Run Hydrus-1D from the command line Hydrus-1D, is a modeling environment for analysis of water flow and solute transport in variably saturated porous media. This program has a graphical environment which works very well, however a lot of input data is needed to prepare for each run. Is it possible to run Hydrus-1D from the commandline in Windows? Assuming that I have generated the input files?

Since this is a rather technical question is it recommended to post this on a more technical Stack Exchange site?

Yes, it is possible. The documentation for Hydrus-3D give you the syntax (http://www.pc-progress.com/en/OnlineHelp/HYDRUS3/Hydrus.html?RunningComputationalModulesinaBa.html)
In brief here is what you need to do:

In the installation folder of Hydrus, create a text file, name it run.bat
You need to write two lines of code for every  simulation you wish to perform:

copy path1 level_01.dir      (here path1 can be replace what what ever name you want)
h2d_calc                     (this is the executable so depending on the type of model you want to run you may have to adjust the name)

In the installation folder of Hydrus create a text file and name it path1 (or whatever name you wrote in step 2), do not forget to remove the .txt extension for the case display here)
In the path1 file, write the path to your input files
for example: c:\program files\ussl\hydrus3d\mydirect\run1

Then double clicking on the bat file will trigger the model to run. By adding successive copy ... and h2d_calc commands you can chain model execution

In addition some tricks are available here: https://www.pc-progress.com/forum/viewtopic.php?f=4&t=679


Why is CO2 considered a greenhouse gas? Can you explain the principles? I think the title says it all...

Yes, you are right, the title says it all. The presence of greenhouse gases, of which there are several, allows radiant energy from the sun to pass through the atmosphere but hinders the longer wavelength, infra red, thermal radiation from getting back out again, thus acting like the glass in a greenhouse. CO2 is a less effective greenhouse gas than methane, but there is much more of it in the atmosphere and it stays there longer, so this is the one which causes most concern. There are natural processes which reduce the amount of CO2 and methane in the atmosphere as long as the input, mainly from human activity, is not more than they can deal with.


Have two hurricanes ever merged? And what was the result? I was just reading this about how Hurricane Ethel could have merged with Hurricane Dora in 1964.

Has such a merge ever happened before in history? If so, what was the result? Would storms become twice as powerful? Or would they disrupt and dissipate each other?

They don't have to be hurricanes or typhoons per se, just large storms. I would think the low pressure regions of two storms would tend to attract each other if they were nearby, but it's apparently rare or unheard of because a quick google search showed nothing.

Yes two hurricanes/tropical cyclones/typhoons can merge with each other and the effect is known as Fujiwhara effect- Fujiwhara effect.

The National Weather Service defines the Fujiwhara effect as "Binary Interaction where tropical cyclones within a certain distance(300-375 nautical miles depending on the size of the cyclones) of each other begin to rotate about a common midpoint". What really happens is that centers of both systems begin to orbit in a counter clockwise direction about a midpoint that is determined by the relative mass and cyclone intensity. Eventually the smaller cyclone may merge into the larger cyclone.
There are several examples of the Fujiwhara effect and one example would be  Hurricane Connie Hurricane Connie and Diane Hurricane Diane way back in 1955. Shimokawa et al Fujiwhara Effect Types talk about the various kinds of interactions that can take place among various typhoons(Please note that the Fujiwhara effect is not restricted to two systems). The various kinds of interactions are

Complete Merger
Partial Merger
Complete Straining Out
Partial Straining Out
Elastic Straining Out

Complete straining and complete merger interactions lead to destruction of one of the vortices. Partial merger and partial straining lead to partial destruction of one vortex and elastic straining is an interaction in which both vortices survive with their initial circulation. Partial merger and partial straining out have received less attention in the literature on binary tropical cyclone interactions as the interactions are extremely complex. Prieto et al claim that during a partial merger repeated mass exchanges occur between vortices. As these are nonlinear effects a quantification is only possible by a direct numerical integration  and precise initial condition Binary TC Vortex Like Interactions

The period of orbit maybe as small as one day or there are others such as Cyclone Kathy and Cyclone Marie Kathy/Marie Fujiwhara orbited for a period of 5 days prior to merging into each other as pointed out by Lander et al. If the period of orbit is longer then there is a greater probability of a merger.

Region wise binary cyclones are more common in the Western North Pacific than the North Atlantic as pointed by Dong et al Relative Motion Of Binary Tropical Cyclones
Regarding the predictability of the track of binary cyclones Dong et al. state that prediction of steering forces of a single tropical cyclone are replete with numerical forecasting uncertainties and the problem is accentuated by the presence of another tropical cyclone in close proximity.
Those who followed the progress of Hurricane Sandy in late October 2012 (an instance of the Fujiwhara effect but in this case a tropical cyclone merged with an extra tropical storm) will remember the ECMWF model correctly predicted the landfall location.


What are the high field strength and large ion lithophile (HFS or HFSE & LIL or LILE) elements? There are two groups of elements that are frequently mentioned when discussing incompatible trace elements. They are the high field strength elements (HFS or HFSE) and the large ion lithophile elements (LIL or LILE).

What are these groups? How are they used in geochemistry and petrology?

First, a short introduction to incompatible elements

The Earth's mantle is mostly composed of the minerals olivine, pyroxene, anorthite, spinel and garnet. These minerals are made from the elements Si, Al, Fe, Mg and Ca. In the figure below I've put them in the MRFE field (Mantle Rock Forming Elements). The trace elements, the elements that occur in very low concentrations, do not form their own minerals and instead are incorporated into the crystal lattice of the common minerals. This is easy in the case elements that share the radius and charge with the major elements because they can easily fit into the crystal lattice (for example Ni in olivine, Cr in clinopyroxene).

Most elements, however, plot out of the MRFE field in the figure and are considered incompatible elements. That is, in the case of mantle melting, these incompatible elements are partitioned to the magma and eventually migrate with it when it goes to form new rocks (for example basalts). Because different processes and conditions of mantle melting result in different patterns and contents of incompatible elements in the new rocks, we can learn about the mantle melting process by studying these elements in more accessible rocks (such as basalts in volcanoes).

Note that I am referring to incompatible elements as incompatible with respect to mantle minerals. In some crustal rocks K, Na and Ti become major elements. In that case the MRFE should be renamed CRFE (Crustal Rock Forming Elements) and expanded to include these elements as well.

HFSE and LILE

The incompatible elements are then subdivided into two groups: the high field strength elements (HFS or HFSE) and the large ion lithophile elements (LIL or LILE).

The LIL name partly gives away why they are called like that: the LIL are indeed larger than other cations. They are lithophile in the sense that they are incompatible and usually end up enriched in the crust (also lithosphere).

The HFS are also enriched in the crust (eventually) but their name derives from their small radius compared to their high cationic charge: the z/r ratio. As a result, their bonding to nearby anions is very strong, that is - they have a high electrical field strength.

The subdivision between the two groups has been defined at z/r = 2.0, but as this is a continuous value, no strict theoretical definition of where the boundary lies can be given. Historically, the REE have been considered as LIL. In more modern times, the REE may be excluded when discussing HFS.

Why do we need the two groups?

Even though both the LILE and HFSE behave in an incompatible way during mantle melting, their response to post-magmatic processes differ. The HFSE are usually immobile: that is, they are mostly resistant to metamorphism and hydrothermal alteration. On the other hand, the LILE are fluid-mobile and hydrothermal alteration may change their contents in the studied rock.

Fresh rocks are a scarce luxury and many rocks that we study have experienced some kind of alteration. Because HFSE are resistant to these processes, their contents are likely to be representative of the original rock. This is extremely important: it is possible to look at a rock beyond the altered mineral composition and the modified major element contents. The LIL can teach us the opposite - we can learn about the alteration processes. If we do find fresh rocks and we find anomalies in the LIL systematics, we can learn about hydrothermal processes that occurred in the mantle that would otherwise not be able to see.

What about hexavalent cations?

One would think that hexavalent cations such as Mo6+, Cr6+, V6+ and U6+ should also appear in the figure as cations with an even more HFS character. However, when in the hexavalent state they form anionic complexes and do not behave like the cations in the figure.

Further reading

MIT OpenCourseWare - Trace-Element Geochemistry

The Use of Trace Elements in Igneous Petrology

About the figure

Inspired by figure 2.2 from Ore Deposit Geology / Scott. Data for figure from An Earth Scientist's Periodic Table of the Elements and Their Ions (also doi)


How does CO2 contribute to global warming? CO2 is a common agent in fire extinguishers, which suppresses fire.  How does this same chemical contribute to global warming when it also puts out fires?

It seems that you are wondering how a chemical that prevents heat (putting out a fire) can also cause heating (global warming).  These two things happen through unrelated processes.

Fire extinguishers that use CO2 act by displacing oxygen.  The CO2 doesn't directly interact with the fire but just takes up space so that oxygen cannot interact with the fire.  There is a secondary effect that the CO2 exiting the extinguisher is cooler than the air it is displacing so it helps to remove heat from the fire (by putting it somewhere else).
These are reasons that CO2 extinguishers are not suitable for all kinds of fire suppression, particular for fires that have oxidizers and do not rely on atmospheric oxygen for combustion.

The contribution to global warming from CO2 (and all other greenhouse gases) is a radiative effect.  Every molecule has specific frequencies of electromagnetic radiation they absorb and emit.  The earth (and all things) emit electromagnetic radiation based upon its surface temperature.  This energy would be lost to space (cooling the earth) except that the greenhouse gases absorb radiation at the same wavelengths the earth emits at.  This means that, e.g. CO2, intercepts this energy headed for space and instead absorbs it, causing the CO2 to warm up a little.  This CO2 also emits radiation but will emit less than it absorbs (and some of its emission is back toward the earth, not space), so there is a net energy gain due to atmospheric GHG, which causes warming.

As you can see, the mechanisms that CO2 contributes to global warming and fire suppression are unrelated (radiative vs displacement) which is why this molecule can be used in these seemingly contradictory applications.


Waves on sandy beach separating differently-sized rocks? I recently went to a beach, and I noticed that the sand seemed to have a few distinct regions.  I'm wondering what would cause this, and how it works.

One region is the part of the beach which is kept wet by the waves, but is far enough away that most waves don't seem to reach all the way to the end of it.  This part consisted of small-grained, "soft" sand.

This region is followed by a region with a lot of small rocks (mostly the size of, say, someone's smallest toe).  This region was located a bit past (i.e.: further into the water) the lowest point the water tended to reach.  This size of the grains of sand of this region blends smoothly into the previous region, so they get progressively larger as you walk further out to the water.

The last region is another one of fine-grain sand, and it also had ripples in it (I'm assuming that this is just because of the waves, because I noticed that the waves picked up sand from the peaks of the ripples and pulled it back out to sea).

The first two distinct regions seem to be the result of some type of sorting mechanism induced by the wave.  If so, how does this work?

And why was there a second region of fine-grain sand after the coarse-grain region?

There are two ways in which waves can sort particles on a beach, and both depend on surface area to weight ratio. The larger, toe-sized particles you describe have less surface area to volume (weight) ratio than the sand-sized particles, so were first to drop out of the water flow. The lighter particles had more surface area per unit of weight for the waves to act on, so were slower to drop out and were carried further up the beach. Why the lowest level sand grains were precipitated in deeper water, before the toe-sized particles, is less easy to understand, but one possible reason is that they contained some heavy mineral such as tin, which altered the surface area to weight ratio and caused them to drop out first. This principle is well seen in gold panning machines, where the heavy gold particles drop out of the flowing water first,while the lighter particles are carried further on, even when they are larger than the flecks of gold.


Is there an upper bound to the amount of rain that can fall in an hour? The record for most rainfall in a single hour is 12 inches (30.5 cm), set in Holt, Missouri, in 1947. What is the maximum amount of rainfall that could theoretically occur in an hour?

From http://www.srh.noaa.gov/eax/?n=holtmorecrain1947

A very moist airmass was in place across Missouri during the afternoon and evening of 22 June 1947, as evident by dewpoint temperatures in the middle 70s across Missouri during the afternoon hours
Advances in meteorological science led Locatelli to speculate that the thunderstorm that produced the historic rainfall of 22 June 1947, did not develop along a classic surface cold front, but to the east of a surface dryline (drytrough) and underneath a cold front aloft that had origins in the Mexican plateau.  Regardless of the causative surface and upper air features, a complex of storms at a scale not measured well in the data-spare period of the 1940s developed near Kansas City and moved across Holt, Missouri, depositing 12 inches of rain in less than one hour.  Rain continued to fall on Holt after the 12 inch deluge for the next couple hours, but only amounted to an additional one-half inch.

A rare meteorological event occurred that day.  I offer a semi-empirical frame of reference that takes  into account that the most extreme rainfall rates occur for a short duration (e.g. a few minutes).
In "A methodology to classify extreme rainfall events in the western mediterranean area" by Casas et al., (2004):
http://link.springer.com/article/10.1007%2Fs00704-003-0003-x
they show rain rates of up to 0.5 cm/min sustained for several minutes (based on a large network of rain monitors in Barcelona).   IF that could somehow be sustained for an hour, that would give a rate of 30 cm/hr (which is what Holt saw).
For comparison, the most extreme rainfall rate measured in one minute in the USA is 3.1 cm (1.2 in; see http://wmo.asu.edu/world-greatest-one-minute-rainfall ). Actual rain doesn't continue at such an extreme rate for much longer, but would equate to 186 cm per hour (6 times what Holt, Missouri saw in 1946).  The link that kwinkunks provides http://www.bom.gov.au/water/designRainfalls/rainfallEvents/worldRecRainfall.shtml shows a world rate record of 3.8 cm/min which, if sustained, would equate to 228 cm per hour.


Number of tectonic plates I came across a question asking what's the number of tectonic plates in this illustration:

I don't know on which basis we count the tectonic plates.
And I'm confused because I think they are 5 but the answer is 3.
As the illustration shows that there are a mid oceanic ridge which is formed because of a divergent plate motion between two oceanic plates and an oceanic trench which is formed due to covergent plate motion between two oceanic plates, so I think that there are three oceanic plates plus two continental plates which are at the two edges of the illustration. Am I right?

This is primarily an exercise in interpreting a minimalist diagram. Believe me, you will have to learn to read even sketchier diagrams.

That said, the test had the correct answer to the question. Unambiguously, there are only three plates.

The left and right plates each contain a piece of continental crust and a piece of oceanic crust connected by a passive continental margin. In each case, the oceanic terrane and the continental terrane move as a unit, so there's only one plate on the left and only one on the right. With the middle, oceanic-only plate, that makes three.

Although the diagram you gave us is a little more simplified than I'm comfortable with, you can tell that whoever drew the diagram meant for the left and right plates to contain passive margins. The elliptical loops of arrows are intended to be interpreted as convection cells in the mantle, and each cell drags the lithosphere above as a unit. So, anything above any one convection cell should be interpreted as one plate.

Here is a slightly more detailed diagram showing a passive margin:

(Source: Wikipedia, CC 3.0)


What was the lowest temperature ever recorded on the surface of Earth? This article Lowest recorded temperatures lists a -89 Degrees Celsius in Vostok, Antartica as the lowest recorded temperature. However, this other article List of weather records lists a −93.2 °C (−135.8 °F) on 10 August 2010, at   81.8°S 59.3°E. measured by Satellite. And this other article Coldest temperature on Earth in Antarctica lists a -97,8 °C , also using satellite measurements. Which one is the lowest temperature ever recorded on the surface of Earth then? Are satellite measurements reliable and do they count?

The wikipedia article List of weather records explicitly states

  This list does not include remotely sensed observations such as satellite measurements, since those values are not considered official records.[1]

Reference 1 in that article, a web archive link to a page on World Meteorological Organization Global Weather & Climate Extremes, adds that (emphasis mine)

  Although claims of a "world-record coldest temperature" have been made for a remote-sensed location in Antarctica, the WMO official coldest temperature remains -89.2°C (-128.5°F) recorded on 21/7/1983 at Vostok, Antarctica. Official weather measurements are made at using standard equipment at a fixed height of between 1.25 m (4 ft 1 in) and 2 m (6 ft 7 in) above the ground for a fixed location over a specific length-of-record. Remoted-sensed values of temperature are not at this time regarded as official weather measurements.

There are many reasons why remote sensed temperature values (especially extreme ones) should not be considered as official with regard to record temperatures. First and foremost, those remotely sensed values are not measuring temperature. They instead measure proxies for temperature in the form of intensities of electromagnetic radiation in various frequency bands in the thermal infrared. The surface temperature is derived from these observations by a complex set of algorithms that make various assumptions regarding the nature of the sensed data.

These algorithms need to be calibrated against ground truth. These is no ground truth data for temperatures that low. The interpreted data were well outside the sensors calibrated rate. Moreover, the "ground truth" data is actually the recorded temperature at 1.25 meters to 2 meters above the ground. Official weather stations are supposed to be slightly elevated to avoid boundary layer effects. The sensed data on the other hand are primarily  a result of surface temperatures, confounded by the fact that snow is a lousy thermal infrared emitter ("a good reflector is a lousy emitter") and confounded by contributions from the atmosphere between the surface and the satellite.

That said, those satellite readings almost certainly do indicate temperatures well below the reading at Vostok that officially counts as the lowest temperature recorded on the Earth.


Can someone help me identify this cloud formation? These pictures were taken today in Oklahoma City and I am both baffled and curious as to what formation this may be. I was wondering if anyone had any idea?

Thank you!

Well, after a bit of research, I stumbled upon the following image:

This is from a blog of two storm chasers Roger and Elke who I believe witnessed the same cloud formation as you. In the following link:

http://stormeyes.org/latest/tag/left-moving-supercell/

They refer to the formation as a 'rear flank arc cloud'.

So in conclusion I believe, the formation is a kind of arcus cloud. You can learn more about arcus clouds on wikipedia by following the link:

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

I hope I have been of help.


How is a UV Index calculated? I have three parameters for a particular location, namely:

Ozone:- A numerical value representing the columnar density of total atmospheric ozone at the given time in Dobson units
Elevation: The elevation of the location in meters.
Cloud Cover: A numerical value between 0 and 1 (inclusive) representing the percentage of sky occluded by clouds.

Is it possible to calculate the UV index of that location using this information?

The calculation of UV indices requires some effort.

Because different wavelengths of UV radiation have different effects on skin, to calculate the UV index you need to apply "McKinlay-Diffey" weighting factors to various wavelength components of UV radiation and then integrate (sum) those results and then divide by 25.

The procedure does not use ozone readings but it does use elevation and cloud cover.

The following two references list the procedure required:

Smithsonian Environmental Research Center
US EPA
NOAA-EPA Brewer Network


Definitions of tidal harmonic constituents...? Does anyone know where there is a detailed definition for tidal harmonic constituents? There is loads of stuff on $M_2$, $S_2$, $N_2$, etc. (all the common ones), but there are a great many more, some (I believe) involved in the calculation of tidal current speeds and directions. I am interested in what their physical significance is and the relationship to earth/moon/sun positions.

The explanation of all the tidal constituents is pretty complex because of the interactions between the different frequencies involved. The harmonic analysis is an expansion of the Equilibrium Theory of Tides into a set of harmonic terms. The list of relevant periods includes:

the lunar day (period of lunar rotation), 24.84 mean solar hours.
the sidereal month (period of lunar declination), 27.32 mean solar days.
the tropical year (period of solar declination), 365.24 mean solar days.
the period of the lunar perigee, 8.85 years (1 year = 365.2421988 days).
the period of the lunar node, 18.61 years.
the period of the solar perihelion, 20940 years.

The frequency of any tidal constituent can be computed by a combination of small numbers that multiply each of the periods (usually they are expressed as speeds, e.g., degrees per mean solar hour) above. The most complete algebraic expansion of the constituents was produced by Doodson in 1921. The set of small numbers are called Doodson numbers and represent the importance of each of the period in the specific constituent.

For instance, the set of Doodson numbers for the $M_2$ is (2,0,0,0,0,0), with the ”2” referring to "twice per lunar day" and the rest of the terms are zero (no influence). This is expected as the $M_2$ represents the passage of the same point on Earth through the "tidal bulge", created by the tidal forces, twice in a lunar day. The set of Doodson numbers for the $O_1$ is (1,-1,0,0,0,0), which represents 1 cycle/lunar day minus 1 cycle/tropical month. This is the result of the inclination between the Earth's axis and the Moon's orbit that causes the "tidal bulge" to be offset from the Equator and thus a point on Earth will experience one single absolute maximum per day.

The explanation of the lesser tidal constituents become rather tricky as the combination of Doodson numbers increases. For instance, $MSN_2$ is a combination of lunar, solar, and nodal influences and has a set of Doodson numbers of (2,3,-2,-1,0,0) making the interpretation rather complex.

While a list of origins of the constituents can be found (e.g., Table 4.1 in Pugh, 1996), ultimately it is simpler to try to understand each constituent as the result of a harmonic (~ Fourier expansion) decomposition, rather than a complex interaction between the bodies and their periods.

A few good books dealing with the analysis of tides are:

Pugh, D. T. (1996). Tides, surges and mean sea-level. John Wiley & Sons Ltd. (check Table 4.1 for a list of constituents and their origin).
Godin, G. (1972). The analysis of tides, 264 pp. University of Toronto.
Kowalik, Z., & Luick, J. (2013). The Oceanography of Tides. University of Alaska Fairbanks.


Why do manganese nodules have different constitution than sea water? Analysing the constituents of manganese nodules, we find that the relative proportion of minerals differs from that of the surrounding sea water.

Can someone explain to me why the proportion of the main minerals is so different?

Many reasons: First, the sea water does not have a uniform composition of dissolved metals. Second, if the nodule, either now or in the past, has been in proximity to an oceanic hydrothermal vent ('black smoker') then the source metal concentrations will have been dramatically different. Third, at thermodynamic equilibrium, each metal will have a different liquid-solid phase partition coefficient, and even slow precipitation isn't necessarily at thermodynamic equilibrium. Fourth, the Mn-nodule mineralogy may contain some proportion of clay with different adsorption capacities for different metals. Fifth, These nodules are lying on the sea bed, so it isn't just pure sea water that we are dealing with. There is also slowly circulating pore water from the underlying sediments. This pore water can have a huge range of composition derived from water-rock interaction, depending upon temperature-pressure history, pH/Eh, rock composition, depth of circulation and history of water-rock interaction. Finally, it is more than likely that microbial mediation is involved in metal oxide deposition at the liquid-solid interface (in which case all bets are off in respect of thermodynamic equilibrium), and almost anything can happen, depending upon microbial species, metabolism and micro-ecology.


How is land subsidence measured? When groundwater is pumped out of the ground by wells, and not replenished fast enough, the groundwater level sinks.

With it, the surface of the area sinks also. Locally, this effect is not apparent, because heights of objects are specified relative to the surface. The change in height stays zero by definition. But relative to the average elevation of surrounding land not connected in terms of ground water, there is a change. What changes is the distance between soil surface and center of gravity of the earth. The subsidence is a change in the shape of the earth, so its center of gravity changes itself, but the magnitude of that change is small enough compared to the surface change to ignore it.

How can the change in surface elevation of a fixed point on the surface of the Earth be measured?

One approach would be to use the fact that the surface of a water volume in equilibrium is the same height everywhere, even if the surface is separated. The water level in both ends of a U-shaped pipe is the same. One could use a long pipe that reaches from the measured location to a reference point. Connected bodies of groundwater are large, so that may require pipes of a length in the order of kilometers. Also, with a large distance between the end the air pressure may be different, so there is no equilibrium.

The ground water level itself is a possible reference point, because the ground water can permeate the ground. But we know that it is not in equilibrium, because ground water is removed only in parts of the surface - the wells, and the permeation is slow.

Ground elevation can be measured from satellites, as GPS does. I suspect that the accuracy is too low for many purposes because the relative change in the measured distance is very small. Also, the orbit of a satellite changes with the change of the center of gravity. Because the change is slow, elevation changes in distant regions influencing the satellite create noise in the measurement.

Land that has been heavily disturbed by humans in most developed countries, such as urban and rural regions will have been surveyed for topographical & sub-division purposes.

Such data allows for a digital terrain model (DTM) to be created for such regions. When subsidence occurs, the subsided area can be resurveyed & compared to the original DTM to ascertain the amount of subsidence that has occurred.

Undisturbed or poorly surveyed regions become problematic. The subsidence area & the surrounding area can be surveyed, but then someone has to make a judgement call & decide what the original surface may have looked like to infer an estimate for the degree of subsidence.

The other way is to have satellites periodically measure surface elevations & then to do comparisons between each satellite measurement.

Radar could be used as the measuring system, but LIDAR (& this reference also) can produce more accurate results.


Why is the core of Earth in a reduced state? ($\text{Fe}$ and $\text{Ni}$) I understand gravitational differentiation caused the layered structure of Earth when it is still molten. However, why are the heavier constituents in a reduced state, i.e. metal $\text{Fe}$ and $\text{Ni}$, instead of an oxidized state? Is this because of the high temperature and pressure?

Because there wasn't enough oxygen to oxidise all of it. There is only so much oxygen on Earth. Most of it went to oxidise the elements that have higher affinities to oxygen: silicon, magnesium, calcium, aluminium, etc. Iron and nickel have lesser affinity to oxygen, so you start by oxidising some of it, until there is no oxygen left.

But there is still unoxidised iron and nickel left! So this just sinks to the core.

Further reading.


Hazard event predictions. Examples of predictions causing more harm than good Could anyone give me any examples of attempts to predict earthquakes AND tropical storms that have caused more harm then good (e.g: because an area was predicted to have low levels of risk and therefore people were not prepared / the pathway of tropical storm predicted was inaccurate).

I am aware that predictions are far from being 100%.

One example that you may be able to research is the configuration of the tailings storage at the Ranger Uranium Mine in Australia's Northern Territory. The choices they had were either to dig a pit for the tailings, or build a dam for the tailings. A pit would leak a certain amount of contaminants into the surrounding waterways in the Kakadu National Park, and be more susceptible to flooding, but be more resistant to a catastrophic event such as a tropical cyclone, as there is no wall for the high winds to destroy. A tailings dam would be resistant to flooding, and as the construction of a dam can include control over the materials used to line and seal the dam, it would also not continually release contaminants into the environment. However, the dam wall would be susceptible to catastrophic failure in the event of a tropical cyclone, releasing the entire contents of the tailings storage into the environment.

This situation highlights the wicked problem nature of environmental risk assessment. The choice was made in the end to build a dam, and the result of that choice could, at some point in time in the future, result in the escape of millions of tons of toxic and radioactive contaminants into an extremely sensitive waterway.


Where can obsidian be found? Where is obsidian found?
Is it typically found on the surface or underground?
If underground, how far under (meters or feet would be perfect)?

Also, is it found everywhere on Earth, or just in areas where volcanic activity is (or was recently) high?

The processes forming obsidian are not well understood because an active obsidian-forming eruption has never been recorded by humans. However, we can make many inferences from the composition of the rock and settings in which it is found.

Obsidian is more than 70% weight percent SiO2 (i.e. rhyolitic), but has less than 0.5 weight percent H2O, and almost 0% gas bubbles (vescicles). This is very unusual because high-silica magma typically also contains a high volatile content. That means they can contain up to 8% H2O, CO2 and other species that easily become gasses. Because the rock is "missing" water and has no gas bubbles, we know that the gas escaped the rock while it was molten. This process normally takes quite a bit of time, so you might think obsidian cools slowly so that all the volatiles could diffuse out of the rock without forming bubbles.

If you thought that, you would be wrong.

Here's why: The SiO2 is almost 100% in glass form (amorphous) rather than in crystals. Any crystals that do exist are microscopic. This is strong evidence saying the rock cooled quickly, because if it cooled slowly the SiO2 would have had time to organize itself into crystals as it cooled. Further supporting the idea that it cools quickly is the fact that it is not observed underground (as an intrusive rock, which would have cooled slowly.)

One way to explain this "low volatile, glassy texture" paradox is to say the lava was kept hot for long enough time that the gasses were able to escape, and then cooled very suddenly. Another possibility is that the parental magma was extremely dry (low-volatile) to begin with for some reason.

Modern humans have never seen obsidian erupt primarily because rhyolitic eruptions are rare. However, obsidian is rare even among rhyolitic eruptions, presumably because lots of open-system degassing followed by rapid cooling is an unusual phenomenon. There are many places in the world that seem to habitually produce obsidian and have produced enormous volumes of it. The Valles Caldera in New Mexico is a particularly good example, with a huge lava flow and several lava domes all constructed from obsidian. Similar lava domes called the Inyo Domes near Mono Lake, CA have been fundamental to the understanding of the behavior of stable isotopes in magmatic systems and are probably the most well-known outcrops of obsidian among geologists.


Can planes damage the ozone layer? So I heard that the Ozone Layer is a layer of gas in Earth's atmosphere. And I also heard once that the Ozone Layer is crucial in protecting life on Earth, as it blocks out harmful rays emitted by the Sun. But over the years, the Ozone layer is slowly degrading due to the constant emission of chemicals. That's straight forward stuff...

But I once heard that super sonic jets can also contribute to the degradation of the Ozone Layer. What!? I didn't know jets could do that! This is what I would like to know:

Is this claim true?
And if it is, how high up and fast do the jets have to be?
Also, how is this even possible?

Does the jet create strong winds to blow the Ozone Layer away or something? Any feedback would be highly appreciated, thanks!

Yes, high flying jets can damage the ozone layer, but the consensus of opinion is that at present this damage is trivial and nothing to worry about. If, on the other hand, Concorde-type supersonic transports were to become commonplace, it might be another matter. It was found that Concorde's engines produced much more sulphuric acid particles than the exhausts of subsonic aircraft, and it was this sulphuric acid that damaged the ozone layer. Whether or not enough supersonic military aircraft fly at the relevant altitude and cause significant damage is something nobody seems to know, but probably not. The jets need to fly at altitudes between about 30,000 feet and 45,000 feet to cause ozone damage.


How are low pressure zones tracked across the ocean? When you look at a surface pressure chart e.g.:

(from http://www.metoffice.gov.uk/public/weather/surface-pressure/#?tab=surfacePressureColour&fcTime=1437480000)

you can see low pressure zones over the North Atlantic ocean. How are these zones tracked? I cannot imagine there are many monitoring stations in the Atlantic ocean.

Possible ways:

Ships - but I doubt there are enough to get readings over a wide enough area.
Comparison of pressure readings from coastal monitoring stations. Are there enough points for accurate interpolation of the readings?
Aircraft - comparison of GPS altitude to barometric pressure readings could give the surface pressure in a given area. That said, most aircraft travelling over the Atlantic are on specified tracks which may not cover a given area.
Monitoring stations on buoys at well spaced locations in the ocean. Potentially impractical and a hazard to shipping.

It is a combination of points 1,2 and 4.
Ships
Ships can provide observations, but they are generally confined to shipping lanes rather than distributed all over the oceans.   NOAA operates a volunteer observing program and you can find recent ship obs here.  The ships can report location, wind direction, wind speed, pressure, pressure tendency, air temperature, water temperature, dew point, wave information and a few other fields.  Not all ships report all of the data, but pressure is generally reported by all ships participating.
Buoys
NOAA operates a global buoy network though these are generally located in coastal regions.  There are regions of regularly spaced buoys in the ENSO regions.  There are also some buoys in the Indian Ocean (not pictured).

Drifters
The buoy network leaves vast swathes of ocean unmonitored and to get these obs NOAA uses a network of drifters that, as the name implies, drift along the ocean surface.

The blue points in the map above are drifters than can report sea level pressure.
Summary
Weather models that assimilate these observations will use sophisticated algorithms to "fill in the gaps" and produce a continuous field of global sea level pressure.
Aircraft can report pressure, but knowing pressure at altitude won't yield sea level pressure without knowing (or making assumptions) about the state of the atmosphere between the airplane and the surface.  Upper air observations are good though, and quite important to forecasting and generally much more sparse than ocean surface observations are.


How to identify low or high pressure area If rain is due to the flow of humid air from a high pressure area to a low pressure area, without the use of devices, technology or mass media is it possible to detect regions of high or low atmospheric pressure and know their locations?

For example: from my terrace or open land - and how do I spot regions of low or high atmospheric pressure?

Because you specifically asked about winds and pressure, there is a fairly applicable rule of thumb.  It's called Buys Ballot's Law.  Basically, if the wind is to your back (coming behind you), and you're in the Northern Hemisphere, generally low pressure is to your left and high pressure is to your right.  This graphic from http://www.maiamarinelli.com/ illustrates it:

However, do note that Buys Ballot is really an imperfect estimation.  There's three big caveats/adjustments to consider:
[in all following description, replace left with right (and vice versa) for Southern Hemisphere]

The Buys Ballot Relationship fundamentally relies upon the Earth's rotation, i.e. the always vaunted apparent force termed the Coriolis Effect.  Coriolis actually causes wind NOT to flow towards low pressure, but instead along equal pressure contours.  If it weren't for the Coriolis Effect, low pressure centers would quickly fill in with air, and we wouldn't have the complex weather that we have.  That said, at the equator, where the differences in rotation with latitude are smallest, Buys Ballot no longer works as there's limited/no Coriolis.  So the nearer the equator you are, the more low pressure would be more infront left, or even straight in front of you if wind is to your back.
Friction also slightly imbalances the relationship near the ground, such that wind actually flows towards low pressure again.  So once again, wind to your back may actually indicate the low pressure center is more to your front left than your left at ground level.  If you were up off the ground, or out in a body of water, this friction adjustment would be minimized, and low pressure is indeed more to your left.
Local effects, such as terrain (or buildings) definitely overwhelm the larger pattern at times.  And because the Coriolis force isn't significant in smaller, more localized features, Buys Ballot's becomes shakier in those situations.  The impetus from the broader wind flow does feed down to guide even pressure local features.  So wind to your back may well be telling you that a smaller area of low pressure is somewhere between to your left and in front of you... but that low pressure could be local: a building... a thunderstorm... even a tornado.  That said, as the pressure gradient gets greater, Coriolis is more and more marginalized, and the low pressure can be almost directly in front of you... and there are even rare circumstances where it is strong that the low can rotate backwards, and low pressure may be to your right.  As far as I know, this scenario only can maintain itself at all in strong thunderstorms, with the quite rare antimesocyclones and anticyclonic tornadoes.  However, perhaps it could also happen on the microscale, such as around buildings, but those circumstances are no within my area of knowledge.

So all that put together:
If indeed you can get away from those big buildings, are fairly removed from the regional impacts of mountains and smaller nearby terrain features, and ideally can escape areas with dense foliage... then if the wind is coming from behind you, you can be almost certain that large low pressure is to your left or front left (in the NH, right/front right in the SH)... if you can find the wind direction.

And if there isn't much wind?  Well then you're probably fairly near a high pressure center!  But that will make it fairly tough to diagnose exactly where high pressure centers/low pressure centers are in relationship to you.

(And if there is a great deal of wind... well maybe you should just get inside, and turn on your tv to find out when the big tornado/hurricane/winter storm is going to end!)

Other options:

You could also use a barometer to diagnose falling/rising pressure trends.  Those indicate that a low/high is moving towards you.  However, this doesn't tell you what direction the low or high is located [though you can often make an educated guess based upon predominant wind flow; most pressure systems come from the west in the mid-latitudes, which include much of the US/Europe/Asia].
As gansub noted in the comments, you could watch how atmospheric conditions evolve, such as the cloud patterns/types.  https://www.youtube.com/watch?v=tsD6zkBMmck is a reasonable description of what goes on around fronts, which could help alert you to incoming storms (both warm and cold fronts are dips of low pressure, and indicate a large low pressure system is coming).  The continuing lack of cloudcover might be an indication of high pressure in the vicinity.


What causes the different colours of the salt pits in the Saloum Delta in Senegal What causes the different colours of the salts pits in the Saloum Delta in Senegal?

Writing about the San Francisco Bay salt ponds, Dr R. J. Rusay notes:

  Due to variable algal concentrations, vivid colors, from pale green to bright red are created. The color indicates the salinity of the ponds.  Micro-organisms change their hues as the salinity of the pond increases.  In low to mid-salinity ponds, green algae are predominant. In middle to high salinity ponds, an algae called Dunaliella salina shifts the color to red. Millions of tiny brine shrimp create an orange cast in mid-salinity ponds. Other bacteria such as Stichococcus also contribute tints.

Rusay says nothing about the Saloum Delta, but the explanation could be similar there.


Could further oil drilling remove an insulation layer of the Earth cores heat? Putting aside burning fossil fuels, what are the consequences of another 100 years of drilling deeper and deeper to extract oil reserves globally?

Would this significant extraction remove an insulation layer of the core's heat enabling for heat to rise more freely towards the crust?  How much would this effect the earth's ground temperature?

I think your basic assumption is incorrect. Removing oil and the 80 to 90% water associated with it would reduce the thermal conductivity of the rock formations. It removes these liquids which aid thermal conductivity across the myriad of very tiny pores that contained the liquids. In the US regulations have the affect of the water being pumped back into the ground , not necessarily into the same formation. Outside the US that is not generally the case. Without doing any arithmetic, this appears to be a minuscule affect on earth temperature.....Thinking about it a little , you could likely make a better case on the basis  of the heat in the produced fluids ( water ,oil, gas): I know difficult wells go into formations that are 400 F+ , overall average the average temperature of production is likely between 200 and 300 F. No doubt SPE has real data but I am no longer a member.


What is the difference between a carbon sink and a carbon reservoir? I am trying to figure out the difference between a carbon sink and a carbon reservoir.

The definition for a carbon sink from Wikipedia is

  carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period.

And the definition for carbon reservoir is

  Carbon-storing natural feature (such as a forest or the land mass) that exchanges carbon with other reservoirs.

My textbook says that mature forests are carbon reservoirs but they are not carbon sinks. So what is the difference between a carbon sink and a carbon reservoir on earth?

The difference is that a carbon sink accumulates carbon, whereas a carbon reservoir has accumulated carbon.

That is to say:

A carbon sink is an ongoing process which is increasing the amount of carbon stored in it.

Whereas although a carbon reservoir might exchange individual carbon-based molecules with other parts of the carbon cycle, as much will go out as goes in, keeping the amount of carbon in the reservoir broadly constant.

Both of these contrast with things such as coal seams and natural gas & crude oil reservoirs that humans have tapped as sources of fuel; and leakages of methane from the ground: these were carbon reservoirs until the amount of carbon in them began depleting (e.g. through mining, well-drilling, or - in the case of methane clathrate leakages - ice melt), at which point they became carbon sources.


Is there a place where the sea floor descends into the mantle of the earth? My understanding of plate tectonics is that in the middle of the oceans magma rises from the mantle of the earth, cools and then spreads out, building up the sea floor. These places are pretty obvious because they have lava coming out of them.

On the other hand, there are places that sink into the earth, subduction zones, where the reverse happens; the existing crust slides into the mantle. Is there any place where this is visible, like the lava, or does it only take place invisibly far below the surface?

For example, let's say I have an object, like a shipwreck hulk. If I put the hulk on the sea floor in a subduction zone will it get sucked into the earth and vanish? If so, how long would it take for it to disappear?

The subduction zones are more easily spotted by the phenomena they cause in the subsurface than their features on the surface. I found this schematic image which shows almost all the features, from https://www.researchgate.net/publication/318684905_The_Nahuel_Niyeu_basin_A_Cambrian_forearc_basin_in_the_eastern_North_Patagonian_Massif :

So what you see is the thin black plate subducting under the grey continental rocks. There are two features that it causes in an indirect way.

The first of those is the forearc basin, which is a sometimes present region with thrust faults in the direction of the subduction point. Thus, there is a local basin with a lot of space for sedimentation.
The volcanism, then, is the most obvious and always-present feature. All the chemicals that the ocean floor brings into the Earth at relatively low temperature create a 'melt' that can eventually reach the Earth's surface.

The reason why we don't see the actual subduction happening with our own eyes is because of the formation of the 'accretionary prism'. This is the triangle-shaped feature on the figure. It consists of sediment that is held on the interface between the moving oceanic plate and the stationary continental plate. It's a bit like a bulldozer. Hence, the real subduction action is covered by kilometers of piled up sediment! The deepest natural trench in the world, the Mariana Trench, is only about 11 km deep, while the continental plate is probably at least ~40 km deep. Hence, we don't really see the actual subduction in action...

If you have a shripwreck hulk and place it in the Mariana trench, it will get covered with sediment with a speed of ~0.02cm/year, so assuming your ship is about 30 meters high it will take 150 000 years before it is covered and can become part of the accretionary prism. Then it has to be dragged into the Earth somehow. The Nazca plate moves at ~5 cm/year, so it'll be moved by 7.5 kilometers forward. As I wrote, it'll have to subduct at least 30 more kilometers before it's below any continental plate, which would take at least 600 000 years at the speed of the plate motion, and assuming that it somehow moves at the same speed as the crust rather than getting bulldozered into the accretionary prism. In other words, it would probably take much much longer in practice before it reached far enough down. As said, that means that in the meantime your space ship will have been chemically weathered and mechanically deformed (by the enormous mass of sediments), and won't really be recognizable as a space ship anymore!


What are 'articulate shells'? I can not really find a definition, not even in a geologic dictionnary: What are articulate (resp. inarticulate) shells?

To be more specific, the term is related to tsunami deposits (tsunamite).

If I remember correctly from my intro to paleo class, the terms articulate and inarticulate refer to a classification of brachiopods depending on the nature of their hinge. Articulate brachiopods have something like interlocking hinges (like a door hinge) made from serrated (or tooth like) parts of the shell. On the other hand, inarticulate brachiopods hold their shells together using only their muscles.

This means that the upper and lower shells of an inarticulate brachiopod will separate after it dies and its muscles decay. However, the shells on an articulate one will pretty much hold together unless a very strong mechanical force is applied. I don't know much about tsunami deposits, but this may have something to with that.

I'm not sure if this terminology extends to other phyla like molluscs, but I remember it from brachipods.

And here's a little picture because pictures make everything better.

Hope this helps!

-Antonio


How are the patterns in solid rock born I took this photo on my vacation in Finland showing white stripes in the rock going different ways. How are these patterns born?

One can only speculate based upon a photograph - however they look very much like mineralized fractures. At some time in the past this rock mass may have fractured in response to thermal or tectonic stresses. Fluid may have then penetrated relatively long distances along the fractures into the area and infiltrated shorter distances into the wall rock along small scale porosity such as cracks and grain boundaries (and also possibly diffusions.)  The fluid and rock were most likely not in chemical equilibrium when they came into contact and there were chemical reactions that produced additional minerals along the trace of the original fracture. This is probably what you see - the result of a process of fracture, mass transport, and fluid-rock chemical reaction. But a geologist would need much more information about this system (than available from one photograph) to describe the details.

Seeing something like this in the field is always very exciting because it raises so many questions. Where did the fluid come from? What was the temperature? When did the rock fracture?


Why does atmospheric oxygen remain so "constant"? I've always wondering why the oxygen in the atmosphere remains so perfectly at the level required for air-breathing life. What causes it to remain so perfect?

Also, a side question, why aren't their pressure bubbles with higher or lower levels of oxygen that could drift through a town and make it hard/impossible to breathe?

The main reasons the atmospheric oxygen remains constant are:

The sheer quantity of it. Not even a large forest fire will
measurably deplete it. Most of it is fossil oxygen created many
millions of years ago by photosynthetic organisms.
It is constantly being replenished by photosynthetic organisms,
mainly in the ocean.
Measurements of the percentage of oxygen in the atmosphere are a
modern phenomenon. There are no accurate measurements of atmospheric
oxygen in previous geological periods, but we know the percentage
has not always been 21 percent.


Why does seismic activity shed light on the inner core rigidity? Reading Introduction to Geology (MIT 2005) and Wikipedia's article on Earth's inner core, it is specified that:

  Earth was discovered to have a solid inner core distinct from its liquid outer
  core in 1936, by the seismologist Inge Lehmann, who deduced its presence from observations of earthquake-generated seismic waves that reflect off the boundary of the inner core and can be detected by sensitive seismographs on the Earth's surface.

Why does seismic activity would result in the conclusion that the inner core is rigid? What is the link between seismism and inner core?

The question that Azzie Rogers linked to: How can we determine the size and composition of Earth's inner core?

Does answer the theory part of the question, but I will extrapolate a little more to answer the question.

The question becomes, what kind of waves travel through what? Both shear and compressional seismic waves can travel through solids, but as it turns out, you cannot shear a liquid. As you look at teleseismic raypaths (waves traveling far from the source) you can see that the wave must travel deep into the earth and then back up again. The wave forms, and directions of these wavepaths will be altered by the different compositions of Earth's layers as it travels through: a wave just traveling through the mantle will have both its shear and compressional component.  A wave traveling through the mantle and outer core will lose its original shear component, and either develop a new one as it leaves the core (but distinct from the wave that travels through the mantle only) or not have one at all. And finally, a wave that travels through the mantle, outer core and inner core will have distinct wave patters as well. Its by this comparison of waveforms that we realize that the earth not only has different compositional layers, but phase boundaries as well. I am not sure seismology alone would lead to a solid inner core, but there is abundant evidence  supporting that fact. When you combine Seismology, rare bits of geochemistry, the calculation of Earth's gravity , and perhaps the most important part, the magnetic dynamo generating our magnetic field, we see a fairly clear ( albeit incomplete) story.


How does rotating water affect turbulence? I have been doing some DIYnamics with rotating water and non-rotating water. So I had a bucket filled with water on a rotating table, and waited for it to be in solid body rotation. I then dropped some droplets of fooddye in the water. I observed that the dye sank vertical to the bottom of the bucket without mixing with the water horizontally. I remember that my teather called this 2D turbulence. However, I can't find a reason for why the dye does not mix horizontally. What is so special with rotating water, that makes 2D tubulence occur and not 3D?
After this experiment was done, we added more dye. But now we mixed it gently with a stroke of a pen, to make turbulence. I then see some spirals being formed, so the water must mix a bit horizontally now. But why? And how does the rotating water affect turbulence?

The dye diffuses vertically because it has a higher density. So when you put the dye in from the top, it wants to go to the bottom, albeit slowly. If it were more buoyant, it would float. It does diffuse horizontally, though much slower. This can be shown that, after a long time, the water will turn the color of the dye.

As far as rotation affecting the dye, that is complicated. If you start the rotation before you put the dye in, you can get Taylor Columns. Throw in different variables/change different things about the tank, and you can find different phenomenon (see the Weather in a tank experiments).
What you see in your experiment is called "shear-induced diffusion." The movement of your pen makes shear, and that shear increases the diffusion rate. I would also think that the eddies generated help diffuse the dye.


Can someone help me identify this crystal So the actual rock looks black but I put it up to the light n I see green n black.... can you help me figure out what it is ?  my grandfather gave it to me years ago n I’d like to find out more about it...

It looks like Tourmaline which can be a lot of different colours but green-black is, I believe, the most common.


Is it coincidence that Antarctica is centered on the south pole? Looking at a globe, Antarctica looks remarkably centered on the south pole. Has the rotation of the earth had any effect on the position of the landmass?

It's an interesting thought.

Antarctica is not so balanced as it might appear on the maps. East Antarctica is old, consisting probably of cratons and Proterozoic orogenic domains whiles West Antarctica is much younger, thinner and have mostly been accreted during the formation of Gondwana (See e.g Boger 2011). If there was a direct control of the location of the continents from the rotation, one would expect East Antarctica to be centered rather than the whole landmass as it appears today, moreover one would expect a similar continent, resting at the North Pole.

However, Antarctica have been relatively stable, at least for the last 200My. The breakup of Gondwana could partly be simplified as one continent after the other radiating away from Antarctica, that mostly stayed in the same latitudes (See e.g Torsvik et al. 2010). Today Antarctica has relatively low tectonic activity and little continental drift, mostly a rotational component.

My personal believe is that astronomic potential fields, as gravitational tidal forces, might become a more important parameter in future for mantle dynamic models and maybe even some tectonic mechanisms, but I might be wrong and studies so far (e.g. this) have not shown good evidences and didn't attract much attention.


Does the size of Earth increase due to volcanism? In a volcanic eruption, magma rushes to the 'outside' of the Earth. Does this mean the size of Earth also increases? If not, how is the volume left after the magma rushed out refilled?

This is actually a more complicated question than it seems on the surface (no pun intended). The short answer is that the volume vacated by the magma is eventually refilled by the very tectonic processes that filled it in the first place. Crust is subducted, molten, and then rises to fill magma chambers. The process goes on and on. In some cases the plate that was being subducted eventually disappears (this will happen to the Juan de Fuca plate in a few million years), and the volcanoes associated with become extinct, not dormant but extinct. But generally speaking, volcanism is an ongoing process; the Earth is constantly recycling crustal material


What is a vertical wavenumber? I can understand that the wavenumber is number of waves or cycles in a given distance. But what would a vertical wavenumber mean? Is it just another term for the wavenumber of a wave that is propagating vertically? I came across this in the context of oceanic internal waves.

Precisely, how is it (if it is) different from the wavenumber of a wave in general?

In the picture above we see an internal wave propagating in the direction of the wavenumber vector
$$\mathbf{K} = k \mathbf{e_x} + m \mathbf{e_z}$$
which (in 2D) is given by the vector sum of its components. $\mathbf{e_x}$ and $\mathbf{e_z}$ are unit vectors in the horizontal and vertical directions, respectively.

The continuity condition implies that $\mathbf{K} \cdot
\mathbf{u}=0$. Hence, the direction of
energy propagation (group velocity) is perpendicular to the direction of
propagation of wave crests and troughs (phase velocity). Internal gravity waves are transverse waves so the fluid motion is parallel to lines of
constant phase as indicated by the Eulerian velocity vector, $\mathbf{u}$.

The vertical wave number $m$ is the vertical component of the wavenumber vector because in a continuously stratified fluid internal waves can propagate in all directions. In fact, in the real ocean there is a third component, denoted by $l$ which is in the transverse direction so that the full wavenumber vector is

$$\mathbf{K} = k \mathbf{e_x} +  l \mathbf{e_y} + m \mathbf{e_z}$$


Realtime planetary gravity maps? I'm trying to find maps of realtime (or at least periodically updated / semi-realtime) gravity maps of Earth.

I was hoping that GOCE might have something like this available, but I've been hitting a wall.

Any such maps available?

For sure this is not available.

To create those maps takes several dozens Earth orbits by GOCE (one orbit ~90 minutes) and possibly many more to bring up the signal to noise
Which gravitational features would you expect to vary significantly on any human timescale, so that creating such a scan would make sense?

This does not mean however, that no gravitational changes over time can be detected. ESA produced a video visualising data that showcases how GRACE and GOCE worked to produce ~10 snapshots per year from 2009-2012 to measure Antarctic ice loss. So continuing your search along those lines will surely lead to positive results.


How can I define frost based on a weather record? If I want to (programatically, in a plant growth model) define a growing season as last frost in spring to first frost in fall, how might I determine these dates based on a weather record that contains hourly temperature and humidity? Perhaps temp < 0 and dew point > 0?

A canonical reference would be appreciated.

The dew point is the temperature at which water condenses from the atmosphere. When the dew point temperature is below the freezing point of water ($0$ $^oC$, $32$ $^oF$) frost forms.

Most weather data includes dew point temperatures. Search your data for when the dew point is below the freezing point of water.

If your data does not you will need to calculate it to find when it is below the freezing point of water. The formulas here will help.


Recharge a dry aquifer? Aquifers have a natural recharge rate.  However, some aquifers rely on fossil water for their primary (or even sole) water supply.  When water in a well is pulled from these aquifers faster than they can replenish, the level drops and they eventually "dry up" (or the water table drops below the bottom of the well, at least).  In the case of aquifers with no recharge, such as fossil water, it seems that the water could literally be used up so that the aquifer becomes completely dry.

For these fossil water aquifers, is there any known technique to recharge them?  Since they're labelled as a non-renewable resource, I presume the answer is "no", but I'd like to get a better understanding of this.

For aquifers with a low recharge rate and a severly dropped water table, is there any known way to increase their recharge rate?

Fossil groundwater is water that has been trapped below the surface for several thousands of years. It is considered non-renewable as natural recharge on human timescales is practically zero. This is because the permeability/transmissivity of the overlying strata is very low.

However, on geological timescales the aquifer will recharge as pumping the water out of the aquifer decreases the hydraulic head, and therefore increases the gradient over the aquitards sealing the aquifer. Therefore the recharge of the aquifer actually speeds up by withdrawing water, although probably not in amounts humans can profit from.

Since you're asking about techniques to recharge, techniques similar to those used for shallower aquifers could be applied. In the Netherlands regeneration of groundwater is performed to decrease the stationary drawdown of the groundwater by the pumping which leads to damages for farmers. This is often performed by pumping surface water into the aquifer at some distance so the aquifer is recharges artificially and the groundwater table rises.

On the other hand, recharge of these fossil water aquifers in arid areas such as the subtropics is probably infeasible, even though it would be technically possible.


Plotting the wind direction in 3D? How can I plot the wind direction in 3D, using the 3 wind vectors u, v and w?
Normally, I create 2D wind rose plots in the traditional way, using R or MATLAB.

Which ways do you know for plotting this in 3D, using the additional w vector?Do you have code examples or tips for packages?

The context I often see the u,v,w components shown in one plot are forward and backward trajectory plots like those from the NOAA HYSPLIT Model, which provides separate panels for horizontal and vertical movement.  There is also 3-D imagery like what's available from UCAR in the cross sections examples for WRF, shown below.


How was Nastapoka arc formed? As wikipedia says, the Nastapoka arc is a geological feature located on the southeastern shore of Hudson Bay, Canada.
(Other description with picture at the Royal Astronomical Society of Canada)

No signatures of an impact event was found. However, 'A hole was drilled on Neilson Island, within the arc, in 1962. The core lacked any evidence of shock metamorphism, but one hole was not regarded as sufficient to settle the question of possible meteoric origin. '

Is that possible that the impact material was buried deep in the past hundreds of thousands of years?

There is other believable mechanism that can form that shape?

Gravity anomalies surveys are used to understand the nature of the crustal material. Positive anomalies, or higher gravity than surroundings suggests higher density (heavier) material, (iron, metallic composition) where lower some lighter alternatives.

A good example of this is the Chicxulub impact. The map of gravity anomalies show the crater quite clearly, even if it is buried under thick layers of sea sediments or surface (Yucatan, MX).

On the other hand, Nastapoka arc is harder to define using similar methods. This recent paper (PDF) (now published here) discusses that it may have more to do with crustal dynamics than an impact. Nevertheless they present an  interesting gravity map of the site (See figure), where any links to an impact in this area would not be obvious.

It is true that major glacial activity occurred repeatedly during the Pleistocene east of the Hudson Bay (eg: Laurentidian Ice Sheet sweeping again and again), but yet the Chicxulub impact was subject to many factors of erosion as well since its formation near the K-T boundary.

Still these kind of surveys indicate the nature of the material in the crust - so even if several glaciations impacted the Nastapoka arc area, there would be some kind of patterns still present indicating heavy metals (Chondrite or anything typical of an impact, iron or circular metamorphism).

To conclude, unless other surveys suggests an alternative interpretation path in the future, few evidences strongly support the theory of an ancient impact at Nastapoka.


What map projection preserves latitude? I just want see which cities are on the same latitude as others. Please recommend latitude-preserving projection that's free and online.

A cylindrical projection with a vertically oriented cylinder which is tangent to the Equator produces a map that you are looking for. In this kind of map projection, all the points on the same latitude (all the points that are at the same distance from Equator) stays on the same horizontal line on the projected map.


What is Boomy McBoomFace? The EarthSky article Great Pacific Garbage Patch now 3 times size of France links both to the newly published article in Scientific Reports Evidence that the Great Pacific Garbage Patch is rapidly accumulating plastic and to the YouTube video of one of the authors Boyan Slat - The New Picture of the Great Pacific Garbage Patch (2018), which discusses both data collection and analysis, and the possibility and scope of potential cleanup efforts of a huge patch of garbage within the North Pacific Subtropical Gyre.

Near the end of the video, after 07:00 is shown a very large structure being welded. It's been humorously named Boomy McBoomFace in reference to the RRS Sir David Attenborough story and the UAV Boaty McBoatface.

Is this boom part of a subsequent garbage collection experiment, or a cleanup prototype, or something else?

Click the screen shots below for full size display:

The boom* is a cleanup prototype. From the OceanCleanup website:

  The Ocean Cleanup deployed a 100 meter-long barrier segment in the North Sea, 23 km off the coast of The Netherlands on the 22nd of June 2016.

  OBJECTIVE AND SET-UP

  To investigate the durability of our design, we deployed a system segment in the North Sea. At this test site, conditions are more severe than those in the Pacific Ocean, due to the North Sea's strong tidal currents, and the test site's short, steep wave patterns.

  The objective of the North Sea prototype was twofold;

  Test the boom design on a small-scale for survivability in extreme conditions
  Gaining experience as an organization in the ocean deployment of a cleanup array

  FINDINGS

  During an inspection of the North Sea prototype in August, we noticed the two outermost air chambers were bent out of shape. Thanks to underwater footage we were quickly able pinpoint the cause; shackles had disconnected from the mooring, which increased the forces on the ones remaining as well as the floater. After our diagnosis, we continued to closely observe the situation and decided to take the barrier back to shore after close to two months.

The design has changed since (bottom of page).

These Youtube fragments have some more shots:

Video 1
Video 2 (Dutch)
Video 3

That last video goes into detail about it's design and later versions. The comments state that

  the new North Sea tests are aimed at assessing two variations of floater-screen connections as well as the application of antifouling on the screen

* A long pole, often heavy, e.g. along the foot of a sail. In this case, sheets/screens are hanging down from it.


Are there seamounts as close as 100 m to the water surface and not inside any Exclusive Economic Zone? I did not find any seamounts as close as 100 m to the water surface (100m from the mean surface level at the location of the mountain) that are not part of any Exclusive Economic Zone (EEZ.)

Do any such seamounts exist?

Yes, there are many. According to the seafloor topographic data of ETOPO (1 arc second resolution), and the Exclusive Economic Zones (EEZ) database of marineregions.org. There are at least 157 seafloor features higher than -100 m (closer than 100 m to the sea surface). With that data, I made the following figure that shows:

ETOPO topographic data
All EEZ polygons
All 157 -100 m contour lines that are completely or partially outside any EEZ.
A red point at the centroid of each contour line (to make even the smaller seamounts visible).

Some of them are just a few meters below sea level according to ETOPO.

But note that with this data we can only see large features. ETOPO resolution is about 2 km. Therefore, a seamount with a sharp summit just above -100 m would probably not show up on ETOPO data.

For more information about individual seamounts you can query the Seamount Catalog of EarthRef.org. There you can find high resolution multibeam seafloor topographic data for many seamounts, there are more than 1,800 seamounts in the catalog so far.

For example, for Vema seamount that was mention by @arkaia and that corresponds to the point just West of South Africa in my figure, you can find data like this:


How much mass has humanity added to the planet? If anyone could work out how much mass (not weight :) ) have humanity added to the Earth, seeing that the LHC (atlas, I believe, weighs 7000 tonnes), and the Three Gorges dam in China slowed the Earth's rotation by 0.06 micrometers. How much does the collective building of humanity added to the mass of the Earth?

All mass used in construction on Earth comes from material on Earth.  Since mass is conserved, there is no change.  If we start harvesting material from the moon or asteroids for use in construction on Earth, then there would be a net increase in mass.  But currently, the net mass of Earth has decreased due to man, since we have launched many satellites into space which came from material on Earth.


Can an earthquake occurring within two plates trigger another earthquake in a far away plate boundary? Can an earthquake occurring between two plates, like the Pacific Plate and North American Plate cause any effect which would trigger an earthquake in a far away place like the boundary between the Eurasian and Indian Plates, as we know it is a mosaic of plates?

I guess that it is possible.

As mentioned by others, on top of static stress triggering, which is the effect of an earthquake in its vicinity (typically up to 2-3 rupture lengths away), another way by which an earthquake can trigger others is by dynamic stress triggering, which may have effects farther away but are hard to identify and measure.

So far, the only earthquake that seems to have demonstrated how dynamic triggering over long distances can take place is the 2012 Indian Ocean earthquakes. This earthquake had an unusual combination of characteristics: it was a very large strike-slip earthquake, it took place in oceanic crust (which allows surface waves to travel longer) and had a very large concentrated burst of Mw 8.4 - 8.5 with large slip over limited distance (I do not post sources since there are at least 3 apparently good studies with very different results, for example one study says that slip exceeded 80m locally (!)). These characteristics suggest that this earthquake was very efficient at radiating energy through the crust rather than towards the interior or through very fragmented crust.

So, what this earthquake showed, is that it is possible to speed up significant earthquakes (earthquakes that were almost ready to happen, but they were sped up up to 90 days). Still, it is only one case, the mechanism is not well understood, we are not sure why this earthquake seemed to have caused this phenomenon while other earthquakes with higher magnitudes did not show the same effects.

Concluding, while static stress triggering has only a fairly local effect, dynamic stress triggering may have a wider effect but we only have detected one such case, which could very well have been a coincidence or due to an unusual mechanism. So the answer to your question seems to be yes, but with doubts and in any case for very special earthquakes.


Pressure as a function of altitude My city's altitude is almost 950 meters, yet the weather stations provide a read of 102.14 kPa which is around 1 atm!

Shouldn't the pressure be a function of elevation?

I doubted that the data provided could be wrong, so I checked New York and got almost the very same results.

All reading are very close to 30 in.Hg (around 1 atm), yet the elevation varies from 0 to 550m.
So, what is going on?

The reported pressures are sea level pressure.  For stations not at sea level (most of them), they can be corrected to sea level through use of the hypsometric equation.  The reason the values are reported as sea level pressure is so that pressure values between stations can be interpreted in meaningful ways.  See for example a typical sea level pressure plot:

In order to produce such a plot, you need pressures on a common reference plane, which is often mean sea level or some other reference pressure level (e.g. 850mb, 500mb, 250mb).  This is why stations report sea level pressure rather than actual station pressure.  This also has applications for aviation, where aircraft operating below a specific altitude (18,000 ft in the US) have to reference their altimeters to a common value regionally and must know the local sea level pressure.


Why do modern windmills turn clockwise, but classic mills turn counter-clockwise? Most modern windmills appears to rotate clockwise. I know that is has something to do with the direction were the wind is coming from. But how to understand this?

It is to do with the angle of the blade, it has nothing to do with the direction of the wind. If the blade is slightly facing clockwise then the wind will push it to turning anticlockwise. If the blade is slightly facing anticlockwise then the wind will push it up and become clockwise. There is no reason from a physics perspective that governs which direction of rotation is best. Modern wind turbines are manufactured in factories who use the same design of blades, this can reduce the cost of production and present a coherent view. While windmills in the past are produced in small local subsistence workshop and don't have standardization.


Did Jupiter really make Earth (in)habitable? A new study by Batygyin and Laughlin suggest that a Jupiter migration toward the inner region of the Solar System during the early stages of system formation cleared the habitable region (Goldilocks zone) around the Sun from early planets that too large and with atmospheres too dense to support life. As they put it:

  Jupiter migrates inward from a > 5 astronomical units (AU) to a ≈ 1.5 AU before reversing direction, can explain the low overall mass of the Solar System’s terrestrial planets.

They propose this scenario to explain the differences between the Solar System and other planetary systems in which large planets are found in the proximity of the starts.

Among the many questions I have: How is it physically possible for such a migration to occur? Is there a way to verify the migration hypothesis with observations? How different would have been the hypothetical planets in the area currently occupied by Earth? If such a migration toward the Sun started, what prevented Jupiter from continuing inward and collapsing with the Sun? Is it possible for such a migration to occur again?

Did Jupiter really make Earth (in)habitable?

Perhaps, but it's tough to tell.

I wrote up an answer for a question on Physics getting at some more specific issues here; bear with me if I re-use a little bit of it.

  How is it physically possible for such a migration to occur?

Planetary migration in the Solar System is described by the Nice Model (or, actually, the Nice II Model, its successor). Basically, the gas giants started out at different orbital semi-major axes than they are in today. There is one change in order, though: Neptune is closer in than Uranus (making the order Jupiter, Saturn, Neptune, Uranus). Also, there may have been a 5th giant (actually an ice giant), which was subsequently ejected. It would have been similar to Uranus and Neptune in composition and size.

Here's a quick summary of the Nice Model:

Planetesimals and Kuiper Belt Objects interact with the giants, moving Jupiter inwards a tad and the other three (or four) outwards.
Eventually, resonances come into play. These are ratios between orbital periods. Jupiter and Saturn cross a mutual threshold.
Saturn moves outward and Jupiter moves inward. A chain of events happens, where Neptune and Uranus are dramatically moved outwards, with Neptune being chucked to the rear (and the hypothetical 5th giant being ejected). You can watch the video given in that question here.

Here are the before and after pictures, stolen borrowed from that question:

I can, specifically, recommend the papers I mentioned there: Fassett & Minton (2013), Deienno & Nesvorny (2014), Brasser et al. (2009), Nesvorny (2011), Nesvorny & Morbidelli (2012), and Gomes, Levison, Tsiganis and Morbidelli (2005) - in no particular order, I think.

  Is there a way to verify the migration hypothesis with observations?

Well, simulations were used in some of the mentioned papers, especially in those co-authored by Nesvorny, who was involved in recent developments of the Nice Model. These lead to the hypothetical 5th giant, because in some cases, it is necessary as a sort of sacrificial lamb, to prevent Uranus or Neptune from being flung out.

We really can't observe this happening in real time, so simulations are our best shot.

  How different would have been the hypothetical planets in the area currently occupied by Earth?

The Late Heavy Bombardment might not have happened. That's a whole avenue of investigation into alternative astronomical history. It would involve fewer craters and possibly less fewer small collisions between some objects. It would be a calmer place. No migration = no LHB.

Beyond that, it's hard for anyone to say. Detailed simulations are really difficult, because the exact conditions that matter - not just orbital positions - are hard to model.

  If such a migration toward the Sun started, what prevented Jupiter from continuing inward and collapsing with the Sun?

There just wasn't enough impetus from the encounter with Saturn to fling it inwards. A migration isn't just a planet rushing willy-nilly into space; it's a delicate system of slight orbital changes. All odds were against something like this happening.

  Is it possible for such a migration to occur again?

Only if the right resonances appear, which is unlikely.


Review of calculation of CO$_2$ contribution to warming In a Swedish Facebook group for "climate change skeptics" Erik Larsen has shared his calculation of how big part of temperature change can be attributed to human emissions of carbon dioxide. His reasoning goes as follows:

Temperature has raised by 1 °C since 1850.
Carbon dioxide has raised by 30%.
Carbon dioxide only constitute 4% of the greenhouse gases (the main part consists of water vapor).
Carbon dioxide is only 1/4 as efficient as water vapor per molecule as a greenhouse gas.

From this he concludes that the temperature raise from carbon dioxide is only 1 °C × 0.30 × 0.04 × 1/4 = 0.003 °C.
I have tried to explain (in Swedish) that this calculation is not correct, but of course he refuses to accept that and writes that my objections are not logical. Today I wrote that it's lucky for him that his calculation is not peer-reviewed and suggested that I could share it in a physics and/or mathematics group for review. He complied. So here it is.
What do you think of his calculation?

This reminds me of using Bjørn Lomborg's book in statistics, as examples how not to do statistics, his calculations never make any sense or just make unfounded leaps to conclusions.
Erik seems to have the same problem he just throws numbers together with no rhyme or reason.
Let's just break down his calculation.
1 °C × 0.30 × 0.04 × 1/4 = 0.003 °C.
Why are we multiplying by 0.25, he says CO$_2$ is only 25% as good as water, but water is nowhere in this calculation, there is no reason for this to even be here much less to be multiplied. Also why can't he solve 1/4?
1 °C × 0.30 × 0.04 = ??
This is just plain wrong, CO$_2$ comprises 0.04% of total gas and ~93% of trace gasses, even more of greenhouse gasses, unless he is arguing some undiscovered change in nitrogen or argon is acting as a greenhouse gas, this has no place in the calculation. Also again why is he multiplying by the increase in CO$_2$? Does he think ALL gasses in the atmosphere increased by 30% that the atmosphere got 30% heavier in 150 years?
1 °C × 0.30 = ??
What is this calculation meant to do? One times anything is always whatever you multiply it by, so all you are calculating is units, but units are ignored in the calculation, and what purpose does multiplying degrees of change times percentage of increase do?
There is no point arguing with Larsen, either he does not understand math (in which case you are wasting your time) or he is purposefully being misleading (and it just gives him attention). Either way there is no benefit to arguing with him. Your best case is he does not understand math otherwise he is just using a completely unjustified string of numbers to have something that looks scientific because it has a equation in it counting on the fact most people who read it don't know enough about math to see the problem.


Do there exist reasonable numbers on the density/radius/mass of the various geological layers of the Earth? I've been doing some math on the radius of the core (inner core in particular), and I keep getting what look like nonsense results. The composition is supposedly nearly all iron, close enough to it anyway... and I've been using (avg) densities as high as 13,000kg/m3. However, even with density this high I can't get a lower radius than about 2500km. This is using a 0.16 mass for the inner core.

Google returns a radius of 1220km for the inner core. It also returns a diameter of 1220km for the inner core.

I went so far as to reimplement this an an Excel spreadsheet to double check my code, and I get consistent results.

Is there a good source for the (rough is fine) densities, mass, and radii of the geological layers? I don't trust Google and Wikipedia at this point, and even if I find the answer somewhere else I won't know for sure if they're even close to correct.

One model that will help you is the admittedly dated (1981) Preliminary Reference Earth Model. It provides density models for the inner and outer core as functions of distance from the center of the Earth:
$$
\rho =
\begin{cases}
13.0885 - 8.8381 x^2 & \quad \phantom{000}0\phantom{.0} \le r \le 1221.5 \\
12.5815 - 1.2638 x - 3.6426 x^2 - 5.5281 x^3 & \quad 1221.5 \le r \le 3480.0
\end{cases}
$$
where

$\rho$ is the density in grams per cubic centimeter,
$r$ is distance from the center of the Earth to the point of interest in kilometers, and
$x$ is the normalized radius: $x\equiv\frac r {6371}$.

Note that this results in a slight density discontinuity at the boundary between the inner and outer core (1221.5 km). That's intentional. There have been later upgrades to the PREM, but the PREM is where it all starts.

Reference:

Dziewonski, Adam M., and Don L. Anderson. "Preliminary reference Earth model." Physics of the earth and planetary interiors 25.4 (1981): 297-356.


How are subsurface wave speeds determined without subsurface sensors? This is something I've never quite understood from a geology class I took years ago:

Consider the following picture (courtesy of wikipedia)

Obviously, we can't possibly have sensors deep in the mantle (or core).  So, how exactly are these wave speeds determined?

This is a good question, and the basic answer is earthquake seismology. To answer this question, lets accept a fact: Waves propagate through the least time pathway, and not the least distance path. This property of physics is known as Fermat's principle.

When an Earthquake occurs, energy propagates similar to a ripple of water, and spreads. Each point on this ripple can be modeled as a ray, each following its least time path through the Earth. As these rays propagate, they reflect and refract  off heterogeneities inside the earth. These reflections are important: we can detect these reflections using surface seismometers. Using multiple seismometers, and the location of the source (earthquake), we can calculate the "lag" between when the closest seismometer detects the earthquake and the others(further from the source). This lag time can be used as a proxy for the depth of the reflected wave's heterogeneity. Using how deep this reflection originates, we can then figure out the least time path of the wave in terms of actual distance. Velocity is just distance over time, even for seismic waves. So since we have the distance traveled by the wave, and the time the wave took to get to the receiver, we can complete the equation (distance/time).

In actual practice, this process is far more complex, as you have to look for many different waveforms:

The picture above illustrates an earthquake sending waveforms through the earth. The SKS wave is a shear wave that refracts into the liquid outer core, turns into a compressional wave (since shear waves cannot propagate through liquid), and then is converted again to a shear wave as it enters the mantle and goes to the surface. A trained seismologist looks at the readings from seismometers to tease out specific waves, which we know the properties of, to determine properties of the planet's interior. The speeds of these waves are highly dependent on the assumed densities and other rock properties of the crust, mantle, and core.


Can pyroclastic flows cross water? While reading the Wikipedia article on pyroclastic flows, I noticed that there's a section called 'Interaction with water'. This piqued my interest, as I was under the impression that lava generally doesn't interact much with water other than cooling down.

To my surprise, this claim is made in the article:

  Testimonial evidence from the 1883 eruption of Krakatoa, supported by experimental evidence, shows that pyroclastic flows can cross significant bodies of water. One flow reached the Sumatran coast as much as 48 km (30 mi) away.

I tried to look up the citations, but they're both in books that I don't have access to at the moment. Can these flows cross water, and how?

In answer to the title question, "yes"!
Here are some videos from Montserrat Soufriere Hills where the phenomenon has been extensively studied (probably more than anywhere else):

http://www.geo.mtu.edu/volcanoes/west.indies/soufriere/govt/images/051296/

As well as Krakatoa, Mt Pelee's (Martinique) 1902 eruption managed to ignite ships in the harbour when the main town was destroyed - which suggests the pyroclastic flows crossed the harbour.

Also my u/g mapping area in North Wales included the Snowdon Volcanic Group. It and related tuffs appear to have been erupted over water and/or wet estuary type environments (there is open to debate).


What denotes a parameterization in a model? (semantics ) I know that WRF has many different uses and options, from atmospheric chemistry to uses with fires, and so on. What exactly denotes a parameterization? For example, in WRF-Chem, is the chemistry considered a parameterization? If not, what separates a mechanism from a parameterization? Is photolysis a parameterization? Are the biogenic emissions parameterized?

As defined in the AMS glossary, a parameterization is a simplification of one or several processes in a model. I add that a parameterization commonly adds an error and increases the uncertainty in the model results. In most cases, a parameterization is not derived from physical laws but a fit to data.

These simplifications are employed for different reasons. You probably know the following examples and this answer could have been shorter ;-) but I added them for other readers who might not be aware of them.

Parameterization due to spatial constraints

When we model meteorological and atmospheric chemistry processes in a certain domain, we split this domain into individual grid cells of a given size - such as grid cells of 10 km x 10 km size. Some atmospheric processes have a lower spatial extend than the grid cells - such as small scale turbulence and clouds smaller than 10 km. These things cannot be explicitly calculated by the model (except if we reduce the model resolution). Therefore, we approximate these things taking place on a spatial scale below 10 km. These approximations are denoted as parameterizations.

Parameterizations due to computing effort

When we consider processes such as particle formation, growth, and coagulation we could consider every particle or even every molecule in a model. However, in real world atmospheric applications we have too much particles than we could consider them individually. Therefore, we need to calculate the growth of particles on the base of some parameters and apply it on (log-normal) particle number/volume/... distributions.

Parameterizations due to missing and condensed information

Biogenic emissions are a nice example. We do not know exactly where which trees and plants are located (and which atmospheric conditions like humidity and temperature prevail). For some regions we know it: e.g. for the city of Hamburg there is a detailed (non-public) tree inventory existing. When we do not have this information and work in a gridded domain (i.e. 10 km x 10 km) we need to make a simplified assumption - such as 10% of the grid cell ground is covered by urban area, 30% by grassland, 10% by desert and 50% by forest (of which 70% are pine trees and 30% other trees). From this information and the average ground level temperature and humidity we need to estimate the amount of various emitted volatile organic compounds. Doing this, is a parameterizations because we over-simplify the actual real world.

But

From my feeling I would describe a process representation in a model as explicit/non-parameterized when it is included according to the best current/state-of-the-art knowledge. In contrast, when it is considerably simplified, I would denote it as a parameterization.

However, when we presented gas phase chemical processes by differential equations - like as it is done in the gas phase chemistry mechanisms of chemistry transport models -, I would not consider it as parameterizations because due to a large number of identical molecules (and the law of large numbers - probably) we do not actually introduce a large error.


Moon tilt against the horizon in a single day Where I can find a graph of the apparent rotation of the illuminated portion of the moon against the horizon in a single day? And is there a place where I can read about all the variations which dictate this angle?

Mooncalc.org offers a pretty comprehensive set of tools for viewing the moon.  Click on the location you want, then drag the slider on top through the day to see which direction's sky the moon will be in (or times where it will not be visible).  And it shows the moon's shape you will see (I presume that's as viewed with nearest horizon down?)
(For those interested, suncalc.org is their sister site for the sun.)

I'm not an astronomer, but this article from Goddard Space Flight Center looks like it offers a very solid discussion of libration, and the causes due to moon's orbit, the relative location of the moon from different viewing locations, and the tilt of the Earth in relation to the sun.


Climate change impact / risk assessment I work for a local council in the UK. We want to include climate change as a mandatory consideration in all of our decision making. This would require project managers to look at the risk (what adaptation measures we need to consider) and impact (how the project would affect our emissions budget) of any large decisions.
I expect that this has been done before, but I can't find a guide or discussion of it anywhere. Please can you suggest sources of information / existing implementations?
Sorry if this isn't the most appropriate place to post this, if anybody knows of a more appropriate forum, I'd be happy to go there instead!

The UK Government already publishes information on this at the national level, which may be a useful guide for how to proceed at the local government level.
The last UK Climate Change Risk Assessment was published in 2017 and the next one is imminent in mid-2021.  They follow risk assessment methods set out in things like the HM Treasury Green Book, which, despite the name, is not about environmental assessment specifically (there are Orange, Aqua and Magenta Books too).  The Green Book
has a shorter, climate-specific supplement that may be a good place to start.  In particular, Annex B of the supplement has lots of links to other resources and tools for doing the assessment.
There’s also a local government website that hosts a slightly random selection of plans that various regions have put together over the last few years.
This all looks like a daunting amount of paperwork to a scientist like me, so good luck!


What are the properties of the back arc extension related volcanic rocks? What are the properties of the back arc extension related volcanic rocks and/or related magma? (e.g. Basin and Range region)

Back arc basin lavas are basaltic and similar to the magma from mid ocean ridges, except that the magma from back arc basins is about four times as rich in magmatic water, which is typically 1.5 percent by weight of the rock.