How much does sea level rise due to sediment deposition? There has been a lot of noise in the news in the last few days because Congressman Mo Brooks from Alabama claimed that erosion played a role in rising sea levels. Quoting from Science magazine:

Brooks then said that erosion plays a significant role in sea-level rise, which is not an idea embraced by mainstream climate researchers. He said the California coastline and the White Cliffs of Dover tumble into the sea every year, and that contributes to sea-level rise. He also said that silt washing into the ocean from the world's major rivers, including the Mississippi, the Amazon and the Nile, is contributing to sea-level rise.
"Every time you have that soil or rock or whatever it is that is deposited into the seas, that forces the sea levels to rise, because now you have less space in those oceans, because the bottom is moving up," Brooks said.
Duffy responded: "I'm pretty sure that on human time scales, those are minuscule effects."

Everywhere I have read, people just say "that man is an idiot"; but nowhere have I seen an authoritative, fact-based response to prove this.
How much does the sediment carried into the oceans by rivers contribute to the rise in sea level?

In a 1983 Journal of Geology paper by Milliman and Meade, "World-Wide Delivery of River Sediment to the Oceans" (link) it is estimated that the world's rivers carry about $13.5\times 10^9$ tonnes of sediment per year. If we assume an average density of $2.5~\rm{g/cm^3}$, this corresponds to a volume of 8.8 cubic kilometers. The total surface area of the world's oceans is 360 million square kilometers. This means that the sediment of the rivers contributes to a rise in sea level of 15 µm per year, or 1.5 mm per century.

The IPCC estimated in its fifth report that the average rate of sea level rise is about 3.2 mm per year. That means that about 0.5 % of that rise could be attributed to sediment. It is certainly not a major factor, but is non-zero all the same.


Humidity and Rainfall Usually the higher the humidity the more rainfall we get like in the summer here in Asheville, North Carolina we get a lot of showers and thunderstorms in the summer from the high humidity but I saw that in April is when humidity is at its lowest. How is that possible because we get lots of rain showers in April here in Asheville so how can humidity be at its lowest?

Now you see, humidity and rainfall are connected, but not in the way that you'd expect...

Let's suppose that their are rain clouds already in the air, maybe a couple hundred meters to a kilometer or so. Now imagine two scenarios:

1) Humidity of the air is low

2) Humidity of the air is high

Oh, and there is one more thing you need to understand before we move on. As raindrops fall, some of the water will evaporate into the atmosphere, increasing the humidity; but the air can only absorb the water if it has low humidity. Okay, back to our example.

1) Humidity of the air is low

Air can absorb a lot of water
As the rain drops fall, most, if not all of the water will be absorbed (evaporated) in the surrounding air

2) Humidity of the air is high

Air can absorb little to no water
As raindrops fall, the water will not be absorbed into the air

The second example is called rain. The first example is called virga. And yes, when virga happens, some of the rain drops don't even reach the ground! Crazy, right?

But now to answer your question...

I'm assuming that your clouds are relatively low to the ground, maybe no more than a kilometer. Also in April, the sun isn't that strong, so it doesn't have a chance to evaporate that much water.

Just remember, all scenarios are different, but as a general rule of thumb, the less humidity, the more rainfall.

EDIT:

This doesn't mean that places with less humidity must get rain. No. Rain cloud formation and humidity are completely unrelated. Rain clouds can form in whatever condition and in any place at any time. Humidity on the other hand affects whether or not the raindrops actually touch the ground.

It'll still rain with low humidity, but the raindrops might get absorbed into the air before they hit the ground. In some cases with low humidity, the sun isn't strong enough to evaporate all the water, so there'll only be a light shower. Sorry for the confusion.


Timescale of the biological pump？ I'm tying to find any clue about the timescale of the biological pump. That the carbon is recycled to the surface ca. 1,000 years is clear but the timescale of the biological pump seems hard to find. There is an report I saw when I was surfing the internet saying that the timescale can range from 45 days to 5 years which I find is a little shocking. Does it truly vary that much, or there is something wrong about the data?

I'm going to answer assuming you are referring to the time between the moment when the organism absorbs the carbon and the moment when it is trapped in sediments. I'm also going to answer by talking about what I know best, i. e. diatoms, which happens to be the major component of the biological pump.

The variation you are referring to is consistent with the fact that coastal diatoms only have a few hundred meters to sink before reaching the seafloor, whereas open-ocean diatoms are sinking for ca. 1000 to 5000 meters.
According to a compilation by Lisitzin (1972), so arguably a little dated, the settling velocity of marine diatoms in the water column is only of a few meters per day (he advances the number of 0.2 to 1.2m/day for 20 to 50µm-sized marine diatoms). But it can vary according to many factors and some of the coarsest, heaviest forms (such as resting spores) or diatoms that travel down in fecal pellets of copepods can be faster and reach the seafloor in an open ocean setting in only a few hundred days.

We don't usually consider this as being part of the biological pump sensu stricto but of course most of the organic matters created by diatoms from atmospheric CO2 is recycled by the zooplankton that grazes on them, which is in turn recycled by what feeds on that zooplankton, etc. Eventually some of them will end up trapped in sediments as well. This lengthens the process of course.

Lisitzin, A. P., 1972. Sedimentation in the world ocean. Society of Economic Paleontologists and Mineralogists, Special Publication 17: 218pp.


The sun sometimes appears pure white after rainfall, how can this be explained? I've noticed on multiple occasions, that after heavy rainfall, the sun appears a pure glistening white, even if it's already standing low in the sky. I can't discount psycho-visual effects as an explanation, such as cloud shadows from above affecting color perception. Yet considering the many warm cloudy sunrises/sets I've seen, I'd be surprised if that's all there is to it.

Is anyone familiar with what I'm describing and knows of a scientific description of the phenomenon?

Edit: I've gathered a few images which I think show what I'm seeing sometimes: http://imgur.com/a/evENm

When it rains the raindrops nucleate around aerosol particles of salt, dust, clay, soot, dimethyl sulphide, etc. In addition a falling raindrop may pick up any particulate matter that may be in its trajectory. The net result is that rain 'scrubs' the atmosphere clean. Without all these polluting particles to diffuse different wavelengths of the spectrum, the eye perceives the 'full spectrum', which the brain interprets as 'white light'.

In addition, you are quite correct that the eye's response to light, and to what constitutes 'white light' is very variable, depending upon light intensity, extent of blue sky vs. cloud, direction relative to the sun, reflections from buildings, the sea, etc. and other factors.


How much area in the world is under SemiArid climate? I am studying the L.C. King's "Normal Cycle of Erosion".

Apparently, he suggests that Davis was incorrect to have assumed Temperate Humid conditions as "normal conditions" of the world when suggesting his (Davisain) Normal Cycle of Erosion.

King goes on to suggest that it should be "semi-arid" conditions instead which should be assumed to be "normal conditions" (representative of the world's climate) and hence, suggested his (King's) "Normal Cycle of Erosion".

So my questions are:

How did L.C. King define SemiArid climate?
How much area in the world is under SemiArid climate as defined by L.C. King?
How much area in the world is under Temperate climate?

P.S.: I suppose if a figure isn't available for Temperate/SemiArid climate, a figure for the 6 Temperate Biomes and the 3 SemiArid Biomes would also do the trick...

6 Temperate Biomes: Warm Temperate Eastern Margin (China/Gulf Type), Warm Temperate Continental (Steppe Grasslands Type), Warm Temperate Western Margin (Mediterranean type), Cool Temperate Eastern Margin (Laurentian type), Cool Temperate Continental (Taiga type), Cool Temperate Western Margin (British type).
3 Semi Arid Biomes: Warm Temperate Continental (Steppe Grasslands Type), Warm Temperate Western Margin (Mediterranean type), Tropical Grasslands (Savanna type)

According to this link is 14% for Köppen classification.

The precise cite is:

"BS - dry semiarid (steppe). Is a grassland climate that covers 14% of the Earth's land surface."


There are cloud identification guides, are there also (guided) rock identification websites? Seeing all these rock identification questions, got me wondering, is there no straightforward guided rock identification website?

In Intro to Geology lab, I remember going through a bit of a process towards trying to identify different rocks.  There are some pretty decent cloud sites/charts around these days, not just basic descriptions like here, here, and here, but great in-depth site like here, and and especially these step-by step guides like here and here.

I know there are a lot more types and complexity to rocks than clouds, and clouds typing tends to be a little less useful (in part because the formation mechanisms are fairly non-distinct).  I've slowly started to see apps to lead you through plant/creature identification increasing, which is great, but are there any places we can point people to do the same for rocks?

I looked through your step-by-step cloud identification guides, and they seem pretty easy. The overwhelming criterion for which cloud it is is "how does it look", with the addition of the obvious "is it raining" or "do you hear thunder". After that, you only get 10 different types.

Here's why it would not work for rocks:

"How does it look" is only one criterion out of many for rocks, and it is commonly the most misleading. A granite has many different appearances. Quartzite, limestone, basalt, can all take many forms. Weathering, alteration, fresh surfaces vs broken surfaces, desert patina or stream-polished can all change a rock's appearance completely. Grain size affects colour. Lighting affects colour.
There are many more than 10 types of rocks. Basalt, gabbro, granite, rhyolite, dolomite, limestone, sandstone, shale, diorite, trachyte, ijolite, kimberlite, komatiite, eclogite, blueschist, greenschist, a conglomerate containing all of the above, and the list goes on and on. Some rocks may not even be rocks. Smelting slag, coal, hardened dung, a piece of concrete or any other kind of synthetic construction stone.
The many other tests used to identify rocks may not be applied properly by people with little experience. Is the mark left by your knife on the rock really a scratch on the rock, or is it the streak of the knife? Is it really hard or is the scratch you just did was actually silt sized grains of quartz dislodged? What's "heavy for its size"? Everything is relative. Where a geologist sees green, brown, yellow, black or red, a non-geologist sees brown, brown, brown, brown and brown.
Even professional geologists sometime disagree on what a rock is. I've seen (and been part of) so many arguments about rocks, and I have 7 years of experience in this thing. Occasionally the verdict is given by...
Methods to positively identify a rock (thin sectioning, scanning electron microscopy) that are not available to the general public and probably not even to the amateur geologist.

Therefore, if a key would exist, it would be extremely complicated and pretty much useless.


Identification of limestone type These are images of a stone found and used extensively in the Jammu & Kashmir region between India and Pakistan. These are called devir or devri in the local parlance.

Following is the description of the stone according to one website that I looked up:

  Devri stone is an impure lime stone extracted from earth at various parts of the Kashmir. The stone is soft in its nature and gives white appearance after carving. The stone can be molded to any form or shape.

I am planning to write a research paper on 'hamam' which is an underfloor heating system used in the kashmir valley, devri stones are commonly used as the floor surface for the hamams. I would like to know if there is an globally accepted name for this type of stone, so that I can report that in my paper. Also, it would make easy for me to acquire scientific data about these stones.

Limestones are usually categorized following the Dunham & Folk classification. Only very rare or special limestones were given a name and these are often named after the location where they can be found e.g. Travertine.

The images you provided are not very explicit which makes it literally impossible to clearly identify the limestone. Please consider next time to upload close up pictures that show the composition e.g. bioclasts and cements of the limestone.

However, there is a paper by the Geological Society of India were the authors date a limestone from the Jammu region which they refer to as Jammu limestone or Great limestone. The authors suggest that the limestones are from the Precambrian due to stromatolites that were found there in.

I hope this helps!


Can El Niño/La Niña occur again after normal state? As I know, El Niño and La Niña usually occurs alternatively, but is it possible that El Niño occurs again after El Niño and return to normal state?

If you look at the ENSO index record, you can see many instances of El Niño or La Niña occurring multiple times in a row. For instance, the period 1977-1983 and even after that is a succession of El Niño events with normal conditions in between and no La Niña period.

Multivariate ENSO Index (MEI) from NOAA


Where did all the CO₂ come from that was deposited as coal during the Carboniferous? During the Carboniferous, vast deposits of coal (or peat at that time) were created because – as far as I understand – decomposition of wood (white rot?) was not yet "invented" at that time.  This means CO2 and finally carbon was being removed from the atmosphere by photosynthesis and hence removed from the carbon cycle.

This must have led to a depletion of CO2 in the Carboniferous atmosphere because the deposition of peat lasted for quite some time.  And even today with wood decomposition, in the north summer the levels of CO2 are dropping as the Keeling curve is showing.

Was there enough CO2 in the atmosphere to support peat deposition over such a long time?  Or was there some refuel mechanism like vulcanism or some other process(es)?

Prior to the carboniferous period, and until the human industrial era, the majority of carbon dioxide in the atmosphere was due to volcanoes.

  For billions of years, geological processes like volcanic eruptions controlled the carbon concentration in the atmosphere, as volcanism is the major way that carbon rises from the mantle into the atmosphere. Most of the carbon stored in the mantle is in the form of carbonate (a salt of carbonic acid), but there are also huge stores of actual carbon dioxide sequestered deep within the mantle as a dissolved gas within the liquid rock.

  We can measure the degassing of Mt. Etna extremely well, and find that it adds about 16,000 tons of CO2 to the atmosphere each day, or 5.8 million tons per year. This might not sound impressive, but it's only one volcano. Interestingly, it's not just smoking, actively erupting volcanoes that emit CO2, but seemingly inactive volcanoes around arcs and rift zones. Persistent degassing still occurs around a great number of volcanoes worldwide, on a continuous basis.


When did people first realize that hurricanes are a particular type of storm system? To a person living on a beach in the Caribbean or crossing the Atlantic on a sailing ship, it's not obvious whether a commotion in the sky is a hurricane or some other storm system. When did people realize that hurricanes are a unique type of storm?

Trade winds from a general easterly direction occur almost all of the time in the Caribbean and tropical Atlantic. A hurricane approaching from any direction except from the south would change the wind direction because winds spiral counterclockwise into the hurricane. For example, a hurricane approaching from the east would cause the wind direction to back to northerly, while one approaching from the west (very rare in the tropics before recurvature occurs) would cause the wind direction to veer to southerly. If a hurricane approached from a general southerly direction, the wind would remain generally easterly but would gradually increase in speed and gustiness. Hurricanes are often accompanied by anticlyclonic outflow at upper levels; this could be observed via the motion of cirrus clouds.


Might continental drift ever stabilize? Is it possible that, one day in the distant future, it might be true that continental drift would stabilize? For the sake of discussion, we could suppose "stability" would mean less than a meter of movement within a thousand-year span relative to surrounding continents, across all continents (or something along those lines - I'm also curious if there's another definition of "stability" that would be more meaningful here).

Most likely.

I say that because it is heavily supposed that Mars, which is now tectonically stable, was active in the past. The reason why it has reached equilibrium is still a matter of discussion, and its tectonic history is merely hypothetical. But right away I'd say that the reason why Earth's tectonic activity could end converges on the reason why Mars, possibly, is stable nowadays: lack of internal energy.

You see, the current geological model that explains the movement of the tectonic plates is based in mantle convection. The mantle is strictly solid, but on a large timespan, i.e., on the geological scale, it behaves as a fluid, which (sort of) means it has enough mobility to move, and therefore for convection to happen. But here's the catch - convection is a form of heat transfer. So we can interpret that convection, and therefore plate tectonics, are but a form of heat to be "expelled" from the inside to the outside. And naturally, at some point energy should end. But at which point? In my opinion, for an astoundingly long time (over 1 billion, and perhaps even 10 billion years). Earth's been spitting energy for almost 4 billion years now (before that, it was actually gathering energy through the kinetic energy from the impact of planetesimals, which can be thought of as huge meteorites) and it still has enough energy to heat the inner core to over 4000 Celsius degrees (that temperature is due to pressure & Earth's remaining energy, though).

It is important to note that maybe due to the fact extreme depth is intrinsically associated with increased temperature, that pressure-driven temperature might suffice to generate mantle convection. But we wouldn't have oceanic crust generation (no inner heat - no partial melting next to mid ocean ridges - no oceanic crust generation), or it would be very limited. And besides, Earth is an open system with the universe, so it loses energy, and eventually it has to run out of it.


Definition of "hundreds of ice accretion" I saw this line today in a NWS weather alert:

ACCUMULATIONS...A FEW HUNDREDS OF ICE ACCRETION.

Is this standard terminology?
Does "hundreds (of)" somehow refer to a unit of measure, or
is there a (likely or standard) unit of measure implied or missing here?

http://alerts.weather.gov/cap/wwacapget.php?x=MA1255EAFEBC38.WinterWeatherAdvisory.1255EB001010MA.BOXWSWBOX.18aa678bad1893fa8f6667c193e56ef4

I think that it's referring to hundredths of an inch, and "hundreds" is a typo for "hundredths". This FAA information sheet says:

  All ice accretion amounts will be reported to the nearest one-hundredth of an inch (0.01 in.). An example of a 1, 3, 6-hour ice accretion remark would be: “I1010 I3015 I6022.” This translates to 0.10 inches of ice in the last hour, 0.15 inches of ice in the last 3 hours, and 0.22 inches of ice in the last 6 hours.

This also matches the terminology used in some other weather reports, such as this one:

  Ice accretion was light, generally only a few hundredths of an inch...


What are some options for online and offline particle tracking in ocean models? I am looking for a few options of particle tracking for ocean modeling to try to do a comparison of different codes.

The main difference between online and offline trajectory calculation is that the online is implemented as part of the model, and the trajectories are part of the model output. Offline trajectory calculation is a separate piece of software that takes Eulerian model output fields as input and calculates the trajectories.

The main advantage of online particle tracking is that the displacement of a particle or tracer can be evaluated every time step, no matter how small it is. As a result, you can obtain a true particle trajectory based on what model produces. The disadvantage of the online tracking is that the user needs to know the particle release location and time ahead of running the model. The models listed below (at least) support online Lagrangian trajectory calculation:

HYbrid Coordinate Ocean Model (HYCOM) is a hydrostatic, hybrid-coordinate ocean circulation model that has particle calculation built-in;
MIT General Circulation Model (MITgcm) is a non-hydrostatic circulation model with many physical parameterization options and a single dynamical kernel for both the atmosphere and ocean;
Regional Ocean Modeling System (ROMS) is a hydrostatic, sigma-coordinate (terrain-following) ocean model with many physical parameterization options a large user community.

On the other side, offline particle tracking can only use the Eulerian fields as often as they are output. Thus, there will be an error in the calculated trajectory depending on the frequency of the output. On the other side, the main advantage of offline calculation is that the user can experiment and play around with deployment locations, times, area of coverage etc., because trajectory calculation typically takes much less computational effort than the actual model. There are several options here:

Connectivity Modeling System (CMS) takes gridded NetCDF files as input and produces Lagrangian trajectory output. Can handle fields from various Arakawa-staggered grids, and may produce probabilistic trajectories, diffusivity specified by user (optional). Compatible with at least HYCOM and ROMS output.
Ariane also takes gridded NetCDF files and is compativle with at least HYCOM, ROMS and NEMO models.
TRACMASS seems to be compatible with many circulation models. It also has a Python interface.

All models and tools listed in this answer are freely available for download under different open source licenses.


Why does an artesian well dry slower than a normal well? In the diagram below, well A is an artesian well and well B is a normal well.
Well B's pipe is lower than the water table. By looking at the picture, I decide that well A would try quicker than well B, but the answer said that well B would try quicker than well A. I researched on the Internet, but all I found was how to improve your well.

Why does an artesian well dry slower than a normal well?

Well B is a normal water table well, which will have a relatively steep, tight, local, and deep 'cone of depression'. Well A doesn't have a 'cone of depression' - it has a 'cone of depressurization', which has an entirely different physical configuration. That is, wide and shallow. So the drawdown in well B will fall rapidly, whilst there isn't really a drawdown in well A, at all. Rather, the pressure surface in well A decreases until much of the aquifer - typically several square kilometres - is depressurized. Note that the two processes are entirely different. In a water table aquifer pumping actually drains the pores between grains in the upper aquifer, like water draining out of a sponge. In a confined aquifer, the yield is supplied by depressurizing the aquifer - so the saturated surface doesn't actually drain at all.


Why is the Atlantic Hurricane Season defined as being between June 1 and November 30? Historically, the Atlantic Hurricane Season has shifted, as close as June 15 to October 31, but since 1965, it has been between June 1 and November 30(1).

Why is the Atlantic Hurricane Season defined as being between June 1 and November 30? I know most hurricanes happen within this timeframe, but it seems, to the civilian eye, to be the strongest during August and September.

The hurricane season is set by the National Hurricane Center.  They use statistics to determine the dates.  Specifically:

  The Atlantic hurricane season is officially from 1 June to 30 November. There is nothing magical in these dates, and hurricanes have occurred outside of these six months, but these dates were selected to encompass over 97% of tropical activity.  June 1st has been the traditional start of the Atlantic hurricane season for decades. However, the end date has been slowly shifted outward, from October 31st to November 15th until its current date of November 30th

  NHC

As for why the dates are spreading out (from October to November), it appears that the dates of the hurricanes themselves are spreading out. (per James P. Kossin [1])

So, the dates are getting wider because the hurricanes are spreading out throughout the season.  So, the NHC widens the dates throughout the years to correctly cover the majority of the hurricanes.

[1] James P. Kossin - Is the North Atlantic hurricane season getting longer? GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L23705, doi:10.1029/2008GL036012, 2008
James P. Kossin


Different peak and mininum discharge times for Newfoundland rivers I have been studying the Humber, Gander and Terra Nova rivers in Newfoundland. I have been given a table of discharges, and for the peak discharges I see:

Gander: around April and May (rougly from day 101 to day 141 if day 1 = January 1st)
Humber slightly after Gander
Terra Nova has a peak discharge around March, before the others

For the minimum discharges I see:

Terra Nova: around day 201 of the year
Gander: around day 211 (June/July)
Humber: January and February and then again slightly after Gander.

So clearly climate, both the precipitation of rain and snow affects this discharge but what is the cause behind the different times in max and min discharge of these three rivers?

All of the following parameters would affect seasonal maximum and minimum flow times. Differences between the river basins:

Size of drainage area
Average relief of topography within the drainage area
Amount of groundwater entering the river (near max)
Amount of water leaking into the local water table (near min),
Underlying differences in geology of the river basins
Water usage from each river
localized weather patterns
Sun exposure (for snow melt)

Careful and detailed geological and hydro-geological study of each rover basin would need to be performed to determine exact cause of differences in timing of max and min flow times.


Oxygen isotope ratio and Glaciers The question is basically:

  During the Cretaceous there were no continental    ice    sheets. The ratio
  of O-18/O-16 in sea water was:

  a) Higher than today
  b) Lower than today

The answer is stated to be b, but it does not make sense as glaciers have a lower 18O/16O ratio and so the ratio should be higher than today. Can someone justify why it's b?

It does make sense.
As you said - glaciers have lower 18O/16O. This is because they have less 18O overall. Therefore, the oceans have more 18O. But this is today.

At the Cretaceous there were no continental ice sheets, so what we said previously is not relevant. There are no ice sheets to take all of the 16O, so it's all in the ocean. This results in a lower overall 18O/16O ratio.


Interpreting a geological map I have a homework question that I'm stuck on, I have attempted interpreting this map but am not sure if I have to correct interpretation.

  What is the youngest/oldest rock in the geological history of this map?

By law of superposition, oldest: limestone, youngest: mudstone. For this question, I'm used to looking at the law of superposition to determine age but in this diagram the contours don't tell me anything. Did I get these right?

  What type of fold is shown on the map?

Anticline.

  Give a brief geological history of map.

This is the one I need most help in. Magma intrusion at fault lines? Maybe some mudstone intrusion over limestone?.

Again, please tell me if these answers are wrong.

1. What is the youngest/oldest rock in the geological history of this map.

Your approach is the right one but isn't the limestone  underlain by something? Drawing the AB cross section would be of great help here, did you manage to do that?

2. What type of fold is shown on the map.

What is the definition of a syncline and does your interpretation agree with your answer to question one?
Are there any legend symbols on the map which would be used to indicate a fold?

3. Brief geological history of map

Putting all the lithologies and the deformation (Question 2) in right order would be a big part of that. After that maybe you have some ideas about a succession of claystone, limestone and mudstone


Why are the Little Colorado River and Havasu Creek blue? In Grand Canyon there are two side streams that carry heavy carbonate loads and deposit travertine along their lengths. The Little Colorado and Havasu Creek both rise from springs a few miles above the river and are separated by over one hundred river miles.

The white carbonate precipitate in each makes the light turquoise color of the water strikingly visible. What mineral in the water gives it the light turquoise color?

The color of the water is determined by depth and mineral composition. Calcium carbonate is carried in the Little Colorado river water column and coats the river bottom. Calcium carbonate scatters white light (aka, looks white), so combined with water, which scatters blue light, a turquoise color is formed. When the water column is thin, white scattering of the calcium carbonate is more pronounced and the color of the water is lightened. In the deeper parts of the river, the color is a darker blue due to the smaller concentration of calcium carbonate (due to more volume of water) and the increased scattering of blue light through a thicker water column.

This blog has a great explanation.


Would pollution really take a lot of years to disappear from the atmosphere once people stop producing them? From a comment in another question here,

  Oh, and a third factor: the added atmospheric CO2 does not magically
  go away once all the fossil fuels are burned. It will stay in the
  atmosphere for thousands of years, if not more, and will keep on
  heating things up. Currently the ocean absorbs a lot of the increased
  heat, and since the circulation time to the deep ocean is 100 years or
  more, heating will keep on for quite a while.

How much could Earth's temperature increase by the time we run out of oil reserves?

But recent reports from ESA satellite and others says,

  Air pollution over Italy is seeing a drop after the country introduced
  a nationwide lockdown in response to the novel coronavirus outbreak

  New data from the European Space Agency’s (ESA) Copernicus Sentinel-5p
  satellite, which can measure concentrations of greenhouse gases and
  pollutants in the atmosphere, shows that between Jan. 1 and March 11,
  concentrations of nitrogen dioxide over Italy fell dramatically

  China has also shown a sharp reduction in pollution and greenhouse gas
  emissions after travel bans and quarantines

Italy sees drop in pollution

Now with this, you still could interpret that by reduction of pollution they only meant Nitrogen dioxide and excluded CO2, but from here,

Italy emissions Coronavirus

  This will have just a minor effect of global concentrations of CO2,
  unless it leads to a really long depression of the world economy

Would pollution / greenhouse houses really take a lot of years to disappear from the atmosphere once people stop producing them?

[I apologise for this long & somewhat scrappy answer.  It may contain significant errors, for which I apologise as well.]

How long something persists in the atmosphere once it's there depends, obviously, on how it gets removed from the atmosphere and also if anything is adding it to the atmosphere.  Different things we might consider pollutants will have different lifetimes, often very different, and it's confusing to lump them together as 'pollution'.

However there is a very important distinction to be made:

one thing we could care about is 'how long do we expect an individual atom/molecule/particle of $x$ to remain in the atmosphere before it leaves it?'
another thing we might care about is 'how should we expect the concentration of $x$ to behave in the atmosphere over time?'

These two things are not the same.  They are not the same because, even considering only 'natural' processes (which we might define as 'processes not resulting from the burning of fossil fuels or industrial activity') absorption is not all that happens: emission also happens.

The thing that is interesting to know is generally the second: 'how does the concentration of $x$ go over time?'  That's because no-one actually cares whether a given unit of something stays in the atmosphere for long: they care about how much of it there is in the atmosphere: I don't care whether I'm breathing some particular oxygen molecules, I care that there is enough oxygen in the atmosphere that I can breathe.

Removal mechanisms

There are at least three mechanisms for removing something from the atmosphere.

It may not be stable in the atmosphere.  A good example of this is methane, which gets turned into other things over a few years.  If methane emissions (including natural ones) stopped it would essentially all disappear within a few decades at most.
It may leave the atmosphere by falling out of it or by being involved in precipitation.  This is true for aerosols (particulates) in the atmosphere: aerosols with large particle sizes really fall out of the atmosphere, aerosols with very small particle sizes get removed by precipitation and intermediate size ones experience both processes.
It may get actively absorbed by something on the surface.

A fourth mechanism is 'it may escape to space' but this is not a significant process anything interesting here, so I'll ignore it.  There may be other mechanisms I have not remembered.

Addition mechanisms

There are, I think, two significant mechanisms for creating stuff in the atmosphere:

it may be emitted by something on the surface;
it may be created by some process in the atmosphere.

(And again, it may arrive from space, but I'll ignore that.)

How long things persist in the atmosphere

So, now, how long things persist in the atmosphere depends on what they are: the term 'pollution' bundles together things which have radically different characteristics.

Human-generated aerosols (smoke, other aerosols) have relatively short lifetimes in the atmosphere and are not created by processes in the atmosphere, and so will fairly quickly decline in concentration once emission stops.
Aerosols of water – clouds – are created in the atmosphere, from water vapour which will continue to be emitted from the surface, and are also removed from the atmosphere as rain, but these processes balance out over time and so clouds will persist in the atmosphere.  Clouds are not a pollutant of course: I just wanted to add them as another type of aerosol with another lifecycle in the atmosphere.
$\mathrm{NO_x}$ has a relatively short lifetime in the atmosphere as it's not stable: its lifetime in the lower atmosphere is hours, and in the upper is not more than few weeks.  Some $\mathrm{NO_x}$ is created in the atmosphere by lightning, but I think the quantities are rather small compared to the amounts created by human emissions.  So the amount in the atmosphere will decline pretty quickly once emission from the surface stops.
and so on.

The elephant in the room: $\mathrm{CO_2}$

$\mathrm{CO_2}$:

is pretty much chemically stable and so does not decay in the atmosphere (it does undergo processes of being dissolved in water droplets and then evaporating from them, and perhaps others);
is not an aerosol and so does not leave the atmosphere by the mechanisms which affect aerosols, unless it is dissolved in aerosols of water;
is absorbed by several processes on the surface;
is also emitted by several natural processes on the surface.

The things which absorb $\mathrm{CO_2}$ on the surface are, among others (not necessarily in order):

plants, which absorb $\mathrm{CO_2}$ and turn it into plant and oxygen;
the oceans, which dissolve $\mathrm{CO_2}$;
rock weathering;
other things.

The natural (see above definition!) processes which emit $\mathrm{CO_2}$ are (not in order):

plants and animals which respire;
plants (and animals) which die & decay or catch fire, releasing $\mathrm{CO_2}$ back to the atmosphere;
the oceans, which release dissolved $\mathrm{CO_2}$ back to the atmosphere;
vulcanism;
other things.

So in order to know how $\mathrm{CO_2}$ behaves over time we need to understand how the various processes work: how fast is $\mathrm{CO_2}$ cycled through the atmosphere and how fast does the concentration change.

Understanding this is not simple, and it's why people write big climate and earth system models.  But it's possible to give ballpark numbers.

The answer to the first question: 'how long does an individual $\mathrm{CO_2}$ molecule spend in the atmosphere' is 'a few years'.

The answer to the second question: 'how long would it take for $\mathrm{CO_2}$ concentrations to decline to preindustrial levels if fossil-fuel burning stopped, is 'from a few hundred to a few thousand years'.

The reason for the large difference between these numbers is that the natural processes that absorb and emit $\mathrm{CO_2}$ are very close to being in balance.  This is easy to see because we know that the concentration of $\mathrm{CO_2}$ in the atmosphere was not zero before we started burning fossil fuels.

Just to give some figures (these are not meant to be accurate):

plants absorb about $120\,\mathrm{GtC/y}$ through photosynthesis;
plants emit about $60\,\mathrm{GtC/y}$ through respiration;
about $60\,\mathrm{GtC/y}$ is emitted from decay of plant matter;
the oceans absorb about $90\,\mathrm{GtC/y}$;
the oceans emit about $90\,\mathrm{GtC/y}$.

As it stands this is completely balanced.  Well, these figures are approximate, and there are other processes both of absorption and emission.  But it's close to being in balance.

This is why the concentration of $\mathrm{CO_2}$ would fall only rather slowly if fossil-fuel burning stopped.


How common is it for warm fronts to be responsible for record high temperatures? Warm fronts are associated with an increase in temperature and precipitation.

But are they often associated with record high daily maximum temperatures, given that they often result in an increase in cloudiness? Or are they more often associated with record high daily minimum temperatures?

I'm not sure that record temperatures occur with enough frequency that we can attribute them to this specific phenomena, though I am no authority on records.

I think that attaining a record high with warm frontal passage is unlikely.  As you mention, the warm front is often accompanied by cloudy weather, and these clouds first manifest as high cirrus clouds well poleward of the surface front, lowering closer to the front.  This combined with possible precipitation will moderate the temperatures.  If rain is falling on the cold side of the front prior to frontal passage (FROPA) it will likely stabilize at the wet-bulb and stay far from the record temperatures.  Places on the warm side, if experiencing precipitation will have a similar experience and probably not near high temperatures.  You may have a case here for potentially warmer night temperatures, but I'm not sure you'll be in record territory.

A better case for potential high temperatures can be just prior to cold frontal passage.  Especially for a strong cold front, the pressure gradient can drive strong southerly flow (in the NH) bringing lots of warm air advection ahead of the front.  If you watch a temperature trace before such FROPA you'll see a sharp rise in temperature before it plummets.

Typical FROPA probably won't set records.  You need some exceptional aspect of it or at least some unseasonable occurance to really threaten the records.

Though I was unable to justify it with data, I do not suspect warm frontals are a common source of high temperature records (high daily max or high daily low).


Placement of crustal thickness estimation from 1D inversion of surface wave dispersion curves Seismic surface waves present a characteristic dispersion behavior in which different frequencies travel at different speeds. This characteristic dispersion curve depends on the shear and compressional wave velocity structure of the crust and upper mantle. These physical parameters can be estimated using some inversion method that can be 1D, 2D, or even 3D. 1D inversions are very common for their relative simplicity and speed. However, the dispersion is usually measured between two stations.

So my question is, where do we "place" the resulting 1D estimated model? Is it the average of the crust between the stations (I did the math for this once long ago and it seems that it is not, but I'm not sure)? Or is there no way to place the estimate at a single point?

This is a very good question, not just important to seismic inversion, but also modeling in general.

Lets set this problem up differently. Lets say point's A and D are nodes.

Each node represents a system of equations, and these equations are only calculated on these points. Therefore, the model can only exist on the points in which they are calculated. Since B and C are dimensionally  between A and D, a smoothing factor must be imposed to graphically represent them. So while there might be a line in between A and D, the model only exists on points A and D. To find the model at point B and C, you would have to build them in your model, creating a higher resolution mesh.  This is perhaps why it is so important to have a dense seismic array when doing seismic studies.

So in your case, the model is dependent on information on information at two stations, making each node TWO STATIONS. This would mean that the it is impossible to give an exact geographic location to where the inversion is, just a generalized idea of between these two stations.


On what basics, can scientists predict the effects of climate change? I don't know much about the topic of climate change to be honest. However, I've been attending a number of talks recently on the topic. As someone who studies mathematical models and uncertainty quantification, one thing that I do know is that weather models are extremely complicated and very sensitive to time. The error in weather model accumulated very fast, which makes long term behaviors fuzzy or uncertain. My knowledge is not related to the study on climate much, so that is about all I know.

I read up a bit on the climate issue and understand that the data suggests that climate change is real. I look at the data (from Nasa website) and agree that it supports that claim.

So my question is not about whether climate change is real or not. My question is how some scientists make claims like "in 50 years..." My guess is that they observe the trends in history and use that as the basis for their prediction. I hope this question is clear. If you have an understanding on the topic, please point me to the right source.

Climate science seems to be as relevant as other types of science. It's just that it has been organized ridiculed after the formation of IPCC in the 80's. It has a lot of heritage from physics and there are a lot of signs of a climate emergency.

Your question is not fully clear. Some effects are impossible to predict in detail while other is not. Down a prediction of the global temperature and the concentration of atmospheric CO₂ made by ExxonMobile's researcher 1980.


What is the correct way to report historical daily Max / Min / Avg Temperature by City? I starting a weather project where I'm using ERA5 hourly dataset (ref: https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-single-levels?tab=form). Using this dataset in python, I have now a dataframe as below.
As you can see, for one State I have n observations considering latitude|longitude and Time of observation. So, now I would like to aggregate this dataset daily, considering Admin2 and Admin1, in order to have Max Temp, Min Temp and Total precipitation. Is there a right way to do this aggregation or is this simple the max / min values from 2m temp and sum of precipitation?
As you can see, by the content of my question, I'm not a meterologist. I'm just trying to build a reliable database for past historical weather data from some cities around the world.

Yes, daily minima, maxima and precipitation totals are calculated simply as you suggested in your question. Take care that there aren't missing values,, but that's more of an issue calculating means. Also check whether the reported values for precipitation are in fact a null value, it's unlikely that it could be measured in such small units.


What is meant by inverted water table? There are some papers in literature which discuss stream-aquifer interaction. They describe that the stream aquifer interaction ranges from connection to disconnection. When there is disconnection, then there is an $\textbf{inverted water table} $ below the stream and above saturated zone. I have not understood what is meant by this kind of water table?

An Inverted or Perched water table is a water table that is above the main or regional water table in an  unconfined aquifer.  The perched water table is generally above a layer of low permeability material such as clay.  In the image below, notice that there is an "inverted" water table along bottom of the perched water table.


Can we store maize along with husk and kernal? I'm a maize farmer and I'm almost ready for harvest.
I'm planning to store my harvest for some time.
Below are my questions:

How long can I store my harvest?
Can I sun dry my harvest with husk and kernel intact?
Can I store this sun-dried harvest with husk and kernel intact?

For the (1) you can store your whole maize for 8 - 12 years or 18 - 36 months if the maize is ground or chopped. Moreover the less moisture the maize has the more it can be stored. If you want to store your harvest for a long period of time then the maximum moisture  percentage is 13.5%.


How to plot lat-lon-rainfall in MATLAB? I have average annual rainfall values at few grids, as shown in below example;

Lat: 25.5 26.5 33.5 34.5 35.5 36.5 41.5 42.5

Lon: 89.5 91.5 78.5 79.5 83.5 84.5 75.5 76.5

Rain: 110 120 122 135 114 116 145 120 110 110

I want to plot it like a map, like this example

Each point will have a cell size of 1 degree, and there must be WGS 84 projection. How to plot them in MATLAB ?

I have around 4000 lat-lon values and these are not in sequence. Moreover the available Lat-Lon represent the irregular shape.

What kind of plot do you want?

  Lat = [25.5 26.5 33.5 34.5 35.5 36.5 41.5 42.5];

  Lon = [89.5 91.5 78.5 79.5 83.5 84.5 75.5 76.5];

  Rain = [110 120 122 135 114 116 145 120 110 110];

  figure();

  plot3(Lat,Lon,Rain,'o')

will give you a scatter plot with Lat being the x, Lon being the y, and rain being the z.

Also note that because your vectors are different legnths, you cannot plot them. You must have vectors of the same lenght to plot (each point must correspond to another point on the axis).

Other types of plots will require you to interpolate between the data points.

If you want to plot it like in the comment below: pcolor is your best choice.

Say your Lat/Lon vectors have n points. Then to make an nxn grid, you can use the command

  [X,Y] = meshgrid(Lat,Lon);

This will give you the grid you want, as long as your Lat/Lon Vectors are spaced how you want. To get the 'color" of the pcolor, you will need to have a nxn matrix of rain values: you will need to know what those are at each point. If you do not know those, then then you cannot plot it in map view unless you do some form of modeling or interpolation.

If you have an irregular shape, I would not use matlab. I would use Visit or Paraview, and there are many guides online on how to use this.

If you must use matlab, I would create "fake points" to make the grid a regular shape, and give them false rain values (such as NaN). I would then edit the plot in a postprocessor (photoshop) so that Only the irregular shape appears.

The spacing of the grid does not matter as its specified via your vectors.


Formation of Iceland Iceland sits atop a divergent ocean-ocean boundary. But there are not many islands which are formed along a divergent boundary. Why is it so? Why do not mid ocean ridges often rise above the sea surface to form islands? Why are islands more common along convergent plate boundaries where they often form archipelagos?

The answers so far are broadly correct. Iceland has formed from a coincidence of a constructive plate margin and a mantle plume, or "hot spot". But to really understand why Iceland is there we need to look at a normal constructive plate boundary.

A normal mid-ocean ridge is formed where two plates spread apart so that the mantle, which is at a certain temperature, rises upwards and experiences a decrease in pressure. The lower pressure together with the temperature of the mantle allows some (not all) of the mantle to melt - a process called partial melting. Only a small proportion of the mantle actually melts. This melt rises up through the overlying crust in a series of magma bodies, dykes, and lavas, to form the crust. Crucially, the thickness of the crust that is formed depends on the amount of melt that is created, referred to as the melt thickness.

A normal mid-ocean ridge creates a very thin crust - usually about 7 km. That's just 7 km between the ocean and the mantle. But Iceland is not normal. It sits above a mantle plume, which is a region of anomalously warm mantle. So what happens when we depressurise an area of mantle at a higher temperature than normal? We create a much greater melt thickness. This means the crust that is produced above the plume is greater - as much as 30 km. Since the icelandic crust is so much thicker than normal oceanic crust, the upper part of it is able to rise above the level of the sea. And thus Iceland exists.

To answer your followup questions:

  Why do not mid ocean ridges often rise above the sea surface to form islands?

Because it's very rare for a hot spot to coincide with a mid-ocean ridge.

  Why are islands more common along convergent plate boundaries where they often form archipelagos?

Because these islands form through very different processes. Convergent plate margins introduce water and other volatiles into the mantle, and these have the effect of reducing the melting temperature of the mantle. This produces melt, which rises up and forms volcanoes and islands. This process occurs at virtually every single destructive plate boundary because the subducting oceanic crust contains water which is liberated during subduction.


Effect on sea level if the Earth stopped rotating Would sea level change at the equator if the Earth stopped spinning? I am assuming it is currently bulging around it due to centrifugal force.

Let's assume that the earth didn't suddenly stop spinning (because intertia and conservation of angular momentum would do all sorts of "interesting" things that are deserving of a What-If answer), and stipulate that the earth slowed down gradually, or possibly that it was never spinning in the first place (although I'm sure this would have all sorts of other effects that wouldn't have got us to where we are...)

Yes, sea levels would change, but not necessarily for the reasons that you think.

Centrifugal force

Part of the bulge in oceans is due to centrifugal force on the water, but much of it is not. There is an underlying bulge in the seabed as well as the ocean. A result of this (and other variations in the thickness and density of the crust) are that the earth's gravitational field is not even across the globe, and where there is a stronger area of gravitational field, more water is pulled towards it and a bulge results. It is this effect that allows for the bathymetry of oceans to be mapped by satellites that sense the elevation of the sea's surface.

I am no geoscientist, but I imagine that this bulge in the crust at the equator is also to do with centrifugal force - but it would take a lot longer to go away, if indeed it did at all, than one caused just by water.

EDITING to add that there is now an answer elsewhere on this site re the bulge in the crust: How viscous is the Earth's mantle?

Changes in tides & ocean currents

If the planet were not rotating, the dominant period for tidal cycles would likely  be related to a lunar month rather than to a day. There would also be no Coriolis effect, and these two factors would result in major differences to tides and to ocean circulations. As such, it is likely that there would be substantial differences in both short- and long-term elevation changes that are due to currents.

Other effects

I suspect that lack of rotation might have effects on the planet's core and its magnetic field, which might result in all sorts of other impacts... but we'll have to wait for a geoscientist in a speculative mood to talk about things like that :-)


How do we know graptolites were pelagic? How do we know that graptolites were pelagic, and not benthic, creatures? I understand it has something to do with their being found in black shale, but I'm not sure why that is particularly relevant.

Basically, we know they were likely pelagic creatures because we find their fossils at essentially all water depths.

If they were benthic creatures, we'd expect their fossils to be limited to a set range of paleo water depths.  It's unlikely that a single benthic (i.e. living on the seabed) marine organism could live in both shallow water and ultra-deep water.

However, for pelagic (i.e. floating or free-swimming) creatures, we'd expect to find their fossils at a huge range of paleo water depths because they live in the water column and don't care where the bottom is.


Pressure Increase in stone and in water Why does the pressure increase only by 0,3-0,4bar per km in stone but 1bar per 10m in water while stone has the higher density?

Why does the pressure increase only by 0,3-0,4bar per km in stone but 1bar per 10m in water while stone has the higher density?

Because it doesn't!

Plots in this Physics SE answer and here and here show about 0.4 or 0.5 $\times 10^6$ bar at 1000 km depth, which is 0.4 or 0.5 bar per meter compared to your 0.1 bar per meter for water. If rock is 4 to 5 times denser than water, then all is well.


How to calculate Lifted Index from ERA5 pressure level data? I have taken a thunderstorm case where I need to calculate indices but I am not getting any code related stability indices in Python language, the code is available in GRADS, NCL for me it's difficult to understand. I used MetPy code but they are not calculated LI, KI, and other indices...Thanks in advance
Below code is wrong that I know I used the formula but tell me the correct way.

nc1=Dataset('pl_120415.nc')
lat1=np.array(nc1.variables['latitude'])
lon1= np.array(nc1.variables['longitude'])
lev= np.array(nc1.variables['level'])
time= nc1.variables['time']
r= nc1.variables['r'][:,:,25:28,20:25]
t= nc1.variables['t']
u= nc1.variables['u'][:,:,25:28,20:25]
v= nc1.variables['v'][:]
w= nc1.variables['w']

t_500= nc1.variables['t'][:,21,:,:] ### domain Air Temperture  at 500 Pressure_level
tp_500= nc1.variables['t'][:,21,25:28,20:25] ## at specfific location temperature (parcel temperture)

li=np.subtract(t_500,tp_500,dtype=np.float32)

print("LI",li)

Metpy 1.0 has a lifted_index function, which requires a profile temperature parameter, which in turn can be calculated using the parcel_profile function. That requires having the dew point temperature, which you would either have to have directly, or calculate from another moisture content variable. I'm not sure what your r variable is, so I'm not sure whether that could help you with such a calculation. Also, rather than using numpy arrays, using xarray for working with netcdf input variables tends to be easier and more efficient.


Result of deterioration of vegetation I had this question in my previous exam, it says:

Deterioration of vegetation resulted by overgrazing results in......
1.desert encroachment.
2.change in climate.

I had to choose 1 or 2 and I chose 2, why? Because my textbook says:

Overgrazing results in deterioration of natural flora, which is always accompanied by deterioration of soil and local climate.

But my answer was wrong, and I was confused which one to choose because both of them seem as correct answers. What I understand from my  text book is that deterioration of vegetation has a direct effect i.e. change in climate and an indirect effect i.e. desert encroachment. So, why was my answer wrong?

I think the reason you were marked wrong is because your text book is using the term "climate" loosely.  The deterioration of vegetation will result in desert encroachment ... which in turn can cause a change in local climate.  After all, if you create more desert, you have changed the local climate, right?  However, it takes many years to define a climate period, whereas desert encroachment can happen year to year.  So, eventually the local climate can change... but not if the desert encroachment reverses for some reason.  It's a very fine line, but answer #1 will most certainly occur while #2 may occur afterward if #1 is sustained.


What is the nature of the "unexpected geomagnetic pulse that took place beneath South America in 2016"? Popular news has several articles linking back to the news article in Nature Earth’s magnetic field is acting up and geologists don’t know why which discusses the need for an early update to the World Geomagnetic Model.
However my question is about one line found in the Independent's Planet’s erratic magnetic field forces emergency update to global navigation system

The shift they observed was so large it was on the verge of exceeding the acceptable limit for navigation errors.
To account for this, scientists at the British Geological Survey and the US National Oceanic and Atmospheric Administration (NOAA) are issuing an unprecedented emergency update to the model.
They have fed in the latest data, including an unexpected geomagnetic pulse that took place beneath South America in 2016, to ensure the system is more accurate.

Question: What is the nature, and underlying cause of the "unexpected geomagnetic pulse that took place beneath South America in 2016"?
AKA geomagnetic jerk.

The "geomagnetic pulse" here refers to a series of academic works studying the Earth's core such as this open access article (other related articles require scientific journal subscriptions to read).

Geomagnetic pulses have been associated with "geomagnetic jerks". A jerk was reported (yay for open access again) to have occurred in 2014, the 2016 pulse under South America is believed to be related to this, both events having been measured and identified after the fact.

The magnetic field is always changing - a "pulse" is a quicker-than-normal (few year) acceleration of magnetic field change in time, in a region at the surface of the Earth's outer core (magnetic field is generated within the core).

A "jerk" is a quick change (few months) of the rate at which magnetic field changes at Earth's surface, making something like a 'V' shape if you plot the field against time at a given location.

The idea is that a pulse occurs at the core, and jerks are an effect seen at the surface just before and after the peak of the pulse, as the field change ramps up and down. The underlying cause of this is not known, and we only identify them after they've occurred, so they're currently unpredictable. That said this behaviour is apparently part of the core's repertoire, and pulses and jerks have been observed before.


Does natural plant decomposition release more greenhouse gases than burning I understand that all plant matter releases CO2 as it decomposes and also when it burns in, for example, a forest fire. My assumption, upon which this question is based, is that the CO2 release is the same in each case.

My main question is, what drives the production of all greenhouse gases in those two situations, e.g. methane in decomposition, NOx in combustion to help determine which is worse in terms of the total radiative effects of the greenhouse gases?

I appreciate the answer is likely to vary according to type of plant matter, the degree of anaerobic decomposition and the intensity of fire. Sub question: Are there any benchmarks that indicate which is worse in some specific situation or controlled trial?

Another way of looking at the question:

I take 2 standard wheelbarrows of bits of plants from my garden. One wheelbarrow is used to fill the compost bin. The other goes to the bonfire.
How much ash do I have from burning compared to how much compost from the compost bin. Any gardener will know that the amount of compost will be much larger than the amount of ash. So now we need to compare the chemical composition of the ash with that of the compost. For Wood Ash there are quite a few research articles. Most of the carbon atoms in wood ash will be in the form of Calcium Carbonate (CaCO3). Percentage in the ash will vary widely but lets take a median of 50%. Ash as a percentage of original organic matter will be maybe of the order of 8% by weight.

For an original 100kg of organic matter (yes, its a big wheelbarrow) we would have 8kg of ash. In this ash would be 4kg of CaCO3. The carbon atoms would be 12% of that (relative atomic masses). So 100kg of organic bits gives you 0.48kg of carbon atoms left in the ash when you burn it.

There seems to be fewer research articles on composting but we found the following approximations. For 100kg of organic matter there will be about 9% organic carbon  (9kg). Composting will turn 100kg of raw material into around 30kg of compost in which the organic carbon content will be around 25% ( 7.5kg of carbon). These figures are median "pot luck selection" as results can vary widely. We can however see that composting retains massively more (7.5kg) of carbon atoms compared with burning (0.48kg). The difference will be in the atmosphere.


Urgent, Please help, where can I find worldwide standards of manganese mining? Hi everybody who sees this post, I need urgent help for finding all official world wide standarts of the manganese mining.
Problem is that, many houses has been damaged in my village with manganese mining, mainly because of underground explosions. Company which runs this type of operations, does not make any information about standarts public.
so my questions are:

where can I found OFFICIAL document which describes calculation formula about how far should the house be to consider it officially damaged, and can ask for compensation from the company.
Is it possible for company to have it's own standard when it comes to damaging properties, I mean their custom formulas or something like that.
Is their any websites which lists the countries which should follow worldwide standards of mining ?

Please don't be lazy to answer, it is really important for people here.

Your issue is an issue for all types of mining near residential or built up areas, not just manganese mining.
The distance that mines should be from built up areas depends on

the competency of the ground
whether the ground is hard or soft
the type of explosive used - more particularly the energy released by
the explosives used. This influences the blast vibrations produced.
Currently Australian and New Zealand recommendation is a maximum
blast vibration of 10 mm/s in residential areas, preferably less than 2.5 m/s.
the amount of explosives detonated at a time. Many smaller blasts are
usually better than one very large blast.
the presence of geological structures that may preferentially carry
and appear to amplify blast energy

The trouble with laws and standards for such things is they vary between mining jurisdictions. Even within countries, such as the US, Canada and Australia they can vary between states or provinces. Such countries do not have national legislation for the operation of mines. Each state of province is responsible for such laws within its jurisdiction.
In the 1980s, in the State of New South Wales in Australia, to protect lakes and dams from unexpected drainage and also to protect underground coal mines and the people that work in them from water inundation from lakes, dams or other such large stores of surface water a 45 degree angle rule was used.

From the edge of the lake draw a 45 degree line downwards. Where that line intersects the horizontal, or near horizontal, coal seam that defines the closest proximity the mine was allowed to get near the surface lake or dam.

Because of the geometry of a 45 degree triangle both of the shorter sides are the same length. In the case of this rule the distance from the edge of the lake or dam is equal to the depth of mining.
One of the problems with this rule is coal mines in Australia do not use explosives. Coal is mined using cutting machines via longwall mining.
In the City of Ballarat, Australia, gold mining resumed in the 1990s, after the closure of mines during the 1914 to 1918 world war because of a labor shortage. The mine operates underneath the city of 105 000 people.
Under the license to operate, from the State Government of Victoria:

Our licence conditions state that the vibration limit for blasting is 10 mm/sec and that 95% of all blasts must be below 5 mm/sec.

The mine has a self imposed limit of 2.5 mm/s.
Existing underground mine development, in blue, as of July 2020.

Under a proposed expansion to the mine, the newer region will be approximately 50 m below the surface. See the sectional diagram at the end of the webpage. The surface is at elevation RL 1205 and the top of the Nick O' Time Shoot is elevation RL 1150. I suspect this region will under fields or forest.
Generally, for mines under urban environments 100 m is the closest that mines come to the foundations of buildings. This is not primarily due to blasting waves and seismic activity from blasting, but the requirement to maintain a thickness of competent rock beneath buildings to minimize potential for future subsidence.
Factors that are considered in this thickness are:

The strength and competency of the ground below the buildings
The largest size of opening that will be developed underground
Whether the stopes, the chambers from where ore is mined, are
backfilled once the ore has been mined.
If the stopes are backfilled, with what will they be backfilled:
loose waste rock, cemented waste rock, loose sand, cemented sand or
paste fill (larger grained tailings from the processing plant that is
mixed with cement so it resembles toothpaste and is pumped into the
mined stopes).
The degree to which the stopes will be backfilled. Except for the
placement of paste fill, stopes cannot be fully backfilled because of
operational restrictions when other methods are used. There is usually
an air gap of between 2 and 5 m in the top portion of the stope that
cannot be filled.

Backfill prevents the wall of the stopes from collapsing and it minimizes the amount of subsidence that can occur above the stopes.

In your situation, something else to be wary of is exposure to manganese dust from the mine or processing plant. The human body requires small amounts of manganese, but too much can be toxic. Excessive exposure can lead to heath problems with the respiratory tract and/or the brain.

Manganese effects occur mainly in the respiratory tract and in the brains. Symptoms of manganese poisoning are hallucinations, forgetfulness and nerve damage. Manganese can also cause Parkinson, lung embolism and bronchitis. When men are exposed to manganese for a longer period of time they may become impotent.
A syndrome that is caused by manganese has symptoms such as schizophrenia, dullness, weak muscles, headaches and insomnia.

Additional references concerning exposure to excessive amounts of manganese:

National Institutes of Health
Impact of open manganese mines on the health of children dwelling
in the surrounding area
Centers for Disease Control and Prevention (USA)
World Health Organization

Edit 5 September 2020
There is no formula, simple or complex, that will let you calculate how close an active underground mining region can be to buildings on the surface. The reasons for this are:

Geology is complex: different rock types, strength of rock masses
laterally and at depth, geological structures such as
discontinuities, faults and folds.
How the ground propagates blast energy.
The magnitude of the blast energy produced during mining.
Quality of construction of surface buildings: flexibility and
rigidity.

Unlike steel, rock is not uniform in its properties everywhere. Various types of steel are made according to a recipe: some much iron, so much carbon, so much nickel or chromium. Steel is also given different types of treatments when produced, such as hot or cold quenching, forging. All this affects the strength and other properties of various types of steel.
When constantly made to the same recipe each type of steel can be tested to determine its properties. With this knowledge, structural and civil engineering can design a building, or any other structure, anywhere in the world with confidence knowing the steel will always behave the same way. Likewise for mechanical engineers when they design parts for machines.
This cannot be said of geological material, such as rock. Limestone behaves differently to sandstone, which behaves differently to basalt, which behaves differently to komatiite or granite.
Even the same type of rock can behave different in different locations. Discontinuities within rock, oxidation, weathering, the effect of water over prolonged periods of time, the effect of ground stresses can all change how a type of rock will behave in different locations.
Unlike structural and mechanical engineers, mining engineers cannot have the same level of confidence in the properties of the materials (different rock types) they use. With experience they know that a certain type of rock will behave in certain way, but that may not be totally applicable elsewhere.
Because of this, it is not possible to create a formula that can be used everywhere that will state how far an active underground mining region must be from surface buildings.
The other factor which would need to considered is the manner of construction of the buildings near the mine. Buildings that are rigid, made of rock or brick will generally experience more damage, if only just cracked walls, than flexible building made of timber or bamboo.
Flexible buildings can move to certain degree, through swaying,  when subjected to forces such as blasting energy, seismic shocks from natural earthquakes and very strong winds. This movement can absorb some of the disruptive energy and the building remains intact.
Rigid buildings have less opportunity to move when subjected to disruptive forces so they have to absorb more of the disruptive energies and in doing so they are more likely to crack and collapse. This is why buildings in earthquake prone regions (such as Italy), or cyclone/hurricane prone regions (such as northern Australia) are now built according to an earthquake or cyclone/hurricane code where reinforcing steel is utilized to increase flexibility of the building, when completed.
From personnel experience I have seen newer, rigidly made, houses such as the one pictured below,

experience clacked walls and other damage from underground mine blasting where the house was 2.5 km laterally from a mine and the blast was 500 m below the surface. The active mining zone was 1.5 km laterally from the house.
An older, more flexible house, shown below, was only 1 km from the mine and it experienced no damage.


Temperature graph for solar Just wondered if this was accurate. Sorry for poor grammar. Typing on pgomw.

This can't possibly be right without some type of filtering applied to the total solar irradiance, at the very least. There's a graph here:
https://www.nasa.gov/topics/earth/features/glory_irradiance.html
showing the total solar irradiance measured primarily from satellites (i.e. from space) over the last several decades. There is no such trend in total solar irradiance from 1970 to now as the one shown.

The attribution is to the Berkeley Earth Surface Temperature Project, now Berkeley Earth. You can see a very different-looking temperature graph under their summary of findings:
http://berkeleyearth.org/summary-of-findings/
Reverse image searching the image led me to this thread (https://www.skepticalscience.com/solar-cycles-global-warming.htm) and a couple others, which point to this article (https://www.washingtontimes.com/news/2012/sep/6/global-warming-fanatics-take-note/) as an original source for the graph. That webpage no longer has any graph, from what I can see, but the thread seemed to imply that the graph may have been hand-drawn and with no real sources.


How to create a model to predict the salmon run Are there any publicly available models that show you how to accurately predict the salmon run in both the Pacific and Atlantic oceans?

This has been such a long interest of mine, I often see the results of this study, but I have never seen the methodology used for prediction.

You can use a program called Stella (which costs money) but there is also a free program that does nearly the same thing called Vensim.  These software packages allow you to build simple dynamic models using a GUI interface.

The materials (including salmon run scenario model files) for Andy Ford's "Modeling the Environment" class, which he taught for  many years, are here:
http://public.wsu.edu/~forda/models.html
with the "Smolts Migration Model" and "Salmon Harvest Simulator" prebuilt.

His text can be obtained online, the title is
"Modeling the Environment: An Introduction To System Dynamics Modeling Of Environmental Systems"

  Andrew Ford is Professor of Environmental Science and Regional Planning at Washington State University. He teaches modeling with an emphasis on environmental problems in the west, and he is the author of the Island Press text on Modeling the Environment. He uses the system dynamics approach to modeling, and he is the recipient of the Jay W. Forrester Award for the outstanding contribution to the field of system dynamics.


How to calculate Wind direction from uwind and vwind? How to calculate wind direction from uwind and vwind?
 if uwind and vwind are -1.82 , -3.18 respectively

The base formula for the direction $\theta$ is

$\theta=atan2\left(\frac{\text{uwind}}{\text{vwind}}\right)$

Where $atan2$ is the four quadrant inverse tangent. Note that if you used the normal inverse tangent your results will be all collapsed to the first quadrant (0° to 90°). Also note that depending on the platform the result can be in radians or degrees (most often in radians, some platforms have a function atan2d that return values in degrees).

If you get a negative value (which is the same direction but measured counterclockwise), you have to add 360° (or $2\pi$ radians).

This will give you the direction the wind is coming from. For the direction is going to, you have to add/substract 180° (or $\pi$ radians).

For the values you provide, the answer would be 210°.


How does new continental crust form? New oceanic crust is formed at mid-ocean ridges, then destroyed during subduction. Continental crust can be destroyed with erosion, or when the crust gets too thick (under mountains) and starts to melt at the base, but how does it form? Or is the continental crust slowly disappearing?

Continental Crust forms because of continual volcanic magma flow and pressure, erosion takes over a period of hundreds to millions of years to completely weather some object. Along with that, tectonic plates can smash into each other to form a continental crust and do land-building (The Himalayas is an exemple)

As with oceanic crust, continental crust is created by plate tectonics. At convergent plate boundaries, where tectonic plates crash into each other, continental crust is thrust up in the process of orogeny, or mountain-building. For this reason, the thickest parts of continental crust are at the world’s tallest mountain ranges. Like icebergs, the tall peaks of the Himalayas and the Andes are only part of the region’s continental crust—the crust extends unevenly below the Earth as well as soaring into the atmosphere.

“Crust” describes  the outermost shell of a terrestrial planet. Our planet’s thin, 40-kilometer (25-mile) deep crust—just 1% of Earth’s mass—contains all known life in the universe.

Earth has three layers: the crust, the mantle, and the core. The crust is made of solid rocks and minerals. Beneath the crust is the mantle, which is also mostly solid rocks and minerals, but punctuated by malleable areas of semi-solid magma. At the center of the Earth is a hot, dense metal core.

Earth’s layers constantly interact with each other, and the crust and upper portion of the mantle are part of a single geologic unit called the lithosphere. The lithosphere’s depth varies, and the Mohorovicic discontinuity (the Moho)—the boundary between the mantle and crust—does not exist at a uniform depth. Isostasy describes the physical, chemical, and mechanical differences between the mantle and crust that allow the crust to “float” on the more malleable mantle. Not all regions of Earth are balanced in isostatic equilibrium. Isostatic equilibrium depends on the density and thickness of the crust, and the dynamic forces at work in the mantle.

Just as the depth of the crust varies, so does its temperature. The upper crust withstands the ambient temperature of the atmosphere or ocean—hot in arid deserts and freezing in ocean trenches. Near the Moho, the temperature of the crust ranges from 200° Celsius (392° Fahrenheit) to 400° Celsius (752° Fahrenheit).

Crafting the Crust

Billions of years ago, the planetary blob that would become the Earth started out as a hot, viscous ball of rock. The heaviest material, mostly iron and nickel, sank to the center of the new planet and became its core. The molten material that surrounded the core was the early mantle.

Over millions of years, the mantle cooled. Water trapped inside minerals erupted with lava, a process called “outgassing.” As more water was outgassed, the mantle solidified. Materials that initially stayed in their liquid phase during this process, called “incompatible elements,” ultimately became Earth’s brittle crust.


Time of concentration - Difference between large and small basins I am looking for any academic reference (i.e. articles) regarding the time of concentration for large and small basins.

E.g. I would expect that a large basin (area > 1,500 km^2) will flood (or reach its max peak flow) later in time (e.g. 1-2 days later) when compared to a small basin if the same amount of rain will fall in both of them.

This is a difficult question since time of concentration ($t_c$) can in theory,  vary substantially, for two basins of equal size.

Off the top of my head, I can imagine several other variables that would be necessary to determine $t_c$: drainage density, basin relief, basin length, surface roughness (Mannings coefficient), and rainfall statistics. There's certainly others too.

I found a paper titled The characteristic time scale for basin hydrological response using radar data is freely available. There is a discussion of $t_c$ beginning on page 93 at bullet point number 2. They cite other papers in their discussion that would be worth tracking down and reading.

Note they present an empirical equation for $t_c$:

$$t_c=5.4\left(\frac{L}{S^{0.5}}\right)^{0.75}$$

L is basin length, and S is slope/relief. It's weird, yet I'm not surprised since it's empirical. Evidently the 5.4 has dimensions of $time$ and $length^{-0.75}$. It's hard to imagine that this equation would actually be useful.


How can I convert the negative values of the ERA5 PET data into positive? I planned to use the ERA5 Potential evapotranspiration data for drought analsysis (SPEI), however values are presented in negative number. Of course I understand the logic for presenting PET negative. But, I want to convert it into positive and I should all the PET data positive. I knowledge those who help me to change the negative value in to positive. I am using cdo for data processing. Thank you!
Mekonnen Adnew Degefu

You can multiply all the values by -1

cdo mulc,-1 infile.nc outfile.nc

If you want also to get rid of the condensation data (and, please, note that I am not implying that that is the right thing to do), you can do something like this

cdo setrtoc,0,9999,0 ifile.nc ofile.nc

Hope this helps


Is there a name for a "moving meridian" corresponding to particular solar time? Imagine a meridian that moves over the Earth's surface such that it remains at the longitude that corresponds to a particular solar time (e.g. midday).

This meridian would remain stationary relative to the Sun as the Earth revolves under it.

Is there a name for such a meridian?

This is better suited for English Language &Usage SE, but the word you're looking for is

Isochron

  an imaginary line or a line on a chart connecting points at which an event occurs simultaneously or which represents the same time or time difference

(Source: Merriam-Webster)

Isochrons are typically used in diagrams rather than maps, for techniques like rock dating, where correlating things by time is more important.

But cartographers are used to putting all types of isarithms on maps, and would understand what an isochron was meant on a map.

The trick is to define "same time" as "same solar time", giving you the "moving meridian" you're looking for.

You could contrive a more specific term like isoheliochron but it hardly seems worth the effort, because they're pretty boring on a map.


What is the explanation of using pressure units (hPa) to express height when dealing with wind speeds? I am trying to understand how prevailing winds and jet stream currents are formed and how they are varying in speed and direction.

When looking at different wind speeds at different altitudes on earth.nullschool.net I noticed that the height is expressed in hectoPascals (10hPa, 70hPa, 250hPa, 1000hPa) instead of feets or meters .

What is the explanation of choosing pressure for expresing height instead of another unit of length ?

There are several reasons. From the theoretical point of view it is beneficial to use isobaric coordinates, due to the vanishing density in the equations of motion. While in cartesian coordinates the wind is determined by the pressure gradient in isobaric coordinates the wind is determined by the geopotential gradient. The geopotential is defined by $\Phi = gz$. In the hydrostatic relation $p = \rho g z$ we can relpace $gz = \Phi$ and therefore any term containing $p/\rho = \Phi$. The geostrophic wind relation for example differ as follows:
Pressure coordinates: $\vec{V_g} = \frac{1}{f} \vec{k} \times \nabla \Phi$
Cartesian coordinates: $\vec{V_g} = \frac{1}{\rho f} \vec{k} \times \nabla p$
Notice the density as an additional variable in the latter formula.
Another reason arises historically. The vertical structure of the atmosphere could only be measured using balloons or radiosondes until around the seventies when satellites became an additional source of information. Until today radiosondes provide the most detailed profile of a vertical slice in the atmosphere. Radiosondes can not measure height in meter or feet but they can measure pressure. Also GPS is not be the best alternative. While it is quite accurate regarding the horizontal position it lacks accuracy in the vertical compared to pressure measurements.
Edit:
I forgot one of the most important aspects: Looking at pressure surfaces also allows us to compare heights in a more meaningful way. What we experience as weather happens to 99% within the troposphere. However, height of the tropopause varies a lot from poles (~9km) to equator (~16km). Looking at a pressure level allows us to make sure the mass of air above that level is approximately the same everywhere and thus makes variables comparable. Note that comparing what happens at 12 km altitude in the tropics to 12 km altitude at the poles does not make sense at all, because at the poles we are already dealing with the stratosphere, while in the tropics we are still way below the tropopause. Staying on a pressure level ensures that we take these differences into account.


How do the known abrupt climate change events fit into the xkcd Earth temperature timeline? The xkcd "Earth Temperature Timeline" depicts the global average temperature during the past 20,000 years, based on the known data. We already have a question about the chart's general accuracy, but I have a more specific question.

The chart says that multi-decade, multi-degree global climate shifts should be easily visible, and the fact that the chart is smooth and shows no such variances until it suddenly jumps in the past hundred years gives the graphic its visceral power.

But then, I found out about a myriad of known abrupt climate change events, such as the Younger Dryas 12,000 years ago, during which the temperature of large parts of the northern hemisphere decreased in temperature by 2 to 6 degrees Celsius over mere decades, then stayed that way for a millennium. Yet no rapid shifts like this are visible in the xkcd chart. This seems to imply that either

the temperature shift in much of the northern hemisphere during the Younger Dryas was exactly counterbalanced by concurrent temperature shifts in the rest of the world so that the global average looks virtually the same; or
the xkcd chart omits important details; or
there are major contradictions in climate data from various sources.

Are one of these options correct, or is something else going on?

The apparent contradiction comes primarily from #1 but #2 also pays a small role here...

Temperature decreases during the Younger Dryas greater than $2^{\circ}$C are believed to have occurred almost exclusively above $30^{\circ}$N in latitude. The bulk of the tropics are thought to have been relatively stable during this time and the southern polar region showed slight warming. Additionally, global temperature averages are generally weighted by area and only one fourth of the earths surface lies between $30^{\circ}$N and the North Pole. All this combines to produce what is thought to be around 0.6$^{\circ}$C of global cooling at the start of the Younger Dryas (Carlson, 2013).

Randall does cite several sources in the top right of his graphic but Shakun et al. (2012) is the only one that presents meaningful temperature data during the Younger Dryas. And in fact, the comic's proxy data (dashed) temperature curve closely matches the temperature curve presented in this article over this period (curve d in the figure below).

Interestingly, while Shakun et al. (2012) does show a global temperature decrease close to $0.6^{\circ}$C 12,000 years ago, the change doesn't appear to happen abruptly (at least not on the scale of decades). In the text of the paper the authors state that they built their temperature data set from 80 different proxy measurements taken over a wide range of locations. It turns out that these proxy measurements have a relatively long time resolution (a median value of about 200 years). That means that while the changes may have occurred very quickly this temperature curve is going to fail to capture that variability and appear "smoothed out". This does make the xkcd graphic a little misleading since the large temperature increase at the end is produced from data using a much finer time resolution, but this is a flaw common to all "hockey stick" temperature plots.


Identifying trichroic crystal systems An unknown mineral shows three distinct pleochroic colours. Explain what observations you need to make in order to decide which crystal system it belongs to.

If it has three pleochroic colours this means that it must have a biaxial indicatrix and must therefore be orthorhombic, monoclinic or triclinic. In order to work out which one of these it is you need to work out the orientation of the indicatrix with respect to the crystallographic axes but I'm not sure how you can do this. You can measure the extinction angle with respect to things like cleavage but if it's an unknown mineral then you don't know how the cleavage is oriented with respect to the axes. How do you determine which direction the crystallographic axes are in using a petrographic microscope?

Theoretical answer:

You need to measure extinction angles. If it is always extinct when aligned to cleavage or crystal faces, then it is orthorhombic. If it sometimes aligns and the colour is consistent, it's monoclinic. Otherwise it's triclinic. You do not need to know how cleavage is oriented with respect to the axes in advance because there very few orthorhombic minerals with oblique cleavage (if any at all).

Practical answer (and a rant):

I have no idea why is this still taught in 2016. The motivation of this thing is to know optical properties so you can derive chemical information from them. These days it's probably cheaper and faster to put the sample in XRD or SEM-EDS to know what it is. Even when three colours exist, it is usually very subtle and you will need a lot of self-convincing to see the third colour on its own and not as a combination of the other two. Then there's the issue of a real mineral actually having a proper crystal shape and cleavage (good luck doing this on a 10 micrometre wide anhedral crystal in a thin section).


Can we predict the earthquake before it occurs a while? What is the maximum period?What are the signs of an earthquake soon? I want to know the signs before earthquakes and how long it would talk

Short answer is no.  Earthquakes often occur in clusters but the problem is there is no way of knowing when the largest quake has occurred until the series of quakes is completed.  Studies in fault areas measuring changes in magnetic fields, changes in the local water table, radon gas and radio wave emissions have shown to not be reliable indicators of an impending earthquake.

The United States Geological Survey (USGS) has a publication discussing the possibility that animals feel earthquakes before people.  The basic premise is that animals can feel the P waves, the fastest waves coming from an earthquake, that few humans can feel.  However, a baseline behavior for each animal would need to be measured and the stimuli that an animal would react to would have to be present before the earthquake.  So again, animals are not a reliable precursor to an earthquake.

Given no reliable indicator of an impending earthquake, the most important development in saving lives is the use of early warning systems.  There are several countries that have been implementing these for years including Japan, Mexico, and China.  Many seismologists believe that a warning of up to a minute could be given.  Three of the many factors that determine the effectiveness of an early warning are:

Distance between the earthquake source and the closest seismic
network seismometer (station)
Transfer of information to the regional networks
Detection and characterization of an earthquake

This graph presents estimated warning times from distance of epicenter.

Estimated warning times for locations at different distances from the earthquake epicenter. Locations within 20 miles of the fault will likely not receive any warning as, on average, it will take 10 seconds to detect and locate the earthquake.

Source:https://earthquake.usgs.gov/research/earlywarning/background.php


What does it mean when polar nights have twilight? My family and I want travel somewhere with polar night. I looked up  Tromsø, Norway.

"Down all day" beneath means 24 h darkness, no sun and thus no sun-light. Right?
But if  no sun and sun-light, why's there still twilight?

Civil twilight: the sun is between 0 and 6 degrees below the horizon
Nautical twilight: the sun is between 6 and 12 degrees below the horizon
Astronomical twilight: the sun is between 12 and 18 degrees below the horizon

I believe if the sun is lower than 18 degrees below the horizon, all sun rays can no longer reach your location. Hence it is completely dark.


Will the sea get saltier forever? The sea wasn't always salty. It's been getting saltier over millions of years as minerals dissolve.
Is there a natural limit to this process, or the will the sea keep getting saltier forever?
Is there a natural process which removes salt from the sea at a significant rate?
How long would it take for the sea to get too salty to support life as we know it?

@John has answered to the second question: "Is there a natural process which removes salt from the sea at a significant rate?" This is an answer to the first one: "Is there a natural limit to this process, or the will the sea keep getting saltier forever?"
Yes, there is a limit, sea water cannot keep getting saltier forever.
Sea water is a solution of water and salt, i.e., the salt is dissolved in the water. But solubility, the ability of a material to dissolve in another, has a limit called saturation. Once this limit is reached, the material cannot dissolve anymore and precipitate.
Saturation of salt in water is 357 g L$^{-1}$ (at 20 °C, it depends on temperature), about 10 times the current salinity of seawater. If you keep adding more salt to such water, it will not longer be able to dissolve but will instead precipitate at the bottom of the sea.