CFSR hourly surface wind time series I am looking for hourly surface wind reanalysis data for the past two years. I am looking at the CFSR/CFSv2 data accessible from UCAR:
http://rda.ucar.edu/datasets/ds094.1

The 6-hourly products are "complete" (http://rda.ucar.edu/datasets/ds093.0/), while the hourly dataset (http://rda.ucar.edu/datasets/ds094.1) is "Selected". I take "Selected" to mean a subset of some kind. For those familiar with CFSR, what exactly is selected, and what is not contained in the dataset?

Suggestions on other sources of hourly reanalysis surface wind datasets would be appreciated as well.

If you check the 6-hourly products in the links you shared, you can see that CFSR includes 50 variables in the "complete" dataset. The hourly dataset has a limited number of variables (25 in total). That's what they mean by "selected". Hope this help.


At what latitudes does daytime last exactly 24 hours once in the year? I assume at the Solstice - a definite latitude would have exactly 24 hours of daylight. What latitudes (North and South) are these - they might vary a little with longitude?

The latitudes today are 66°33′46.1″ N and S, the Arctic and Antarctic Circles.

By definition, north of the Arctic circle, and south of the Antarctic circle, everywhere gets at least one day with no sunset, which I guess is what you mean by 'exactly 24 hours of daylight'?

From the linked article:

  North of the Arctic Circle, the sun is above the horizon for 24 continuous hours at least once per year (and therefore visible at midnight) and below the horizon for 24 continuous hours at least once per year (and therefore not visible at noon).


Is continental drift caused by lava pushing the seabed apart? My daughter has a writing assignment based on a handout about plate tectonics. One paragraph says:

  Molten rock from the earth's mantle pushes up through the surface at the mid-Atlanic ridge. The rock cools and forms new sections of crust on the ocean floor. The ocean floor has to make room for the new crust. To make enough room, the ocean floor must spread out. As a result, the earth's plates shift.

It's been a long time since I was in school and this is far from my field, but this doesn't sound right to me. Isn't the main cause convection currents in the earth's mantle? Is cooling lava pushing the plates apart a cause? I thought it was basically an effect — where the plates diverge, molten rock pushes up and fills in. (Or, is this just two ways of looking at the same thing?)

No, lava does not push the plates apart.

The mid-ocean ridge basalt is passively filling the space left by the plates moving apart. Plate motion is driven by gravity (image by Vic DiVenere at Columbia; see note below):

There are thought to be two main effects at play: ridge push, and slab pull. We don't know much about their relative importance, but it probably varies spatially (e.g. Ribeiro, 2012, Soft Plate and Impact Tectonics, Springer).

Ridge push happens not because the new lava is pushing, but because the ridge is high up. It's so high that in some places it sticks out of the water (e.g. Iceland). It's high because it's hot — but not from deep convection. A geophysical technique called seismic tomography suggests that the hot zone is relatively shallow. As the new plate cools, it thickens and sinks 'downhill', pushing the older plate ahead.

Slab pull is easier to imagine: a subducting plate, sinking into the asthenosphere (uppermost mantle), pulls the younger plate behind it. Not all margins are destructive, however, so slab pull does not operate everywhere. Indeed, the relative important of push and pull is debated.

You will sometimes see figures like this one, strongly implying that convection and plate motion are strongly coupled. The earth is a complex system so the processes are certainly related, but we don't understand the frictional forces (drag) at the lithosphere–asthenosphere boundary well (e.g. read this primer by DiVenere). These images, while prevalent, are an unhelpful over-simplification.

Note: I'm using DiVenere's copyrighted image under 'fair use' terms. Please replace it with an open version if you find one! (But not one with convection cells :)


Do Earth's layers move at different speeds? I don't have a background in Geology but this question popped in my head the other day and can't find an answer anywhere else.

If I remember science class correctly, Earth's layers have different element compositions. Would it be correct to assume that they have different densities and different frictions as a result? And if they do, does it follow from it that they rotate at different speeds?

Thanks.

Im am currently doing my masters in geophysics (last semester) and before that I did a bachelor in geoscience.

I assume by layers you mean the crust, the mantle and the core.
These all have different composition and also different densities. But the earth rotates as a whole, not the individual layers, all layers have the same angular velocity. That means they all make one rotation per day.
These layers are also not the perfect boundaries we like to imagine, but more a change in properties around a finite depth. This depth can even change at different places.


Where is the Arctic Circle for civil and astronomical twilight? The Polar Circles are located at 66°33′46.7″ North and South, defining the minimum latitudes at which, for at least one 24 hour period during the year, the limb of the Sun never becomes invisible below the horizon.

However, because of the familiar phenomenon of twilight, where the Sun indirectly illuminates Earth's ground level by scattered light from the atmosphere, localities well south of the Arctic Circle still experience long periods without actual nightfall.

What are the latitudes at which there are at least 24 hours of continuous twilight per year? I am interested in both civil twilight – the point at which it's "more or less night now," defined semi-arbitrarily as the Sun's center being 6 degrees below the horizon – and astronomical twilight, the point at which the sun is providing basically no illumination at all, defined as the Sun's center being 18 degrees below the horizon.

As mentioned by Barry in the comments, you just have to substract 6 degrees of latitude to get the ring around areas were it never gets DARKER than civil twilight or darker for 24 or more hours (or 12° for nautical twilight and 18° for astronomical twilight). That would be:

"Never darker than civil twilight circle": : 60° 33′ 46.7″ (orange in the figures below)
"Never darker than nautical twilight circle": : 54° 33′ 46.7″ (green in the figures below)
"Never darker than astronomical twilight circle": : 48° 33′ 46.7″ (light blue in the figures below)

To be clear, those circles surround the places where on summer solstice there is no complete nightfall (i.e. it doesn't get completely dark according to the different twilight standards).

In turn, you can think about other set of equivalent circles where it never get BRIGHTER than a given type of twilight for at least 24 hours, those would be

"Never brighter than civil twilight circle": : 72° 33′ 46.7″ (orange dotted)
"Never brighter than nautical twilight circle": : 78° 33′ 46.7″ (green dotted)
"Never brighter than  astronomical twilight circle": : 84° 33′ 46.7″ (light blue dotted)

To be clear again, those circles surround the places where on winter solstice there is no tace of daylight (i.e. they doesn't get any daylight according to the different twilight standards).

In a map, these 6 circles, plus the Polar circle (at latitude 66° 33′ 46.7″ and in red) would look like this around the North pole

And like this around the South Pole

And to have a world view, in geographic projection, they would look like this

The twilights are defined like that (i.e. Sun 6, 12, 18° below the horizon), so no corrections have to be made due to refraction or the size of the solar disk. Such corrections would only apply if you want to find the "effective" polar circle where the Sun would/would not be visible for 24 hours even with an horizon perfectly free of obstacles.
Due to those corrections, the polar night (at the Winter Solstice) only really happens some 80-100 km poleward of the polar circle. In contrast, at the polar circle itself, the Sun can be seen even at the winter solstice.


How can the 'crystal cleavage' of apatite have a four-digit number? On Wikipedia's page for apatite, the crystal cleavage is listed as [0001] or [0101], which I assume are Miller indices....
But how can there be four numbers/digits instead of two, like there usually are?

This is not a four- digit number but four separare numbers called Bravais-Miller indices.  Bravais-Miller indices descrive the orientation of a crystal plane relative to the symmetry axes of a crystal, as described in Wikipedia.  Put very briefly, a zero index means the plane is parallel to that axis, while nonzero indices encode the relative values of the intercepts on axes to which the plane is not parallel.  These pieces of information about parallel and nonparallel axes, together, specify the orientation of any plane that passes through the lattice points of a crystal.
In cubic crystals there are three principal, fourfold axes and thus you render three (not two) numbers for the Bravais-Miller indices of a plane; this is adapted to most other crystal systems.  But, exceptionally for hexagonal and rhombohedral systems, there are four symmetry axes; three of them in the hexagonally packed basal plane and the fourth perpendicular to them along the sixfold or theefold rotational axis.  Thus four indices are commonly used for that case.  The illustration below (Source) gives some commonly encountered planes in hexagonal crystals.

Putting the first three axes into the same plane means the intercept designations on these axes must be dependent on each other; in fact those three numbers should add up to zero.  Thus $[1010]$ is not correct; it should be $[10(-1)0]$ or using the more common notation for a negative index, $[10\overline10]$.  As shown in the above illustration, physically this corresponds to the lateral face of a hexagonal prism.


What is the source of lava of volcano? From magma below crust? Or from molten crust by rubbing? Ok, it looks like a very simple question but I still have some point want to clarify...

Most images explain volcanos contain some orange stuffs as magma below volcanoes as magma chamber, but the problem is, what is the primary source of the magma? I have 2 assumptions but don't know which is correct:

Magma is directly supplied from magma below crust, in subduction zone the crust rubs and some cracks formed, magma rushes out from mantle and then to the surface of Earth via cracks.
The magma is formed by molten crust cause by rubbing and then heating, then it rushes out via cracks. In other words, the magma is originally a part of crust and it just melt again through rubbing, which is not related to the magma below crust.

Which is correct?

Both are correct to some degree.

Basalts are usually the result of direct mantle melting, below the crust. This is the case in the famous volcanos of Hawaii and this is also the case in the most common type of volcanism on Earth: the mid-ocean ridges (albeit hidden below several kilometres of sea water).

Most other eruptive rocks (rhyolite, andesite, etc) are usually the result of either melting of the crust, or interaction of mantle melts (basalts) with crustal rocks. A very large portion of these rocks erupt above subduction zones (most obvious example being the Ring of Fire). The reason is that wet subducting oceanic lithospheres get heated and lose their water. We usually think of water as something that puts out fires, but in the deep Earth it actually lowers the melting point of rocks. This causes melting in the crust, and eventually erupts as volcanoes.

This is a very simplified overview of the subject, and it's a very active area of scientific research with sometimes opposing opinions. But the basic story is somewhat established: some volcanoes (mostly basalts) are products of mantle melting, while others (mostly other stuff) are products of crustal melting.


Why is Belgium (and Luxembourg, Switzerland, Austria, Norway) still above consumption CO2 levels per capita of 1990? While many others did go down "Consumption-based emissions reflect the consumption and lifestyle
choices of a country’s citizens."

Via this article https://ourworldindata.org/consumption-based-co2 I see that Belgium's consumption-based CO2 emissions per capita in 2018 is still above the level of 1990.

I wonder why?
Why are Belgium, Luxembourg, Switzerland, Austria, Norway still above their CO2 consumption levels, while many other neighbouring countries such as the Netherlands, France, Germany, Italy, Denmark, Poland, Sweden, Ireland, ... did manage to get their levels down?
Further more, I am wondering how they can correctly estimate the CO2 of all consumption? I believe this is not known for all brands/products?
P.S.: In 'Sources' we can read:

Consumption-based emissions are national or regional emissions which
have been adjusted for trade (i.e. territorial/production emissions
minus emissions embedded in exports, plus emissions embedded in
imports). If a country's consumption-based emissions are higher than
its production emissions it is a net importer of carbon dioxide.
The underlying source is an updated version of the paper by "Peters et
al. (2011). Growth in emission transfers via international trade from
1990 to 2008."
► (Updated to 2014) Peters, GP, Minx, JC, Weber, CL and Edenhofer, O 2011. Growth in emission transfers via international trade from 1990 to 2008. Proceedings of the National Academy of Sciences 108, 8903-8908: https://bg.copernicus.org/articles/9/3247/2012/bg-9-3247-2012.html
This updated data is available in the latest version of
the Global Carbon Budget.
► https://www.icos-cp.eu/science-and-impact/global-carbon-budget/2019 via https://www.icos-cp.eu/science-and-impact/global-carbon-budget
Our World in Data has calculated several additional metrics based on
the following metrics:
► Energy consumption data from BP Statistical Review of World Energy: https://www.bp.com/en/global/corporate/energy-economics/statistical-review-of-world-energy.html
► Long-term GDP data from Maddison Project Database: https://www.rug.nl/ggdc/historicaldevelopment/maddison/releases/maddison-project-database-2018
► Population data from the UN World Population Prospects and
Gapminder: https://www.gapminder.org/ https://population.un.org/wpp/

My answer will not be complete, but consider one factor: population.
Belgium population per year:
1990    9,967,000
2000    10,251,000 (+10.2%)
2009    10,796,000 (+5.3%)
2018    11,376,070 (+5.4%)
On top of that, you are considering countries with relatively small population increasing significantly (Belgium, Austria, the Netherlands). Most of the population increase is from immigration and high fertility rate of the new population (see the CO2eq impact of about 9tons per capita on the parents due to a new born), with industrial powerhouses like Germany and Italy where a lot of the production has been delocalized in the same time period (check CO2 of Romania or Spain)


Why are the south, the west and the north of the Caspian sea lush but its east completely dry? About the Caspian sea area today:

The south is very lush with the subtropical forests of the Iranian provinces of Gilan, Mazandaran and Golestan (although less "tropical" in Golestan)
The west tends to be lush with subtropical (?) thicket and also forests around Baku and lots of thicket at least up to Derbent
The north is pretty much part of the Euroasian Steppe but might not have been until the rise of the Khazar empire or earlier --- Scythian empire in the region which might have caused significant deforestation although still has some rich thicket/grove areas left today

And yet, the eastern coast of the Caspian sea seemed to me from almost any image as a dry "wasteland", with almost no thicket and certainly nothing I would name "a forest".
Why are the south, the west and the north of the Caspian sea lush but its east completely dry?

The mountains.

The south has a steep relief, as well as the west. That means that there is much precipitation. The clouds throw every drop on these mountains, so almost nothing is left. The east is pretty low, so the remaining clouds (not much left) just fly over. In fact, deserts are generally not steep and they are usually behind the mountains. That is right what happens here. On the north, the effects of the west are still felt, so it isn't so dry, but it is pretty low, too. Also, I wouldn't say that it's lush : )


Why aren't the Hawaiian islands a continuous strip of land? My understanding is that the Hawaiian islands were produced as the Pacific plate moved over a stationary hot spot, which sent magma burning up through the plate as it passed over, forming a trail of volcanic islands on top.

But why dots instead of a line? In other words, why did that process produce islands instead of a continuous piece of land? Does the rising magma start and stop periodically?

Don't be mislead by the subaerial part, it is actually a ridge on a large scale but neither the lava production rate nor erosion rates are constants. That leaves the ridge with higher and lower parts, as well as gaps. Furthermore reef building biocenoses change shape and appearance of the eroding volcanic edifices.

Hawaiian (and other like for instance the Canarian) volcanoes go through stages during their lifetime with different production rates and magma composition. Connections to the magma chamber(s) may remain in place for some time while the volcanic edifice moves relative to the magma source(*), until it has moved so far away that rising magma seeks new ascent channels to rise and deformation forms new dykes and cracks and so it may erupt from different vents, and that from a possible complex and subdivided magma chamber(s) fed by the plume underneath.

That process may leave an appearance of single detached volcanoes like e.g. M. Loa and M. Kea, but they are just similar things at different stages. Many volcanoes never reach a subaerial state and remain submerged, contributing to the appearance of detached islands.

(*) i would say, whether it is the plate that moves or the plume or the connections between plume and magma chambers is mostly irrelevant. Base argument is that the rate is not constant and eruptions may seek different paths during time. As to the exact why and how, that's ongoing discussion.


Why does Coriolis determine the rotation direction of a cyclone but not my drain? It is a common misconception that Coriolis is responsible for the direction the water swirls down a toilet, tub or sink drain.  E.g. does a toilet flush the other way in the southern hemisphere? (If it does, it is due to the construction of the basin, not Coriolis).  This misconception has been debunked many times and leads to a new issue I ran into recently.

I was talking to someone about low pressure systems (cyclones, e.g. mid-latitude storms and tropical cyclones) spinning in the opposite sense in the the north and south hemispheres and they questioned this fact because "Coriolis does not determine how something spins, Mythbusters showed that with a toilet". This demonstrates a lack of understanding in how Coriolis works and leads to this question:

Why does Coriolis determine the sense of rotation of a cyclone but not my drain?  How can it work on one phenomenon but not the other?

The answer is the scale.
The fluid movement of a sink has a much smaller curvature radius than the grand-scale movements of a hurricane.
This curvature radius plays a big role on whether your movement due to a pressure gradient will be balanced by coriolis, or centrifugal forces, as thorougly discussed here.

You can read this wikipage, but the essence is the following:

If you transform the equations that govern the movement of a fluid parcel into a coordinate system that moves along with the flow, you find the following force balance that counteracts the pressure gradient:
$$ \frac{v^2}{R} + f v = - \frac{1}{\rho} \nabla P $$

Here we have simply two effects that arise from the translation to a rotating reference frame balancing the pressure gradient. The first one is known as the centrifugal pseudoforce, the second one is the coriolis force.
If you're interested in a derivation, see here, the linearization is then straightforward.

From those terms one can clearly see that fast dynamics (tornado!), or small curvature (toilet) will lead to the l.h.s dominated by the centrifugal term. However for large-scale and slow flows (hurricanes, cyclones etc.) the left side will be dominated by the coriolis term.

As to the question in which direction a certain flow can occur, let's remember that in co-moving coordinates each scalar quantity has however a sign. $v$ changes sign if we turn the wind direction, $R$ the curvature radius sign depends on where the movement is going, $f$ on which hemisphere we are.

If we now take a look at coriolis vs. pressure gradient force (geostrophic balance), we see that this balance has only one direct solution for a sign of $v$ for a given f. Therefore the predetermined direction of geostrophic cyclones for each hemisphere.

However the solution for $v$ in the cyclostrophic case is obviously
$$v = \sqrt{-\frac{R}{\rho} \nabla P} $$

Which can never be satisfied for high-pressure systems as then curvature sign and gradient sign cancel out and leave the term imaginary.

However one can easily visualize where the forces are pointing:

($F_p$ is the pressure gradient force, $F_c$ Coriolis and $F_{ce}$ the centrifugal force. + and - denote the root's solution. Property of K. Roth, Heidelberg University.)

Here in the case of cyclostrophic balance just look where the red arrow can cancel the green one and you see how Tornadoes do not care for the hemisphere, but just for low-pressure systems and can go in any direction around this.


Do the rocks below an active sill go down, or those above go up, or both? Having read a little about sill formations like the Palisades Sill (eastern USA) and Whin Sill (UK), I understand that strata became separated by the injected layer of magma, with monumental thicknesses achieved in the two examples mentioned.

However, when one considers the weight of the overlying rock, especially if a sill has formed up to several kilometres below the surface, is it the case that the strata and rocks immediately beneath the growing, injected magma layer were sinking, i.e. a descent of the lower solid layer(s) — with magma being injected from somewhere via fissures, etc., to form the sill above — until static equilibrium was achieved? Or did the pressure from the injected magma layer cause the overlying rocks — and therefore the ground surface — to be forced up?

Are there studies that have shown what occurs, for old sills or even ones that have been monitored whilst actively forming?

It's both. The rocks above the sill go up, whereas those below it go down. For shallow diking events it's mostly up.

This is all based on theory of linear elasticity. People model deformation using elasticity all the time, especially for studying deformation at volcanoes which one can measure using GPS, leveling, InSAR, etc.


How are the thickness of ice sheets from previous glaciation periods determined? How is the thickness/depth of ice sheets from previous glaciation periods determined? I've for instance often seen statements that the ice sheet over Scandinavia at the last glacial period maximum (i.e. Weichel) was 3-4 km thick, but haven't seen how this is calculated. Is this determined only by the rate of subsequent post-glacial rebound, basically the inferred weight of the ice sheet, or is it based on other information as well (e.g. historical sea levels as an estimate of the amount of water tied up in ice sheets)?

There is no direct way to determine past ice thickness. The only solid information that exists are past areal extent. But, even this information is not necessarily clear since later advances may have overridden the past terminal positions and dating may not be exact. A main issue is the synchronicity of all such positions.

With a past extent it is possible to calibrate numerical ice sheet models, based on our understanding of ice physics and dynamics and generate likely ice sheet configurations. Such models generate a three-dimensional ice sheet which includes ice thickness. In essence this is the best possible scenario for estimating such past ice thicknesses. Advanced models also include some form of isostacy depending on the overlying ice load. For the last Glacial Maximum, the rebound values are also used to constrain the ice sheet geometry.

The problem is, however, that the response of the Earth's crust to loading depends on the loading history and it would be possible to accomplish similar results with different scenarios since the depression of the crust is in part the loading but also the time scale of the loading. For a long time we though the latest glaciation was one long period of glaciation but we now know that, at least the Fennoscandian ice sheet, experienced two major advances, the mid-Weichselian and the Last Glacial maximum and both were relatively short in duration. This allows us to modify the loading history of the latest glacation. With the earlier glaciations, we do not yet have such detailed loading histories and are thus not able to make detailed models of ice thickness.

It should be added the the understanding of the variations of the last ice sheet come from a series of indirect sources such as sea-level changes, paleo-climate records e.g., (ice cores) and interstadial paleoclimate reconstructions. This means that as our understanding of these indirect records are improved, we can also improve our ice sheet forcing. Add to that uncertainties about basal conditions beneath past ice sheets that affect their dynamics and it is easy to see that past ice thickness values are uncertain. We can, however, obtain reasonable estimates from the models which could be accurate to within, perhaps 500 m (my guestimate).


With so many positive feedbacks accelerating global warming, how did the earth ever re-enter ice ages after it came out of one? We hear a lot about positive feedbacks when it comes to global warming. For example: ice reflects solar radiation, so as the ice melts more solar radiation is absorbed which accelerates warming; rising temperatures create more deserts; release of stored methane; water-vapour feedback; etc.

With so many positive feedbacks it would seem that once the earth has flipped out of an ice age it would take an absolutely tremendous amount of change to get us back into one. Yet the explanations given for the onset and offset of ice ages (subtle orbital variations, continental movements) do not seem that great.

So how can these subtle changes ever be enough to flip us back into an ice age?

Do we have long time span climate-models to validate our theories?

It is not only Milankovic cycles, these are often overrated.

Starting in the Cretaceous, thoughout the Paleo- and Neogene the world went from a greenhouse to an ice age that culminated in the Pleistocene. Much is attributed to the arrangement of continents (large landmass to the southpole), change in ocean currents,
and slow accumulation of ice shields and rising albedo. This is a positive feedback actually, whose reversal (observations from Greenland and recently even Antactica) have led to corrections in climate models, making the projected ocean level rise and arrival of tipping points that will develop their own dynamic even worse. This is very concerning !

But back to the question with two examples, that can be researched:

First, when Antarctica and Australia separated ~35My ago, a circumpolar current developed that cut off the continent from global circulation so that the iceshields could be maintained and more accumulated.

Second, when the isthmus between the Americas closed ~3My ago, ocean currents changed, the gulf stream developed that transports heat and moisture to Europe and north eastern America. The gulf stream can switch states (See: north atlantic deep water (NADW) forming), changing temperature and precipitation patterns, contributing to ice shield build up and retreat in the north.

These are just a few highlights to answer how the earth entered the current ice age, there would be much more to write. Other "ice houses" in earth's history (e.g. Permian glaciation) may have had other causes.

Hope that helped a bit :-)

Edit: but a related, mesmerizing question is: if a hypothetical global ice age really existed, how did the earth find out of that ? The high albedo from a global snow/ice cover would prevent that. Somebody painted it black :-) ?


How can I improve the numerical stability of a coastal hydrodynamic model? I am working with a coastal hydrodynamic model in the MIKE3 modelling package. MIKE3 uses the finite volume method to solve the shallow water equations with explicit timestepping, over a triangular mesh.

My model frequently "blows up" (numerically diverges) in a few cells around a headland, at times of peak flow. What steps can I take to improve the numerical stability, either through modifications to the mesh or other measures?

Almost all finite methods that use forward time models adhere to the Courant-Friedrichs-Lewy law which calculates a courant number and compares it to a $C_{max}$, which is what determines stability, so for 2-D:

$$C = \frac {V_xdt}{dx}  + \frac{V_ydt}{dy} \ge C_{max}$$

Where $C$ is the courant number, $V_i$ is the velocity in subscripted direction, $dx$ or $dy$ is the length interval in specified direction and $dt$ is the specified time step. If you are getting numerical instability, increasing the mesh spacing will lower the courant number, but then you might be missing the dynamics you want to capture. If you decrease the time step, it will take longer for the dynamics to develop computationally.

One way to solve this computational problem is to code in a dynamic time step: Keep calculating the $C$ and $C_{max}$. If $C > C_{max}$, then have the model lower the step by half. Check again, then reset for the next step so you can have larger timesteps for "less dynamic" times. I have implemented this many times in other models and it has worked well.

Another possibility might be that you have high aspect ratios in your mesh: if your $x$ direction is 10 km and your $y$ is 1 km, a $10:1$ aspect ratio is very high. In your case, since the model package you use are triangles, you want the angles in the triangle grid to be as acute as possible. Obtuse angles would mean high aspect ration, in general.

Like llmari, I am not familiar with hydrodynamic models, so I do not do specifics. My expertise are in both mantle convection and plate flexure models. I hope this helps.


How do optical satellites detect different leaf types? In various land cover classification systems, trees are also categorised on the basis of broadleaf or needleleaf. Can someone please tell me the mechanism through which satellites detect this leaf type? Does normalized difference vegetation index (NDVI) plays any role in it?

For example, in GlobCover project, the land cover maps that were generated consisted of 23 land cover classes including classes like broadleaf forests and needleleaf forest. There, the satellite sensors collected data on various phenological metrics like NDVI, etc. and averaged them temporarily to get a single value for such metrics. But not much has been given in http://due.esrin.esa.int/files/GLOBCOVER2009_Validation_Report_2.2.pdf about what all phenological metrics were computed. So basically my question is, how did the MERIS sensor differentiated between broadleaf forest and needleleaf forest?

Short answer

Different plants reflect light at different wavelengths with specific patterns. If you know the reflection pattern of a broad-leaved forest and that of a needle-leaved forest, you can compare them with the pattern observed with a satellite and conclude to which forest it is more similar.

Long answer

Optical remote sensing

Optical sensors record electromagnetic radiation at different wavelengths between 400 and 2400 nanometers. This radiation came from the sun and impacting surfaces of different materials on Earth surface is either absorbed by, transmitted through or scattered back. The amount of radiation that is scattered back is then detected and recorded by an Earth-Observing sensor such as MERIS', MODIS' or Landsat's. Due to chemical and physical properties of different materials, they can absorb, transmit and reflect different proportions of radiation at each wavelength. The reflectance recorded by a sensor for a pure material is called spectral signature. This signature is often unique for a material. This can help identify the presence of different materials on the Earth surface when a spectral signature is known.

In the laboratory, with more sophisticated and accurate sensors, is possible to identify the spectral pattern of single pure chemical compounds or molecules. However, if we scale up and consider the spectral response of a whole forest, you can easily imagine how everything gets mixed up: the spectral signature of many pure molecules in different proportions, scattered back and forth in more or less dense and geometrically various canopies are all sensed by a single sensor unit (for example, one pixel of our satellite image).

Estimating the presence and amount of different materials on the heterogeneous Earth surface becomes a very complex problem and researchers have found many a method to partially overcome it and obtain reasonably accurate estimations of what covers Earth surface and in which amount.
Predominantly, 1) the observed mixed spectral response of a material is statistically linked to in situ measurements, or 2) the spectral response of mixed materials is simulated with computational models and is statistically compared with the observed one.

In both cases, it is possible to use the whole spectral signature or specific metrics derived from specific regions of the spectrum, that we know are related to the presence of some substance that is related to what we are trying to describe.

The spectral properties of plants

The spectral properties of plants have received quite the interest in the past 50 years and one undeniable spectral feature that all green vegetation has, that substantially differentiates it from that of soils, rocks, artificial materials and water is the so-called red-edge. The red-edge is characterised by a low reflectance in the visible radiation (due to chlorophyll absorption) and a high reflectance in the near infrared region.

The Normalised Difference Vegetation Index (NDVI) is one of the many metrics proposed to quantify the red-edge feature. The index is very simple and needs only two bands and no site-specific adjusting constants:

NDVI = (Red-NIR)/(Red+NIR)
Red = reflectance of the red radiation
NIR = reflectance of the near infrared radiation

Since its simplicity, the NDVI is probably the single most used index in optical remote sensing of the vegetation.

The NDVI is a metric for the red-edge feature and thus it is influenced by chlorophyll activity and the presence of other vegetative tissues. And it was successfully (empirically) related to the phenologic stage, plant health, biomass and leaf area index.

In conclusion, if you know the expected spectral signature of a pine forest and that of an oak forest, you can compare them with the spectral signature of any pixel you observe and estimate to which forest the pixel's spectral signature is the most similar.

Clearly, the NDVI can be used for that comparison rather than the whole signature due to its simplicity and versatility; additionally, its interannual patterns can differentiate between annual and perennial, and evergreen and deciduous forests.

However, depending on the resolution of the sensor and the scope of the project, more metrics are possible and different classification methods become available.
There are several other features that have been identified in plant spectral response. For example, the lignin, starch, cellulose and water absorption features in the short wave infrared.

If you have a look at the image below, you can notice that even the age between needles is differentiable by the spectral signature detected by very high spectral resolution sensors. Such sensors are typically handheld while satellite sensors commonly have between 5 and 15 points where you see a continuous line below.

Image from: Rautiainen, M., Lukeš, P., Homolová, L., Hovi, A., Pisek, J., & Mõttus, M. (2018). Spectral Properties of Coniferous Forests: A Review of In Situ and Laboratory Measurements. Remote Sensing, 10


Predicting earthquakes using disturbances in DTH TV transmission It is said that before an earthquake happens, a viewer experiences disturbances in DTH TV transmission in the form of distorted images on the screen which automatically correct after a few seconds.

Is it possible to identify patterns of such disturbances by continuously monitoring TV images so that earthquakes can potentially be predicted at least few minutes in advance and many lives could be saved?

Earthquake prediction have been discussed before in this forum and is rather dispiriting. Distortion in transmitted signals could be an early indication of earthquake, but seismometers (geophones) are still a far better instrument to detect vibrations. In future satellites could be an option in remote areas.

However, damage from an earthquake can be mitigated if warning signals can be transmitted to reach people before the actual arrival of the most devastating surface waves. It helps, in this context, that the surface waves that are  relatively slow.

Early warning systems are used in e.g Japan to slow down trains and automatically alert people through radio and internet. Similar systems are used and developed in other earthquake affected regions.

The challenge is that such systems are expensive and moreover, people with limited access to radio and other sources of information might not be able to receive the warnings. The problem is similar to the Tsunami warnings, that the most vulnerable people are the those receiving least help.


What kind of data is best shown in a rose diagram? I am looking for some geological data where presenting it in a rose diagram is desirable. I don't really know what kind of data is suitable. Any suggestion of data — preferably from the field of stratigraphy or petrology (igneous, sedimentary, metamorphic) — would be useful.

Also are there any good reference book on rose diagrams? Thank you.

Rose diagrams, also called polar bar plots, are useful for showing azimuthal (directional) data. Any dataset consisting of lots of measurements of direction or orientation could be visualized this way.

A common application in sedimentology is visualizing measured cross-bedding azimuths. This can help work out the palaeocurrent direction (that is, the direction of the prevailing wind or current at the time). This paper by Sengupta and Rao has some examples and some data.

The rose diagram display is also often used by structual geologists, to visualize the measured orientations of folds, faults, or other strain indicators. Here's an example (on page 10 of the PDF) from Twiss & Moores's Structural Geology book.

One way to generate a lot of data yourself would be to find a geological map with lots of faults or dip/strike indicators on it, and then measure their angles (clockwise from N).

I'm not sure which came first, but I suspect the design was originally conceived for wind data.


Where can I find a database of historical wildfires in the USA back to 1960? Not sure if it is the right place to post this question but I'd like to know where to find a wildfire database? I don't need any geospatial data.  Just a list of the wildfires that happened in USA from 1960 to present is needed. Wildfires of interest include both human and lightning caused.

I would suggest the National Interagency Fire Center, which keeps statistics in a variety of formats as well as lists of historical fires.  For instance, you can see a list of historically significant fires as far back as 1804 here.  In general, the closer you get to present, the more information about fires there is.

Other websites with historical wildfire lists include:

Wikipedia list of large fires
USGS spatial data back to 1980 with a viewer here
NOAA World Data Center


Could parallel rivers flow in opposite directions? Some rivers have been moving backwards. This got me thinking about an unusual idea.

Could there be terrain that causes two rivers, within a few miles of each other (10?), to flow in opposite directions? One flows east, the other flows west, passing each other by.

Is there anything like this on Earth already? Is it even possible?

One of my favorites: The Columbia and Kootenay rivers. The Kootenay River initially flows southeast, parallel to the initial northwest flow of the Columbia River. The Kootenay passes within 2 kilometers of Columbia Lake, the source of the Columbia.

Source: https://en.wikipedia.org/wiki/File:Kootenay_River_Map.png


Conditions of Thunderstorms Why do some heavy rainstorms and hailstorms not produce any lightning or thunder at all when I thought that these conditions of heavy rain and hail are right to bring lightning and thunder but don’t and why some tornadoes don’t produced lightning or thunder when the conditions are right for lightning and thunder to form?

For lightning to form there has to be a rising current of air within the cloud, carrying ice crystals and water droplets upwards. The droplets become hail, and start to fall as the air becomes thinner, rubbing some electrons off the minute ice crystals, which continue to rise, now positively charged. The soft hail falls to lower levels and is now negatively charged. Positive and negative charges have a great attraction for each other, as the electromagnetic force is almost unbelievably powerful.

Air is a bad conductor, so although the separated charges gradually build up they won't recombine until the build-up of charge is sufficiently strong to overcome the resistance of the air. Leaders from the oppositely charged regions are constantly probing for a viable passage where a lightning flash can get through to recombine their positive and negative charges.

Sometimes a way is found where the build-up of charge is sufficiently strong to overcome air resistance and a lightning stroke occurs, but if the charge build up is not sufficiently strong no spectacular flash will occur. Instead, the separated charges gradually leak away until charge equilibrium is established. So although it may seem to you that conditions are right for lightning to occur, that may not actually be the case.

More unusually, separation of charge can also happen in dry conditions like dust storms and forest fires, where rising dust particles take the place of water. A vaguely similar process of charge separation takes place in a Van der Graaf generator, which can produce artificial miniature lightning discharges.


How are spherulitic structures formed in basalt rock? After having studied the thin sections of basalt under the microscope, I have come across many spherulitic structures occurring in clusters.

How can this happen?

Is it due to devitrification or is it something else? What is the natural process behind formation of such structures?

Image for reference:

According to the image that you provided, what you are seeing are not spherulites, but rather epoxy bubbles. More on that later. I will first answer what are spherulites:

Spherical features observed in thin sections can form by several ways.

Devitrification - this is the recrystallisation of glass. I think it is more common in rhyolitic rocks than in basaltic rocks. As the glass is a non-stable amorphous phase, there is a solid state transition of the glass to quartz or feldspars. The centre of the spherulite is usually some kind of an disturbance in the glass. Could be a crystal nuclei or a small bubble. Here is a magnificent example of a spherulite in rhyolite, from the beautiful collection of Bernardo Cesare:

Filling of amygdules - this usually happens in more basic rocks, for example basalts. A rounded cavity is left due to the presence of gas bubbles during solidification. In this case, the minerals grow from the walls of the cavity inwards, filling the empty space (in contrast to the inside to outside growth pattern of spherulites). The minerals that grow are usually zeolites, clays, quartz and various other hydrothermal minerals. I remember seeing a magnificent example of epidote filling an amygdule once in a basalt. Here's an example of an amygdule from the Imperial College Rock Library:

Notice how it doesn't completely fill in the gas cavity.

These are the two most common ways in which this can form. However, in your case I think the answer is less exciting than this. I am pretty sure that your rounded objects are simply bubbles in the epoxy. Here's why:

They are perfectly rounded. This rarely happens naturally.
They are completely empty.
The actual rock is to the left of that image. Most of the area covered in your image does not seem to have any real rock in it, unless it is glassy but I doubt it because there is rock on the left.
That 4-sided halo around it occurs almost entirely in artificial bubbles created during the sample preparation process. You can put it a λ plate and see that opposite sides have similar colours (either red or blue).


How much water is the atmosphere losing to space? Up until recently, I was under a (wrong) impression that the amount of planetary cumulative water resources was finite as I believed its escape from the atmosphere was impossible. I believed that, unlike other planetary resources, it was impossible to "waste" water as any waste would simply recycle itself in nature, i.e. municipal waste would be treated and get into the oceans from where it would eventually evaporate and precipitate back into continental waters renewing our water supply.

Recently, I learned I was wrong and that there is such a phenomenon called sequestration and that it is indeed possible for the total water resources on the planet to vary.

I am curious if there are metrics on how much water the planet has been losing (or gaining in case of a reverse phenomenon). Additionally, is there anything we can do to reduce this effect?

This article says that we've lost a quarter of our water total but I was looking for more granular statistics.

It is not actual water what is lost to space, because in the high atmosphere water usually dissociate into other molecules or ions. The oxygen ion outflow is frequently assumed to be a proxy for the loss of water from the planetary atmosphere. In terms of global outflow rates for the Earth the rate varies from $10^{25}$ to $10^{26} s^{-1}$, depending on geomagnetic activity (reference).

On the poster of the reference (sent to me by the author) we can read:

  If we assume oxygen corresponds to water loss (self-regulation, Hunten
  and McElroy [1970]), then an oxygen loss rate of ~$10^{25} s^{-1}$
  corresponds to ~300 $\text{g s}^{-1}$ of water loss. Over the age of the
  solar system (4.5 billion years ~ $1.4 \times 10^{17}$ s) this loss
  rate gives $4.2 \times 10^{19}$ g of water.

The current loss figure is equivalent ~25,920 liters per day, or 9,467 $\text{m}^3$ per year. And the reference of that figure seem to be the paper Escape of O+ through the distant tail plasma sheet, that used measurements from the STEREO‐B (Solar Terrestrial Relations Observatory) spacecraft.

That would correspond to a total loss over Earth's history of 42,000 $\text{km}^3$ of water, equivalent to about 12 cm of sea level change. However, that's a straightforward extrapolation of the current rate, because they acknowledge that they don't know how to model how Earth's magnetosphere would have behaved in the past when the Sun was weaker. Although, for a weaker Sun it would be reasonable expect smaller losses.

This value is radically different to that of the article you pointed to. In that case they use the loss of hydrogen instead of oxygen as proxy for water loss:

  Knowing how much hydrogen had disappeared from the oceans over the
  last four billion years enabled the researchers to calculate that the
  oceans have lost about a quarter of their water since the Earth’s
  early days.

They the say:

  Today the atmosphere is rich in oxygen, which reacts with both
  hydrogen and deuterium to recreate water, which falls back to the
  Earth's surface. So the vast bulk of the water on Earth is held in a
  closed system that prevents the planet from gradually drying out.

That suggests that the limiting factor for the existence of water is now the abundance atmospheric oxygen (although oxygen in rocks if very abundant). So it would make sense to use now Oxygen loss as proxy for water loss, but in the past, before the atmosphere was flooded with oxygen, maybe hydrogen loss was a better proxy.

They suggests that methanogenesis can free hydrogen atoms and make them liable to be loss to space, but when it is part of a water molecule it is safe. Methanogenesis would have been much more common in the past when the atmosphere was rich in methane (50 to 500 richer than today).

To wrap up, it seem that there is no consensus about the actual amount of water loss trough Earth's history. Different proxies give different values. Some proxies might be representative to some periods in Earth's past, but other proxies are more representative of other periods. And unfortunately we don't have yet a good reconstruction of the composition and density of the atmosphere throughout Earth's history.

But we do know with some confidence, that while you where reading this answer, one or two liters of water were loss to space.


Is there consensus amongst climatologists that cold weather extremes are caused by global warming or human influence? Is there consensus amongst climatologists that cold weather extremes are caused by global warming or human influence?

I hear the claim a lot that the recent cold weather extremes (such as the polar vortex affecting the US) are caused by global warming, but haven't seen many scientific papers supporting it. I'm not sure if I just haven't come across more. And, I'm not sure if the ones that exist are even considered compelling by climatologists.

It is common sense. The more energy in the Atmosphere the most intense will be the stirring up of it, so you will get cold polar air and hot tropical air moving around further and producing extreme weather.


If the Earth were a smooth spheroid, how deep would the ocean be? At the moment there are deep seas and high mountains. But imagine that the land elevation of the Earth is equal everywhere. How deep would the ocean be in that case?

An approximation can be obtained quite simply by dividing the volume of water in the oceans by the surface area of an ellipsoid with a smooth surface representing the idealized Earth in your question.

The volume of Earth's oceans, seas and bays is $1.332 \times 10^9 \text{ km}^3$.

The equatorial radius of Earth (semi-major axis of the spheroid) is $a = 6378.1 \text{ km}$. The polar radius of Earth (semi-minor axis) is $c = 6356.8 \text{ km}$.

The surface area of the oblate ($c < a$) spheroid is:

$$S = 2 \pi a^2 \left( 1 + \frac{1 - e^2}{e}\tanh^{-1} e \right)$$

where $e^2 = 1 - \frac{c^2}{a^2}$.

Which gives us $\approx 0.51 \times 10^9 \text{ km}^2$.

Dividing the volume of the oceans by this results gives us $\approx 2.6 \text{ km}$.

Note: Earth is not a sphere. An ellipsoid is a better representation of our Earth. Nevertheless, the answer to your question would have been approximately the same had I used a sphere instead, as suggested in the title of your question.


How can linear oceanic ridges (like the East Pacific Rise) be explained by single point mantle plumes? I'm a bit confused about how divergent boundaries between tectonic plates work, or just why plates move. I've read that these ridges that are in the place of divergent boundaries are created when magma arises from the mantle convection, probably powered by a mantle plume. This creates a hotspot, but in every illustration I have seen, they use these plumes or just the mantle convection force to explain why plates move apart each other:

Here, that convection of the mantle is used to explain the formation of a ridge and why the plates move apart.

However, this is easy to understand with a cross section of the Earth like in that picture. But I can't wrap my head around the idea of this phenomenon creating the linear ridges we see extending across thousands of kilometers, like the East Pacific Rise. Because, that "ridge" we see in the above picture is just an elevation seen in a cross section of the Earth, that could very well be just a volcano or a single oceanic mountain, not a linear ridge of continental dimensions.

I mean this:

That can't be produced by a single mantle plume, right? Because a mantle plume is just in one spot. Is the convection force of the mantle rising across that entire line that is kilometers wide, creating a linear mantle plume? If that last one is the case, I would be even more confused about the shape of the convection cells in the mantle. Or are there multiple individual mantle plumes conveniently aligned across and beneath that ridge?

So, I don't understand how the ridge is formed. Because the first picture helps me only to understand how a single elevation spot is created, like an underwater mountain, or a volcano, or even a volcanic island, but not an entire ridge.

Now, I do know that the chain of Hawaiian islands up to Siberia was created due to the tectonic plate passing above a plume, or just a hotspot, and that created the entire "ridge". But are all oceanic ridges formed in that same way? Due to a single plume creating a hotspot and the plate moving above it drawing the ridge as it passes? Or is this a different process? Because I also know this is happening in the middle of a plate, not a divergent boundary

This is a picture about the Hawaiian island formation I read:

I hope someone can help me understand this a little better! Thanks!

Hot spots and ridges are two different things.

Hot spots stay in one place while the earth crust above them drifts and thus create a line of dormant volcanoes, they are a point features so to say.

Ridges are places where the mantle convection wells up and spreads in two directions, gently pulling the earth crust with them and creating new crust where the magma wells up. Ridges may be described as linear features.

So, without convection and thus without ridges, which form new earth crust, the hot spots wouldn't create a chain of volcanoes.


How do I estimate the mass of a deciduous tree's leaves? Regarding the amount of biomass in a tree, what would be the approximate total mass of leaves on a large deciduous tree (e.g. maple, oak) while green in spring? Or, how many leaves could be on such a tree.  This would allow me to multiply by the mass per leaf, which I can measure.

David LeBauer is correct in saying that there are 'allometric equations' to estimate the leaf biomass, but they only refer to small experimental plots in such places as Hawaii, Japan, Singapore and Malaysia. The number of species involved is a few dozen at most. As 'N9ZN' points out, trying to develop generalizations would be a titanic task, and essentially impossible without a vast amount of experimental work. There are about 50,000 tree species in the tropics alone, each with its own calibration curve, not to mention ecologic, microclimatic and nutrient constraints upon leaf development.

I would suggest that, instead of trying to develop a deterministic result, since leaf biomass is approximately related to potential evapotranspiration and water availability/constraints, it would be easier to estimate average water usage by stem dendrometry, crunch the numbers for ET0 based upon climatic data, and then develop a biomass conversion efficiency. As far as I know, this hasn't yet been done, at least on anything other than a very small scale - but theoretically it should be doable.


Naming convention for sea ice thickness per unit area of ice or ocean When defining an area average of sea ice thickness, it is important to distinguish between an average taken over an ocean area

$$h_1 = \sum \frac{\text{sea ice thickness (in area)}}{\text{area}_\text{ice} + \text{area}_\text{water}}$$

and an average taken over the ice covered area

$$h_2 = \sum \frac{\text{sea ice thickness (in area)}}{\text{area}_\text{ice}}$$

The notations $h_1$ and $h_2$ are mine. I've seen both quantities referred to as “effective ice thickness”. I might go with Holland et al 2014 and call $h_1$ “effective ice thickness” and $h_2$ “average ice thickness”.

As an example think of a multi-category sea ice model: Let's say an ocean grid cell has a sea ice concentration of 50 %. Thus 50 % of the ocean grid cell is covered by water. The other 50 % of the grid cell is half-filled with 50 cm thick ice and half filled with 30 cm thick ice. For this case $h_1$ and $h_2$ would be 0.2 m and 0.4 m:

$$\begin{align}
h_1 &= 0.5 \times 0 \text{m} + 0.25 \times 0.5 \text{m} + 0.25 \times 0.3 \text{m} = 0.2 \text{m} \\
h_2 &= 0.5 \times 0.5 \text{m} + 0.5 \times 0.3 \text{m} = 0.4 \text{m}
\end{align}$$

Both variables can be useful. As I have seen conflicting names, I am a bit puzzled with the naming for $h_1$ and $h_2$. What are the standard names for $h_1$ and $h_2$ used in the sea ice community?

It would appear that you are spot on with the commonly used terms in your question.  A well-referenced post on the Arctic forums (not by me) entitled 'Average sea ice thickness vs effective sea ice thickness', provide information about this very question.  Specifically:

Average Sea Ice Thickness = Volume of Sea Ice/Ice Covered Area

Effective Sea Ice Thickness = Volume of Sea Ice/Grid Cell Area

According to the author of the post, (an Administrator of that site), these terms are imbedded in a lot of the published literature - for example, in the article "Uncertainties in Arctic sea ice thickness and volume: new estimates and implications for trends".


Southern Hemisphere climate Does oceanic and land mass positioning affect tropical storm evolution in the southern hemisphere? And, do cold fronts migrate latitudinally " upwards " the way they drift "downwards" in the northern?

The fact that there is much less land mass in the southern hemisphere affects the climate and sea currents, but the situation is otherwise much the same as the northern hemisphere. Cold fronts tend to move north, whereas in the northern hemisphere they tend to move south. Hurricanes and typhoons are less common in the southern hemisphere, especially in the south Atlantic, and drift south, where there is less land to get in their way.

Cyclonic tropical storms form where ocean waters are heated by tropical or subtropical sun, and this heat is the source of their power. In the north, the Caribbean and Gulf of Mexico are a prime source of hurricanes because the ocean is hemmed in by land and heats up more easily than the south Atlantic. Hurricanes here do more damage and attract more attention than they would in the less populated vastness of southern hemisphere oceans. Just as hurricanes from the Caribbean tend to move north, those forming below the equator in the Indian ocean, where they are called typhoons, tend to drift south toward the vast emptiness of the Southern Ocean.


How much total heat is contained in the upper layers of the atmosphere? In particular, I'm interested in the heat contained in the stratosphere, mesophere, and thermosphere.

Mass at 21.9.1998 for Height 140 km -1000 km was $6.16\cdot10^{10} \mathrm{kg}$.
Avg. Temperature; $725 \mathrm{K}$

Roughly the mass is divided as follows;
$\mathrm{O}$, $\mathrm{O}_2$; $252 \cdot10^9 \mathrm{kg}$, “16” Molecule amount $N = 9.5\cdot10^{35}$,
Heat capacity; $920 \mathrm{J}/(\mathrm{kg} \mathrm{K})$

$\mathrm{N}$, $\mathrm{N}_2$; $364 \cdot10^9 \mathrm{kg}$; “14” Molecule amount $N = 1.56\cdot10^{36}$,
Heat capacity; $1040 \mathrm{J}/(\mathrm{kg}\mathrm{K})$

$\mathrm{He}$; $35.2\cdot10^6 \mathrm{kg}$, “4” Molecule amount $N = 5.3\cdot10^{33}$,
 Heat capacity; $5193 \mathrm{J}/(\mathrm{kg} \mathrm{K})$

$\mathrm{H}$; $1.34\cdot10^6 \mathrm{kg}$, “1” Molecule amount $N = 0.8\cdot10^{33}$,
Heat capacity; $14304 \mathrm{J}/(\mathrm{kg}\mathrm{K})$

Total Heat capacity; $61.2\cdot10^{12} \mathrm{J}/\mathrm{K}$
Quelle; My own work.

From here you can calculate $725 \mathrm{K} \cdot 61.2 \cdot10^{12} \mathrm{J}/\mathrm{K} =44.4 \cdot10^{15} \mathrm{J}$

Please note that most of the heat is at the lower atmosphere plain because >99% of the mass is there.


How to determine the transmissivity of a system of rocks and faults from the stationary drawdown pattern? I have a dataset containing high frequency measurements of the hydraulic head at different locations in a 5x6km area. Also known are the precipitation, evaporation, and pumped discharges from a number of wells (unfortunately only monthly totals for the latter). Using the Menyanthes software, timeseries analysis is performed returning the stationary drawdown at each location as a result of the groundwater withdrawal.

A very schematic crosssection of the pumping wells and measurement wells is given below. The red lines indicate pumping wells, blue lines are some of measurement locations, in reality there are 10 pumping wells and some 40 measurement wells. The thick dotted lines are faults, hatched lines indicate an aquitard, while crosshatching indicates an aquiclude. I'm mainly interested in the top layer as that is where the drinking water is extracted from, but I included the deeper layers for completeness.

From the calculated drawdown at each location I want to calculate (or at least estimate) the transmissivity of each aquifer so I can hopefully tell a bit more about the resistance caused by the faults (by smeared out clay layers mostly). I know of the Thiem and Theis models (see for example this article) for the drawdown in equilibrium and fluctuating situations, but are there any other models around that might be helpful to determine the geohydrological properties of the different compartments?

I realise this question probably doesn't have a single conclusive answer, but I think it is relevant for this site anyway as it tries to compare the available models/equations for evaluation of a definitely on-topic problem.

I would suggest Bense (Hydrologische Karakterisering van Breukzones in Zuid-Oost Nederland), as a starting point. It provides a clear view of a few methods used in the past and an indication of the level of detail needed for the analysis, possibly helping you narrow down your search to a suitable method. Mostly Dutch (not a problem, judging by your name), but few international sources too.

I have attempted to ascertain something similar in a spatial model (MODFLOW) recently. From experience, I can tell you that the placement of measurement locations is vital, especially when estimating fault resistances. In my case, the available observations offered no evidence supporting the presence of a fault, even though upward seepage and indicator species were widely observed.