Simple and realistic data for glacier modeling I'm programming the nonlinear Stokes problem (with a finite element method),

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

where $\mu(u)$ is the Glen's power flow law (typical for glaciers). I want to test the model with simple and realistic data. Do you know where can I find simple tests and realistic examples (e.g. a mesh of a glacier and the physical constants)?

Testing and model inter-comparison have been an important part of glacier models developments. One of the main numerical modelling suites used by the glaciology community is Elmer Ice, a full-Stokes, finite element, ice sheet/ice flow model. As part of the effort to test models the community around Elmer Ice developed ISMIP-HOM (Ice Sheet Model Intercomparison Project-Higher-Order ice-sheet Model). ISMIP-HOM consists of five diagnostic and one prognostic experiments, for both 2-D and 3-D geometries. For all the tests, the full-Stokes equations are solved. One of the experiments has an analytical solution obtained from perturbation analysis.

The details of each experiment, including input data can be found at the ISMIP-HOM project page maintained by Frank Pattyn at: http://homepages.ulb.ac.be/~fpattyn/ismip/

Some papers that I would recommend looking at to find out more details about the experiments are:

Benchmark experiments for higher-order and full-Stokes ice sheet models (ISMIP–HOM)
The ISMIP-HOM benchmark experiments performed using the Finite-Element code Elmer
Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP


How to tell if a single day of weather is an anomaly or due to climate change? I am interested in understanding how to tell if a single day of 'abnormal' weather is due to climate change or not.

From my understanding, you would compare this day's weather to historical weather. However, is a day-to-day comparison accurate? Or would you have to take a large sample, like week, month, or season?

It seems to me like it would be hard to compare one day to another historical weather average, because the day could just be an outlier not due to climate change...

In other words, how do you tell if a seasonal storm or really hot summer day is due to climate change?

I am interested in understanding how to tell if a single day of 'abnormal' weather is due to climate change or not.

You can't. The day-to-day, locale-to-locale variations in weather are huge compared to the changes that occur from year-to-year and decade-to-decade, averaged over the surface of the Earth. Most of those climatological variations are periodic in nature (e.g., El Niño Southern Oscillation, North Atlantic Oscillation; note the "oscillation" in the names). Climate change is the small but steady secular change in climate.

Another way to look at it: Even the most pessimistic of projections is for a 4°C increase over the course of a hundred years. That corresponds to 0.04°C change per year. Weather can bring about a 4°C change over the course of a few minutes. Any one weather event can be attributed to the noisy, flukey nature of weather. Climate change begins to become apparent when one looks at weather events that occur all over the face of the Earth, and over the course of several decades.


How far away can you see a thunderstorm? At 9:30 PM on July 13, 2015, I was looking due south from Oshkosh, WI. I saw very clearly a large storm with 1-2 lightning strikes per second. I could see cloud-to-cloud lightning traces, as well as the cloud lit up from within.

Looking at the radar, the only storm in that direction was near Rockford, IL, 125 miles away as the crow flies.

Is it possible to see the top of a thunderstorm from that far away?

The top of a cumulonimbus cloud is usually about 40,000 feet and can reach heights of over 60,000 feet, which would be visible for a distance of 245 or 300 miles, respectively.  Of course, that would be the very top that would be visible at those distances, but it puts it well within the 125 mile distance from which you saw the storm.

The following formula was used:

$$\text{distance} = 3958.8 * \arccos(3958.8/(3958.8+\text{height}))$$

where $3958.8 \ \mathrm{mi}$ is the mean radius of earth.

This formula calculates the distance from an observer to the horizon, which for a six-foot tall person is close enough. If you wanted to calculate the distance an object would be visible from (given absolute atmospheric clarity) you'd have to calculate this twice (from observer to horizon and horizon to object) and add the results.


How do you calculate the depth of penetration in a Schlumberger array? In a resistivity survey, how do we calculate the depth of penetration for a Schlumberger array?

Short answer: 0.2 times the total length of your cable(s).

100m rollout --> ~20m depth

Bear in mind that the deeper you get, the more you have to be careful with your data interpretation. Also if you do a roll-along your depth doesn't get deeper.

Long answer see Bernard J (2003): Short note on the depth of investigation of electrical methods. Heritage Geophysics.


An oblique-square-prism crystal? Does any mineral crystallize in the shape of an oblique square prism? If so, what crystal system (monoclinic, cubic, hexagonal, etc.) would such a mineral fall under?

If "oblique square prism" is this, where the top and bottom planes are parallel, then yes, there are. Carbonates (members of the Calcite and Dolomite, but not Aragonite, groups) have perfect cleavages that leave them with such habit. But be warned that they do not crystallize with such habit, it is a product of an effort that forced it to break accordingly to its cleavages.

A beautifully euhedral calcite crystal.

If, however, you're looking for a mineral which crystallizes in such shape, then the answer is no. There are 14 Bravais lattices (to put it simply, a Bravais lattice is the atomic arrangement that makes the smallest unit of a crystal, and so a crystal is a repetition of it). Each vary on edge ('line') length and angular relationship and obey some rules which are irrelevant for this discussion. The point is, none of the Bravais lattices has the edge parameters a, b and c (thickness/depth, width and height edges, respectively) in equal sizes (i.e. a = b = c) and angles different than 90 degrees between them. Which means that no crystal will ever be fundamentally crystallized in such a form.

The 14 Bravais lattices. Any solid must obrigatorily crystallize in one of these 14 lattices. It's a natural rule.


Deposition in epioceanic areas I found allochthonous (I don´t know the 2 locations) fined grained
carbonate sediment in Ammonitico Rosso, which is possibly mudstone in
the South Iberian Peninsule, specifically in Carcabuey (Córdoba). It is
known that this sediment was formed in the Kimmeridgian and the area was
located in epioceanic shelf, upper waters/mixed layer. There are several
bioclasts in a good state of preservation, so it was covered quickly
enough (high deposition rate) to avoid dissolution. It is not
possible to know how much, I just have a hand sample from the field.
With this information: How can we explain these factors happen together?
- Fine grained sediment, so low energy - high deposition rate -
allochthonous carbonates - good state of preservation of bioclasts

If you need more information to try to answer this question, please let
me know.

Thank you in advance

A turbidity current can easily account for what you've observed. It could be part of a repetitive sequence of shallow angle sloughs caused by accumulating overburden, much like the Bouma Sequences that make up a Turbidite Deposit, or it could be a one-time gravity flow caused by an earthquake.


What is the importance of mixing caused by outgassing in the ocean? I have been asked the following question for which I have no clear answer:
What is the relative importance on mixing of the vertical flow of gases (e.g., Oxygen produced by photosynthesis, CO2 produced in respiration, methane produce from hydrates) in the ocean water column? How does the mixing compare with physical mixing (e.g., wind, internal wave breaking) and molecular diffusion?

My first thought is that the ocean tends to not be saturated in oxygen and CO2, but is there some outgassing as a result of those processes? The question of methane hydrates is probably more complex and likely has links to climate change.

Outgassing is a process by which $O_{2}$, $CO_{2}$ and other chemicals are released as a result of heat or increase in temperature. It is different from advection and diffusion which are mixing processes as a result of temperature and concentration gradient. Outgassing is an abrupt release of gases from where they are stored trapped dissolved, in this case  $O_{2}$ and  $CO_{2}$ in the ocean. Like the ocean some materials are prone to outgassing when heated. For example chemicals released from plastics (e.g. the odor of a new car).

  What is the relative importance on mixing of the vertical flow of
  gases in the ocean water column?
  How does the mixing compare with physical mixing (e.g., wind, internal wave breaking) and molecular diffusion?

The rate of outgassing in ocean is comparable to molecular diffusion of the gases. However, the mechanisms of outgassing and diffusion are different,i.e, outgassing occurs due to some sort of pumping mechanism but diffusion occurs due concentration gradient. Both mechanisms are important to stratify saturation,i.e. homogeneous distribution of chemicals.
Having said this, comparison of diffusion and outgassing needs further investigation. However, I don't think outgassing like diffusion can be triggered by saturation. Some kind of pumping mechanism attributed to difference in surface layers (e.g. the creation of temporary vacuum layer) may trigger outgassing.
In connection with climate change, ocean oxygen and carbon dioxide outgassing into the atmosphere are decreasing ocean oxygen and increasing atmospheric carbon dioxde. Both events have negative consequences. Decrease in ocean oxygen has impacted ocean plants and animals. So, outgassing if occurs within the ocean can be taken as a mixing process but if it throws out the molecules out of the ocean has negative consequences both for the ocean and atmosphere.


What would be the sea level rise if all fossil fuel resources are burned? Tokarska et al. (2016), a Nature article from a team of the University of Victoria, predicted a global temperature increase of 7±2.5°C and 17.2±2.5°C at the equator and at the poles respectively if all proven fossil carbon resources are burned (about 5 trillion tons of carbon).

What would be the sea level rise with this temperature?

At the upper end of that range, all ice on Earth would melt.

That would ultimately give roughly 70 metre sea level rise from melting ice alone, but it may take thousands of years before it reaches equilibrium.

Add a bit to that to account for the thermal expansion of sea water.


Why is Egypt so dry? If you look at this wind map (for July, but following the link you can also view other months):

you will see that Egypt gets its air from the Mediterranean sea. During other months it could get less moist air, but still from the same direction.

If you look at the topography of Egypt:

(taken from Wikipedia), you will see that it doesn't have any mountain ranges that could intercept the precipitation. But it still receives very little rain.

I don't quite understand why. Is the Mediterranean air not moist enough?

If you take a look at the atmospheric circulation pattern, the Hadley Cells in particular, they tell the story. The northern edge of Africa is on the descending edge of a Hadley Cell, which means

  Having lost most of its water vapor to condensation and precipitation
  in the upward branch of the Hadley cell circulation, the descending
  air is dry. As the air descends, low relative humidities are produced
  as the air is warmed adiabatically by compression from the overlying
  air, producing a region of higher pressure.

The main air mass being dry already, and the High pressure system generated by the descending air mass along the 30 degree lines work to make the physics required for precipitation just not want to happen in these regions. You have to get a combination of enough humidity to reach saturation, and then cool the air to reach its dew point.  The desert region formed by the lack of atmospheric moisture(remember Hadley cell) can't add any humidity of its own through evaporation or transpiration, so the global patterns dominate, even being right on the oceans edge.

Note that Hadley cell edges at the 30 degree south also cut through the Namib,Kalahari, and in South America the Atacama deserts, with their own ocean exposure.


What is the origin of the River Citarum on Java, Indonesia? The Citarum river seems to pass through Bandung. The Cikapundung River seems to empty into the Citarum, but this means Citarum starts somewhere else, right?

I tried to follow it in a map. It seems to end in the sea and pass a national park (Cagar Alam Gunung Tangkuban Perahu) in between, but where does it actually start?

The Citarum River,

  originates in Situ Cisanti located at the foot of Mount Wayang, which lies to the south of the city of Bandung, and travels to the north until it empties into the Java Sea.

Situ Cisanti is a artificial lake, about 5 to 10 ha in size, depending on which sources one reads. It is fed by seven springs: Citarum, Cikoleberes, Cikahuripan, Cihaniwung, Cisadane, Cikawudukan, and Cisanti springs.

The picture below shows the designated origin of the Citarum River.

Aerial view of the lake.


Seismic inversion: High-Frequency approximation In numerous textbooks and papers, the phrase "high-frequency" approximation is used in regards to different types of seismic inversion. What exactly is meant by this? Also, what are the implications if this approximation is in no way satisfied?

The propagation of seismic waves is described by the wave equation: $$\mathrm{\nabla \cdot \sigma = \frac{\partial ^2 u}{\partial t^2}}$$
Where $\sigma$ is the stress and $u$ is the displacement.

Geometric ray theory is an approximation to the full wave equation where the length scale of variation in seismic wavespeed is much larger than the seismic wavelength (i.e. a high frequency approximation). Typical seismic wavelengths are anything from $\mathrm{\text{~}50-5000~m}$ depending on the application so the ray approximation is generally valid, unless you are trying to resolve very high resolution structure. It is used widely because it is computationally much less expensive than solving the full wave equation.

This book has a very detailed explanation of many aspects of seismic inversion if you need more detail.


If the study of "minerals" is covered by inorganic chemistry I am wondering what field studies "minerals", such as the minerals in Wikipedia's list. I keep thinking that perhaps it would be covered in inorganic chemistry (list of inorganic compounds wiki), but for example the mineral "Abelsonite" is not in the inorganic list, though it does seem to have a chemical formula, C₃₁H₃₂N₄Ni. I am not sure where the boundary is between "minerals" and "inorganic molecules".

I would like to know so that in terms of data, if pubmed lists the data for inorganic compounds, then perhaps it also includes the data on minerals. But if the two fields are separate (mineralogy and inorganic chemistry), then perhaps the data for each is treated separately as well.

The study of minerals is the field "mineralogy" In some ways it would be a subset of inorganic chemistry, restricted to crystaline materials of natural origin. However, mineralogy includes the physical as well as chemical properties, especially crystallography, X-Ray diffraction and optical properties. It also includes aspects of how the minerals were formed in nature. Minerals also may be named by their chemical formula, but some chemicals have different crystal forms so two minerals can have the same formula. For example the minerals calcite and aragonite are forms of calcium carbonate, $\ce{CaCO_3}$. So you may need to broaden your search in pubmed and they may not include data for all minerals.


Estimate cloudbase height I am trying to estimate cloudbase height using calculations from my weather station temperature/humidity, by calculating those two variables I can get estimated cloudbase height but what puzzles me now is inversion layers and temperature at different heights.

I know grib and grib2 files contain those data but I can't seem to figure out how to pull that data in Java even though I tried like every possible library.

Is there any other way I can accurately estimate cloudbase levels by using some API which gives temperature by height for given latitude and longitude.

You are right, you can't get cloudbase height without 3D data. You can do that using radiosondes. However, if your weather station has a ceilometer, then you don't actually need many calculations. However, they are usually quite expensive.

If you want a real rough calculation, you can just use the Lifted Condensation Level, which is more valid estimate during the day than at night.

Note on the grib files: They may not always have all of the variables. For example, the WAVE ocean model (see NCEP NOMADS) won't have cloud base, because it is in fact for oceans. However, what you can do is use models like the GFS, which tell you what model levels have clouds, and then find the height of the lowest level that has cloud cover. It will take some programming though.


Does the snow come from local moisture or transported moisture? Currently there is a snow storm coming from Europe over the UK. This is drastically dropping the temperature and making it snow lots.

Is the snow coming from moisture that has been brought over from Europe (as part of the storm), or is it coming from moisture that was already in the atmosphere above the UK?

It comes from nearby bodies of water, such as the ocean.

Precipitation of any kind (in this case snow) comes from water that is evaporated from bodies of water like lakes or oceans nearby due to heat (usually not far from where it's going to precipitate). The evaporation forms clouds, which move a certain distance (depending on the cloud, cloud type, and atmosphere temperature and/or conditions) across the globe. Eventually, the vapor in the clouds condenses into rain after cooling enough to do so; thus, creating precipitation.

Even though only half of the water cycle is explained in my first paragraph, the other half is not needed to answer the question. If you wish to learn more about the water cycle, please visit this link.

So to answer your question, a little bit of precipitation is from the atmosphere, but most of it is from water that has been evaporated from bodies of water nearby. And in the scenario you've mentioned, the moisture most likely came from the Atlantic Ocean.

  So the real answer is kinda both :/

The moisture comes from nearby water bodies, and then it's transported to where it's going to precipitate. It is local and transported moisture.

Sources:

Worldbuilding SE (convenient)
Rookie Parenting Science (same link as shown in second paragraph)
Google search for Atlantic Ocean (and I guess all the links on that google search too)


Is it true that distance between earth and sun is closer in winter season (January) and farther in summer season in the Northern Hemisphere? Recently I heard that in winter season the distance between the Earth and the Sun will be closest and it is farthest in summer. If it is true then why is it hotter in summer and cooler in winter?

Yes, it's true (in the northern hemisphere). The small eccentricity of the Earth's orbit is not anywhere close to a key driver in the seasons. The key driver of the seasons is the Earth's obliquity. In the northern hemisphere, the axial tilt of Earth's rotation axis has the northern half of the Earth facing a bit toward the Sun in June/July/August and away from the Sun in December/January/February. The opposite is true in the southern hemisphere.

Eccentricity would be a driver of the seasons if the Earth's rotation and orbital axes were much closer in line with one another than they are. If that were the case, summer and winter would be world-wide phenomena. As it stands, when its summertime in the northern hemisphere its wintertime in the southern hemisphere, and vice versa.

Somewhat paradoxically, even though the Earth is closest to the Sun in early January and furthest from the Sun in early July, the Earth as a whole is cooler during December/January/February than it is during June/July/August. The reason is the uneven distribution of land and ocean between the northern and southern hemispheres.

In 13000 years, northern hemisphere summers will occur near perihelion passage and winters near aphelion passage. Those will be brutal times! Fortunately, I won't be around to see them.


Interpretation of a seismogram (three components) In most cases (as shown in the figure below), a seismogram shows data from three components:

North-South
East-West
Vertical/depth(z)

However, if these components are not marked and all we have are three figures, then is there a way to identity which figure corresponds to which component?

Yes, the vertical component of the seismogram looks different than the horizontal components. There are surface seismic waves (Love waves or Q-waves) that are horizontally-polarized. The ground motion due to these waves is horizontal and parallel to the plane of the ground surface. Therefore these waves will be most visible in the horizontal components of the seismogram. In some cases it may be possible to use the horizontal components to estimate the bearing to the epicenter.  Surface waves travel more slowly than body waves, and their amplitude decays at a lower rate, therefore they may be easier to recognize in seismograms measured farther from the epicenter.


Has our understanding of the East African Rift significantly changed recently? I've noticed many reports in the media about the East African Rift Valley recently, apparently because some large fissures opened up.

Washington Post: A huge crack provides evidence that Africa is slowly splitting into two
CNN: Big crack is evidence that East Africa could be splitting in two
Fox News: Africa is splitting in two, and here's proof
USA Today: Breaking up is hard to do: Africa could eventually split into two continents

Many of them seem to suggest that this is significant new evidence that Africa is going to split in two, but my understanding was that this was not at all in question and hasn't been for quite some time.  Is this just a case of science journalism exaggerating things as it often does or is there something significant in that the existence of these two plates diverging was less firmly established than I thought or that these recent events have significantly changed our understanding of them that justifies all the hoopla, but is not being adequately conveyed.

tl;dr

  Has our understanding of the East African Rift significantly changed recently?

No.

We already know that it is splitting

The headlines suggest that the fact there is splitting (i.e. a rift) is a "maybe": "East Africa could be splitting in two", "Africa could eventually split into two continents".

We already know that it is splitting. There is plenty of evidence for that happening from a variety of fields in geoscience. GPS measurements, geodesy and kinematics tell us how fast it is splitting. The type of magma erupted in volcanoes located in the rift is consistent with what you would expect in a rift (alkaline volcanism and carbonatites). We know that there's a mantle plume below the rift, which is one of the causes of the rifting. We can even see it with deep earth geophysics.

The Kenya crack is not because of said splitting

  apparently because some large fissures opened up.

The crack in Kenya is not the result of this rifting. The link provided by JeopardyTempest in the comments is an excellent summary of what it is: erosion caused by heavy rains.

I will note though that some people suggested the crack to follow a pre-existing fault line, so splitting and earthquakes in the past may have formed a "weak spot" for the erosion to occur, but the erosion itself did was not triggered by any seismic or tectonic activity.


Specific Chemical Composition of Nero Marquina Marble I'm looking to understand the chemical composition of the Spanish Nero Marquina Stone. Specifically, are the white veins of different composition than the black?

We are design studio pursuing work in this stone and are looking to deepen our knowledge of how we can manipulate it.

To a first order approximation, the black stuff and white stuff are the same. Both are calcite (CaCO3).

The only information I could find online was that it contains some impurities of Mg (as dolomite maybe?) and of Al2O3. This shouldn't matter too much to you. The black stuff is black because it is very fine grained, and of organic origin. This is a limestone - made from millions of dead animals. The mass of the rock is their shells, made of calcium carbonate. However, you need just a little bit of organic material and heat, and it all turns to graphite. Graphite is an excellent material in making stuff black. Even a small percentage of fine grained graphite dispersed in the rock will make it black. The white stuff is pure calcite. Dissolved and reprecipitated in fractures as coarse grained crystals without any graphite or other impurities. That's why it's white.

I'm not sure what do you mean by "manipulating". This rock (as all limestones) is very sensitive to acids: vinegar, lemon juice, carbonated drinks, etc. Put it out in the rain for several decades and you will see the damage. It's also very soft. Unlike granite, which can hardly be scratched, limestone will be scratched very easily.


How to make Martian soil My son wants to replicate some experiments and try to grow plants in Martian soil for his A-level science project.  I know NASA have managed to produce soil that mimics Martian soil, however I also know how expensive it is.

My question is, what is the closest proxy to real Martian soil that I can create using readily available supplies from builders merchants, garden suppliers, chemists, and supermarkets?

Many thanks in advance.

https://en.wikipedia.org/wiki/Martian_regolith_simulant#MGS-1 has a link to a standard for Martian regolith that includes recipes. It will, though, not be trivial to replicate the grain size from the minerals. Silicate stuff is hard, one might need an expensive mill or grinder to produce it, or a friend who works at a stonecutter's workshop. Perchlorates are not included in the standard, yet, but maybe its healthier to leave that unimportant detail (slight sarkasm :-)) away.

Mind potential health risks !

Suggestion: maybe it would suffice for an A level project to visit a site where one could take away a basalt, grind it somewhere and sterilize it (heat it to >100°C for an hour or so).


Historically, how has the fraction of Earth covered by water changed? Today, 70.8% of the Earth is covered in water (± a few tenths of a percent depending on how you account for lakes).1 How has this figure changed over the history of the Earth, and why?

Of course, if we go back to the early Hadean Eon, there were no oceans at all, so obviously there was an upward trend, at least initially - but what was the nature of that upward trend? And, once the oceans were more or less "done" forming, was the fraction of Earth covered by water reasonably constant, or not?

Can't say much about the later epochs, but the 'hellish Hadean' epoch without oceans is kind of an outdated idea.
We have zircon records indicating that crust and oceanic formation was already done to some unknown extent 4.4 Gyrs ago. The zircon analyzed in the nature paper given originates from interaction with sub-crustal material in a watery environment at this date.


What exactly is an "upper air station"? What exactly is an "upper air station"? I know they release radiosondes and manage the resulting data, but how does that occur?

I notice that some seem to be at universities. Does the National Weather Service basically hire a professor to release the radiosondes every day and then he pays graduate students, or local random people or what? What if the guy is sick? Is the system automated so no person is needed to launch the balloon?

What does the station look like? Is it like a warehouse, or an office at the university next to a launching field, or what? What are the facilities? Obviously they must have an antenna. Is that some gigantic tower, or is it just a little UHF antenna?

You noticed they're often in University towns... but you may've missed that most sites are also in locations with National Weather Service offices:

Upper air stations (left) and NWS offices (right)

So NWS offices that are launch locations in the US include the twice (or more) per day launches in the responsibilities of its employees.

A few NWS Offices are indeed in buildings at universities (to foster cooperation between the office and research purposes); those include Tallahassee/FSU, Norman/SPC/NSSL/OU, Miami/NHC/FIU.

There may be a few launch sites not located NWS Office locations.  Most such sites are likely at other scientific facilities; I know XMR is actually at NASA's facilities in Cape Canaveral.  (Note: launches at XMR have indeed often been at odd times and been a bit less reliably done)  Still, it's possible that a few such stations are also standalone or at separate airports.  Indeed there certainly historically have been employees hired at many airport observation stations to supplement the (now) automated instruments with visual observations - I had a friend work at the Tallahassee Airport doing so only about a decade ago.  So it shouldn't be beyond reasoning that launches could be done at such spots if uniquely needed.  And I do expect some launch sites in other parts of the world are perhaps staffed in such ways (or by automated measures???).

I haven't actually been in the room where official launches are made, but at FSU saw quite a few from nearby offices, and have been around other sites too.  Still I don't know the precise specs on the equipment, but as far as I understand it, launch sites typically include either a shed/garage or rooftop platform room with a built-in large tube to launch into.  Such rooms hold the supplies and equipment.  Then there is indeed also a radio receiving station to get observations and movements back from the balloon:

From what I've seen, it typically takes a single person a few minutes to inflate the balloon, attach the equipment, and make the launch.  I know that at some sites in very difficult conditions (heavy winds)  multiple people may sometimes be needed to make the launch in order to control the large unwieldy balloon and equipment to prevent issues with tangling in nearby structures.  As mentioned, launch sites in built up areas often have a launch tube to help guide it on a safe starting trajectory.  In more sparse sites or NWS Offices at airports, they are indeed more like fields... so I believe they typically just go outside and release it from a spot clear of downwind obstructions.  Not the most fun in a thunderstorm or hurricane!  (Yes, there have been some amazing launches in such conditions!)


The fertility of the soil I came across this question in my book, it says:

  The fertility of the soil increases when there is a lot of ....... in it.

The choices to fill the space were:

  Nitrogen - nodular bacteria - fungi

I would exclude fungi as in my course I don't have anything says that fungi affect the fertility of the soil. Both nitrogen and nodular bacteria are good choices and I am confused between them. Nitrogen is an important nutrient, nodular bacteria are the nitrogent-fixing bacteria, so both are important to the firtility of the soil, but I chose nitrogen, as I thought it is more correct, but I found that the answer was "nodular bacteria" so why is this? Is there anything I don't understand?

From this paper from 1958 (page 2),

  ... gaseous nitrogen of the atmosphere represents a vast store of potential
  fertility. It is not directly available to plants. Nitrogen-fixing bacteria, how-
  ever, absorb this gas from the soil solution and convert it to cell protein.
  When the cells die, other microbes attack the protein and convert the nitro-
  genous constituents to ammonium, which then becomes an available nutrient.
  Similarly, microbial action on plant and animal residues releases the many
  combined nutrients from their unavailable forms.

From this, one of the criteria for soil to be fertile is the availability of nitrogen to be available to plants in a readily usable form. In a two stage process, one group of microbes (bacteria) fixes the nitrogen by converting into a protein, within their cells. When this group of microbes die, another group of microbes uses these proteins to produce ammonia, which is a nutrient that plants can use.

Also, as this article states, dead bacteria are critical to soil fertility, because nearly 40 percent of a the biomass of bacteria are converted to organic soil components.
strong text

The Nitrogen Cycle


Earth's Internal Heat Engine What is the internal heat engine of the Earth?

Doing research, I found out that the external heat engine of the Earth is the Sun. However, when I did research on the internal heat engine of the Earth, I received multiple answers. Are there multiple answers to this question?

For this question, Wikipedia is probably your best recourse.

To summarize, the heat in the earth's core comes from two places: it is left over from the formation of the earth and it is still being generated by radioactive decay of isotopes that were trapped in the earth as it formed.

The radiogenic heat is still being added to the earth through decay of long lasting isotopes. When the earth formed, there were probably many significant heat generating isotopes, but now after 4.5 billion years, it is pretty much just Thorium-232, Uranium-238, Potassium-40, and Uranium-235.

So there are multiple answers to this question in the sense that there are the two sources listed above, but otherwise, no, this is the answer.

This question has some more information related to heat transport to the surface that you may find relevant.


difference between different meteorological models I need to work with historical weather data (temperature and precipitation), we use meteoblue.com.
There (https://docs.meteoblue.com/en/meteo/data-sources/data-sources#data-sources) they write about three different types of models:

weather reanalysis models
weather simulation models
satellite (observation) data

Comparing ERA5 (reanalysis) vs NEMS (simulation):

daily mean temperature is almost the same in both models
ERA often gives 2-4 times higher amounts for total monthly precipitation, which is just too big difference (it's for Europe, I'm interested in past 20 years)

I tried to read about the models, but couldn't find any comparison. Also don't really understand how such big differences might occur and which model shall I use.

In general, the relation between the three datasets is as follows:

The simulation model is initiated with a set of boundary and initial conditions, and will on the long-term provide good mean conditions. However, depending on the frequency of data assimilation, the results on short-term time spans can deviate from the observations, due to internal variability of the model. Besides, models aren't perfect and sometimes have biases for some variables.
In contrast, the satellite data provides observations. These are of course limited by technical aspects, but as indicated by the table in Section 3 of the link you provided, the quality of the precipitation measurements is very good. However, satellites often have a poorer temporal/spatial resolution than models (a satellite can't be everywhere at once and depending on the type, cannot measure at a very high resolution).
The reanalysis is a combination of the model simulation and the observations, where both sets are merged (via data assimilation) to provide a coherent dataset. This provides a dataset that can be considered 'pseudo-observations' (they are often used as continental-scale or global scale 'observation' datasets in climate studies), but without the poor spatial/temporal resolution of satellite observations. The biases in the reanalyses should be lower than in the original weather simulation, but may still be present.

Concerning the difference between temperature and precipitation: temperature is much easier to correctly simulate than precipitation (e.g. because of the dry/wet-day transition). As such, on a monthly scale, precipitation biases might be already quite large. For more information on precipitation biases, this paper might be relevant: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010jd014532 (Stephens et al. (2010): The dreary state of precipitation in global models)
In essence, the dataset you want to use should depend on your needs. If spatial/temporal coverage and historical data is the most important, the reanalysis is probably your best choice. If you want to know more about this dataset and its biases, this article is a good starting point: https://hess.copernicus.org/articles/24/2527/2020/ (Tarek et al. (2020): Evaluation of the ERA5 reanalysis as a potential reference dataset for hydrological modelling over North America). Or, if your goal is impact assessment, you might immediately check this one: https://essd.copernicus.org/articles/12/2097/2020/ (Cucchi et al. (2020): WFDE5: bias-adjusted ERA5 reanalysis data for impact studies)


Is it possible that a reduction in vegetation is a cause of global warming? A lot of people seem to believe that the entire cause of global warming is that humans are emitting lots of carbon dioxide. However, according to a source I found online (I accept it may not be entirely trustworthy) roughly 46% of trees on the planet have been destroyed since the dawn of the human race, we cut down 15 billion trees every year! Another source I found says that 16 trees absorb the amount of CO2 the average active person emits every day (an active person emits roughly 1kg of CO2 every day). This means we have destroyed enough trees that we no longer can support 937.5 million people! It also means that those trees are no longer taking in 937.5 million kg of CO2 . Here's a line chart showing deforestation from 1800 to 2010. The deforestation rate has gone up.

Credits to the appropriate  authors.

Clearly, the global temperature of the Earth has gone up because of carbon dioxide, however the carbon dioxide has gone up because we are destroying plantlife. So, my question is: "When talking about global warming, why does nobody talk about plantlife? Wouldn't plantlife have a more immediate effect on getting rid of carbon dioxide than limiting how much carbon dioxide we emit?".

The short answer is that people do talk about it.  It is commonly referred to as "land use change".  In general, the carbon dioxide equivalent of the effects of land-use change is on the order of 10% of the total anthropogenic contribution to CO2 emissions.  This may seem small, but it is important to realize that land-based plants are only a portion of the carbon dioxide sinks. You can see below an image from globalcarbonproject.org that shows the relationship.  See here for full presentation.


Formula for rising temperatures I'm looking to extrapolate rising temperatures based on the increasing CO2 levels. From this article: CO2 in 2050, with the following formula used to extrapolate the CO2 levels:

  $CO_2\ level = 280 \cdot \left( 1+\exp(0.0222\cdot \left(year-2052\right)) \right)$. This formula gives the projected CO2 level in parts per million (ppm) for any year from 1958 on, assuming the growth rate is constant at 2.22%.

This seems fair since CO2 increases by 2.2% per year and it's effects are exponential.

I want to roughly use the same formula to extrapolate future temperatures based on this same CO2 increase as the accompanying document suggests: Temps using CO2. The issue is the constants used... because if the same formula is used, then at year 2052, the temperature would be doubled which is obviously not realistic.

So my question is: what coefficients should be used in this: $T=\left(1+\exp(ct)\right)$ formula, where $c$ is a constant ($0.0222$ I would think) and $t$ being a some measure of time.

Or is there a better formula to use which correlates exponentially increasing CO2 with increasing temperatures?

I suggest you consider the concept of radiative forcing. It is the net change in energy balance at the top of the atmosphere due to imposed perturbation. The change in radiative forcing is a function of multiples of factors: water vapor, solar radiation, anthropogenic and natural emissions of CO$_{2}$, etc. So, attempting to quantify future temperature to a single forcing may not be a good way of relating the two vars. You may consider running climate models that consider the above factors.
However, you can play around with single var relation you suggested. I can proved an alternative derivation that considers radiative forcing.
The relation between temperature perturbation and radiative forcing is
$$\Delta T = \lambda RF$$
where $\lambda$ is the climate sensitivity parameter and RF is a radiative forcing due to a particular perturbation.

The above equation can be re-written,
$$T - T_{o} = \lambda RF $$
where $T_{o}$ is a particular reference temperature. You can take base period temperature (e.g., 1980 to 2015).

Assuming temperature increases steadily in time, $T=T_{o}e^{ct}$, and inserting into the above equation,

$$T=\lambda RF (\frac{1}{1-e^{-ct}})$$
 Now you have $\lambda $ and  RF as coefficients.


Is the whole San Francisco Bay Area essentially one giant fault? Put another way, if you go back far enough in earth history, was there never a San Francisco Bay, and the mountains in the Peninsula and east of the "East Bay" were essentially a contiguous mass of hills?

PS - I live in the Bay Area, and I know some of the features formed by the San Andreas fault.

Much of western California is composed of small lighter landmasses scraped off of the Pacific Plate as the heavier mantle sank under the North American Plate, and the San Francisco Bay Area is no exception. Here's an illustration of how some of CA was formed as the Pacific Plate was subducted under the North American Plate:

As these separate landmasses were scraped off the Pacific Plate, they formed distinct rock types, with the boundary of each forming a distinct fault.  Here's a good illustration of what that looks today:Of course, these faults and rock types will be different depending on what cross section you're looking at.I know this isn't a complete description, but I think it's a good starting point. These illustrations came from USGS bulletin 2195, which can be found here. It's an interesting read in and of itself.


What is the difference between GFS analysis and GFS forecast data? gfsanl_3_20151201_0000_006 means that the analysis was made at 0000 UTC and is valid at 0600 UTC, doesn't it? But for how long, 3 hours?
And what is the difference to gfs_4_20151201_0000_006, which is listed under GFS forecast?
I cannot figure out the difference between those two.

I'm no expert at this, I've just been working with a variety of gfs gribs for a while now.  The only thing I know about them is what I've read and I'll cite them here.  I don't know where you got those files.  It looks like you're looking at the files that are sub areas, but in general the file format goes as shown more clearly on this website:

data/nccf/com/gfs/prod/gfs.YYYYMMDDHH/gfs.tHHz.formidffhour !GRIB_version/ncep/model/#000/YYYYMMDDHHNNFfff/parm/level! ######

Grid #004, 0.5x0.5 degree lat/lon grid, formid = pgrb2 (Hours F000-F180) GRIB_version=grib2 (grid number appears as #000)
Note: fhour: anl, f00, f06, f12....f384 (note: 2 or 3 digit fhour as on ftp server)
GRIB2 Note: "model date" and "forecast hour" fields are not separated by "/"

I suggest you pull your files from here to start with.

The anl vs fxxx is the fxxx are intermediate simulation runs that often contain uninitialized data.

  Forecasts contain the same parameters as analysis AND accumulated forecast variables such as precipitation.  Analysis files, if they contain the forecast-only fields, set them to zero.  For instance, both FNL and GFS files obtained directly from NCEP, contain the CRAIN variable.  But, in the FNL file, all of the CRAIN fields will be zero.

  In summary, the FNL analysis incorporates ~10% more data than the GFS by waiting for ~3 hours longer for the data stragglers.  GFS forecasts contain accumulated fields, such as precipitation, that are missing or set to zero in the analysis fields. - link

This analysis-forecast cycle is complex and iterative.  Here's a bit more detail.

And here is the current status in real time of models running.


mountain database of elevation and distance from saddle (as a proxy for gradient) I'm interested in doing data visualization projects about mountains.

We have data from http://www.peaklist.org/ultras.html complied by Aaron Maizlish (Who we tried to contact but not sure of his contact details these days?)

The data he was curating contains name, elevation, co-ordinates and Key Saddle.  The key bit of data we're after is the distance from elevation to either key saddle  or sea level to get a very rough outline of shape.

I'm not sure if such data exists or we would have to derive it from some topography database?  Would anyone have any ideas on how we might go about getting said data or access to free topographic data that we may be able to somehow match in?

I've attached the below artwork that inspired this project - while we wouldn't necessarily look to get all the shape types here, it would be nice to have some different natural shapes.

The idea being somewhere in between pure Art & pure geography

Thanks, Damian.


Release mechanism for methane clathrate at the PETM The Paleocene-Eocene Thermal Maximum (PETM) is a well-studied warming event near the Paleocene-Eocene boundary.
It is characterized by its extreme warming rate: from onset to recovery the event lasted ca. 100 kyrs, and the global temperature is thought to have increased by ~6 °C in barely 20 kyrs.
This event is of particular interest not only for its $\delta^{18}\rm O$ but also a sharp negative excursion in the $\delta^{13}\rm C$, implying a strong input of $^{13}\rm C$-depleted carbon into the system.

Simplified and redrawn after Zachos et al. 2001

One frequently invoked hypothesis to explain this input is the leakage of methane from clathrates trapped in seafloor sediments.
Being a paleontologist and not a geochemist, I struggle to understand the actual chemical mechanism involved.
I was thus wondering if someone could explain the mechanisms allowing the destabilization of methane clathrates at the same time on a global scale.
If it's just linked to a temperature threshold, how come it wasn't reach prior to that (warmer temperature were reached during the Cretaceous)?

There seems to be some uncertainty as to the cause and mechanism for the PETM.  In the Science Daily article Methane may be answer to 56-million-year question: Ocean could have contained enough methane to cause drastic climate change (2011) reporting research from Rice University, they claim that the seafloor was already warmer, thus according to their models:

  if the oceans were warmer, they would contain less dissolved oxygen and the kinetics for methane formation would have been faster.
  With less oxygen to consume organic matter on the way down, more sank to the ocean floor, Gu said, and there, with seafloor temperatures higher than they are today, microbes that turn organic matter into methane work faster.

Thus, they claim, the amount methane in the form of clathrates would have been approximately the same amount as today, but in a thinner stability zone.  They are not clear about what caused the destabilisation, but made the analogy of a charging-discharging capacitor (shown below, from the same source):

A recent article A seasonality trigger for carbon injection at the Paleocene–Eocene
Thermal Maximum (Eldrett et al. 2014) details of research into what vegetation eisted at the time to determine the species that were present in the time leading up to the PETM (or CIE = Carbon Isotope Excursion), they found that the seasons were already becoming warmer prior to the CIE (which led to the PETM).  The reason for the seasonal warming trend is modelled by the authors as being due to

  enhanced seasonal contrasts through Milankovitch forcing
  (Lourens et al., 2005)*, combined with a gradually warming
  late Paleocene to early Eocene, forced a non-linear response
  in ocean circulation to warm intermediate waters.

Implying that orbital influences may have had a role in causing the increased seasonal warming leading up to the CIE.

They conclude that the modelled seasonal extremes prior to the onset of the CIE

  represent the smoking gun of a climatologically forced
  threshold in the carbon cycle that caused the PETM.

Essentially by destabilising and altering the stability zone (as shown in the diagram above).

Your question about the Cretaceous raises an important point presented in the earlier article Beyond methane: Towards a theory for the Paleocene–Eocene
Thermal Maximum (Higgins and Schrag, 2006), who suggested that the carbon released from methane clathrates would not have been sufficient for the warming experienced during the PETM.

  High global sea-level
  and flooded continental interiors in the Cretaceous and
  early Tertiary may have also reduced the export of
  organic carbon from the shelves to the continental slope
  by promoting sedimentation on continental shelves that
  were 75% larger than present

suggesting that there was not enough methane clathrate, that it was 'building up' during the Cretaceous and early Palaeogene.

Astronomical pacing of late Palaeocene to early Eocene global warming events (Lourens et al. 2005) (Abstract only).


Natural nuclear explosions I'm aware of the Oklo reactor and other natural nuclear fission reactors, in which geological processes can lead to the formation of a sustained, self-regulating uranium fission reactor.

Is it also possible for geological processes (on Earth or elsewhere) to form a critical mass of radioactive elements, leading to a runaway chain reaction and resulting in a nuclear explosion? I realise that nowadays the proportion of ${}^{235}\mathrm{U}$ in uranium deposits is too small to achieve criticality, but if it was large enough in the past for the Oklo reactor to form then that seems to imply that it was high enough for uncontrolled fission to occur as well.

Is it likely that such an event has happened on Earth in the past (on the surface or in the interior), and if so is there any known geological evidence that suggests an actual instance of it?

This hypothesis has been studied here as a possible explanation of selenogenesis (formation of the Moon). (Forming the Moon from terrestrial silicate-rich material. R.J. de Meijer, V.F. Anisichkin, W. van Westrenen. 2013.)
The only place cited as suitable for spontaneous criticality is the Core-Mantle Boundary (CMB).

The calculations above show that without additional concentration factors, $\mathrm{U}$, $\mathrm{Th}$ and $\mathrm{Pu}$ concentrations in the CMB are insufficient to reach criticality. Additional concentrations can be achieved by a combination of two processes: growth of the relative concentration of the fissile materials by a transient pressure wave, induced by an impact at the Earth’s surface (Anisichkin, 1997; Voronin and Anisichkin, 2001), and/or the development of compositional heterogeneities (de Meijer and Van Westrenen, 2008).
As shown by Voronin (2011) for fissile material at the CMB, an impact of a 100km- diameter asteroid can create a transient pressure increase of several TPa at the CMB, sufficient to concentrate fissile material from a subcritical to a supercritical condition followed by a nuclear explosion. Regarding the development of compositional heterogeneities, it should be noted that small-scale heterogeneities exist in the core-mantle boundary region even today (e.g., van der Hilst et al., 2007): volumes exhibiting both higher-than-average and lower-than-average wave propagation speeds, with diameters as small as 30 km, are now resolvable. Some studies suggest that the bottom of the mantle is partially molten today, forming a so-called ‘basal magma ocean’ (e.g. Williams and Garnero, 1996; Labrosse et al., 2007; Lee et al., 2010).

For another take on natural nuclear explosions, see this paper (Evidence for a large, natural, paleo-nuclear reactor on Mars. J. E. Brandenburg, Orbital Technologies Corporation. LPI 2011 Proceedings.), citing an anomaly in Mare Acidalium on Mars.
It should be noted that nuclear explosions need both critical mass and very low times of reactivity insertion. A gun-type bomb would be the best analogy for low-yield natural explosions on the surface/in the crust, and it is very unlikely to have a naturally occurring acceleration hurl a uranium-rich boulder against a uranium-rich wall.
To detect natural explosions on the surface, one would need to look for fused silica and anomalous $\mathrm{Xe}$ and $\mathrm{Kr}$ isotope ratios at the margins of our instruments' sensitivities.


What are the applications of hydrostatic solvers vs non-hydrostatic solvers in numerical weather prediction? In the atmospheric dynamics research community, many colleagues of mine happen to use atmospheric models that have non-hydrostatic equation solvers, e.g. the UK MetOffice model, and WRF-ARW:

  The equation set for ARW is fully compressible, Eulerian and nonhydrostatic...

There are another group of models that use a hydrostatic solver by default (e.g. ECMWF), and presumably make the following assumption about the Earth's atmosphere.

  Hydrostatic equilibrium describes the atmospheric state in which the upward directed pressure gradient force (the decrease of pressure with height) is balanced by the downward-directed gravitational pull of the Earth. On average the Earth’s atmosphere is always close to hydrostatic equilibrium.

My question is what are the applications of each type of solver, i.e. when would you chose to use a non-hydrostatic model over a hydrostatic one? (which is presumably less computationally expensive?)

The hydrostatic approximation begins with the full 3-D momentum equation (Navier-Stokes) and through scale analysis the vertical momentum equation reduces to:

$$\dfrac{\partial p}{\partial z} = -\rho g$$

This is a balance between the vertical pressure gradient force and gravity with no net acceleration.  This tends to hold for atmospheric phenomena that are much wider than they are tall.  On the synoptic scale where vertical motions are on the order of 1 cm s$^{-1}$ this holds, but in a thunderstorm where updrafts can attain speeds of 100 m s$^{-1}$ this approximation doesn't work.

A hydrostatic model uses the hydrostatic approximation in place of an equation for $w$, while a non-hydrostatic model uses the momentum equation for $w$.  As the ECMWF  page you link to suggests, models with low grid resolution can get by with the hydrostatic approximation.  A model with dx=dy=10 km means the grid volume is 100 km$^{2}$ times whatever the vertical grid spacing is.  The $w$ value for that grid box needs to be representative of the entire volume and you aren't going to explicitly resolve convection at this resolution (convection will be parameterized and in general a model can only resolve features that are about 4x bigger than the grid spacing).

As you reduce grid spacing (increase resolution) and start to resolve non-hydrostatic features (thunderstorm updrafts, downdrafts, etc), then you need to make sure you are using a non-hydrostatic solver.  For high resolution operational regional modeling and research modeling in the mesoscale using WRF-NMM, WRF-ARW, CM1, ARPS you'll find non-hydrostatic solvers.

The non-hydrostatic solver is more computationally expensive than a hydrostatic solver, and is often found in higher resolution models which themselves are more computationally expensive than coarse grids.


How can I normalize this chemical analysis to a mineral with 3 cations? $\ce{FeO}$ = 70 wt%

$\ce{TiO2}$ = 30 wt%

The molecular weight given of $\ce{FeO}$ = 72, and the mw of $\ce{TiO2}$ = 80.

The first step I did was divide each wt% by their molecular weights to get a molecular proportion:

$$\ce{FeO}: {70 \over 72} = 0.972 $$

$$\ce{TiO_2}: {30 \over 80} = 0.375$$

Then, I multiplied each proportion by the number of oxygens in each chemical formula

$$0.972 \times 1 \ \rm{oxygen} = 0.972$$
$$0.375 \times 2 \ \rm{oxygens} = 0.75$$

The next step is where I get really confused. I think I'm supposed to add the two numbers above together, and divide that number into a number that is supposedly the cations assumed of the mineral? (As in 5 for plagioclase, 4 for pyroxene, 3 for olivine, etc) But I do not understand how I'm supposed to gather which number to use based on only the data given. If anyone can point me in the right direction it would be greatly appreciated.

The first step I did was divide each wt% by their molecular weights to get a molecular proportion:

Actually that's not what you did. What you did is how much moles of each oxide you have assuming 100 grams of mineral. But that's less important now.

You are mostly correct in your steps.
Eventually you have 0.972 Fe, 0.375 Ti, and 0.972 + 2×0.375 = 1.722 O.
The (non normalised) mineral formula is then:
Fe0.972Ti0.375O1.722.

You can easily check that it's correct using charge balance:

0.972×2 + 0.375×4 - 1.722×2 = 0

The question now is how to normalise it. Since you were asking about 3 cations, you need to multiply everything by 3/(0.972 + 0.375), giving you:

Fe2.165Ti0.835O3.835

But that's also ugly. Usually mineral formulas are normalised to round anion numbers, so let's say you multiply it all by 5/1.722 you get:

Fe2.822Ti1.089O5

which is slightly prettier.

Without having any more information on the mineral as to what's it supposed to be, you can only guess. This is what we do in EMPA analyses - we know what mineral it is and we calculate the formula according to that. If we don't, we guess and try to figure out which one it is, and then calculate according to that.

I don't know much about the question, but it could be that not all iron in the mineral is Fe2+. Some of it may be Fe3+, but analysing both is not an easy task so most iron in minerals is reported as either all FeO or all Fe2O3 regardless of what oxidation state it is actually in. So it's possible that you have (FeO + Fe2O3) = 70 wt%. If you play enough with that, you might end up with a better looking formula. Again, I don't know the question and I don't know if that is what you're supposed to do in the question.


Does the climate have any effect on plate tectonics? After reading the question and answer Is there any correlation between La Niña/El Niño and seismic activity?, I am wondering if there is any evidence (case studies) to suggest that longer term climatic dynamics (long term trends in seasonality, ambient temperature and pressure, such as ice ages, warm epochs) has any effect on plate tectonic dynamics (rate of plate movement, frequency of megathrust events, earthquake and volcanic eruption frequency and severity etc)?

According to the article Cenozoic climate change as a possible cause for the rise of the Andes, the climate could affect mountain building by altering the amount of erosion, and therefore sediment deposits, which could act as a lubricant in subduction zones. In the example given, the lack of sediment increased friction, causing "crumpling" and the building of the Andes.

Given that the climate impacts erosion, that erosion may then affect the stress loading of thrust faults, affecting the earthquake frequency and magnitude, the same as post-glacial rebound.

Isostatic rebound resulting from melting glaciers may also impact volcanics, by changing the pressures, and so lowering the melting point if the rocks. "The average melting rate is increased by about 30 times its steady state value when a 2-km-thick ice sheet melts in 1000 years." In Iceland, the melting of the glaciers at the end of the last ice age correlates with a 30-fold increase in eruption rate. (Source)in


How do scientists know the precise location, etc. of the earliest supercontinents? Or their configurations far, far into the future? Obviously, we can look at where continental plates are currently moving, and extrapolate both forwards and backwards in time...
But there have (allegedly) been more than supercontinent in the past... What lines of evidence could give such precise maps of pre-Pangeae supercontinent as I have seen in various places?

Please take a look at this website, Dr Scotese explains what methods we use to determine how the earth was in the past, and indeed, what it might do in the future. We can never be sure however. He has also posted numerous videos on You Tube.
From Dr Scotese's website :

The past positions of the continents can be determined using the
following five lines of evidence: paleomagnetism, linear magnetic
anomalies, paleobiogeography, paleoclimatology, and geologic history.
Paleomagnetism is the study of the record of the Earth's magnetic field in rocks, sediment, or archeological materials. Magnetic minerals in rocks can lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of tectonic plates. The record of geomagnetic reversals preserved in volcanic and sedimentary rock sequences (magnetostratigraphy) provides a time-scale that is used as a geochronologic tool. By measuring the remanent magnetic field often
preserved in iron-bearing rock formations, paleomagnetic analysis can
determine whether a rock was magnetized near the Pole or near the
Equator. Paleomagnetism provides direct evidence of a continent's N-S
(latitudinal) position, but does not constrain its E-W (longitudinal)
position.
Linear Magnetic Anomalies. The Earth's magnetic field has another
important property. Like the Sun's magnetic field, the Earth's
magnetic field "flips" or reverses polarity. Fluctuations, or
"anomalies", in the intensity of the magnetic field, occur at the
boundaries between normally magnetized sea floor, and sea floor
magnetized in the "reverse" direction. The age of these linear
magnetic anomalies can be determined using fossil evidence and
radiometric age determinations. Because these magnetic anomalies form
at the mid-ocean ridges, they tend to be long, linear features (hence
the name "linear magnetic anomalies") that are symmetrically disposed
about the ridges axes. The past positions of the continents during the
last 150 million years can be directly reconstructed by superimposing
linear magnetic anomalies of the same age.
Paleobiogeography. The past distribution of plants and animals can
give important clues concerning the latitudinal position of the
continents as well as their relative positions. Cold-water faunas can
aften be distinguished from warm-water faunas, and ancient floras both
reflect paleo-temperature and paleo-rainfall. The similarity or
dissimilarity of faunas and floras on different continents can be used
to estimate their geographic proximity. In addition, the evolutionary
history of groups of plants and animals on different continents can
reveal when these continents were connected or isolated from each
other.
Paleoclimatology. The Earth's climate is primarily a result of the
redistribution of the Sun's energy across the surface of the globe. It
is warm near the Equator and cool near the Poles. Wetness, or
rainfall, also varies systematically from the equator to the pole. It
is wet near the equator, dry in the subtropics, wet in the temperate
belts and dry near the poles. Certain kinds of rocks form under
specific climatic conditions. For example coals occur where it is wet,
bauxite occurs where it is warm and wet, evaporites and calcretes
occur where it is warm and dry, and tillites occur where it is wet and
cool. The ancient distribution of these, and other, rock types can
tell us how the global climate has changed through time and how the
continents have travelled across climatic belts.
Geologic and Tectonic History. In order to reconstruct the past
positions of the continents it is necessary to understand the
development of the plate tectonic boundaries that separate continents
and bring them back together again. Only by understanding the regional
geological and tectonic evolution of an area can you determine the
location and timing of rifting, subduction, continental collision and
other major plate tectonic events.


Large scale structures in the Sahara – what are they? In Google Earth we can see some very clear lines in the Sahara.  In the screenshot below you can clearly see these lines starting at the top going southward, then gently curving westward towards the bottom.

What are these structures and how were they formed?  Are they related to the wind?  Some sort of flow?  Are they surface structures or they are embedded deep in the rock?  Or something else?

I realize that this may be a trivial question for anyone with some knowledge of geology, but I really wasn't able to google up the answer.

These features are created by the wind.You will note that the upper left portion has a small dark spot. This is known as Waw al-Namus, or the "Oasis of Mosquitoes." It has a path of material in the same curved  manner as the surrounding features you mention.

From the link provided below:

  However, Waw al-Namus and its plume are not the only "wind records"
  in the area. As you utilise higher resolution images - of the order of
  1 km or better, other, somewhat different "long-term wind tracers" are
  revealed at almost every place across the Sahara Desert. These
  generally take the form of small-scale, long, parallel thin lines, as
  if being drawn across the desert by a giant pencil. One of the most
  spectacular places with long-term wind streamlines imprinted into the
  landscape can be found further southeast of Waw al-Namus, to the
  southeast of the Tibesti Mountains.

http://oiswww.eumetsat.org/WEBOPS/iotm/iotm/20060115_wind/20060115_wind.html


Is San Andreas fault horizontal or vertical? I was reading a book about tectonic plate boundaries, and I came across this paragraph:

It says that when a plate edge slides with another plate edge it causes a vertical fault, as San Andreas fault. I thought that SAF is a horizontal fault i.e. strike-slip fault. So what does the book mean by vertical faults?

See the image below. In the picture, the San Andreas Fault dip is nearly 90 degrees or exactly vertical; The strike is pointing North.

Most normal faults and reverse faults (such as the Sierra Madre) are not vertical, but rather dip in either direction. (In the picture the Sierra Madre appears to have a dip of about 45 degrees).

In real life, the dip of the San Andreas is not perfectly vertical, but is variable, depending on where in California you are.

Strike and dip can be measured using a Brutton Compass.


Accepting/refusing high rainfall measurement I have a series of records of annual maximum daily rainfall for a station for about 80 years (1935-2014). Only one value is very high compared with the others, but in this year, the other close rain-gauges didn't record such a high value. What are the conditions/tests to remove or keep this high value in the statistical analysis of rainfall data?

As you have multiple nearby gauge stations. I would suggest to compute a multiple linear regression that would allow you to estimate the rain in one station using the data from the others.

Then, compute the historical standard  deviation of the measurements in that station relative to the prediction using the linear regression model.

With this, you can filter data errors by rejecting all points that deviate more than X standard deviations from the prediction based on nearby stations. You have to define your threshold X based on experience, and by looking at the data. It will depend in the quality of the correlation between the precipitation in the different stations, so no universal value can be defined.


Detecting seismic waves using Software Defined Radio I understand about physic and waves, but I am a totally rookie in this topic. I was wondering which are the typical frequency ranges of the S-waves, P-waves and surface waves.

My idea would be to detect any seismic event using Software Defined Radio, but I am not sure at all If any peripheral could detect these kind of waves properly. For example, a HackRF peripheral works between 1 MHz to 6 GHz. And, as far as I know, lower frequencies below 3MHz travel efficiently as ground waves. Because of that I was wondering If I could detect anything through Medium Frequencies (0.3 to 3 MHz). For example, a HackRF would detect between 1 MHz to 6 GHz operating frequency, so it may detect something, but I don't know "what to look for".

If MF is too high, would there be any chance to detect anything through their harmonics?

I hope I understand your question right, I think there are some confusion about frequency range and wave-types.

Seismic waves are acceleration of matter that transfer kinetic energy from a seismic source (e.g. an earthquake, an explosion or ambient noise) to heat.

It's similar to sound waves, vibrations from the surface of e.g. a music instrument set the air in motion and compress the molecules of the air to transfer a wave that eventually reach e.g the eardrum. However, to add to the complexity, in solid matter some additional elastic properties are in play, as you notice. Waves can progress not only as pressure waves (P) but also as shear waves (S) and at boundaries special surface waves can form, often of high amplitude. The progression of the seismic waves depends on the elastic properties of the Earth.

A large part of the terminology used for seismic waves are similar to how we describe electromagnetic waves. E.g. frequency, damping and resonance are relevant for seismic waves as well. However, the ranges are very different and electromagnetic waves and acoustic waves behaves different. The earth is a efficient filter, and even transient energy, that contains high frequencies, is limited to low frequencies as it progress through the Earth. Ground wave propagation, as know from radio signals, are different from the properties of seismic surface waves.

An interesting coincidence is that wavelengths can be in the same magnitude, but that is because radio waves progress about 100.000 times faster than crustal seismic waves.

A figure, prepared by Professor Charles J. Ammon, shows the ranges of frequency and amplitude. Source here. The amplitude and period have a large range, that's why prefixes as milli or micro can be used and a logarithmic scale is used for amplitude.

In shallow active reflection seismic surveys, we sometimes can use frequencies up to maybe 200Hz, but in the range the penetration depth is very small. For very local events, e.g. in mines and infrastructure frequency range up to 500-1000Hz might be used.

Most energy for P and S waves used in teleseismics are in the range of a few Hertz and maybe up to 10-20Hz.

Surface waves have the interesting property that the velocity depends on the frequency because low frequency content is affected by deeper elastic properties whiles high frequency content is more affected by shallow geological features. This is used for lithosphere tomography with rather good vertical resolution. The frequency range is 0.005Hz and up to 0.5Hz. This is the frequencies that you can actually see in ground motions caused by earthquakes, if you take resonance in consideration.

Normal modes are often in the range 0.3 - 1mHz. (m, as in milli, not M, as in Mega). That is frequencies about one billiard times lower than some radio frequency bands.

Another thing to remember in the context of Software defined radio, is that there is no carrier wave for seismicity. When seismologists talk about frequency, we mean energy content of a signal. We are looking at the convoluted wavelet, not continuous signals.

If you are interested in working with earthquake detection and to improve algorithms of signal processing of seismic waves, I'd suggest you to take a look at the Obspy package, there are some nice examples and tutorials that can get you started. There are also some project where people are constructing open architecture seismometers, eg the Raspberry Shake. For less than $100 or so you can build a seismograph and start to monitor local seismic events. Most geophones work by transfering ground acceleration to an induced electric current in a coil.

It's very possible that inspiration from other fields of signal processing, as in Software defined radio can improve seismic techniques in future. It is always great to get inspiration from other fields of research.


Appearance of Tornado Does the appearance of a tornado come from the dust or is there some characteristic of swirling wind? Additionally many experiments shows a tornado-like phenomena in a jar of water, is this possible without water?

The characteristic funnel of a tornado is caused by condensed water.  A tornado is a swirling mass of air with very high vertical vorticity and a corresponding drop in pressure.  Large tornados can have pressure deficits on the order of 100 hPa, which is significant compared to synoptic horizontal pressure gradients.  The drop in pressure causes air to expand and cool and if the air is humid enough this will be accompanied by condensation and the visible appearance of the funnel.

It is also worth mentioning that the visible tornado funnel does not have be in contact with the surface to be a tornado, it is only required that the surface wind circulation is connected.  In these cases the lowest part of the tornado may remain invisible.

As a tornado persists the funnel cloud can pick up debris (dust, dirt, plants, parts of destroyed structures, etc) and some of this debris can orbit the tornado (other parts may end up lofted into the upper troposphere or centrifuged out at low levels) adding to its visual presentation.


How does agriculture release so much greenhouse gas? I recently came over some numbers of GHGs released per energy in food produced, and the result is pretty flooring. I can see how animal-based food production is quite inefficient so let's ignore that for now and just look at plants.

For example rice releases 2 kg carbon =  7.6 kg CO2-equivalents per 1000 kcal. This would actually mean that it is more environmentally friendly to drive a car 10 km than to bike 10 km on a rice-based diet, because biking burns around 300 kcal = ~2.28 kg CO2e, while a normal compact car burns 0.5 liters of gasoline = ~1.9  kg CO2e. Are my numbers wrong? If not, how can this be?

There are several contributing factors,

livestock, Livestock is easy animals produce co2 but their methane is a bigger problem, methane is a better greenhouse gas than the co2 that the feed plants took in.   Livestock waste is also a problem , people do not realize how much waste modern factory farms produce, specially when stored as a liquid is it produces all the problems of rice production with addition release of methane from the waste itself.
transportation, transportation of ag products to market are almost all petroleum based. Depending on the source this may or may not be included in agricultural emissions.
Landuse, changing land, especially things like draining wetlands and burning forest for farmland are big contributors, Wetlands in particular produce huge amounts of co2 and keep doing so for decades if not centuries, all the organics built up in wetland start oxidizing when drained, this is basically the same as burning petroleum without actually getting any usable energy out of it.
Fertilizer produces a plethora of problems, and could justify an question all its own.
Rice, rice production has been called out as particularly problematic.  You would think this would produce the opposite effect to draining wetland but it is actually worse. Bacteria in flooded soil produces methane instead of co2 and as I said methane is better greenhouse gas, too top it off rice fields are supplied with enough nutrients to keep the bacteria producing way above normal wetland levels and keep it from being trapped the way carbon in mostly anaerobic wetlands will be.

Source


What part does methane play in the process of producing biogas? I should point out first that I don't know the first thing about environmental science, I study mathematics, and the reason I am asking this question is because I want to understand the processes behind climate change better. And, after hearing that methane is such a powerful greenhouse gas, it sounded weird to me that it was also produced during the process of producing biogas, so I basically want to understand how that process works and why the production of methane in it isn't harmful.

When you say produced, do you mean chemically made from another substance, or you do mean released into the atmosphere, or do you mean captured and stored?
Methane, or CH4, is a biogas as it is gas biologically created by organisms. Methane is created in natural processes from which it may be immediately released into the atmosphere or on much slower time scales, such as millennia and more. Methane is also released in some artificial processes, such as the flaring on oil wells. Likewise, in petroleum processing facilities, methane can leak out in other ways than is intended. So, that is how it gets out, or is "produced" as a free gas.
However, if you are asking if CH4 is produced chemically as a product of processing OTHER gases, then the answer is only a mild "sort of". When natural gas from within the Earth is removed from the ground, it contains methane, propane and other gases that are separated into their components. However, most of the nat gas IS methane to begin with. So, saying it is "produced" is sort of true and easily misunderstood.


"The world will start COOLING DOWN in 2017"? There's a story going around the low-grade news factories that one Dr. David Evans has predicted that the world will start cooling down in 2017. One source reports:

  He says fundamental flaws in how future temperatures may rise have been included in the 'standard models' and this has led to inflated mathematical - and therefore temperature - predictions.

Googling finds a number of other sites with the same story. Some identify Dr. Evans as a "former climate modeler for the Australian Greenhouse Office", others as an electrical engineer. None seem to provide any skepticism about Dr. Evans' statements.

I'm sure this is a sham, as otherwise it would be an enormously important story that would be reported everywhere. If so, I'm a little surprised that I found no "boy is this stupid" responses. Perhaps the real climate experts are tired of playing "climate conspiracy Whack-A-Mole".

If a climate change denier were to use this story as proof that anthropogenic global warming is a scam to keep earth scientists employed, what would be the best way to show that he is wrong?

Edit: I just found that Dr. Evans serves on the Board of Advisors of the Committee for a Constructive Tomorrow, an NGO that denies man-made global warming exists.

I gave a longer answer linked to a similar question in the comments above, I'll give a quick one here:

  There's a story going around the low-grade news factories that one Dr.
  David Evans . . .

Everyone knows there's a fair bit of "I know you are but what am I" in the climate change debate (if you can even call it a debate), but whichever side you agree with, David Evans is without question, actively arguing the skeptic side.  His position has been consistently in disagreement with man made climate change for nearly a decade, so anything of his you read, keep that in mind.

He's made two climate "denier lists" here and here and he has been called out by skeptical science, here.    In another article related to yours, here, it says his work is "undergoing peer review", so for now, his calculations aren't publicly available or verified.

  . . . has predicted that the world will start cooling down in 2017

One problem here.  We're currently in an El Nino and 2014 was the warmest year on record (38% probability to some, but lets not go there) with 2015 likely to break that record and 2016 - too soon to say but the El Nino is expected to extend into 2016, so 2017 is an ideal year to predict cooling.  The global temperature often drops within a year after an El Nino ends, but this is a normal cycle and temporary and it has nothing to do with man made climate change.

  What would be the best way to show that he is wrong?

Well, a personal favorite, I'd go with something like:

"He's just using a mathematical model to predict the future.  I thought you people hated mathematical models to predict the future. -

You could also bring up this list of examples where David Evans has been wrong in the recent past.

But the more scientific answer to your question is that until his research is available and peer reviewed, then there's no way to disprove it, but there's also, no good reason to agree with it.   Without peer review and transparency, it's not science.   It's just a blog.


Comparing 2D fields - how do you quantify similarity? I have a number of arrays describing both forecasts and observations of geospatial data (e.g. precipitation intensity, cloud fields...). Included are four animated gifs, each looping back and forth between an observation (of precipitation) & a forecast covering the period of the observation. The four forecasts vary markedly in quality (from extremely good in the first case to terrible in the fourth).
I would like to have some way of systematically quantifying the similarity between two such arrays (e.g. between an observation and its associated forecast). I don't really know any more sophisticated way than to simply take the difference between two arrays (normalized somehow, e.g. by dividing by the mean of one of the first).
The problem is that 'scoring' the forecasts in this way gives case #3 & #4 equally bad marks - even though from visual inspection case #3 appears substantially better than #4. Clouds which are in slightly the wrong place (e.g. the ones in central Germany, or in Switzerland & Western Austria, in case #3) score equally poorly to those which are in entirely the wrong place, or simply absent.
Ideally, I'd like some measure of the minimum amount by which one image needs to be 'deformed' to yield another one, but I have no idea how to approach that in anything like a systematic manner.

Model data seta can vary in several ways from a reference data set. Taylor diagrams visually compare multiple datasets output to a reference dataset (e.g., model experiments to observations). This is done by exploiting the geometric relationship between centered RMS, correlation, and standard deviation when computing differences between datasets. Several software packages exist to produce Taylor diagrams.
wiki: https://en.wikipedia.org/wiki/Taylor_diagram
publication: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2000JD900719
python, e.g.: https://pypi.org/project/SkillMetrics/


How to calculate maximum and minimum mean monthly temperatures? A quite simple question that I hope someone can help me with. I have a massive database of hourly minimum and maximum temperatures, from many automatic weather stations. I need to estimate the average monthly minimum, maximum and mean temperatures for each stations, like that provided by climatologies such as bioclim, worldclim, CHELSA, etc.

Given the following one-day example data:

         Date Time tMin tMax
1  2009-05-01    0 24.2 24.4
2  2009-05-01  100 24.1 24.3
3  2009-05-01  200 24.0 24.2
4  2009-05-01  300 23.8 24.1
5  2009-05-01  400 23.7 23.9
6  2009-05-01  500 23.6 23.8
7  2009-05-01  600 23.5 23.6
8  2009-05-01  700 23.5 23.7
9  2009-05-01  800 23.3 23.7
10 2009-05-01  900 23.4 23.5
11 2009-05-01 1000 23.4 24.2
12 2009-05-01 1100 24.2 26.2
13 2009-05-01 1200 26.2 28.4
14 2009-05-01 1300 27.5 29.8
15 2009-05-01 1400 28.3 30.1
16 2009-05-01 1500 28.4 30.9
17 2009-05-01 1600 30.5 31.7
18 2009-05-01 1700 30.7 31.9
19 2009-05-01 1800 29.5 31.2
20 2009-05-01 1900 27.9 30.6
21 2009-05-01 2000 27.6 28.6
22 2009-05-01 2100 26.3 27.6
23 2009-05-01 2200 25.3 26.2
24 2009-05-01 2300 24.6 25.7

How do I calculate the required parameters? I'm confused between two options:

1) Simply by calculating the average of each column each day, and then averaging these averages to calculate the mean temperature: (tMin average: 25.7; tMax average:  26.8; and tMean: 26.2).

2) Picking the lowest daily minimum temperature (23.3), and the highest daily maximum temperature (31.9), and then averaging both (27.6).

Then, once I've got the dailies information estimated, I think I must to calculate the overall average for each of the three parameters each month.

Any feedback will be more than appreciated!

Best!

From my experience, first of all, you should calculate the hourly average, in your case should be the average of the 2 minimum and 2 maximum temperatures. (In your sample data you need the 0:00 hours of 2009-05-02, as it is covering 23 hours)

Once you have the average by hour in a day, you can go for the daily average, then monthly average and so on...

For the minimum and maximum, there is no average, it should be just one value. If you want to calculate a monthly minimum average, then it should be calculated with the same process, so there is just one minimum by hour (the minimum in the range, f.e. 0:00-1:00), then one average of all the hourly minimums to get the daily minimum, and the same system for the monthly one.

If you try, you will see that you don´t have exactly the same result than making a daily average. For your sample, the daily average by hour is 26.31 degrees and by the daily average of all data is 26.25 degrees.

Hope it helps!


Distance to epicenter vs distance to focus I am not really a "budding seismologist." I am a chemistry/physics teacher teaching an Earth science class (low academic level) in a small-town high school. (My college coursework in earth sciences = 0) I understand the concept of triangulation to determine an earthquake's origin, and I realize there are some subtleties in wave analysis such as pP and sP waves. What I don't understand is how the triangulation determines the epicenter instead  of the focus. Wouldn't the S-P lag times for 3 stations give an intersection point at the focus since that is the actual point of origin for the waves?

This is a good question, but it really has a simple answer. How can you determine the depth of an object when you are not even calculating it? Triangulation uses circles, 2-D shapes, so when finding the solution to the equations of circles that solve all 3 circles, you only find X and Y. Z isn't even being solved for.

Triangulation is not precise. In practice, we end up using much more than 3 stations and statistical methods to find the precise epicenter (and other methods to find the focus).


What is the second thermometer in the image from the Esperanza Antarctic temperature record? Today, the Argentinian meteorological service tweeted about a new temperature record for Antarctica of 18.3°C, made on the Espezanza peninsula. This was subsequently reported by many other sources.

twitter.com
wmo.int
bloomberg.com
nytimes.com
theguardian.com

The tweet contained an image of a literal analogue thermometer which did show the 18.3°C... but curiously enough, also another thermometer showing merely 10.0°C.

What's that about? Is that 10°C another means of measuring temperature, e.g. some kind of running average temperature? Or is one of the readings simply faulty?

Doing a quick calculation that looks to be around the wet-bulb temperature at the time of observation so that thermometer on the right side should be a hygrometer. Hygrometers measure the level of moisture in the air as opposed to a thermometer that measures the temperature level.

Edit: The calculation was based on a recorded observation scoured from here as finding the history of observations at the station was proving difficult. The observation marked a temperature around 64 degrees F with a relative humidity value of 34%. Using this online based calculator which gives a rough estimate of the Wet Bulb Temperature, the calculated value came out to be 49.47 (F) or 9.7 (C) which was close enough for me to determine that the thermometer on the right was a hygrometer. Aiding that assumption was the fact that thermometers and hygrometers are sometimes paired together for observations.


Are there any uncharted waters left on earth? While reading about the ghost ship Jiang Seng I noticed that Wikipedia claimed it was drifting in uncharted waters in the Gulf of Carpentaria. I tried to find a primary source referencing uncharted waters but couldn't find any so this may just be one editor's penchant for artistic license.

Regardless it got me thinking: are there any oceans or perhaps other parts of the world that can still be called uncharted? Or has satellite navigation and imaging given us a complete picture of our globe?

There are many "uncharted waters".  Nautical charts have information about water depths, dangers to navigation, aids to navigation, anchorages, and other features.  You can see here what might be included in a nautical chart: U.S. Chart No. 1

The area in question is a shallow sea... so boats of different sizes may or may not be able to take certain routes depending on tides etc.  Thus a nautical chart is important in these types of regions.

Yes satellites have mapped the world... and coastline is well defined.   You can even learn about underwater depths using satellite instrumentation that detects gravity (e.g. CryoSat2) as discussed here: Global seafloor map reveals uncharted sea mountains, stunning details of Earth's oceans which discusses recent measurements of the seafloor from space.

  University of Sydney geophysicist Dietmar Müller said about 71% of the Earth's surface is covered by water and roughly 90% of the seafloor is uncharted by survey ships that employ acoustic beams to map the depths. ... Müller said the conclusions the [satellite] researchers made about seabed topography may be less accurate than acoustic beam methods employed by ships.

and the article Gravity’s Magic: New Seafloor Map Shows Earth’s Uncharted Depths says:

  The effect of the slight increase in gravity caused by the mass of rock in an undersea mountain is to attract a mound of water several meters high over the seamount. Deep ocean trenches have the reverse effect,” ESA wrote in a statement.  “These features can only be detected by using radar altimetry from space.


Why is earth's axis tilted? Why is the axis of earth tilted?  It can't possibly be that the Northern hemisphere is larger causing it to be pulled toward the sun, because then it would always be summer in the N hemisphere and winter in the S hemisphere.  If the cause for the tilt is because a large space object collided with earth offsetting the axis, then wouldn't earth keep moving in the direction of the collision?  Any insite would be appreciated.

The simple answer: Because it is.

There's a nice theory that explains why the rotation axis of a big gas giant is more or less coaligned with its orbital angular momentum vector. Those big gas giants form somewhat like a snowball rolling downhill becomes bigger and bigger and bigger. This doesn't apply to rocky planets, let alone lesser gas giants and ice giants. Saturn's rotation axis is inclined by 27°, Uranus by 98°, Neptune by 30°. It's a bit random.

With regard to the rocky planets, whatever rotation Mercury had in the distant past is long lost. Tidal interactions with the Sun will necessarily have locked Mercury into a resonance between rotation and orbital rotations. That the resonance is 3:2 rather than 1:1 is a result of the largish eccentricity of Mercury's orbit.

Mars is not tidally locked, but it's obliquity is notoriously chaotic. A number of past and future recreations of Mars' rotation show chaotic behavior. Whatever rotation Mars had when it formed has long been lost thanks to that chaos. The obliquity of Mars has gone through huge changes over the last few billion years, occasionally changing rapidly, occasionally remaining stable. That's the nature of chaos.

Venus also isn't tidally locked per se, but essentially it is. The rotation of Venus is rather bizarre. The solid part of the planet rotates retrograde at a very slow rate. On the other hand, the upper parts of Venus' thick atmosphere rotate prograde. The combined rotation represents one of the four final states in which Venus as a whole can rotate (multiple articles by Laskar, and by others). Venys is in its final rotational state.

The Earth is a marked exception amongst the rocky planets. The key to that marked exception is our exceptionally massive moon. The Earth's moon acts to stabilize the Earth's rotation. Whatever obliquity the proto-Earth had prior to the giant impact is long lost. On the other hand, the obliquity after that giant impact has remained fairly constant thanks to that stabilizing influence.


Fault Lines in North America I was trying to figure out what areas in North America would be most likely to have earthquakes, but I couldn't come across a good map for this. It's easy to find the areas with the highest incidence of hurricanes and tornadoes, and I know California has a high rate of earthquakes. What fault lines are there in North America (besides the obvious San Andreas fault)? Are there any maps that clearly show this?

Here is a map of seismic hazards for the United States from the United States Geological Survey. Link.

Link to interactive fault map for the US (source: USGS)
Here is a link to a nice article on top 5 earthquake prone areas outside California.

It is presence of fault zones, geological structures (like volcanos, subduction zones, tectonic plate junctions, basins, and mountains), geological evidence of past events, and record of earthquake events that go into the calculation of a seismic hazard for a specific region.


How the stepness can be computed at NDBC from site with only dominant wave data and windwave data Hi guys I have an small question here. At the NDBC website they have at most of the buoys the steepness of the sea at that time and date: http://www.ndbc.noaa.gov/station_page.php?station=46012

However this stations collect all the wave spectrum data and direction of it, so I suppose they use the cut frequency and then from then they decide how step is the sea at that moment at that place. At other places they don't get all the data, being more specific on the device: http://www.ndbc.noaa.gov/station_page.php?station=46214 they only have the dominant wave period and the wave height at the files: http://www.ndbc.noaa.gov/station_history.php?station=46214

The data in the file looks like this:

#YY  MM DD hh mm WDIR WSPD GST  WVHT   DPD   APD MWD   PRES  ATMP  WTMP  DEWP  VIS  TIDE
#yr  mo dy hr mn degT m/s  m/s     m   sec   sec degT   hPa  degC  degC  degC   mi    ft
2017 01 01 00 22 999 99.0 99.0  3.40 12.50  9.60 311 9999.0 999.0  12.2 999.0 99.0 99.00
2017 01 01 00 52 999 99.0 99.0  3.30 11.76  9.48 322 9999.0 999.0  12.2 999.0 99.0 99.00
2017 01 01 01 22 999 99.0 99.0  3.18 11.11  9.24 329 9999.0 999.0  12.2 999.0 99.0 99.00
2017 01 01 01 52 999 99.0 99.0  3.29 11.11  9.54 314 9999.0 999.0  12.1 999.0 99.0 99.00

Then using only that data how I can obtain the sea steepness?.

The methodology to calculate wave steepness used by NDBC is explained in: http://www.ndbc.noaa.gov/algor.shtml

Steepness is defined as
$\xi=\frac{2\pi H_s}{gT_z^2}$ where $H_s$ is the significant wave height and $T_z$ is the average wave period.

From your dataset, you have significant wave height and average wave period so you should be fine.


How did the continental plates came above the oceanic plates? The continental plates are more or less loose from the oceanic plates which are heavier and of other material (basalt) and because continental plates are lighter they 'float' on top of the oceanic plates. But how did they get there?

I don't know if I'm right that islands like Iceland is made of the oceanicp plate because it is in middle of the oceanic plates? But did all 'countries' start like that? It doesn't seem so as most countries/continents are made of lighter material. So how did that lighter material get on top of the oceanic plate?

The explanation of an other answer was: ' This is because the magma that solidifies to form each of these crusts travels, by partially melting its way up, through different materials and different thicknesses. The consequence of this is that the crust making up the continents is less dense than that making up the bottom of the oceans.'

Does this mean that the magma comming from beneath (hotspot etc.) is getting mixed with different materials? Or is this magma already a mix of different material where the heavier ones would stay more or sink at the bottom of the solidifieing two plates? But what makes the upper one not tight joined or gradually to the one beneath?

Too long for a comment, so I'll post here, but it's far from a complete answer.

Basalt can't become continental crust because the elements are different.  Iceland is made up of primarily basalt rock.  (80% per this article).  So it's made up of a different material than continental crusts.   Basalt rock is also less sturdy and less enduring than granite, so it's unlikely that a continental crust could be formed out of Icelandic eruptions or any similar eruptions.   My best guess is that Iceland will break apart over time, preventing the formation of a permanent land-mass.

Granite, the primary material in continental crust, has more Aluminum and Potassium in it.    Basalt, the heavier stuff, has more Magnesium.  Source.    They are made from distinctly separate processes and material, so one can't simply be turned into the other.

While I have no doubt that some mixing goes on within the earth's mantle, I don't believe a significant amount of new continental crust is regularly being formed because to form new crust, you would need free aluminum ready to bind with Oxygen and Silicates and I believe most of the aluminum has already done that.    That's my layman's answer anyway.  I'm open to being corrected.