What are rare earths and why do they cluster near alkaline magmatism? 'Rare earths' play a vital role in the modern economy, and they are becoming more of a point of focus in geopolitical realms.  What are 'rare earths' and why do they appear to cluster in association with:

alkaline to peralkaline igneous complexes
pegmatites associated with alkaline magmas/carbonatite intrusives
perovskite mineral phases within akaline complexes
mantle derived carbonate melts
hydrothermal deposits associated with alkaline magmatism

"Rare earth" metals consist of Scandium, Yttrium, and 15 other metals of the so-called "Lanthanide" series toward the bottom of the Periodic Table of elements. Basically, these are the chemicals that we didn't study in chemistry class at school.

Like other metals, they have two electrons in the outer shell, but unlike "metallic" chemicals such as sodium or magnesium, they have a special "metal" shell for electrons. They are located at the "left" (relative to the carbon family) or akaline end of the Periodic Table, which is why they are found near alkaline magnatism, in alkaline "compounds."

This is in contrast to the more common chemicals, which are typically found as "oxides," or "sulfides," or possibly in combination with fluorine or chlorine. These common chemical compounds are on the right, or acid side of the periodic table.


The free oxygen (O$_2$) in the atmosphere is largely a result of what process? Does it come from
a)atmospheric lightning and ozone dissociation.

b)meteorite impacts early in the earth's geological history.

c)Paleozoic volcanic activity.

d)photosynthetic processes.

e)photodissociation of water molecules (from solar ultraviolet light).

I believe it is D, but not 100%.

Thanks

You are correct in thinking that oxygen comes from photosynthesis. In fact it is so much associated with photosynthesis, as opposed to any inorganic process, that the presence of oxygen in the atmospheric spectrum of other planets (solar or exoplanets) is reckoned to be one of the best indicators of life beyond Earth - not that such oxygen has been discovered yet.
Ozone is made from pre-existing oxygen but with an atmospheric half life of only about 12 minutes, it spontaneously turns back into oxygen again very rapidly, and is highly sensitive to ozone-disrupting agents such as CFCs.
Meteorites have little, if any free oxygen. Indeed, many meteorites contain Ni-Fe which would rapidly mop up any free oxygen if it were originally present. Volcanic activity reflects the fugitive gasses of a magma chamber, which contains F, Cl, CO2, CO, H2O, H2S, N2, inert gasses, and hydrogen. Oxygen can occur in in a few volcanic emanations but this is rare and of small scale. On balance, volcanoes are oxygen absorbers rather than emitters. Photo-dissociation occurs to some extent high in our atmosphere in response to both solar and cosmic radiation. The result is H2O = H+ +OH- so there is no free oxygen involved. In any case, the two ions recombine fairly rapidly. Photo-dissociation is important in dense interstellar gas clouds far out in space where they may be subject to intense UV-radiation. Even here, the tendency is to mop up rather than release free oxygen.
The photosynthetic activity and mechanism on Earth has changed dramatically. It is the only known mechanism which can and does release large quantities of free oxygen. This started more than 3 billion years ago, but didn't raise the atmospheric oxygen level significantly prior to about 2.5 billion years ago. Evolution of the Earth's oxygen has been a long and complex affair, with high levels of oxygen only starting to emerge in the Eocambrian. The Earth's first oxygen would have been a noxious, toxic, and horribly reactive gas from the perspective of the Earth's earliest unicellular organisms.

New information just in: Nature magazine, 28th October 2015, has reported an astonishingly high oxygen concentration, of 3.8%, from the gaseous emissions from comet 67P, as measured by the Rosetta space probe. This has taken everyone by surprise (including myself) and may require a re-think about comet formation.


Feedback loops between soil chemistry and plant growth Would the dynamic between soil nitrogen and plant growth be a positive or negative feedback loop

I think it is a negative feedback loop because as soil nitrogen increases then plant growth increases, and as plant growth increases, soil nitrogen decreases, is this correct? Therefore, since $+ × - = -$, it's a negative feedback loop.

Also, what about the feedback loop between temperature and soil organic matter? As temperature increases so does soil organic matter, as soil organic matter increases so does the release of CO2 thus causing more warming. A positive feedback loop.

Is this reasoning correct?

You're on the right track, though the positive and negative aspect of feedback loops is more about dynamics of the overall system rather than just the increase or decrease of components in the feedback loop. This website offers a straight forward explanation of positive vs. negative feedback loops https://serc.carleton.edu/introgeo/models/loops.html :

  Feedback Loops can enhance or buffer changes that occur in a system.

  Positive feedback loops enhance or amplify changes; this tends to move a system away from its equilibrium state and make it more
  unstable.
  Negative feedbacks tend to dampen or buffer changes; this tends to hold a system to some equilibrium state making it more stable.

In your second example, the feedback loop between temperature and soil organic matter leads to amplified changes in the system, making it more unstable. You're correct in identifying this as a positive feedback loop.

In the first example about plant available nitrogen and plant growth, there is a feedback loop there but is it positive or negative? You noted that the effect of increased plant growth would reduce available nitrogen. That isn't necessary the case, but even if it was, reduced nitrogen itself could actually be a positive feedback loop because it would lead the system out of equilibrium and into an unstable state (with the plants present no longer able to sustain themselves). However, in an undisturbed ecosystem I'd expect this to actually increase available nitrogen and also increase stability of the system over time, making this a negative feedback loop.

The relationship between soil nutrients and plants can be complex and vary between plants (e.g. leguminous plants would certainly create a negative feedback loop, enhancing the stability of the system they are thriving in). In general plants left to their own succession would increase organic matter which serves as a nutrient reservoir, further enhancing nutrient availability. In our more controlled agricultural systems, you can see this effect applied in crop rotation and allowing fields to go fallow as a means to increase available nutrients among other potential benefits.

Note that the nature of a feedback loop also depends on how the system's boundaries are defined. This is especially true looking at industrial agriculture and other systems that rely heavily on external inputs or otherwise have far-removed externalities.


How long does it take air to circle the world? I live in New York and I am investing in a carbon offset program in Korea to decommission a coal electricity generation plant.

Will I ever breathe the cleaner air as a result of that project? And how long with that air to get here (and back around)?

It takes about 2 weeks for a mass of air to circle the globe along its latitude from West to east. I used to work for a French climate research lab in the 70s, and was based on Crozet island (South Indian Ocean) . At the time I was carrying atmospheric radioactivity measurements, and the French army was carrying nuclear test above ground in the pacific, I could see the radioactive cloud passing above me about 10 days later and then again about every second week after that and about completely disappeared after 6 months.
In the case you raise, you will benefit from cleaner air about one week after the decommissioning


Why is the density of Earth higher at the core If gravitation decreases as we approach the core and if density is a function of gravity we should expect a void core.
Unless the accretion disk was formed starting with the objects of highest mass available first.
But as soon as the whole planet would have been liquefied the core should have voided according to 1.

Gravity is a weird force.

All mass has, and is affected by, gravity. That means you, me, your cat, black holes, the sun and the earth.

It also means each little bit of the earth is attracted to every other little bit. So every bit tries to get as close to every other bit as it can.

The shape that these bits form is a sphere - because every bit is as close as it can get to all the other bits.

Now you are right - an earth which is matter all the way through would attract in the same way as one which had all the mass concentrated around the edge. But we know that the centre isn't hollow for two reasons:

Volcanoes and Earthquakes. Volcanoes erupt liquid rock from the ground, which shows that there is something down there. And we know that there is something because we feel the shaking from earthquakes on the other side on the earth - and we can map the layers of solid and liquid from these.

  If gravitation decreases as we approach the core and if density is a function of gravity we should expect a void core.

No, because every bit wants to be close to every other bit. It doesn't just want to be near the bits on it's side, it wants to be near the ones on the other side, and so the "void" would close.

  Why is the density of Earth higher at the core?

The denser stuff sinks. This is how it works everywhere that gravity applies. We can explain why.

The denser objects have more gravity than the less dense objects. This means all the objects are attracted to the more dense objects more than they are the less dense objects. Here, red is more dense.

But the ones over the other side, are also attracted to that dense object, so this happens:

Eventually, you end up with all the less dense objects surrounding the more dense object, as they try to be as close as they can to it. But the more dense objects are attracted more to the other dense objects (as they both have more mass). This means all the dense objects clump together, surrounded by the less dense ones.


Does the Earth produces measurable gravity waves? Does the Earth exhibit measurable gravity waves? Note: I'm not asking about gravitational waves.
Some recent experiments looking at low-frequency (3$\times 10^{-5}$Hz) accelerometer data are showing some features that might be explained by this. The signal that I and others have measured shows a signal at least 10 to 15 dB above the noise floor that appears to change somewhat based on local geology as determined between measurements in Japan, Hawaii, and the continental US.
Any insight into crustal gravity waves with a period of roughly 9 hours, or other phenomena that might result in reproducible signals like this in accelerometers is appreciated.
Any suggestions for further analysis that might differentiate among different possible explanations is also welcome!

Edit: This answer refers to the first version of this question which asked about "gravitational waves".
Typically, the term "gravitational wave" is reserved for distortions ("strain") in spacetime, in accordance with General Relativity. Gravitational waves are a property of spacetime and can thus propagate in empty space. In contrast, what you measure here are simply seismic waves, such as pressure waves propagating through Earth and your setup. In fact, seismic waves are the limiting noise that prevents gravitational wave detectors such as aLIGO to measure at lower frequencies, see e.g. this paper for a discussion and plots.


Are clouds a gas, liquid, and/or solid? Are clouds a solid, liquid, or gas?

I have been looking online and they are often described ambiguously as a "mass". For instance, from NASA:

  A cloud is a mass of water drops or ice crystals suspended in the
  atmosphere. Clouds form when water condenses in the sky. The
  condensation lets us see the water vapor. There are many different
  types of clouds. Clouds are an important part of Earth’s weather and
  climate.

Since they describe it as a vapor, that makes me think it is indeed a gas. But condensation is by definition the change of state from a gas to a liquid. So that makes it sound like it could be a liquid, or contain liquid droplets rather than "freely moving" molecules that typically make up a gas.

But at another web site, which doesn't seem all that authoritative, it says that clouds are a solid, liquid, and gas simultaneously!

  A cloud is a liquid, a solid, and a gas.

That does seem intriguing. If I remember correctly, liquids are supposed to be incompressible, and clouds are likely compressible.

The cloud that you see is a mixture of solids and liquids.  The liquid is water and the solids are ice, cloud condensation nuclei and ice condensation nuclei (tiny particulates that water and ice condense on).  The invisible part of clouds that you cannot see is water vapor and dry air.  The majority of the cloud is just plain air in which the invisible water vapor is mixed with and the very tiny water drops and ice particles are suspended in.

A cloud is a mixture of gas, liquid and solids.


Please help in understanding redox buffers I'm trying to gain a firmer conceptual understanding of how redox buffers work in petrology, specifically how oxygen fugacity influences mineral crystallization.

While I understand the mathematical and thermodynamic principles underlying these concepts, I'm not seeing how changes in the partial pressure (fugacity) of an element such as oxygen can impact what minerals crystallize.

First let me start by saying that redox buffers are a made-up thing. All these QFM (actually FMQ) or NNO or other abbreviations don't exist in nature. They were developed as a way to "cheat" in experiments to get the desired Fe(II)/Fe(III) ratio, and later extended for more uses. High temperature and pressure experiments are permeable to hydrogen: it just goes through the experimental capsule. Depending on the direction of diffusion, it can either oxidise or reduce the contents of the capsule, changing the desired Fe(II)/Fe(III) ratio. Buffers "force" a certain oxygen fugacity. In reality, redox (or not) is buffered by a variety of reactions that we may not even know exist.

  partial pressure (fugacity) of an element such as oxygen

In the deep Earth, there is no free O2 gas phase, so it doesn't make sense anymore to talk about the "partial pressure". But the oxygen fugacity controls the reactions involved electron transfer (i.e. buffers).

  how oxygen fugacity influences mineral crystallization

In general, higher oxygen fugacity means there's a higher ratio of Fe3+ to Fe2+. This is particularly true in melts. So a melt with lots of Fe3+ will crystallise magnetite (for example) whereas a reduced melt with little Fe3+ will not. This is one of the differences between tholeiitic and calc-alkaline differentiation trends. Calc-alkaline melts are oxidised, so they crystallise magnetite early. Therefore, they never reach high Fe contents. Tholeiitic melts re reduced, and magnetite does not crystallise until very late, so it is possible for them to reach high Fe contents.

This is also important for sulfur. Will a volcano erupt SO2 or H2S? It all depends on the oxygen fugacity of the system.

I will also add that the bulk amount of Fe3+ and Fe2+ does not directly tell you where a rock is oxidised or not (with respect to oxygen fugacity). For example, a rock with 1% hematite, 98% enstatite and 1% magnetite will have more bulk Fe2+ than a rock with 50% magnetite, 49% quartz and 1% fayalite. But, the former is at the HM buffer while the latter is at the FMQ buffer (reduced).

I highly recommend reading this (preferably more than once):

Frost, B. R. (1991). "Introduction to oxygen fugacity and its petrologic importance." Reviews in Mineralogy and Geochemistry 25: 1-10.


What is oldest known coal source? I read coal form in all geologic times but what is oldest know coal source?

The first coal deposits were laid during the Carboniferous period, between 358.9 million years ago and 298.9 million years ago.
Within this period, the early Mississippian period from 358.9 to 346.7 Mya, was when the first coal deposits were being laid. During this period, coal was being laid in what is now eastern North America, specifically the Kentucky region.


Where do rivers like the Rio de la Plata end and the ocean begin? We just had visitors (in Monterey, California) from Montevideo, Uruguay.

Not being very familiar with Uruguay, after having taken them to Big Sur, I asked them how far they lived from the ocean.

They said it was hours away, and that they lived on a river.

I later looked at a map and, AFAICT, they do live right on the Atlantic Ocean.

If they view the river that flows into the Atlantic to the west of them to be the river they live on, that seems very odd to me - from my point of view, once the river dumps into the ocean, that's ocean, and the river stops where they meet.

The body of water gets very much wider at that spot, so it certainly "looks" more like the ocean on the map than a continuation of the river. But it leads to the question: when a river dumps into an ocean, exactly where does it transition from being the river to being the ocean?

In the case of Río de la Plata, part of it is history and politics, and part of it is oceanography.

Most of Argentina and Uruguay considers Río de la Plata as a river (thus, the name, río) and as such it is the widest river in the world (maximum width >200km). Río de la Plata is formed as the confluence of the Paraná and Uruguay rivers and results in a pretty wide estuary with Montevideo (Uruguay) in the northern shore.

As can be seen in the following satellite image, the combined discharge from the Paraná and Uruguay rivers creates a current that flows into the Atlantic Ocean and that is visible under calm wind conditions and high discharge periods.

Source: https://eoimages.gsfc.nasa.gov/

Spanish and Portuguese explorers in the XVI century described Rio de la Plata as a "Mar Dulce" (freshwater sea). The Italian explorer Sebastiano Caboto explored the area and traded silver with the local Guaraní tribes and thus gave it the name of "River of Silver".

In practice, the system is best described as an estuary: neither river nor ocean, but an area of freshwater and saltwater mixing. In the area of Montevideo, the salinity in spring is around 10 g/kg (way lower than ocean salinities ~30-35g/kg), but it can be higher in periods of low discharge. In the area of Buenos Aires, salinities below 5 g/kg are commonly found and thus, it makes sense to call it a river. Most oceanographers agree that the system is a salt-wedge estuary, with freshwater flowing near the surface toward the ocean and saltwater intruding landward near the bottom of the estuary.

Salinity of the Rio de la Plata: Source: Guerrero, R.A., Lasta, C., Acha, E.M., Mianzan, H., Framiñan, M., 1997. Hydrographic Atlas of the Río de la Plata. CARP-INIDEP, Buenos Aires, Montevideo.


Is there a way to approximate the density of air during rain? Given a rate of precipitation (in mm3/hour), and average droplet diameter, is is it possible to calculate (or even ballpark) the density of the air+rain droplets at time of rainfall?
What I mean is, if I were to take a random metric cube of rain + air during rainfall, how much would it weigh?

Air without rain has a mass of about $\ce{1200 g/m^3}$ at 20°C.

You can figure out the amount of water in falling rain if you know the rate of accumulation (how much rain falls through a given volume in a given time, landing on the ground) and the velocity of the falling rain.

Here's a link to a post elsewhere on this same question. In that discussion, they assume a rainfall rate of 1 inch (2.54cm) per hour, and estimate a raindrop's terminal velocity (from observation) at about 9 m/s. They divide that rate by that velocity (converting units), and come up with about $\ce{3/4 cm^3}$ of water per $\ce{m^3}$ of rain.

So, given those assumptions, the density of (rain + air) is about .06% higher than the density of air without rain. Interestingly, that's much less than the difference in density between dry and humidity-saturated air (about 1% at 20°C). In other words, air at 100% relative humidity with heavy rain falling through it is still less dense than dry air.


If we assume the mega impact hypothesis for the formation of Moon, where on Earth is the impact point? Given that Pangaea had C-shape can we assume that the point of impact was in the center of this C-shape? In modern world it would be under Tibet?

Or should we assume the oldest shape of the supercontinent was circular so that the impact point was somewhere in North America?

I think you are confused about the timescales and the magnitude of the impact that is being talked about here.

The collision between the early Earth and a roughly Mars sized body, Theia is thought to have happened between 4.4 and 4.45 billion years ago. The Pangaea supercontinent had fully assembled by around 250 million years ago. Previous to this there are a number of other supercontinents which have been recognised, the oldest speculative ones dating back to around 3 billion years ago. The Earth's crust is constantly being reshaped by plate tectonics and so the location of an impact at 4.4 billion years ago has no bearing whatsoever on the orientation of the Pangaea (or any other) supercontinent.

In addition, based on computer simulations of the impact, we know that the impactor mass must have been on the order of 0.1 Earth masses and the initial impactor velocity must have been something like 5 km/s. This means that a colossal quantity of energy would have been released by the impact which would completely reshape any surface structure (and much of the internal structure) that the Earth may have had at that early stage. Indeed, a significant quantity of the mass of the two impactors was put into orbit around the Earth by the impact, either as solid debris, some of which coalesced to form the Moon, or as vaporised rock. Due to the complete lack of direct evidence, it is difficult to determine the exact impact parameters, including the impact angle. Some simulations suggest a fairly moderate angle of impact of around 45° [1], but there is some geochemical evidence from the Moon to suggest a higher angle of impact, with higher energies involved [2][3].

References:
  [1] http://www.sciencedirect.com/science/article/pii/S0019103503002999
  [2] http://science.sciencemag.org/content/351/6272/493.full
  [3] http://science.sciencemag.org/content/338/6110/1052.full


What causes intra-plate faults, such as the New Madrid fault? There's been news (some recently) about the New Madrid fault and other active intra-plate faults.  For those living in the midwest of the United States, it's been a bit of a shock to learn they have to worry about earthquakes as well as tornadoes.

Inter-plate faults, such as the San Andreas fault, get a lot of attention.  Plate friction from movement makes sense.  But, what is the current theory on these intra-plate fault zones?

Good question!  I'll lay out the prevalent idea, originally (I think) put forward by Sykes, 1978 and supported by a large body of subsequent work by many authors. There are other models, however.

In the most general sense: Intra-plate faulting is due to old, pre-existing weaknesses that are reactivated due to the plate interiors being very close to critically stressed.

In other words, they're weak points in the interior of the plate.

However, we don't fully understand why some old fault zones get reactivated while others in the same orientation don't.  (It probably has a lot to do with pore pressure and fluid movement at depth.) There's a lot we don't completely understand about intra-plate earthquakes.

Also, please don't use the term "fault line". It offends my geologic sensibilities! :)  (Faults are 2D surfaces, not lines, thus the nitpicky objection.)

Most of the crust is close to being critically stressed (breaking)

There's a lot of evidence that the continental crust everywhere is close to being critically stressed -- in other words, failing in an earthquake.  (e.g. see the various Townend and Zoback papers.) The crust isn't just critically stressed near the plate boundaries, but also away from them. This may also be true for oceanic crust, but we don't have as much data there.

Another way of saying this is that the plates are being pushed along as hard as they can without crumpling.

Basically, this is why things like building a dam or deep fluid injection trigger small earthquakes.  The crust is already close to failure, so adding load or increasing pore pressure often triggers small fractures.  (However, these sort of things can't trigger a major earthquake unless they're on an already active fault.  You need continuous slip along a very large surface for a large earthquake.)

The plates being critically stressed is actually is what we'd expect. We see deformation at plate boundaries whenever they collide. Therefore, we know that the stresses driving the plates are greater than the "breaking" strength of the crust.  Because stresses from a collision at the boundary will be transmitted to the interior, it intuitively makes sense that the interiors should be close to, but just below (otherwise they'd be deforming), the failure threshold. (For the complete argument, see Zoback and Townend, 2001)

Continental crust is full of old zones of weakness

The continents are very old. Much older than the oceanic crust. The continents are like rafts that keep bumping into each other. Therefore, they have lots of "scars" (i.e. old fault zones).

There's a saying in structural geology: "once a weakness, always a weakness". Fault zones are typically much weaker than the crust around them.  Once a fault breaks through, it tends to be a permanent weakness that will be reactivated even if it's not in a perfectly favorable orientation.

Critically stressed crust + weak zones --> intra-plate earthquakes.

But why don't we see activity on all old fault zones?

Short answer, we don't really know.  It probably has a lot to do with pore pressure and fluid movement.

Some old fault zones have intra-plate earthquakes, while others don't, even if they're in the same orientation.  Pore pressure plays a huge role in faulting (it make rocks much easier to break).  There's a lot of speculation that active intra-plate fault zones may have more fluids at depth, though explaining why is difficult.


What are the natural causes for methane formation? Natural gas is mostly made of methane ($\ce{CH4}$). Methane can be produced as a result of microbes eating organic matter. But can it also be naturally formed without any assistance from organic matter?  Perhaps in conditions such as those found on the early Earth?

The 'natural causes' of global methane emissions are, as you indicate, mostly of biological origin. To some extent it depends upon what you regard as 'natural'. There are many and differing estimates of global methane generation, of which I list a summary below. Those in bold you may regard as abiological. Values are in Mega-tonnes per year released to the atmosphere:

Wetlands 217

Fossil Fuels 96

Ruminants 89

Landfill 75

Geological sources 54

Freshwater 40

Biofuels 38

Rice growing 36

Oceans - DMS  20

Termites 11

Wildfires 10

It's a moot point as to whether degradation of dimethyl sulphide (DMS) is biological or not.


Are average daily temperatures affected by DST? To calculate the average daily temperatures, do meteo professionals still use the Mannheim procedure with twice weighted measurement in the evening? (It could be obsolete by automated weather stations.)

If so, does DST affect the daily average by getting that measurement one hour earlier?

I'm not asking if that invalidates the results, just whether there is a measurable impact.

They compensate for DST.

That is, for any daily measurement, they use the same universal time every day of the year.  If they take a measurement at 7:00 local time in summer, they will take the same measurement at 6:00 in winter.

(So if you do see a DST effect in the data, that would be due to traffic and other local anthropogenic effects shifting by an hour relative to the time of measurement!  Perhaps due to urban heat island effect, or forcing by anthropogenic aerosols from traffic or industry.)


Is the theory of hot spots compatible with lengthy volcanism? The island of St Helena was volcanically active for five million years or longer. The island is located on the African plate and in that period of time would have moved at least a hundred miles or more. Surely the idea of a single hot spot cannot apply in such a case - it seems more akin to a hot streak. I also wonder whether other mid-oceanic volcanoes were active for similar lengthy periods and whether or not these conform to the idea of single hot spots.

Tectonic plates are not single blocks of geology. The Africa Plate, like other tectonic plates, consist of cratons  which are "stable blocks of old crust with deep roots in the subcontinental lithospheric mantle, and less stable terranes, which came together to form plates".

The Africa Plates contains the "Kalahari craton, Congo craton, Tanzania craton and West African craton".

The island and volcano of St Helena, though on the edge of the Africa Plate, is more associated with the Mid Atlantic Ridge than it is with the Africa Plate.

The cratons and other land masses that form the Africa Plate may be mobile, but St Helena and the Mid Atlantic Ridge are not.


Remote Sensing System (RSS) historical atmospheric data continually updated Does anyone know why every month there are updates to the RSS historical atmospheric data? How can data that is 10 years old need adjusting every month?

For instance, here's the difference in data points from July 2015 and October 2015 for the total tropospheric.

Being remote sensing, algorithms for inverting the raw data to get physical quantities may be improving with time. Perhaps a slight adjustment in algorithm or calibration happened between July and Sept of this year. However you would expect this to introduce a systematic adjustment, not a scatter.

One might reasonably wonder why the data is steady before 1999. That may be because there were fewer (or different) remote sensor parameters measured then, or the data wasn't as precise.

Another possibility is that the calculation was simply done more precisely, and you are looking at the elimination of round off errors, or different round offs.


What is the mass of our planet's atmosphere, hydrosphere, and cryosphere combined? What is the mass of our planet's atmosphere, hydrosphere, and cryosphere combined?

How accurate can our estimates be?

Pretty darn accurate. To first order, the atmosphere's mass is the average atmospheric pressure at the Earth's surface times the total surface area divided by the acceleration due to Earth's gravity. Or if you prefer, $$ M_{\mathrm{atm}_\bigoplus} = \frac1{g_{_\bigoplus}}\int_{{\textstyle\!A}_\bigoplus} \!\!\!\!\! P_{\mathrm{surf}} = \frac1{g_{_\bigoplus}}\int_{\theta} \! \int_{\phi} \sin (\phi) R^2_{\scriptscriptstyle \bigoplus} P_{\mathrm{surf}}(\theta,\phi) $$ This is very slightly wrong because some of the atmosphere is further away where gravity is less, leading to a ~0.25% underestimate of the mass of $ M_{\mathrm{atm}_\bigoplus} $. The quick estimate would be pressure at sea level times total area of the Earth divided by gravitational acceleration, $$ M_{\mathrm{atm}_\bigoplus} \approx \frac{4\pi R^2_{\scriptscriptstyle \bigoplus} P_{\mathrm{sea\,level}}}{g_{_\bigoplus}} $$ Plugging in actual numbers, $$ M_{\mathrm{atm}_\bigoplus} \approx \frac{(12.6) \,\,(6.4 \times10^6\mathrm{m})^{\textstyle 2} \,(1.01\times10^5 \mathrm{kg}\,\,\mathrm{m}^{-1}\mathrm{s}^{-2})}{(9.8\,\mathrm{ms}^{-2})} \approx \underline{\mathbf{5.3 \times 10^{18}\,kg}} $$ or about 58 quadrillion American tons.

Water is rather incompressible, so integrating the density of water (1 g/cm$^2$) times ocean depth over the surface of the oceans will get you close. This is a data intensive calculation, but all the data is well known. Then, there is the liquid water outside the oceans, about 1.75% of total water, most of which is subsurface groundwater (fresh and saline). Free surface water, like lakes, is negligible. See Where is the Earth's Water.

Another 1.75% of water is frozen in glaciers and ice caps. This is the hardest to calculate because the depths of the ice caps over land and sea is not precisely known.

Using the table at the bottom of Where is the Earth's Water we find that there is about 1.34 billion cubic kilometers $(1.34\times10^9\,\mathrm{km}^3)$ of ocean and sea water. Add groundwater, and it becomes $1.36\times10^9\,\mathrm{km}^3$. Each cubic kilometer weighs a trillion kilograms $(10^{12}\,\mathrm{kg})$ so $M_{\mathrm{hydro}_\bigoplus}$ is about $\,$ $\underline{\mathbf{1.36\times10^{21}\,kg}}\,$, or 250 times the mass of the atmosphere.

Using the same source, the $M_{\mathrm{cryo}_\bigoplus}$ is about $\,\,\underline{\mathbf{2.4\times10^{19}\,kg}}$ .


How to model bed load transport in channels of non-rectangular cross sections All the formulas presented in the relevant technical literature refer to channels of rectangular cross section — the formulas assume a constant depth of flow right across the channel section.

I need to calculate the bed load in a channel of roughly triangular cross section. I do not think that calculating the bed load discharge with the average depth of flow is appropriate or theoretically justified, so I am looking for a special hydraulic analysis of the situation which may be applied to channels of triangular or trapezoidal cross section.

There are several approaches to answer this question. One is simple, but not that accurate. This approach would be to to discretize points along the perimeter and calculate a per point boundary shear stress. The equation would be the same as the depth averaged, except you would solve for each individual depth h1, ..., hn.

One thing to note is that the bed load will mostly be concentrated at the lowest point in the channel.

The easiest accurate method to implement is the WTA method, which uses the law of the wall to calculate boundary shear stress. The papers outlining the method are Wobus et al. (2006, 2008) titled "Self-formed bedrock channels"[1], and "Modeling the evolution of channel shape: Balancing computational efficiency with hydraulic fidelity" [2]. I have a python code that implements this, but in closed conduit conditions. It can be modified to work in the open channel case.

References:

Wobus et al., 2006: Self-formed bedrock channels. doi: 10.1029/2006GL027182
Wobus et al., 2008: Modeling the evolution of channel shape: Balancing computational efficiency with hydraulic fidelity. doi: 10.1029/2007JF000914


On what authority are carbon credits issued? Carbon Credits are a weird thing. Businesses can buy and sell them, and having enough carbon credits to offset your CO2 output suddenly makes you a Green Business. That being said, who issues Carbon Credits, and on what authority? Is a Carbon Credit a promise to remove an amount of CO2 from the atmosphere?

Last I checked that was a massively expensive technology still in it's infancy, but Carbon Credits have been around for quite some time.  Does it work like a Futures market ("When the tech becomes available I promise to remove 30 bln tons of C02")?

Carbon credit accreditation is a process done by independent accrediting agencies. It is comparable to the way that universities are accredited by various agencies saying that their degrees are legit. You sign up to do a project to reduce carbon output, and then the accrediting agency confirms that you did just that.

Carbon offsetting isn't a future's market, it is a (financial) commitment to a project right now that is dedicated to lowering greenhouse gasses. Here is a list of potential projects, and here is a map showing projects in progress with a certain company.

I'm actually really glad you asked this question, because I just assumed that carbon offsets were effective proven means, like planting trees. But looking at some of these projects is bringing up some doubt in my mind. I don't see how burning methane into CO$_2$ is doing anything except turning a larger short-term problem into a smaller long-term problem. Or how to measure the exact number of tons of carbon you are saving by changing domestic behavior.


ECMWF data as WRF input I have earlier used FNL, CFSR, Reanalysis-2 data set as input in WRF. However, I am finding it difficult to download ECMWF data as there are so many variables. Can anyone with experience in ECMWF let me know from where to download ECMWF data for WRF?

I need ERA-Interim Project to input into WRF. I have the link, I just don't know which variables to download and how to input in WRF.

For any of the basic forecast runs (10 day, ensembles, monthly/seasonal forecasts), I do not believe ECMWF data access is general controlled to ECMWF.INT.  Generally most data, including anywhere near enough to use in a WRF forecast, is only available for purchase at extreme fees (generally we're talking 5+ figures per year).  The only option you might have is if you are doing your modeling for strictly research purposes, in which case you may qualify for a research license at reduced or free cost, or be able to access it from servers at the institution you are associated with.

It does appear that reanalysis data and various other specialized products are available free with an account at their website as described here.  I believe reanalysis would only get you initial conditions which I don't believe is sufficient to run a mesoscale model like WRF(?), and that they are also poorer quality/resolution (please correct me if I'm wrong on any of these beliefs!!)  Archived actual ECMWF output is still pay (see the bottom option on the license page).

I worked with ECM for a few years while producing content at StormVistaWxModels and definitely indeed found most things with them to be quite a challenge, limitation, and pity!  At the time it was fairly abstruse to find what you needed or communicate with them, though it appears to have improved some.


How will climate change affect the latitudinal distribution of precipitation over each latitudinal region? In other words... How will it affect precipitation in the tropics? The mid-latitudes? And the polar latitudes?

I'm interested in both the mean and variance of the precipitation.

The continued trend of a warming climate that is expected due to increased GHGs will lead to a net increase in total moisture, since the atmosphere can hold more water vapor at higher temperatures.  In general, the equatorial zones and poles will have a net increase in precipitation while lower mid-latitude zones will have reduced precip, with the rain belt moving poleward.   Climate models generally show a pole-ward shift of extra-tropical precipitation because the increased heat energy allows convective systems in low latitudes to loft the convective air higher up, which in turn leads to greater horizontal transport (generally poleward) before air completely descends and contributes to the development of an associated storm system. You can also expect the poleward shift since cold temperatures accelerate the precipitation process, and since systems will have to travel a little further poleward to reach those cold temperatures.

A 2014 IPCC Technical Summary figure (below) shows change in precipitation forecasted ~65 yrs into the future.  The image on the left represents a best-case scenario if we reduce carbon emissions while the right represents more of a business-as-usual scenario.


Is there a method to determine the point rainfall intensity for small catchments? I need to design a weir for a small earth dam in an arid area with a small (smaller than 200 ha), fairly flat catchment area in southern Africa. The idea behind the dam is to collect not more than 10 000 cubic metres of water for small stock watering purposes for the immediate time after the rainy season, somewhat reducing the dependency on ground water.

The challenge lies in applying the "rational method" (hydrology) where time of concentration is the determining factor to determine the peak flood. This method however was developed for larger catchment areas.

Is there an alternative to the rational method for smaller catchments, or alternatively an adjusted methodology?

The rational method is especially usefull for small areas. For larger catchments it is less accurate. Then you should use a rainfall-runoff model but that is only possible when you have sufficient data. A more simple method is the use of runoff coefficients. Maybe something like the SCS method.


Need help understanding variables that relate to meterology terminology I am working on a project in predicting the weather and I had a few brief questions.

I understand that radar works by bouncing waves off of precipitation and measuring reflectivity. I have a variable and the definition for the variable is as follows, "10th percentile of reflectivity values in 5x5 neighborhood around the gauge." Can someone please explain this? I am guessing that this means it measures the strength of the signal returning from a 5x5 area around the measuring gauge? Is this correct? What does it mean that it is in the 10th percentile? The 50th percentile? The 90th?
The next variable is, "Maximum reflectivity values in the vertical column above gauge in dBZ". I know that dBZ is used to measure reflectivity, but what does it mean in the vertical column above the gauge?
I understand Correlation Coefficient to be the measure of how similarly the horizontally and vertically polarized pulses are behaving within a pulse volume. Can someone please tell me what a pulse volume is?

I really appreciate any help. Most answers I found through my own digging, but I really need help to understand these few questions.

Here are the answers that I received for anyone interested:

1) Regarding the question about 10th percentile: The 10th percentile of reflectivity in a 5x5 neighborhood of the gauge means that they take the 25 reflectivity values surrounding the gauge (horizontally), sort them, and return one of the lowest values. The table in the attached image shows an example of this. In this case, the gauge is assumed to be in the green box, and bold value to the bottom right is the 10th percentile value returned by Excel.

2) Regarding the question about the vertical column: The radar scans at multiple elevation angles (between 0.5 and 19.5 degrees above horizontal), and so each one of those scans will be at a different height when it passes over the location of the gauge, sampling a different set of particles (rain, hail, etc). So the vertical maximum reflectivity at that point is simply taking the maximum value at the gauge location from all the available elevations within a complete set of scans. This “maximum reflectivity in the vertical column” variable is sometimes referred to as “composite reflectivity”.

3) Pulse volume refers to the volume of air that is sampled by the radar beam at a given instant. This volume is defined by a horizontal extent, a vertical extent, and a range extent. The horizontal and vertical extents are determined by the characteristics of the antenna and the range being considered. For most radars, this cross-section is circular, since the horizontal and vertical beamwidths are the same, often around 1 degree. The range extent is determined by the amount of time the radar transmits between periods of listening. The physical length of the pulse is the speed of light times the amount of time the pulse is being transmitted, and is typically on the order of a couple hundred meters. The formula for pulse volume is pi(range*vertical beamwidth/2)(rangehorizontal beamwidth/2)(pulse length/2).


What causes the colors seen during a sunset / sunrise? What causes the typical red, pink or orange colors seen in sun-rises and sun-sets?

How come the sky doesn't just turn a darker blue?

There are many references about this on the web, such as Wikipedia and the NOAA site.

At sunrise and sunset the angle the Sun's light makes with the Earth at those locations is low compared with angle the light makes at midday. Because of the low angle, the light has to travel through more of the atmosphere before it reaches the Earth's surface and the eyes of anyone watching either the Sun rise or the Sun set.

The colour of the Sun's light is white, being composed of the colours of the light spectrum: red, orange, yellow, green, blue, indigo and violet. The wavelength of these component colours are all different. Red has the longest wavelength at 650 nm. Each of the other colours have shorter wavelengths with violet having the shortest at 400 nm.

As the Sun's light passes through the atmosphere it get scattered by the air molecules and particles in the air such as dust and aerosols.

Due to a phenomenon known as Rayleigh scattering the shorter wavelengths of light (greens, blues, violets) are scattered first, leaving the shorter wavelengths (yellows, oranges and reds) to travel further.

The greater the amount of particles in the air, dust and aerosols, the greater the degree of scattering and the more red the sunrises and sunsets will appear. This is particularly evident after large amounts of ash have been ejected by volcanoes, after large forest fires and in locations where air pollution, particularly from industrial chimney stacks and internal combustion engines from road vehicles is a major source of airborne particulate matter such as soot or ash and other very small products of combustion


What is the amplitude of the largest internal wave ever observed? I have read from Vlasenko et al. (2014) that the largest amplitude of an internal wave recorded in the Celtic Sea is 105 m. Is this the largest ever or have any larger ones been recorded elsewhere (eg. the Hawaiian mid-ocean ridge maybe)?

I believe the largest internal waves ever recorded in the ocean were observed in the South China Sea (SCS). The diagram above is from Alford et. al (2010) - see the two ridges near A1 and N2? The gap between them is just the perfect size so that the barotropic tide can interact resonantly and give rise to very long internal tides which radiate away towards MP2 and eventually shoal (they also go the other direction but we ignore that since it's more or less the open ocean).

The internal tide is very long, but its amplitude is not that large. However, as the internal tide shoals it fissions into a train of solitary waves. The leading solitons in the wave train are larger in amplitude but smaller wavelength than the original internal tide that gave rise to them. Each soliton propagates at its own speed with the largest amplitude wave propagating faster. As the amplitude of each individual soliton grows, the fluid velocity will eventually exceed the wave speed and the waves will break due to convective instability (overturning). Thereby depositing their energy nearshore, far away from the generation zone.

The largest amplitude wave measured in this study was around $200$~m, measured at LR2. But I am pretty sure I have seen other studies with larger amplitude waves in the SCS.


Why do the dry and moist adiabatic lapse rates converge with height? Near the surface, the slope of the moist adiabats are much steeper than dry adiabats due (as I understand it) to the the latent heat released as water vapour condenses. The difference is amplified at greater surface temperatures because warmer air can hold more moisture.

Why then, are the two lapse rates very similar in the upper atmosphere? My best guess is that condensation stops for some reason, but I'm not sure why this would be the case.

If you look closely at the diagram you'll notice height isn't the primary cause for the convergence between the adiabats, though it is the driver.

Note that toward the upper right there is still appreciable difference between the adiabats and as you move to the left the height they converge at decreases.

The reason for this, as your intuition suggests, is that condensation ceases. The reason, simply, is that there is no more water left in the parcel to condense and release latent heat.

Recall the lines of constant water vapor mixing ratio (the lines you use to connect surface dewpoint to the LCL). These lines decrease to toward the left and are sloped steeper than the isotherms. As moist parcels ascend the latent heat release is correlated to decreasing water vapor. At some point we exhaust the water vapor and any further ascent cools at the dry adiabatic lapse rate as there is no more condensation. This is what causes the moist and dry adiabats to become parallel at upper levels (higher for warmer / moist surface conditions and lower for cooler / drier source parcels).

In the comments, concern was expressed that the skew-t isn't capturing the relevant physics, including how a parcel runs out of water vapor.  The skew-t does indeed capture this information and one way you can observe this is by calculating equivalent potential temperature, $\theta_e$.  This temperature is the temperature of a parcel with all of the water vapor condensed out of it. The more moisture in a parcel, the higher the equivalent temperature will be over its actual temperature.  To calculate it on a Skew-T you raise a parcel high enough for the moist and dry adiabats to be parallel, then descend the parcel.  On the way up once saturation is reached you'll ascend via moist adiabat and once the water vapor is exhausted you descend via a dry adiabat.  You can try this for various source parcels and convince yourself that the Skew-T captures these physics.  You should note that the more moist a surface parcel is, the higher it must ascend and the warmer the equivalent temperature will be.


Debunking scientific paper "Has global warming already arrived?" I read the IPCC reports, I know global warming is happening and is man-made.

But as any skeptic should do periodically, I went to a few climate deniers websites and stumbled upon this peer-reviewed scientific paper, published in "Journal of Atmospheric and Solar-Terrestrial Physics":

https://www.sciencedirect.com/science/article/abs/pii/S1364682618305030

The paper is coming from Costas Varotsos, a Greek physicist known from his contribution to the global climate-dynamics research and remote sensing.

The full paper is here:
https://sci-hub.tw/https://doi.org/10.1016/j.jastp.2018.10.020

It's too technical for me to point what the mistakes could have been made in that paper.

The only counter-argument I found on the web is a comment about it on the skepticalscience website:
https://skepticalscience.com/news.php?p=3&t=103&&n=292#131401

Could anyone translate that comment in less technical terms for me ?

The comment is saying that the authors are making a fallacy as follows:

Temperature increase will be associated with an increase in tropopause height.
Using instrument/dataset X, we fail to measure a tropopause height increase.
Therefore, there is no temperature increase.

The fallacy here is that instrument/dataset X is not suitable to measure tropopause height, therefore one should not expect it can measure a tropopause height increase.
The comment is referring to the University of Alabama in Huntsville temperature dataset.  This is derived from satellite microwave temperature sounders¹.  From the Wikipedia article, this dataset provides:

UAH provide data on three broad levels of the atmosphere.

The Lower troposphere - TLT (originally called T2LT).
The mid troposphere - TMT
The lower stratosphere - TLS

The tropopause is the boundary between troposphere and stratosphere.  It can be defined in various ways, but to measure tropopause height you generally need to measure the temperature in the vicinity to the tropopause.  As this is apparently not provided by the dataset, it is impossible to use the dataset to measure tropopause height.

¹From personal experience, I can tell you that it is difficult to determine long-term temperature triends from satellite data.  Polar-orbiting satellites in sun-synchronous orbits experience a drift over time, which means that their local time ascending node changes; in lay terms, this means that when they previously always passed at 14:00 over a certain spot, 2 years later this may be at 16:00.  Even if that time wouldn't change, instruments degrade over time and get replaced by new instruments.  You need to be very careful to make sure you're detecting a trend in the temperature and not in the instrument itself!  I've worked on this in the FIDUCEO project, I was doing infrared temperature sounders and colleagues from Hamburg were doing microwave humidity sounders, but microwave temperature sounders were out of scope because none of us had the depth of expertise needed.  Even with the expertise, we underestimated the difficulty of the problem and ran out of time before we could properly declare we had delivered what had been promised to the funding agency, although we learned a lot.


What is the difference between N-MORB, E-MORB and OIB? What are the differences between N-MORB, E-MORB and OIB with regards to:

Tectonic setting
Geochemical features

There are several types of basalts, but I can't find a clearly explained article.

The nomenclature is confusing and recent studies have shown that among mid-ocean ridge basalts (generally called MORBs) that  normal mid-ocean ridge basalts (NMORB) should reflect the statistically usual composition while enhanced MORB (EMORB) and depleted MORB (DMORB) should reflect end-members of the MORB population.  Gale et. al 2013 proposes the use of the term NMORB to refer to the most likely basalt composition encountered along the global ridge system distant from hotspots. The NMORB is given by the lognormal mean of the compositions of ridge segments more than 500 km away from plumes excluding back-arcs.  Contrary to some literature discussion,  NMORBs are NOT depleted in trace elements according to this Gale's work and so linkage between the idea of depletion and NMORBs should be broken.

Gale et.al propose the term DMORB to recognize trace element depleted basalts. DMORBs would not be considered representative of the upper mantle or ocean crust nor would they be commonly found in ridge systems.  Finally, EMORB would refers to incompatible trace element enriched NMORBS via a statistical definition found in Gale et. al.  This statistical definition is due to the fact that current data does not allow clear spatial linkage of EMORBs to any particular form of ridge or plume system or island located near to both.

A good example of an EMORB system is given by Iceland where the rate of magma production has caused volcanism to build the oceanic ridge above sea level.  In this environment, the predominant basalts are also tholeiitic basalts, but there are higher concentrations of incompatible trace elements. EMORBs are enriched in incompatible trace elements such as K, Ba, La, Rb compared to NMORBs.  By incompatible, one means elements that do not fit easily into the crystal structure of mineral elements in the mantle and are usually not found in upper mantle derived rocks because they are preferentially ejected into the melt.

See this paper The mean composition of ocean ridge basalts - Gale - 2013 for a detailed discussion.

Generally, all MORBs are tholeiitic basalts occurring in oceanic spreading centers, such as an ocean ridge away from hot spots and back-arc basins. At these spreading centers, a relatively small range of chemical compositions of basalts are erupted to form the basaltic layer of the oceanic crust.  The main melting mechanism is likely decompression melting due to rising convection cells moving upward through the mantle beneath the ridges. The composition of these basalts typically ranges from olivine to quartz tholeiites. Tholeiitic magmas are sub-alkaline, meaning they contain less sodium and potassium than other basalts and can be distinguished from other basalts by the redox state of the magma from which they crystallized—- tholeiitic parent magmas are reduced whereas calc-alkaline parent magmas are oxidized.  All three NMORBS, DMORBS, and EMORBS share common chemical compositions (ordered by decreasing wt%) of SiO2, Al2O3, MgO, FeO, CaO.  They also share a common mineralogy of plagioclase, pyroxene and olivine. The plutonic equivalents to a tholeiitic basalt are diorite, gabbro, and anorthosite.

For the next section, this is a great reference!

Oceanic Island Basalts –basalts associated with islands in the ocean basins that generally occur away from plate boundaries, and are often associated with hot spots.  Most oceanic islands appear to be related to ascending plumes of hot mantle which operate independent of the main convection cells that ascend beneath ocean ridges and descend at subduction zones.  A wide variety of rocks occur in these islands, not all are basaltic, but all appear to be related to upper mantle melts.  One may find tholeiites, alkaline basalts, Hawaiites, trachytes and rhyolites in an OIB environment which span the compositional spectrum of magnesium, iron and the alkaline elements. From a melting perspective, low pressure environments tend to produce the tholeiitic magmas and high pressures are required to derive alkali basalts.  OIB mantle sources are enriched in incompatible elements and demonstrate a wider variety fractionization than MORBs. How does this occur?  a recent theory for OIB sources posits that subducted lithosphere sinks to the core/mantle boundary and mixes with the mantle to produce an enriched mantle which heats and rises in narrow plumes which channel this enriched mantle melt upward producing hotspots which produce the compositional variety of OIBs observed.


How do we use oxygen isotopes as temperature proxy? As far as I know scientists use oxygen isotope 16 to 18 ratio in air trapped in glaciers (or in old foraminiftera shells) as proxy for temperature in the past. I know that $\ce{^18O}$ is heavier, and it precipitates faster, and $\ce{^16O}$ is lighter, and it evaporates faster.

I understand that when it's warmer, there is more evaporation and more heavy isotope left in water. Vapor moves toward poles, where it falls as rain or snow and goes back to water (this doesn't count) or stays in glacier for hundreds of thousands of years.

So when it's warm, we should have more $\ce{^18O}$ in ocean sediments, and less in arctic glaciers, right? So more $\ce{^16O}$ (less $\ce{^18O}$) in glaciers -> warm period.

On the other hand, when it's cold, precipitation occurs earlier while air moves to the poles, and heavy isotope falls down earlier, on bigger latitudes. In the air that goes to the poles there is only little heavy isotope left. So more $\ce{^16O}$ (and less $\ce{^18O}$) in glaciers -> cold period. This is contrary to the above. So how to figure out temperature from ice and sediments cores?

This is somewhat a general answer.  According to the Royal Chemical Society webpage Chemical climate proxies (Evans, 2013), the rarer and heavier $\ce{^18O}$ isotope in water generally evaporates after and condenses (and precipitates) out earlier than the lighter and more common $\ce{^16O}$ isotope, shown in the diagram below:

Source: University of Michigan's page Past Climates on Earth

The colder the environment, the quicker the atmospheric water vapour condenses, hence the quicker the $\ce{^18O}$ isotope is depleted, giving a lower ratio of $\ce{^18O}$ to $\ce{^16O}$ (referred to by the RSC page as $\delta{\ce{^18O}}$) by the time it reaches the poles.  In contrast, a warmer environment would mean that the water vapour condenses later and slower, meaning that less $\ce{^18O}$ laden water vapour condenses, resulting in a higher $\delta{\ce{^18O}}$ value.

In short, it is not so much of the amount of $\ce{^16O}$, but rather the ratio of $\ce{^18O}$ to $\ce{^16O}$ isotopes present, otherwise known as $\delta{\ce{^18O}}$.

The following Earth Observatory diagram demonstrates the present-time process, showing the differences between warm and cold environments:

Source: Earth Observatory's page: Paleoclimatology: The Oxygen Balance


By how much can rain temperature vary from the ground-level air temperature? I'm guessing that falling rain equilibrates fairly quickly to the temperature of the air it's falling through. However, it isn't always at the exact same temperature, which is why we can get the lovely phenomena called "freezing rain".

How far below the ground-level air temperature can rain be?

Rain is slightly cooler than near-surface temperatures because it condenses at higher altitudes where the air is colder. Thus rain tends to reduce the temperature difference between the surface and higher altitudes. This temperature difference is the free-energy or exergy source that ultimately drives convective weather systems and storms, and is expended or diminished by their operation. Usually the temperature of rain is only a few degrees cooler than that of ambient air by the time it falls to the surface. An extreme example is hail --- because of the large size and rapid fall of hailstones they can reach the surface still frozen even in midsummer. By contrast, freezing rain is often a different phenomenon. Freezing rain often results when rain originating in a warm air mass aloft falls through a subfreezing air mass near the surface, as typically occurs ahead of an advancing warm front.


Lake outflow forming a "reverse delta"? While rivers often form a delta when they flow into a lake, the outflow of a lake is usually a single stream.

Are there lakes where the water flows off in multiple channels that merge into a single stream? If so, why does this happen, and what is it called?

When the flow of water in a river accelerates, it can pick up more sediment from the river bed and transport it downstream. Alternatively, when the flow slows down, the transport capacity drops and the sediments suspended are deposited on the river bed.

When a river goes into a lake, it transitions from the fast-flowing regime in the river to a very slow flow in the lake. Therefore, sediments are deposited as a result of the slowdown, forming a delta.
The inverse happen at the outlet of the lake, where the water accelerates. Therefore there sediments tend to be picked up and transported downstream, not allowing to the formation of a delta.

However, this only partially answer your question, because the terrain around lakes is very often flat, one would might expect to see plenty of examples of lakes being drained by multiple rivers. The answer to this is that multiple rivers in parallel are unstable: if one of the rivers becomes slightly larger, it will have more and faster flow. Therefore, it will increase its capacity to transport sediments, digging into its bed and growing even bigger. If it grows bigger, the sediment transport will increase further and the river will grow even more. This positive feedback leads to the grow of the largest outlet at the expense of the smaller ones, until you have only one river outlet.

However, it takes time for one outlet to monopolize the flow. And in very flat and changing terrain you can find lakes drained by a delta. One example of this is the proglacial lake of Kaskawulsh glacier in the Yukon Territory, Canada:

This lake is in a divide. And it is drained not by one, but by two deltas. Interestingly, the Slims river in the top of the picture has reversed its flow direction in historical times.

In this NASA Earth Observatory article, you can find out more about this interesting river and some great images, plus comparisons of how the flow regime has changed in the past.


Confusion about grid registration concepts and their relevance in modelling I'm trying to make use of the ETOPO1 dataset as the bathymetry input of a wave model. I came upon this discussion of grid registration: Registration of Structured Square-Cell Grids.

I read this material several times and I'm still confused about some things. From what I understand of the diagram on that page: the blue dots represent the data values. We know from the dataset what the latitude and longitude of each of the blue dots is. And for each blue dot, it is always in the center of the cell, which is the area it represents. If I'm right so far, what is the difference or significance of these two schemes? What is the purpose of the red lines? Why might there be an ambiguity, since we already know the locations of the blue dots and the data values at those locations? Does it affect how we interpret the data?

If anyone can help me with this, or point me to relevant resources, it would be much appreciated.

Yes, it makes a difference. In this case the grid-registered dataset is higher fidelity. However, the cell-registered is easier to handle.

As you see, both types of data are available on the dataset's page. The page states:

  The grid-registered is the authoritative registration.

The page also points out:

  The cell-registered is derived from the grid-registered,
  and the conversion produces slightly flattened relief.

So what's the difference? The grid-registered version puts the data points at the grid corners (the red lines, not the grey squares, define the grid boundaries. You have to imagine the grid cells in the left-hand image). So if there are $n \times m$ grid cells, there are $(n+1) \times (m+1)$ data points in the grid-registered data.

Since there are fewer data points in the cell-registered version, making it involves some smoothing (averaging) of the values in the grid-registered version. There's an illustration of this effect on the other page you linked to; notice how the centre cell of value 90 ends up being smoothed away:

So if accuracy is paramount, you should use the grid-registered version.

But...

You might find cell-registered data more convenient to work with (for me at least it's more intuitively analogous to an image).

The catch is that if you have grid-registered but accidentally treat it as cell-registered, then the data will shift by half a cell. So you should keep careful track of what kind of data you have. As the NOAA page states:

  Most grid applications recognize both types and avoid [the grid shift]
  problem but care should be taken.

Indeed, one popular open source GIS tool, GRASS, apparently only handles cell-registered data, as explained in the GRASS wiki. So after loading (to wherever) you should check where the pixels of the raster actually end up.


What caused a measurable patch of Mt. St. Helens' ash to be deposited across Oklahoma? Looking at the ashfall distribution map from the 1980 eruption of Mt. St. Helens (below), there is a measured 'patch' of ash depth significant enough to be measured occurring in Oklahoma.

What caused a measurable patch of Mt. St. Helens' ash to be deposited across Oklahoma?

I will propose an explanation. From experience I would say it have something to do with the US meteorological systems (systems as in masses of air) active the 18th of May 1980 and the week(s) after.

A bit of background : air masses can be high pressure (cool, and stable) or low pressure (warmer, more energy, more volatile, less stable). The next figure show in red a low unstable and warm system, and in blue a cool, stable system. (full website here)

Further, let's take into account the meteorological nature of Oklahoma - as an area in a volatile sector, where warm wet air masses from the gulf collide with colder, dryer masses from the west and the north - area part of what is broadly know as the tornado alley. On the wiki page for OK we see a typical system condition favorable for volatile weather. Green masses are warm, blue are cold and red is where the action is likely to occur.

Tornado or other frequent wild weather events are the result of a clash between those widely different air masses, temperature, moisture and pressures often leading to storm cells or other unpleasant windy/stormy situations.

Now let's get back to our volcano. I found those daily meteorological maps from the NOAA. When entering the proper dates, let's say 18th of May 1980 and the week after, we see the various systems in action. To keep things simple, I picked the 18th of May, and  the 21st.

The 18th of May there was a low pressure system about right over the volcano - which was ideal to transport and displace a lot of ashes very far. The 20th, at 7:00 am, there was a Low in formation over Oklahoma which would become full fledged the 21st (see figure) and there was bad weather that day over Oklahoma City because of clashing cell. Eventually causing precipitation (rain and ash?).

I am not a climate-meteo-specialist, but I have good confidence that this scenario could explain a part of the reason why there is ash in Oklahoma.


At what humidity does it start to rain? As far as I understand it is perfectly valid for air to have 100% humidity. At that point, all water can still exist in form of vapor, non-condensed.

Does it immediately start to rain if humidity is >100%?

If so, why do we have slight rain and heavy rain if any 0.1% above 100% drops out immediately? That should always be only a small amount of rain and rainstorms could not be explained.

If not, what is the limit of humidity if not 100% and why can it exceed 100%?

I have tried to understand the Wikipedia article but I'm stuck in various places:

  Water vapor is the gaseous state of water and is invisible

Invisible to me would mean that clouds are excluded from humidity.

  Absolute humidity is the total mass of water vapor present in a given volume of air.

That again makes me think a cloud must be included.

  The humidity is affected by winds and by rainfall.

Rainfall certainly decreases humidity, but it is not stated at what percentage it starts to rain.

Short answer: humidity is not a proxy for rain starting and no, it does not start raining automatically when 100% humidity is reached (haze or clouds can form though).  The onset of rain is dependent on many things including humidity, but a specific value of humidity is not a sufficient condition for rain.

Water vapor is a gas and invisible.  The amount of water vapor in the air can be expressed as relative humidity (RH) which is the ratio of water vapor pressure ($e$) and saturation water vapor pressure ($e_s$).  Saturation vapor pressure is the partial pressure of vapor when evaporation and condensation rates are equal, represented by RH=100%.  When RH > 100% net condensation occurs, but water has its own ideas.

In a mixture of pure dry air and water vapor, water will not condense until around 400% RH.  Reasons for this are a bit complicated but it has to do with very small droplets being more likely to evaporate as their curvature is very large (Kelvin effect, saturation vapor pressure is higher over curved surfaces than flat ones).  Luckily for us, our atmosphere is not pure air but has small particulates suspended in it (aerosols).  Some of these aerosols are classed as cloud condensation nuclei (CCN) and enable droplet formation at lower relative humidities.  These work by forming a solute in water increasing the energy needed to break bonds and evaporate the water (Raoult's_law)

The combined interaction of these are described by Köhler theory and describe droplet growth in terms of drop size, solute and supersaturation (RH-100%).  In a nutshell, there is a critical drop size below which drop size decreases for decreasing supersaturation and above which drop size increases for decreasing supersaturation.  The critical supersaturation is the supersaturation needed to attain the critical drop size, and is generally small (e.g. 0.3% supersaturation).

Droplets below the critical size are 'haze drops' and these make up the haze you see on very humid days.  Drops that reach the critical size can continue to grow to become cloud drops.  The condensed water is carried in the air but is no longer water vapor and is not part of relative humidity (but does contribute to the parcel density)

So... when does it rain?

It rains when water vapor is in the presence of CCN, driven to a supersaturation causing growth to the critical drop size (on the order of $\mu$m) and continuing to grow to cloud drops and further to the much bigger drop sizes that make up drizzle (100-300 $\mu$m)and rain drops(mm), a process that takes around 40 minutes.  Drops will grow until the updraft can no longer support their mass and then they fall from the cloud as rain.

Your question asks at what humidity does it rain, but what surface humidity determines is how high the cloud bases are.  When the dew point depression (the difference between temperature and dew point) is high, the cloud bases will be higher than when the dew point depression is small.  As air rises it cools, and at some point 100% RH is attained.  If there is forcing for vertical ascent, parcels can rise to this height and then to a height where they freely convect due to decreased parcel density caused by the release of energy during condensation (see: CAPE).

So far to have rain we've needed water vapor (but not at 100% at the surface), aerosols to aid condensation (CCN) and a way to cool the air to reach 100% RH via lifting.  It is these three things -- moisture, aerosols and cooling, that we need for a rain storm.  We can have 100% RH days that are just hazy or foggy that do not rain and we can have days with mextremely little RH (e.g. deserts) that result in little rainstorms or large severe storms.  We also have storms we call 'elevated convection' that are completely disconnected from surface conditions and when these storms cause rain is not related to surface humidity at all.

If you are looking for a magic trigger for rain, your closest bet will be looking at temperature, dew point and the height parcels need to attain to freely convect (LFC).  If there is forcing for parcels to get that high and instability above, then rain is a good bet.  Forcing for lift can be anything from convergence along a boundary (sea breeze, cold front, outflow from another storm), orographic lifting (mountains, hills), thermally or dynamically forced.

To address your specific concerns:

  Water vapor is the gaseous state of water and is invisible

    Invisible to me would mean that clouds are excluded from humidity.

Correct, clouds are not part of humidity, they are suspended liquid water drops, usually condensed onto a solute of some kind.

  Absolute humidity is the total mass of water vapor present in a given volume of air.

    That again makes me think a cloud must be included.

Water vapor contributes to humidity but water vapor does not include liquid water.  Cloud water, ice, snow, rain, grapple, hail all contribute to the total mass of a volume of air, but are not humidity.

  The humidity is affected by winds and by rainfall.

    Rainfall certainly decreases humidity, but it is not stated at what percentage it starts to rain.

Humidity will increase during a rainstorm as rain and puddles evaporate.  Temperature will decrease toward the wet bulb temperature.  As noted in the answer, there isn't a magic number of %humidity that causes rain to start.


Is Iceland an example of a hot-spot overlying a mantle plume? Iceland has been cited as the location of a hot-spot overlying a mantle plume (similar to that of the Hawaii chain in the Pacific), though for some time this model has been challenged (see Gillian Foulger's mantle plumes site, especially Lundin & Doré's article).

How does the recent announcement by Torsvik et al. (2015) — that south east Iceland is underlain by continental crust — affect this debate?

Reference

Torsvik, TH, et al. (2015), PNAS online 30 March 2015. DOI: 10.1073/pnas.1423099112

Yes, Iceland is an example of a hotspot overlying a plume. The plume has been imaged seismically, e.g., see the Science paper (Figure 3) by Montelli et al. (2004). It is available at http://www.sciencemag.org/content/303/5656/338

The 2015 paper you referred doesn't dispute that claim. All is says is that "The plume split off a sliver of continent from Greenland in the Early Eocene. This sliver is now located beneath southeast Iceland where it locally contaminates some of the plume-derived magmas".


Why is lithium so unevenly distributed? According to the US Geological Survey, nearly all of the world's lithium reserves are in Chile/Argentina, China, and Australia. Why is this? Lithium seems to be mostly harvested from brine pools, so are these just the areas where lithium can be economically harvested, or does it represent an uneven distribution in Earth's crust?

The term "reserves" doesn't mean what most people think it does.  A mineral deposit is simply a concentration of a mineral; a reserve is a deposit that is both known and economical to extract.  As an example, oil shale and tar sands have both been known for decades, but only recently became oil reserves as improving technology and rising prices made it practical to extract the crude oil from them.

Chile, Argentina, Australia, and China have quantified their deposits, and local economic/geologic conditions make it profitable to extract those deposits, so they've got most of the world's reserves.


Is there a way to find the direction to land in the middle of an ocean? Can I find the direction to land when I am in the middle of the ocean and can not see any land?
This is a theoretical question.
Any method that doesn't use over-technical methods such as smartphones and GPS will do.
Example: Ocean current direction, wind direction, fluctuation in temperature, etc.

Your best bet without modern tools would be a sextant and the proper maps for celestial navigation.  This is a time-tested and old method of navigation no longer in regular use, but it probably doesn't meet your "no over-technical methods" criterion as it requires a tool, maps and knowledge of its use.  If you only had knowledge of the constellations and a few stars (e.g. Polaris, the Sun) you could probably figure out what region of the globe you were on and make a best-guess as to the direction of land.

You might be able to do a similar guess with surface winds, ocean surface flow and temperature to get a rough location but if any synoptic conditions are masked by storms or local anomalies then this will likely not work.  There are some semi-presistent weather features (e.g. the Bermuda high) that you could use along with knowledge of the general circulation that could potentially help you out.  You could make similar estimates with ocean current and temperature (if you have equipment to measure this), but I think this would only provide regional benefits and may not work everywhere you could find yourself.  These would also be marred by tropical convection (e.g. in the wake of a hurricane sea surface temperatures will be cooler than normal) and other storms.


North Atlantic Oscillation (NAO) future prediction - Academic papers? I am looking for academic papers which show future predictions of the North Atlantic Oscillation (NAO) by considering climate change and the various emission scenarios. Do you have any suggestions?

A good start is the article by Goodkin et al. (2008) that relates past fluctuations of NAO to climate variability and argues that in the late 20th century NAO changes are much more dramatic as a result of enhanced energy (temperature) in the northern hemisphere. (Source WHOI)

Visbeck et al. (2001) describe the complex relationship between NAO and climate change associated with greenhouse gases:

  Because global average temperatures are dominated by temperature variability over the northern land masses, a significant fraction of the recent warming trend in global surface temperatures can be explained as a response to observed changes in atmospheric circulation. Because the NAO is a natural mode of the atmosphere, one could argue that much of the recent warming is not related to the build-up of greenhouse gases in the atmosphere over the past century. This viewpoint, however, ignores the possibility that anthropogenic climate change might influence modes of natural variability, perhaps making it more likely that one phase of the NAO is preferred over the other.

As for predictions of the future effects cause by emission scenarios, that seems to be an ongoing topic of research. A couple of good starting point might be Yeager et al. (2012) and the book chapter by Hurrell et al. (2013) on the effects of climate change on NAO.


Is it possible that the geomagnetic field reversal led to the extinction of Dinosaurs? Is it possible that the geomagnetic field reversal with a weakened geomagnetic field over centuries if not thousands of years (according to the Pittsburgh simulation: https://www.psc.edu/science/glatzmaier.html) and exposure both to cosmic radiation, solar storms and continuous meteor bombardment, multiple "norths and souths" and deregulation of the biospheric clocks e.g. migratory paths of birds and animals using the geomagnetic field for navigation etc., raised volcanic and tectonic activities led to the extinction of Dinosaurs?

Between Matuyama Epoch of 243 million ya to 68 million years ago to Brunhes-Matuyama current epoch

Mark's answer is correct, but in my opinion is not clear enough. Let's make it a bit simpler:

  Is it possible that the geomagnetic field reversal led to the extinction of Dinosaurs?

NO, DEFINITELY NOT

Here's why:

The cause for the K-Pg extinction event (in which many living species, including dinosaurs, died) is well known: volcanic eruptions (the Deccan Traps) and an impact (Chicxulub). It's still debated which one contributed more to the event, or whether one is the result of the other, but that's not the point. It's not related to magnetism.

In fact, all big five extinction events in Earth's history are well linked to increased volcanic activity (including the Siberian Traps at the time of the largest extinction, the P-T extinction event aka the "great dying").

On the other hand, magnetic reversals happen all the time. Yet, there are no extinctions related to them. Your question also lists several incorrect assumptions:

  continuous meteor bombardment

Incorrect: Geomagnetic reversals have no effect on whether we are bombarded by meteors or not.

  raised volcanic and tectonic activities

Incorrect: Geomagnetic reversals are not linked to raised volcanic or tectonic activity.

  Between Matuyama Epoch of 243 million ya to 68 million years ago to Brunhes-Matuyama current epoch

These are recent magnetic epochs from the Pleistocene, only a few million years ago. Thus unrelated to the K-Pg extinction event (or any event for that matter).


Are coral reefs a Biochemical Sedimentary rock? Wikipedia says

  Biochemical sedimentary rocks are created when organisms use materials dissolved in air or water to build their tissue. Examples include:

And then lists Limestone, Coal and Chert.

I'm wondering whether Coral reefs, built by coral polyps, are a sedimentary rocks. They seem to fit the "Biochemical" category on Wikipedia.

Yes, limestone indeed is "biochemical".

The main categories of non biochemical sediments are sandstone, mudstone, shale, conglomerate,.. if you put the Sahara for example under lithification it will become sandstone, since it consists mostly of quartz.. almost all continental sedimentary rocks are "non-chemical" they just vary by the components, whilst most marine sediments are biochemical, as you say..they consist mostly of carbonate and aragonite skeletons (shells in most cases) of dead animals.. that's what makes up limestone.. the main corpus of coral reef is a good example for mostly pure limestone.. The carbonate classification is based on the amount (and form) of the skeletons.. You should have a look at it, if that's interesting to you.
Coal, as you mentioned, would be another biochemical sediment but it's not only made of skeletons but the pure organic matter of dead animals, but it's genesis is rather complicated..

So to answer your question: Yes, coral reefs are biochemical sediments and very important ones, too, since they grow really fast!
As noted in your quotation: Biochemical sedimentary rocks are created when organisms use materials dissolved in air or water to build their tissue!
That's exactly what the mentioned polyps do.. You can also have a look at stromatolithes build by cyanobacteria.. that's a nice and understandable example to understand how that works.


Spectral Whitening, Seismic Interferometry What is the role of spectral whitening in the processing step done before cross-correlations in seismic interferometry?

I'm not an expert on this topic. But my understanding of seismic interferometry is that we try to obtain the 'Green's function' between various receivers. This Green's function is the equivalent of sending a spike pulse (i.e., delta function $\delta$) at one receiver, and recording the result at the other receiver. Once we have plenty of these Green's functions, ideally surrounding an area of interest, we can compute arbitrary Green's function recordings by evaluating a set of convolutions (rather than carrying out computations). It will be as if there is a recorder anywhere we want to record the signal.

In the time-domain, this $\delta$-spiked source is a source that's on for an infinitesimally small amount of time before switching off again. As you can maybe imagine, this source will have an infinitesimally small wavelength. We will thus be able to see every modulation of the signal as a single identifiable event in time: a scatter of amplitude $A_1$ happens after $t_1$ seconds, a reflection with amplitude $A_2$ happens after $t_2$ seconds, etc. Thus, we gain an incredibly high-resolution understanding of the medium in-between!

The frequency spectrum of such a $\delta$-spike has uniform amplitude. All frequencies are thus represented. It is called a 'broadband signal'.

In reality, we do not obtain $\delta$-spikes very often because the predominant frequencies in the data are provided by noise with a specific frequency, usually a very low one. This low-frequency, or long-wavelength, property makes the obtained Green's functions of very low frequency. Different events will smear and overlap in time. This makes it more difficult to interpret the medium from the obtained Green's functions.

Spectral whitening is a process that boosts frequencies with a low amplitude, to try and make any signal more $\delta$-pulse-like. See for example here https://twitter.com/DownUnderGeo/status/984324387720527872 for an example from active seismic exploration, how boosting the amplitude of higher frequencies (while retaining the low ones), doesn't just look nicer, but provides a considerable increase in identifiable events! The same principle applies to seismic interferometry. By filtering the data, we obtain a more $\delta$-like behavior, thus obtain a more broadband signal from a less-than-ideal signal.


How can crystal habit be determined when rock is worn and rounded? In many cases when I find interesting rocks they are worn and rounded off so the crystalline structure is not clear.

How can I determine what kind of crystal it is in those cases?

Is there a simple instrument that can be used to determine the angle of a crystal, even if it is worn and rounded?

Is there a simple instrument

A geological hammer. Seriously. Once you smash a rock, you reveal fresh cleavage planes, grain boundaries, less weathered zones, etc. The downside is that it's destructive.

  angle of a crystal, even if it is worn and rounded?

Here you're assuming that crystals that are not worn or rounded have their original crystal shape. This is rarely the case. These crystals, known as "euhedral" are the exception, not the rule. A good example is feldspar phenocrysts in granites, or some elongated amphiboles. Maybe phenocrysts of pyroxene in basalts. More commonly, crystals are just shapeless, also known as "anhedral".

A more advanced form of rock and mineral study is called petrography - this requires thin sectioning abilities and a petrographical microscope. Basic tools that exist in all geological departments at universities, but probably not accessible to amateurs.


What is the weather data covering the range of 359 to 360 degree I downloaded a grib file of oceanography (Mean Wave Period) from ERA-Interim and the longitude values give the value at the points is 0,1, 2, 3....357, 358, 359

If I have geographical coordinates that fall between the range 359 to 360 degree longitude. How can I represent them?

Thank you for your time and concern reading my question,

Sincerely,

Remember that 360° == 0°. They're the same line of longitude. So the gap between 359° and 0° is no more than the gap between 1° and 2°, and should be handled the same way.


How can flood inundation vary at the same river stage? I've always thought that river flooding would always be the same at the same river stage.  For example, if the river stage is at 20' flooding at location "x" would always be at the same depth.  However, current flood stages along the Mississippi River are not correlating with past photos at the same flood stages in the past.  I'm not aware of there being any major changes upstream that would accommodate the reduced volume we are now seeing.  We are seeing roughly a foot difference (less flooding) along a 4-5 mile stretch of the river at the same location as little as 8 years ago.  What other variables could result in different flood inundation at a given river stage?

Hydrology major here, for whatever that's worth :) Some possibilities from my readings/internships:

First I'd check the gage you're using for stage--if it's moved in the last 8 years, the stage may need to be correlated to what it would be at the former site. If it hasn't, it's more likely something changed in your stretch of channel.

If the channel has deepened at your location and not at wherever the gage is located, then you'll see less flooding. If the gage is upstream of your stretch of stream, I'd be suspicious of any new wetland areas that could accommodate water; if it's downstream, of any dam removal or other loss of channel restriction that could be allowing water to get past your site more quickly. Downstream changes in the channel could also affect your site! And if it's fairly urban, maybe the city has figured out ways to divert runoff farther downstream?


Ions & elements, which is the correct terminology to use when discussing chemical compounds in Earth Science? Different textbooks use different terminologies when discussing the same chemical compounds, for example when discussing the minerals...

Elements / Compounds

Sulfide minerals consist of metallic elements in chemical combination with the element sulfur
Phosphate are a group of minerals of one or more metallic elements chemically associated with the phosphate compound PO4

Ions

Sulfide ions (S$^2$-) bond with a number of positive ions to form the sulfides
Phosphorous in the form of phosphate ions (PO4$^3$-) binds with positive ions to form the phosphate minerals

Are element/compounds and ions the same thing?
If they are the same, why the two terms?
Which is better terminology?

I'm just after a basic understanding of how elements form rocks and being able to differentiate between this terminology is beyond my layman abilities.

Elements are just one specific type of atom. Magnesium, oxygen, sulfur, etc. These are all elements.
Compounds are several different types of atoms (that is, elements) bonded together. For example, magnesium oxide (MgO), or iron sulfide (FeS).
Ions are charged atoms or compounds (also known as species in some cases). Ions can be monoatomic (consisting of only one atom, or element) or polyatomic (consisting of more than one type of atom). Cations are positively charged (like Ca2+) and anions are negatively charged (like O2-). Polyatomic ions that occur in geological contexts are usually anions, with carbonate (CO32-) and sulfate (SO42-) being two good examples.

All ions are elements (or combination of them). Not all elements are ions. We geologists and geochemists use these terms interchangeably all the time. I think that using ions may be slightly better, particularly in the case of sulfur. Because sulfur in minerals can be either in sulfate or sulfide form, just saying "sulfur" gives little information. The properties of sulfate and sulfide minerals are completely different, so it's actually useful to know.

  Sulfide ions (S2-) bond with a number of positive ions to form the sulfides

Not strictly correct, because the bonding in many sulfide minerals is a combination of covalent and metallic bonding, and it only has a little ionic character. Still, even in cases when the bonding is not ionic (such as in sulfide minerals), we still often talk of them of ions because it's convenient and easy.

  Sulfide minerals consist of metallic elements in chemical combination with elemental sulfur

This statement is not correct. When we speak of "elemental" elements, we mean that they are monoatomic compounds (or minerals). In the case of sulfur, it will be the yellow sulfur mineral. Gold, copper and silver and other example of "elemental" minerals. Once the sulfur is bonded to other metals, it is no longer elemental. It is part of a sulfide mineral.


International Timing Zone Why not make International Timing Zone just a straight line like this?

The main reason why the International Date Line doesn't run down the 180° meridian as you have suggested is because all nations determine their own standard time zones, applicable only on land and adjacent territorial waters of that country. This date line is not based on international law, but on national laws. The International Date Line is simply just an artificial-construct decided by cartographers.

This means that any country near the date line can shift their national time to either side of the International Date Line if they wish to. There have been several historical examples of this occurring, such as when the Republic of Kiribati gained independence and acquired new islands as a part of its territory across the International Date Line. Obviously no nation wants different parts of its territory running on different dates so the government of that country will choose unilaterally to change their nations time-zone how they see fit. This creates the zig-zagging International Date Line we have today.

Though, it is worth noting that in international waters time-zones do follow the 15° wide longitudinal lines as you have suggested as being ideal.

You may find this link useful:https://en.wikipedia.org/wiki/International_Date_Line


Why has CO2 decreased in the history of the Earth? I noticed that the $\ce{CO2}$ is actually decreasing in the eon time.

My guess is lush vegetation or forests began to grow which absorbed the $\ce{CO2}$ by photosynthesis?  Would anyone give me any clue?

The short answer is that most of the Earth's original allotment of CO2 got locked up in various carbonate minerals, largely calcite (limestone, marble, and chalk).  According to this article there is currently ~800 gigatons of carbon in the atmosphere today; there is ~39,000,000 gigatons of carbon locked up in calcite minerals. All that carbon was once in the atmosphere as CO2. Rainfall dissolved CO2 into H2CO3 (carbonic acid) which then reacted with calcium-containing minerals and then precipitated out in the world's oceans where they formed early calcite deposits.If not for this process the Earth's climate would not be too unlike Venus'.


How much of the ice on earth is floating? How much of the ice on Earth is floating (such as icebergs, or perhaps all the ice up at the North Pole)?

A first-order estimate is about 5%.

This is a trickier question than it first appears because of ice shelves. Quoting from Kusky (2014):

  Ice shelves form where ice sheets move over ocean waters and form a thick sheet of ice floating on the water and attached to the land on one, two, or three sides. Their seaward sides are typically marked by a steep cliff up to 1500 ft (500 m) high, where many glaciers calve off from forming icebergs.

So they are floating, and they can be up to 2000 m thick, according to antacticglaciers.org. So they definitely make a substantial contribution to the world's sea ice fraction.

Continuing with Kusky:

  Ice shelves are found in Antarctica, Greenland, and along the polar seacoasts of the Canadian Arctic Islands. The largest ice shelves are contained in Antarctica, which contains 91% of the world's glacial ice, around 7% of which is contained in ice shelves. These ice shelves cover 50% of the coast of Antarctica, forming an area 1/10th the size of the continent.

If you don't take ice shelves into account, and only think about pack ice, you end up with about 0%, because pack ice is generally thinner than about 4 m, and so makes up a tiny fraction of global ice volume, in spite of its extensive area.

But if you do account for ice shelves, especially the southern ones, the answer must be much greater. I have not done the research to find the numbers, but the text I quoted suggests something less than 7%, so I'm going with 5% as a first-order, round-number guess.

Reference

Kusky, T M (2014), Encyclopedia of Earth Science, New York Academy of Sciences, 529 pp. In Google Books.


At the same speed, is a tornado as dangerous as straight wind? If we have a place with wind at a given speed, and a tornado at the same speed, are they equally dangerous, or the tornado is more powerful?

I'd have to say a tornado would be more dangerous than a straight wind of equal speed. Tornados have a very low-pressure center and violent updrafts as can be seen in this YouTube video . As the roofs are blown off you'll notice they get blown upward as well as sideways.


Is the sunlight on the GOES-16 Imagery reaching from the east? I was wondering is the sunlight reaching from the general direction east? I came to this conclusion because the image is so dark on the west side however I am not 100% sure.

Yes. The time stamp says that the image is taken at 13:45Z, which means the sun is overhead in the Eastern Atlantic (12:45 PM local time in Cabo Verde and the Azores). In Winnepeg, near the upper arrow, it is 7:45 AM and still in darkness.

Being winter in the NH, places that are more southerly like Louisiana and east Texas in the US have light while places at the same longitude further north do not.

You can tell that the image is taken in winter from the south-west to north-east slope of the terminator (i.e. the line separating the light and dark areas, see discussion here).