The temperature of the ocean below 1000 m I have been trying to find data of sea temperatures in the deep sea (>1000 m), but I still haven't found any scientific papers. I have only seen websites talking about the temperatures, but without providing evidence.

So what's the evidence for very low (<10°C) temperatures in the deep sea and what were the methods used to obtain this evidence?

I know about the websites like https://www.nodc.noaa.gov/cgi-bin/OC5/SELECT/woaselect.pl where I can check the temperature, I'm foremost asking for the methodology.

General Information

One major operational system for the measurement of deep sea temperature, salinity and pressure is the Argo program. Individual Argo floats are distributed in the worlds oceans. Their measurement data are scientifically evaluated and are available for public download. Additionally, several research institutions own gliders. However, I am not sure if they are also used operational for deep sea measurements.

Argo floats

Argo floats are large submerged buoys. They are made for profiling the top 2000 m of the world's oceans. The common depth of an Argo floater is approximately 1000 m. Approximately in 10-day intervals they sink to 2000 m depth and afterwards rise to the sea surface, from where broadcast their position and measurement data. Currently, more than 1000 Argo floats are active in the worlds oceans.

The official Argo homepage is here. Here you find a more detailed description of the function of Argo drifters and here you can download drifter measurements.

Gliders

Gliders are one tool for measuring temperature and salinity on vertical transects (actually not a purely vertical transect). Some gliders can go below 1000 m. The disadvantage of a glider is that it needs considerable horizontal space available straight ahead of his direction of motion.

A nice explanation and applications are given here and here.

This is the homepage of the global scientific glider community.


How did these dark lenticular features form? (Near Hoganekkal Falls India.) These photos were taken near Hoganekkal falls in south India. The darker lenses appear to be the same rock type but have varying thickness and do not form a continuous layer. How did this structure form?

It's hard to tell (don't you have other photos?), but it looks like magma lenses.

The area is known for the Hogenakkal Carbonatite Complex, where lenses of carbonatite (a carbonate-rich magma) are found in pyroxenite dykes. See for instance this paper:

  The carbonatites form a series of discontinuous bodies within two nearly parallel NNE-SSW trending pyroxenite dykes intruding Precambrian chamockites. [...] Each carbonatite body consists of discrete veins and lenses emplaced in pyroxenite which has been permeated and soaked to various degrees by the carbonatites.

But it is hard to say if this is the geological formation that you saw without more information.


How much rain falls on the Earth each year? In this resource, it says that the average amount of precipitation falling on the Earth per year is approximately 100 cm.  Integrated across the surface of the Earth, that yields approximately 5.1 × 1014 m3 of water volume that falls to earth. However, it does not give an estimate of how much of that precipitation is specifically rain. So, how much rain falls on the Earth each year?

That's a tricky question, it will vary from year to year but we can narrow it down with some assumptions so I can give an answer. The assumptions will be:

All precipitation over the sea will become liquid in contact with the sea surface and will be considered as rain.
Precipitation over Antarctica is negligible at a global scale.

The second one is pretty reasonable: look at the global distribution of precipitation on the era of satellite data (reference).

With these assumptions we only need to compute the amount of solid precipitation on land (outside Antarctica) and subtract it from the global total. And we can do so using the data provided by the Global Precipitation Climatology Centre, which provide both the global mean precipitation on land:

And the fraction of liquid precipitation on land:

I've downloaded both datasets in ASCII format, and computed that the mean percentage of liquid precipitation is 74.1%, but we can't use that value, because it might be strongly affected by areas with little precipitation. So if we compute a cell by cell total SOLID precipitation per year, and multiply that for the surface of a 1°x 1° cell (considering the effects of latitude), we get a total of solid precipitation for 2016 of 1.5e13 m³.

So with the additional assumption that 2016 was a representative year. That will take your total precipitation of 5.1e14 m³ per year to 5.0e14 m³ per year of RAIN only.

Perhaps we should have expected that there is not much of a difference given that most of the rainfall happen on the sea (The total precipitation on land for 2016 was 1.1e14 m³ meaning that the 13.6% was solid and 86.4% was rain).

Now if you want to consider snowfall over the sea, I don't know of a model with such output product. Therefore, you can make a simple model or make some assumptions to use Sea Surface Temperature to figure out if precipitation will turn to rain at some high above the surface.

But again, if you look at the map of global distribution of precipitation, the fraction coming from latitudes at which you could expect sea surface snow is rather small, so the correction coming from snowfall over the sea is likely to be a pretty small one too.


For what percentage of the earth's history has there been permanent ice? Wikipedia comments here that "Permanent ice is actually a rare phenomenon in the history of the Earth, occurring only during the 20% of the time that the planet is under an icehouse effect." A "citation needed" tag is attached to this remark.

For what percentage of the Earth's history has there been permanent (year-round) ice?

As has been abundantly said in the comments and on meta, there is no proper answer to this question in the current state of knowledge.
But indeed we can at least check if we can come up with a rough estimate (and thus try to see from where this 20% estimate comes from).

Let's first look at the main known glaciations:

The Current one: there is indeed a permanent ice sheet on the East Antarctic continent since, presumably, the early Oligocene (i. e. 35Ma, see e. g. DeConto & Pollard 2003). There is considerable dispute on the exact timing of the onset of the EAIS but we're talking here about differences of <10Myrs, i. e. <0.25% of Earth history, so we can ignore for now this difference.
The Karoo ice age: the Carboniferous-Permian glaciation is thought to have spanned from the Mississipian (ca. 360Ma, Buggish et al. 2008) to the Sakmarian (ca. 290Ma; Korte et al. 2008), giving us a ca. 70Myr interval. However some studies have shown (e. g. Fielding et al. 2008) that it was most probably an alternance of glacial and nonglacial climate rather than a continuous glaciation, meaning that permanent ice was probably present for way less than 70Myr.
The Ordovician glaciation: it is thought to have started between the late Katian and the early Hirnantian (ca. 445Ma) and to have ended either before the Silurian (see e. g. Finlay et al. 2010) or at the beginning of the Silurian (ca. 440Ma; see e. g. Cooper & Sadler, 2012). Hence an interval of 1 to 5 Myr. This one has been studied extensively as it is thought to be associated with one of the 5 major mass extinctions of the Phanerozoic (see the whole Sepkoski corpus).
The Cryogenian: two glaciations are thought to have marked the Cryogenian (see e. g. Shields-Zhou et al. 2012), the Sturtian (ca. 720 to 660Ma) and the Marinoan glaciations (ca. 650-635Ma), thus accounting for 75 Myr.
The Huronian glaciation lasting presumably from 2.45Ga to 2.22Ga (see a small review in Van Kranendonk, 2012). The issue here being that the accuracy of paleoproterozoic event datation does not really allow to go much more into the details as this (both because of the extreme scarcity of the data and the relative low resolution of the dating techniques). Leaving us with a glaciation (or more probably a series of glaciations) that could have lasted up to 230Myr.

To this, we can add various minor glaciations that are still highly debated such as the Late Devonian or the Middle to Late Jurassic (e. g. Dromart et al. 2003). Whether of not they indeed occur, they hardly account for much of Earth History when aggregated so we can ignore them safely for the purpose of a rough estimate.

This leads us to 35 + 70 + 5 + 75 + 230 = 415 Myr which equates to ~ 9 % of Earth History. Which is still far off 20% and I doubt that the minor glaciations put together account for 500Myr.

Buggish, W., Joachimski, M. M., Sevastopulo, G., Morrow, J. R., 2008. Mississippian $\delta ^{13}C_{carb}$ and conodont apatite $\delta ^{18}O$ records — Their relation to the Late Palaeozoic Glaciation. Palaeogeography, Palaeoclimatology, Palaeoecology, 268: 273-292.
Cooper, R. A., Sadler, P. M., The Ordovician Period. In Gradstein et al. 2012, The Geologic Time Scale 2012: 489-523.
DeConto, R. M., Pollard, D. 2003. Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric $CO_2$. Nature, 421: 245-249.
Dromart, G., Garcia, J.P., Picard, S., Atrops, F., Lécuyer, C., Sheppard, S.M.F., 2003. Ice age at the Middle–Late Jurassic transition? Earth and Planetary Science Letters, 213: 205-220.
Fielding, C. R., Frank, T. D., Birgenheier, L. P., Rygel, M. C., Jones, A. T., Roberts, J., 2008. Stratigraphic imprint of the late Palaeozoic ice age in eastern Australia: A record of alternating glacial and nonglacial climate regime. Journal fo the Geological Society, 165: 129-140.
Korte, C., Jones, P. J., Brand, U., Mertmann, D., Veizer, J. 2008. Oxygen isotope values from high-latitudes: Clues for Permian sea-surface temperature gradients and Late Palaeozoic deglaciation. Palaeogeography, Palaeoclimatology, Palaeoecology, 269: 1-16.
Shields-Zhou, G. A., Hill, A. C., Macgabhann, B. A., 2012. The Cryogenian Period. In Gradstein et al. 2012, The Geologic Time Scale 2012: 393-411.
Van Kranendonk, M. J., 2012. A Chronostratigraphic Division of the Precambrian. In Gradstein et al. 2012, The Geologic Time Scale 2012: 299-392.


Are there datasets like the global land-ocean temperature index for land surface temperature only? I have no background in climate science, but I've become interested in explanations of the so-called "global warming hiatus" from 1998-2013. One explanation that people seem to think is convincing comes from Karl et al who, if I understand correctly, say that the apparent hiatus could actually be an artifact of changes the way we calculate sea-surface temperature -- specifically that during that period we moved from primarily boat-based temperature measurements to primarily buoy and Argo float measurements. Since boat measurements are systematically a bit warmer than buoy measurements, the gradual switchover looks like a slight cooling trend when in fact it's just a difference in measurement technique.

I wanted to assess this argument for myself as well as I could, so I thought, if Karl et al are correct, then we shouldn't see evidence of hiatus in land-based datasets then, right? So I went in search of a dataset like NASA's global land-ocean temperature index but constrained to land only. I have found some very granular LST datasets (like this), but I don't think I've got the expertise I'd need to turn them into a yearly global timeseries (e.g. should I just take a straight mean of all the datapoints? Should I be weighing by landmass or seasonality, etc?).

So my question is, does a high-level aggregated yearly mean LST dataset exist? If not, why not? And at a higher level, does my approach to investigating the Karl et al work make sense, and if so has someone who knows what they're doing already done it?

Yes, NASA GISS has it here . If you go to the main page and search for 'Global Mean Estimates Based on Land-Surface Air Temperature Anomalies Only (Meteorological Station Data, dTs)' within that page you will find the links to the above, plus northern and southern hemispheres.


Source of Dresser Formation 3.5 Ga dating I've seen many papers and sites that give the dating of Australia's Dresser Formation as 3.5 Ga (variously 3.48 or 3.49 Ga), but I can't seem to find the source of this.

Where does the dating come from, and what is it based on?

From Australian Government- Geoscience AustraliaAustralian Stratigraphic Units Database:

Panorama Formation:  Paleoarchean min age: 3427 MA Age method: isotopic, U/Pb-Pb/Pb ion probe

Dresser Formation: Min Age: Ma: 3477 Age method: inferred, overlying unit

McPhee Formation:  Min Age: 3477 Age method: isotopic, U/Pb-Pb/Pb ion probe


How would waves (in a fluid) behave without intermolecular attraction? Water molecules, as many people know, are polarized, and so water molecules tend to have an attractive force between them.  But how would the waves in water behave if this attraction no longer was present, but everything else was the same?

There are different factors that make water a media for waves. For transversal waves the viscosity and cohesion of molecules are essential. Even if the water is assumed not to evaporate. Try to imagine pushing a boat forward in a liquid with low viscosity. The propeller will just easily skid without generating any wave or traction.
However for P waves a liquid with low or no viscosity would still work as long as it can contract and expand under stress. If you in a crude way look at a differential cube of that liquid omega= (k/m)^1/2. K is the water stiffness index and m is its mass.


How do we know the Arctic is just ice? If I look at an Earth's map, the Arctic/North Pole always appears just like water. Evidently this is actually covered by ice, with an area depending on the time of the year. If this area is bigger than than the United States and there have been very few expeditions, how do we know there are not any (big) islands beneath the ice, like a hidden mini continent?
My guess is that submarines may have been able to map all out but it is a very wide area and submarines haven't been around for that long.

The sea floor has been mapped using sonar from ships as shown here, and radar. But the fact was first discovered long before these technologies existed by sailors who got stuck in the ice. The entire ice sheet is floating and spinning at a relatively high rate of speed. When they got stuck, they could see, from the stars, that they were moving. I cannot find it now, but I remember reading on project gutenburg a terrifying historic first hand account of being stuck up there, and seeing that they were moving away from Europe and civilization and could not move their ship.


What are the sunniest places on Earth? (including oceans) This question did arise when thinking on offshore solar power plants, what's their potential, and how efficient would they be compared with land based counterparts.

Recently, it is becoming more common to hear about offshore floating power plants, like this one, this one or this one.

But when it comes to big projects, usually solar power plants are planned in very sunny places, like the Arizona desert to maximize output the power.

And when looking for the sunniest places on Earth, all the lists and ranks I've found only include land areas. All the above had motivated the following related questions:

Is it true that no place in the surface of oceans gets as much solar energy as a sunny place on land?
Are the oceans always cloudy? Or cloudier than land?
How much of the solar energy reaching Earth's surface fall on land and how much on the oceans?

It is an interesting question, and despite that latitude is the main control of the amount of solar radiation that reaches the top of the atmosphere at a given location, the answer will be determined by how exactly weather patterns distribute across the different latitudes. Therefore, a solid answer will require to be supported in data.

A good dataset for this propose is the one at the Surface meteorology and Solar Energy. I recently used it to answer a somewhat similar question. In this case I'll use the Insolation Incident On A Horizontal Surface dataset, that provides a 22-year average (July 1983 - June 2005) of solar insolation in kWh/m^2/day (kWh per square meter per day) derived  from satellite measurements, allowing worldwide coverage at 1° resolution (~110 km).

The dataset looks like this:

Where the numbers in the color scale on the left have to be interpreted as average kWh/m^2/day. We can see a clear latitudinal gradient were the equatorial latitudes receive much more energy than polar ones, however there are significant longitudinal variations due to the different climates that can be found at the same latitude.

In a first look, land areas doesn't seem to receive more energy. Land over the equator seem receive relatively less energy (due to cloud cover), and the deserts "hot spots" like Atacama and Sahara are quite far from the equator (~2000 km). In the other hand, there seem to be extensive equatorial waters that receive a lot of energy.

The figure shows the maximum of the data set (6.98 kWh/m^2/day), giving to the Atacama desert in Chile the title of the area that receive more solar insolation on Earth. However, it is a fairly small area.

The following picture show the same dataset overlaid on top of a world map to make land areas highlight a bit more, and contours on the areas receiving more than 6 kWh/m^2/day

It is clear here that despite that the Sahara and Atacama deserts are within the areas with more insolation, the vast majority of such areas lay over the oceans.

So, in regard to your first question, I would say that despite the first place of the highest solar irradiation contest go to the Atacama desert, the rest of the podium belongs to the oceans. In fact if we look at the "pixels" of the dataset with values above 6.9 kWh/m^2/day, there is two in the Atacama desert and 16 in the Pacific ocean. So in general I would say that it is false to say that no place in the surface of oceans gets as much solar energy as a sunny place on land.

To answer the second question we can have a look at the dataset of the Monthly Averaged Clear Sky Days (i.e.  cloud cover less than 10% over the same 22-year period), and it looks like this:

 This time the color bar numbers have to be interpreted as average clear sky days per month. Here we can see that the high insolation in the Atacama desert is explained by a very large amount of clear sky days (17 per month) while in that sunny Pacific ocean spot there is at most 10 clear sky days in average. But wen it comes to the record of the most clear skies days, the winner is Antarctica, with large expanses with 20-22 clear sky days ion average. However, if there is several month without sunshine I don't know if it could be translated as the "sunniest" place.

So, in regard to your seconds questions, I would say YES, oceans have in average a much more persistent cloud cover than land. In fact, pretty much all the areas with more than 10 clear sky days per month in average are on land, and the vast majority in Antarctica.

Now, to answer your third question we have to separate the data of the first dataset (first figure) into land and sea. To do that, I've used the ETOPO1 Global Relief Model, saying that any place at an elevation of 0 meters or more would be land, and anything below zero is ocean. I've also transformed the data to an equal-area projection, to make the calculation easier, as in the original data a "pixel" near the poles was much smaller than one at the equator.
The land area insolation looks like this:

And the sea insolation like this:

And the mean total insolation received by land is 6.45e14 kWh/day or 645 PWh/day (peta watts per day), in contrast with 1,656 PWh/day by oceans. Therefore 72% of the energy end up in the oceans.
The total is 2,301 PWh/day, which as a sanity check, we can see that it have the same order of magnitude than the total amount of energy hitting the top of the atmosphere, a value that we can easily calculate using the solar constant and Earth's radius (24*1.362*pi*6378100^2 = 4.177e15 Wh/day= 4,177 PWh/day). These two totals don't match as expected because a significant fraction of the energy gets reflected (Earth's albedo is 0.3) or absorbed by the atmosphere.

To wrap up all this information in the context of your question. There is indeed a great potential for offshore solar power, that maybe we will tap into in the future. However, the transport of the energy could be now the main constraint. Making offshore project viable only in areas of high real state prices, making too expensive to build them on land, and therefore making the offshore alternative a sensible one. In those cases the location is mostly dictated by the location of the demand more than the location with higher solar irradiation. If I let the imagination loose, maybe those large high-irradiation zones in the Pacific could one day host floating industrial complexes, producing and using the power on the spot for manufacturing or other industrial processes.


How is Doppler radar used in rain prediction? How is Doppler radar used in rain prediction?

The easiest answer is that Safe Haven is a movie, and the writer made a factual error (which is not uncommon). I have not watched that movie, so I am unsure what type of situation they were dealing with. Doppler radars do not predict, but they observe.

What is possible, however, is extrapolation and the creation of inferences. For example, tornadoes are not directly predicted by Doppler Radar, but by making inferences from the data, a meteorologist may detect a tornado. In a similar sense, if the radar-derived 'storm total precipitation' has estimated an average 0.25 inches of rain from a squall line for the past 200 miles, one may extrapolate, or estimate, that the squall line will produce ~0.25 inches of rain. Could the squall line alter its path or intensity and drastically change the amount? Sure, but without additional information, including information not derived from a radar, that would be a difficult task.

Edit: Ok, I think I have a better idea of what the question was and how it can be answered.
Doppler radar can measure wind speed relative to the radar site. So if can sense how fast a storm is approaching. Assuming the storm does not change it's speed, and given it's history, you can infer when it will arrive at the radar site. For example, if a storm is 50 miles away, and it moves at 25 miles per hour it will arrive in $50\text{ mi}\div 25\frac{\text{mi}}{\text{hr}}=2\text{ hr}$, provided the storm does not change.


Relationship between rainwater and solar radiation I am an enthusiast in this area and reading some scientific articles on precipitation forecasting and solar irradiation, I was wondering if these two variables have any direct correlation or relationship.
I have no experience to start a discussion and would appreciate some insights.
Something like: Is it possible to determine a specific location that gives us both precipitation and solar irradiation, for example, to have a household self-sufficient in drinking water via PV?
Regards!

Any relationship or correlation? That is quite a broad standard. Invoking Tobler's first law of geography, there is a relationship. I would question if there is such a thing universally, but there are some instances that we can see an overlap. For example, many deserts receive plenty of sunlight, but observe little rain.
One of the first things that comes to mind are instances where these overlap. A plant needs both water and radiation to grow.
Another thing that comes to mind is the investigation of land-atmosphere coupling metrics. There are plenty of metrics that try a variety of methods capturing a plethora of different dynamics. These are indirectly associated with sunshine, as the surface fluxes are driven by solar radiation.
As far as finding a specific spot for self-sufficient drinking water, I am afraid that any relationship you get will not be one that will yield such a desired result. If you want an environmentally friendly, generally reliable way of attaining water, try well water.


What is the largest earthquake attributable solely to volcanic activity I was recently and for the first time caught in an earthquake. This being my first time, I freaked out and had no idea whether the building was going to collapse or not.
I was later told that this earthquake was nothing to worry about because it was due to the volcanic activity of a nearby volcano (4.9 on the Richter, 1km depth). It caused minor damages near to the volcano, but nothing measurable in our location about 30 km away.

This got me thinking - if volcanic activity is less dangerous than plate activity (because it's closer to the surface, perhaps?), is there some upper limit to the scale of such earthquakes? I suppose that earthquakes and volcanic activity are correlated in some way, but I'm not considering the volcanic activity due to plate movement, rather the "normal" activity of active volcanos.

Or rather:

What is the largest magnitude measured of an earthquake attributable solely to volcanic activity?

Earthquakes associated with volcanism or volcanic rifting are typically small. They are caused by over-pressurized magma as it moves around and intrudes into brittle rocks.

Sometimes, e.g., in Hawaii, you get earthquakes due to the gravitational sliding (e.g., the M6.9 earthquake in 2018 beneath Kilauea) as new eruption causes the volcano to grow in size (adding mass) which in turn cause it to slide over the older volcanic rocks underneath.

I don't think there's an exact upper bound for such an event but it is unlikely to exceed ~7.5. Another thing to keep in mind is that rocks near active volcanoes tend to be relatively hotter which in theory should cause less shaking during the earthquake (due to lower stress drop).


What is a good definition of the word "rock" for teaching? Note that it needs to include coal and chert, therefore the common answer "a rock is made of minerals" is incomplete.

I usually tend to think that the shorter a definition is the more it introduces ambiguity and errors. So I would just think about your audience and choose an appropriate length (You  didn't mention the level you are teaching for).

Similar to the definition of life you can offer to your audience characteristics, which some rocks will conform more or less. This is just a list I thought out:

Rocks are solids at the Earth's surface

I would definitely include solid ice, which is the primary lithology of Greenland and Antarctica
How solid? Most of them are incompressible to high pressures(Exception porous sediments)
With lower temperatures more things become rocks (even our Sun).
Density varies greatly (bring a lead-ore and a floating tuff)

Rocks are consolidated

To differentiate them from sediments rocks have underwent a certain amount of compaction and cementation

Rocks form through purely anorganic, organic, or a mixture of those processes

This category probably needs the most explanation on how diverse the pathways to a rocks are

Rocks form through natural processes

Human-made rocks exist so instead of tossing that aside, talk about the interesting differences and similarities. Natural rocks fulfill the requirments of chemistry, physics, thermodynamics. Human-made rocks additionally fulfill requirements of pragmatism: a brick needs to be square in order to build a wall; holes make it light and insulate better; etc...

Anorganic rocks fall into natural categories which obey the conditions set by their chemistry and the resulting eutectic points, reduce chemical oversaturations, and minimalization of the Gibbs free energy (There is a reason why granites in all their diversity, are actually pretty similar)
Organic rocks obey the requirements by organisms of which nutrients exist in excess and can be used to synthesize a skeleton or shell.
Rocks don't fulfill the requirements of life

Talk about what makes living matter special. Talk about, that on planets devoid of life everything is a rock or sediment.

Rocks have a scale

One atom or chemical compound is not enough to make a rock. At what scale does language speak of a rock. What scale is so big that other words are introduced. Talk about how words are also just concepts defined by other words which are concepts themselves (This is what makes science fun)


Can Coriolis Effect cancel itself? Say a plane moves from 40° North to 40° South, and the plane flies in straight line without considering the Coriolis effect. Will it still reach the destination.

All I mean is whether the deflection caused in the Northern Hemisphere can be compensated for in Southern Hemisphere

In an idealised scenario (ie where the plane is flying due north or south at a and there are no other perturbations to its course apart from the Coriolis effect), yes. And I guess it would be the most efficient course too!


How can a storm drop 40 inches (1 metre) of rain? Hurricane Harvey dumped more that 20 inches (500 mm) of rain over a large region, with 40+ (>1000 mm) in some spots... and much more expected.

How is that possible?

Does the atmosphere really hold that much water?

Or is it getting repeatedly evaporated from the ocean and dropped onto the land by the circular winds, implying an enormous evaporation rate while over water?

You were right to question whether the atmosphere really held that much water.  It comes nowhere close!  We use precipitable water to track this, which is the measure of all moisture in the entire column of air in the troposphere.  We can get good widespread estimates from remote observations.  This animation shows current amounts of precipitable water levels across the US from satellite.  Here is a still from this afternoon (Sunday, August 27) during the Harvey event:

75 mm is less than 3 inches.

We also get in-situ exact measurements worldwide from twice daily radiosonde balloon launches.  Unfortunately none are located right near the locations receiving excess rainfall.  But you can check US sites of current precipitable water measurements any time by going to SPC's sounding page and looking for the PW value in the left side of the bottom table.  SPC also maintains a climatology page for precipitable water and other values.  You can see there that 3 inches (76 mm) of moisture in the sounding is extremely rare, and no US site has ever had 4 inches (102 mm) of precipitable water.

However, the answer is also not truly found in evaporation rates.  The conditions in strong hurricanes do greatly enhance evaporation rates due to the high wind speeds and warmer waters.  Measurements are actually a bit difficult to come by in such extreme conditions, with challenges in isolating evaporation effects from spray as well as in getting the instruments positioned into such environments (new field campaign: who wants to take the research ship out into the category 5 hurricane!?!).  As this 2007 study by Trenberth et al. noted:

  We are unaware of reliable estimates of evaporation in hurricanes, and published measurements do not exist in winds above about 20 m s−1 although some progress has been made in the Coupled Boundary Layer Air-Sea Transfer Experiment (CBLAST)

However, in that study model analyses suggested that evaporation rates in the core of hurricanes are likely no more than 1-2 inches (25–50 mm) per day.

How is that possible?

It's quite important to notice that heavy rainfall - well over 5 inches (125 mm) - can actually fall in as little as a couple hours almost anywhere, such as in this 2015 flood event in Nebraska.  How can that be?

The secret lies in the nature of even the weakest storm: even as a storm is just beginning to form, it begins to draw in air from surrounding areas.  This is NOAA's diagram of a typical developing thunderstorm cell:

You can see the curve at the arrows near the bottom, indicating inflow of surrounding air into the storm.  This inflow turns a thunderstorm into more of an engine, processing a continuing stream of incoming air, removing its moisture.  In a single cell thunderstorms in an environment without background winds, the "waste" air will eventually pile up and choke off the influx.  But even in such circumstances, a few inches of rain may fall.  That isn't by using up all of the moisture from the cloud's environment, but instead by using just a portion of the moisture from the reservoir in and around the cloud.

If some upper level winds exist to help exhaust the "spent" air, storm systems can persist for even longer periods of time.  For example, the Midwestern United States commonly sees long-duration late summer heavy rainfall initiated along stationary boundaries in which inflow lacks direct access to significant warm water bodies.

Larger systems that dump huge amount of precipitation over greater areas must pull in a more consistent, stronger inflow of warm, moist air from greater distance.  Examples of this happening include the Pineapple Express for rainfall in California/the southwest US, the low-level jet for spring and summer squall lines in the Plains, onshore winds during the Indian monsoon, and air from off the Gulf Stream in Nor'easters.

In all these regional large precipitation events moist air gathered from a great surface area flows into a smaller region.  As the air approaches, it is lifted by the low pressure and its associated features, condenses, and finally falls as rain (or snow).  This process is often termed "moisture convergence".  The Storm Prediction Center also offers plots of localized deep moisture convergence [choose a region, then look under the upper air menu].  The convergence contours, shown in red, really show the piling up of humidity that is causing the heavy rainfall in Harvey:

But perhaps to visualize the scale involved in creating a catastrophic largescale flood such as Harvey, this plot, created from a base image from pivotalweather.com, best shows the conditions around the storm (from the GFS model):

Basically the atmosphere of the entire Gulf (and beyond) is being pumped into the southeast Texas area.  So although the air can only hold a couple inches (some 50 mm) of water, and evaporation rates are typically only a fraction of an inch (several mm) per day... bringing that together from such a large source region, and focusing it down into one small area... can lead to these awful extreme deluges.

Addendum: It should also be highlighted that the NHC adds in their report on Harvey that rising motion was also enhanced by a front which had stalled in the area.  Air being advected in by Harvey's flow would naturally rise over that layer of cooler air when moving inland (a process called isentropic lift), which proves particularly efficient in condensing out the (abundant) moisture en masse into rainfall.  Most substantial regional floods require similar existence of a significant broad lifting mechanisms overlaid with such a relentless inflow of warm, moist air.


Where on Earth has the least changing temperature? Is there a map that shows places where the temperature changes the least season to season? Is there a place on Earth where the temperature is the most constant in a comfortable range?

To answer the first question, yes, there are maps showing the seasonal temperature variation, for example here

Unsurprisingly, the equatorial areas have the least variation because the angle of the sun relatively to the earth changes the least with seasons.

Regarding nice weather- I have worked as a geologist in northern South America and the Caribbean. In the lower lying areas (e.g. Aruba) I often thought it was too hot to be pleasant to work, but beachgoers think that was perfect weather. In the mountains it was often more pleasant, subjectively.
One city I visited where the temperature is remarkably stable is Medellin in Colombia - the "city of eternal spring". Situated close to the equator, temperature is always nice there (daily mean at 22 degrees throughout the year), but it can have a lot of rainy days.


(How long) would Earth's atmosphere last without a global magnetic field? The Earth's magnetic field provides an important protection against the solar wind (for example, see Wikipedia on Earth's magnetic field and references therein).  Mars may have lost its atmosphere because it did not retain such a magnetic field, although Venus does not have an intrinsic magnetic field either.  This raises the question: what will happen to Earth's atmosphere if the global magnetic field would disappear?  Would the solar wind blow it all away?  If so, how long would it take until only a small part (<10 kPa sea level pressure) is left?

Atmospheric escape is a topic with a long research history. It is complex and is being addressed with both measurements and simulations.

For example, the question of atmospheric escape is still actively researched at Mars, and the MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft mission is for example dedicated to this topic. Mars is a planet without a significant global magnetic field (although it does possess crustal magnetic anomalies); in fact its planetary dynamo was active and then stopped about 3.6 billion years ago, which considerably reduced the strength of its magnetic field.
So understanding the evolution of its atmosphere helps to relate to what would happen if Earth would loose its magnetic field. The question of atmospheric escape at Mars is relevant concerning the fate of water (geological evidences indicate the presence of liquid water in the past, which suggests a warm and dense atmosphere able to support it at that time).

Besides thermal atmospheric escape, there is also non thermal escape, including removal by asteroid impact (in the past) and by interaction between the atmosphere and the solar wind leading to pickup of atmospheric ions (in the past and continuing today).

Some examples of references to the scientific literature about atmospheric escape at terrestrial planets (abstracts):
Outgassing History and Escape of the Martian Atmosphere and Water Inventory
or
Nonthermal escape of the atmospheres of Venus, Earth, and Mars


Canadian equivalent to AMLIS database? I am interested in in situ coal fires. In furtherance of this, I am hoping to find a database of Canadian mine reclamation sites, complete with incident or status reports and descriptions of specific problems.

I've poked around a very small bit in the Federal Contaminated Sites Inventory, but I'm hoping there might be something a bit more specific or targeted out there -- something more like the equivalent of the United States' Abandoned Mine Load Inventory System (AMLIS) database.

Any pointers?

Try:

Federal Contaminated Sites Inventory

as well as

Crown Contaminated Sites Database (British Columbia)

Orphaned/Abandoned Mine Site Rehabilitation (Manitoba)

Abandoned Mines Information System-AMIS (Ontario)


How has river to ocean flux changed over the last 500 million years? Do we have any rough indices of how this flux has changed? I'm particularly interested in knowing whether the flux was higher or lower during the time of Pangaea, or during the time of the unusually warm Eocene (or at least up to the earliest time that this flux can been measured from).

There is no direct answer. One way to think about this is to consider the water cycle. Water evaporates from the oceans and is precipitates over land. Distance from the ocean affects the amount of precipitation so at the center of a large contintent you may have less precipitation than over a smaller one. Mountains also drain moisture out of the air as it is heaved. hence the topography of the continents affect this effect. A Pangea directly after collisions will likely have more and higher mountains than a later stage when break-up is imminent. Location on the earth's surface is a third factor since we have larger scale circulation belts that affect the atmospheric conditions so that we have a tropical belt (the Intertropical Convergence Zone) around the equator, a drier zone north and south of the ITCZ, followed by temperate and polar zones towards the poles. Hence the location of the continent(s) and their topography will affect the zones and the zones will will determine which parts receive more or less precipitation. Furthermore the movement of the continent(s) through these climate zones change conditions as well.

In summary, we can be sure it is not constant over geological times. The only possible way to get some relative handle on the question would be to try to apply a global circulation model to past continent configurations, including topographical effects and see what comes out, being aware of all uncertainties and comparing with geological evidence.


How to design an experiment to quantify back radiation from atmospheric carbon dioxide? Based on our current knowledge of CO$_2$ and current instrumental techniques, how big would a laboratory sample of air with 400ppm of CO$_2$ need to be in order to quantify the back radiation from CO$_2$?

I am envisioning a large container with many cubic metres of gas, probably thermally isolated longitudinally and with a radiative IR input at one end (A) plus measuring apparatus at the other end (B) and some distributed thermistors throughout. We know the thermal input at A, measure the thermal output at the B and measure the trapped thermal energy via the thermistors.

I would like to get a result with something like +/- 1% accuracy. Would this be possible? Assume I have a budget of at least $10,000,000.

The thing is, we don´t have any instruments(to my knowledge) to measure the intensity of that radiation. But, we measure the intensity of atmospheric emission from space with satellites, which is seen as the "effective temperature". Logically this is the same as the net radiation downwards. And heat transfer then confirms that no net radiation arrives at the surface. Which is equal to "no radiation at all". Because "net" radiation is the only radiation that can heat anything.

There are lots of people claiming that measurements done with IR sensors and pyrgeometers confirm backradiation. This is not true and it is based on a misunderstanding of the function of the device, as well as misapplication of the stefan-boltzmann equation. Both IR-thermometers and pyrgeometers use the s-b equation  in combination with a thermocouple or thermopile(pyrgeometer). They are both a kind of more advanced and more sensitive thermometers. The thermopile consist of a sensor measuring a gradient across itself indirectly by changes in resistance acting on a current through the thermopile. So, by determining the gradient in the thermopile, it can sense the amount of heat transferred to the surroundings using the s-b equation. When someone claims measurements show "back-radiation", they refer to measurements done with these devices. As most interested people understand, a measurement of heat transfer away from the device, cannot show incoming radiation from a colder atmosphere. If you measure something hotter than the temperature of the thermopile, sure, then you have high accuracy. But a measurement of "back-radiation" from the atmosphere is per definition a measurement of something colder than the device. Because the atmosphere is almost always colder(exception is inversion, but that is not relevant). So any measurement of backradiation made from the surface, is a measurement of nothing. It is simply what the device doesn´t measure coming from the atmosphere. This is what I mean with "misapplication" of the s-b equation. It can not, and should not, be used that way. That is, to add flux densities that are not calculated as "net" transfer.

In regards to your suggested experiment. Unless the gas is hotter than the instruments(if using IR-instruments), you will measure a heat sink, not any backradiation. And, yes, that is what greenhouse gases really are. Heat sinks. The earth emit its heat to the ultimate bottomless heat sink in space, the only observed infinity, and greenhouse gases are added heat sinks along the highway for heat, that leads to 3 Kelvin space.


What is the reason why there are radiosonde measurements in the atmosphere? I have seen weather balloon measurements of air.

Why is this done?  Aren't the measurements we take on the ground enough?

The reason is that we need them!  And we could probably do with more of them (e.g. bigger launch budgets).

Surface observations will tell us where fronts are, where low and high pressure is, and how surface temperature and moisture are being advected.  We can also deduce large scale ascent or descent (vertical motion) from surface divergence and convergence.  We might even be able to provide very short term forecasting, though the skill won't be great. To know how the surface will evolve you need to know what is going on above the surface.

If we know what the 500 mb surface looks like, we can combined this information with the surface fields and some quasi-geostrophic theory and do better with short term forecasts.  With just one upper air layer we can see how the feedbacks between the mid/upper-troposphere and the surface will behave and better predict the development and motion of low pressure systems.

To provide more accurate forecasts, have a shot at predicting convection, and provide longer term forecasts we need more information about the vertical structure of the atmosphere.  The current state of models are such that one of the best things we can do to improve them are to provide better initial conditions (better observations and more of them).  Balloon launches are a great way of getting this data.  Ground and satellite based observations can provide parts of this, but we still benefit from being able to directly sample the atmosphere and to calibrate the remote sensing algorithms with the radiosondes.

One example of the necessity of balloon launches is in convection.  Knowing only surface convergence, temperature and moisture is important, but does not tell the whole story.  If the 850 mb temperatures are too warm, it won't matter how good the surface observations look, you won't get convection.  How much energy the storm can tap into depends on the temperatures all the way up to the tropopause (and higher if you want to know how high the cloud tops will be).  Knowing what type of storm to expect depends on knowing the winds in at least the bottom 6 km of the atmosphere.  Having vertical information provided by a radiosonde is the difference in only being able to say "the air is warm and juicy" versus being able to say "expect isolated supercells today with large hail and straight-line wind damage" or "despite the high dew points, the capping inversion and associated CIN will suppress all convection today -- no storms" given the exact same surface observations.

And yes, models can give us the upper air structure to base these kind of statements on, but remember the radiosonde launches are where a lot of the upper-air data comes from that allows the models to work well comes from.


How to easily remember orientation of latitude and longitude? Ever since the 3rd grade, I've been troubled by the inability to remember if Latitude runs East/West or runs North/South. I would always stress out BIG TIME during my Geography class.

I'm much older now, and I still have trouble telling them apart...

"facepalm"

Are there any good tips or tricks to help me remember which direction each runs?

I also mixed Longitude and Latitude until I heard someone saying '... at high latitudes.' in a conference talk.

In my mind, the picture of the Earth shows the Earth with the North and South poles at the top and bottom (or reversed, doesn't matter). High describes a vertical orientation. Therefore, the latitude changes in North-South direction.

Additionally, because the horizontal degree scale has a discontinuity at 360 degree (0 degree), it does not make much sense to distinguish high and low values in horizontal direction. Hence, high values are in vertical direction (= latitude).


Why did it take so long to discover the volcanic nature of mid-oceanic ridges? I just read this article and was astonished to see the following:

  Oceanographers stumbled on [the mid-oceanic ridges'] volcanic nature in 1973.

What I find surprising is how recent that is.

Considering that

the history of geology in general goes back at least 3 or 4 centuries
the study of plate tectonics goes back to 1912 (even though it took a few more decades to gain wide acceptance)
oceanic ridges were known at least as early as 1872
the correlation between seismic activity and volcanoes has been known for some time (I don't know exactly how long, but certainly the Romans felt the ground shaking when Vesuvius' erupted)

Then my question is, with regards to the (seemingly unusually) recent date quoted in the above article:

Why did the discovery of volcanic activity at sub-oceanic plate boundaries take so long?

If it weren't for WW2 and the search for German submarines, the discovery of mid-ocean ridges might have waited until satellite based gravimetric mapping in the 1980s. It was the use of fine magnetometers (if I remember correctly) used to detect submarines that discovered the banding of magnetic stripes on the Atlantic ocean floor, followed by it's mirror image after a certain mid-point in the ocean basin. When superposed with bathymetric maps, it was further discovered that these magnetic stripes had their counterpoint in the same topographic region on the other side of a high point.

The analysis of thousands of these ship transect records (released by the Navy following WW2)  led to the creation of partial ocean floor maps revealed very long parallel strips of rocks containing magnetic reversals reflected in mirror symmetry on the opposite of a mid-ocean rise. Ocean drilling then confirmed that only a spreading volcanic ridge, spewing magma over tens of millions of years could create such features. Following that, precise seismological mapping also confirmed this developing "theory" of plate tectonics, that laid to rest Alfred Wegener's model.

These were heady times for the geologic community in the 60s and early 70s! All thanks to the Navy and WW2!


What divides Hydrological Unit Code areas of the same level? I'm trying to better understand the Hydrological Unit Code (HUC) system of the United States. I understand the basic hierarchy of it (HUC4, 6, 8, 12) and watersheds/drainage areas. Here's what I want to clarify:

A group of HUC8s can be within a single HUC6, because each HUC8 ultimately drains to the pour point of their parent HUC6. What separates one HUC8 from another HUC8 downstream of it, both within the same parent Hydrologic Unit? I suspect the answer isn't the natural drainage area, because the downstream HUC8 would contain the upstream HUC8 in its natural drainage area - that's based on me thinking that as you shift the discharge point you're examining further downstream, the drainage area you're examining increases.

The most concise, relevant explanation I've come across is from the USEPA's EnviroAtlas Data Fact Sheet on the subject:

  A
  watershed  is
  defined  as  the
  geographic  a
  rea  within  the
  boundary
  of   a   drainage   divide.   Watershed   boundaries
  follow  the  highest  ridgeline  around  the  stream
  drainage
  area;
  the  bottom
  of  the  watershed  or  the  pour  point  is  the
  lowest point of the land
  area
  where water flows out of the
  watershed.
  Hydrologic   unit   boundaries   do   not   always
  surround    a    complete    watershed    but    may    delineate
  truncated portions of a larger watershed
  —
  for example, the
  mid-stem   of   a   larger
  stream   or   river   along   with   the
  tributaries
  in  that  area.
  Hydrologic  units  are
  generally
  synonymous   with   watersheds   when   their   boundaries
  include  all  the  source  area  contributing  surface  water  to
  a
  single   defined   outlet   point.   This   distinction   between
  watersheds and HUCs is important in the context of water
  resources   data   analysis   and   water   quality   monitoring,
  because  the  area  contributing  to  the  downstream  outlet
  point in a single HUC may extend beyond its boundaries in
  an  upstream  direction  to  include  a  number  of  other  sub-basin HUCs.

This still does not clarify exactly what separates one HUCx from another HUCx downstream of it, both within the same parent HUC?

I'm confused about your misunderstanding as the answer to your question is in the Wikipedia link you posted:

  Regions receive a two-digit code. The following levels are designated
  by the addition of another two digits.[8] The hierarchy was designed
  and the units subdivided so that almost all the subbasins (formerly
  called cataloging units) are larger than 700 square miles (1,800 km2).
  Larger closed basins were subdivided until their subunits were less
  than 700 square miles.[7] The 10-digit watersheds were delineated to
  be between 40,000 and 250,000 acres in size, and the 12-digit
  subwatersheds between 10,000 and 40,000 acres.[6] In addition to the
  hydrologic unit codes, each hydrologic unit was assigned a name
  corresponding to the unit's principal hydrologic feature or to a
  cultural or political feature within the unit.[7]

So, once you are outside of the 2 digit regions, HUC boundaries (or dividing/outlet points along a continuous stream) that separate an upstream watershed from one a downstream one (that should incorporate the upstream HUC using the classic definition of a watershed) are set to evenly divide up the larger (or containing) HUC.


Why do human populations concentrate near fault lines, volcanoes, etc.? I've noticed that many places with large populations tend to be prime zones for natural disaster.

Examples: Silicon Valley = earthquakes, Houston = hurricanes and floods, Japan = tsunamis and earthquakes, Santa Maria = volcano, Vesuvius = volcano, etc.

This doesn't seem like a coincidence, especially given that people would naturally want to stay away from disaster-prone sites. Clearly there must be a benefit to living in such places.

My guess has always been that it probably goes something like this:

  Active fault zone → mountains & volcanoes → rain & water → fertile soil & wildlife → food

Or maybe like this:

  Storms/monsoons → rain & water → fertile soil & wildlife → food

But I really have no idea, and this has been a question I've had for a long time.

Is this accurate? Is there more than meets the eye? Is it maybe partly a coincidence?
Explanations would be greatly appreciated, since all I have right now is just a guess.

You're asking

  Why do human populations concentrate near fault lines, volcanoes, etc.?

But the real question is

  Do human populations concentrate near fault lines, volcanoes,
  etc.?

And the answer is not necessarily positive. Let's look at where earthquakes are:

and active volcanism:

Both maps are from Volcano Discovery. Here's a population density map:

Couldn't find the source for that, but a similar interactive website is this one: http://luminocity3d.org/WorldPopDen/

Finding a 1:1 correlation between these two natural hazards and population density is very hard. Most of the World's population reside in India, China, Europe, central Africa, and east North America. All of these areas not particularly hazardous in terms of fault lines and volcanoes. Other volcano-abundant areas are only populated if they're around the tropics (Mexico, Indonesia).

So no, the answer is that human population do not concentrate near fault lines or volcanoes more than they concentrate elsewhere.

On a local scale, however, volcanic soils are fertile and an excellent place to grow food. This might attract people to volcanoes, because food is vital for life and a maybe-yes-maybe-no threat of a volcano (particularly if it's not obviously active) is a lower priority thing for most people. Also see the interesting story of Pinatubo.

Sometimes, people did not know there was a hazard. Parícutin is a volcano in Mexico that just appeared out of nowhere in 1943. Christchurch, NZ, was considered a low earthquake risk zone until it was struck by several quakes in the recent years.

There is some truth to your two guesses that storms provide water for food and mountains lead to rivers which also provide water for food. But it's not a direct relationship. Think of the Nile river, which gets the water from mountains far south but feeds millions in Egypt. There are many more other examples.


Could we cool the ocean by reflecting away sunlight to influence hurricanes? I was wondering if we could possibly reduce the severity of, or steer a hurricane by changing albedo (e.g. dying the part ocean with a temporary light colored dye)?  My thought would be to put this dye well in front of the path of a hurricane, with enough time to reflect the sunlight back off the ocean and cool the ocean surface.  When the hurricane arrives there, the ocean surface should then be cooler, leading to the hurricane being less powerful.  I am also wondering if this could be used to steer the hurricane somehow (e.g. if a hurricane would be drawn to or repelled away from cool ocean surface).  If so, could we use that to steer a hurricane away from populated areas?

Some potential methods (there may be others):

Use light colored dye injected into the ocean
Use light colored smoke to block the sun from reaching the ocean
Possibly use "cloud seeding" ahead of the hurricane and form clouds to block the sun light from warming the ocean. - Covered in the alternate question
Perhaps a "surface film" could also be applied temporarily to part of the ocean (sort of like a "light colored oil spill", hopefully with something safer for the environment than oil). - Covered in the alternate question

If this experiment were to be conducted, I would think it should be done far from inhabited land.  Environmental impacts would need to be thought out too, e.g. would a film block the carbon dioxide / oxygen exchange in that area and cause severe environmental impact?  Could the experiment actually strengthen instead of weaken a hurricane?

Edit:

The linked question and answer addresses some, but not all the methods I propose here.  It also proposes some other methods, definitely an interesting read!

Water has a large thermal capacity.

  which is why the temperature change between seasons is gradual rather than sudden, especially near the oceans.

For water to lose heat time is required. By changing the albedo of the ocean just prior to a hurricane/cyclone/typhoon passing over a section of water will not give the water enough time to cool down to have any significant effect.

If it were possible to change the temperature of water to minimize the strength of hurricanes/typhoons/cyclones, large sections of ocean would need to have their albedos changed for a long period of time.


Mountains and solids on other planets Are there planets that lack mountains or have constrained availablilty of solids. For example a planet that has clay but not more solid stones like normal stones. The direct reason why I wonder is because I started to wonder if there existed planets where one would have to build less solid houses then at the earth due to the solids available if a person would build a house on that planet hypothetically spoken. It would be really nice with a detailed answer of what solids another planet would lack and how it constraints the housings that could be built on that planet in terms of solidness.

A planet has been theorized that forms in a primordial disk of high carbon content. See https://en.wikipedia.org/wiki/Carbon_planet. This planet's crust would have a high hydrocarbon content and thus not be very "solid". However, such a planet might theoretically have volcanoes that erupt diamonds, so an alien could build there home out of diamond!

Another hypothetical planet is a waterworld or ocean planet. If there is indigenous life then the only "above water surface" would be composed of life (ie: mats of algae type material floating on the sea).

As far as mountains go, this is not a question of solid or not solid. A large superearth would likely not have much in the way of mountains because of the high gravity at the surface. It might be noted that with out plate tectonics, we wouldn't have mountains and the Earth could arguably be covered in a global ocean.


Are there areas of desert sands which experience blizzards? Building off of another question I recently asked (Is there sand in Antarctica?) I want to ask a broader question coming from the same motive described there.

Are there desert sands that experience blizzards? I know of places with sand that experience blizzards, for example certain beaches in the Adirondacks or Great Lakes of northeastern USA. But what about desert sands?

The other question identifies Antarctic desert sands, and a comment even notes that where Chicago is now was once covered in desert sands. The latter point made me realize though, do blizzards (snow storms with high winds, to be specific) occur in these sand dune areas? If yes, then are there numerous examples of where this occurs, or is it a somewhat rare thing?

It really depends on what you consider "desert sands".  For instance, Sand Mountain in Nevada https://en.wikipedia.org/wiki/Sand_Mountain_(Nevada) is an area of sand dunes in a desert, and occasionally experiences snowstorms that reach blizzard conditions.

Although most of the lower elevations are sagebrush steppe, there are other areas of sand (and dry lake beds &c) in the Great Basin, and the area experiences winter cold, occasional snow, and high winds.  I'd expect similar conditions in the Gobi Desert, though I have no first-hand experience: https://en.wikipedia.org/wiki/Gobi_Desert


Why are there no wild fires in New England? I used to live in San Diego and I remember the occasional wild fire; My dad standing on the roof, watering it with a garden hose.

I have lived in New England, however, for the last 40 years and have not seen a wild fire yet. Why not? Just too wet here?

Its just too wet there

Generally, fires don't happen where it is wet. Here is a map of the fire regime in Pre-Columbian America:

Northern New England gets practically no fires, with a fire frequency of every 200 years or longer. Southern New England sees more frequent fires, maybe ever 40 years, but those fires are typically understory only.

For a region to be fire resistant, it must meet two criteria: it must be 'humid' and it must be 'humid' year-round. New England meets both of these criteria. Here is a map of precipitation versus evapotranspiration for the US:

Note the areas in green have more water falling from the sky than returning to it via evaporation and transpiration. New England is one of the wettest parts of the nation by this metric. There is plentiful rain/snow, generally heavy cloud cover, and relatively low temperatures to reduce evaporation.

The last piece is being wet all year. By looking at Boston's climate data, we can see that Boston's precipitation is evenly distributed throughout the year.


How to calculate hydrostatic equilibrium? I'm trying to solve the following problem.
The sea level in the past was 200 m higher than today. The seawater became in isostatic equilibrium with the ocean basin. what is the increase in the depth $x$ of the ocean basins? Water density is $\rho_w = 1000\ kg\ m^{-3}$, and mantle density is $3300\ kg\ m^{-3}$.

Using the compensation column, I reach:

$$
x = (\rho_w * 200\ m)/ 3300 = 60.60\ m
$$

but normally I expected to find 290 m.

Can someone explain to me what's wrong?

I am assuming you are asking for the case of sea level being 200m higher and in isostatic equilibrium. In that case we can make use of Airy's isostasy model: https://en.wikipedia.org/wiki/Isostasy#Airy

Applied to a water column over the mantle, you have to replace $\rho_c$ with your $\rho_w$. The total increase in ocean depth is $x = b_1 + h_1$, where $h_1$ are the 200 m extra sea level and $b_1$ is the depth increase to isostasy. Using the equation given in the link:
$$
x =  \frac{h_1 \rho_w}{\rho_m - \rho_w} + h_1,
$$

giving $x =$ 287 m


Can glaciers be less than 30m thick? The wikipedia page on Ice-sheet dynamics claims that:

  Ice will not flow until it has reached a thickness of 30 meters (98 ft)

And this geography website claims that

  To be called a glacier, a mass of ice must be capable of motion.

Together, these two claims seem to imply that if it's not thicker than 30m, it's not a glacier. Are either of these claims correct, and do they indeed imply my conclusion?

N.B. The question arises because I've been working with some literature and databases that refer to things less than 30m thick as glaciers.

Update: looking closer at GlaThiDa, I notice that it contains 490 glaciers listed with mean_depth less than 5m. However, all of these are from a single article (Cogley, 2008) and some of them are apparently only centimeters thick. Something must be wrong with this data; I'm looking into it.

The straight answer is no. The definition of a glacier requires the body to be of ice and snow, to move and deform under its own weight. If the body is pure ice the pressure needed to make ice deform corresponds to about 30-40 m of ice pressure.

The definition makes any body not consisting of ice and snow not a glacier. As an example, so-called "saltiers" are bodies of rock salt that move like glaciers. You find such features in the southern part of Iran. They would not qualify as glaciers from the first part of the definition.

The second part says that they must move. In mountainous terrain snow packs and also thin features of ice can move because they slide downhill. Because these are too thin there is no internal definition so the third part of the definition prevents such features from being glaciers.

Hence what remains are bodies of ice and snow that have sufficient thickness to induce deformation and hence they will be of a  minimum thickness.

As a glaciologist, I do not find this definition very academic. With glaciers reducing in size around the globe many glacier will, in time, pass the limit and cease to be glaciers but knowing when this happens requires physical measurements which for practical reasons (and current technology) can only be made on a  very small subset of the about 160 000 glaciers (not counting the ice sheets) on the earth. It is hence of little practical use when trying to figure out when particular glaciers cease to fit the definition.


What geophysical events can (temporarily) increase the Earth's rate of rotation? My understanding is that the dominant factor behind the slowing of the Earth's rotation (i.e. the lengthening of the day) is tidal friction induced by the Moon's gravity. As seen on the graph below, the general trend is towards slower rotation of the Earth.

  Plot showing the difference UT1−UTC in seconds. Vertical segments correspond to leap seconds. Red part of graph was prediction (future values) at the time the file was made.

However! There are a few cases where the rotation of the Earth appears to have become faster, most noticeably in the 2003-04 and 2004-05 segments. What is the underlying cause of these and other temporary increases in the Earth's rate of rotation? (I'm asking this in a general sense, though I would also be interested to know what events any of the specific upswings on the graph correspond to.)

TL;DR
The Earth's rotational angular momentum is indeed being transferred to the Moon's orbit. However, this is a very slow process that is barely noticeable even over the course of hundreds of years. That long-term trend is invisible in the short thirty year span shown in the graph in the question. The variations seen in the plot result from transfer of angular momentum amongst components of the Earth (solid Earth, the atmosphere, the oceans, and the outer and inner core) and from changes in the Earth's inertia tensor.
About the Graph in the Question
Regarding that graph, what you are seeing are

The cumulative effect of transfer of angular momentum to the Moon since the early 1800s, and
Short-term effects that have nothing to do with that long-term trend.

Regarding the first item, our 86,400 seconds per day is based on the length of day in about 1821. The CGS second was defined in the late 1800s based on data collected over a ~100 year period, centered around 1821. The SI second is now based on atomic clocks, but the definition was intentionally made consistent with that old CGS second. The length of day has increased by about 2 milliseconds since the early 1800s.
Suppose the Earth's rotation rate held steady at one mean solar day per 86,400.002 seconds, the average rotation rate over the last several decades. We would still need to add a leap second every 500 days or so because of that 2 milliseconds increase in the length of day. That's the primary feature you are seeing in the plot shown in the question.
Regarding the second item, the variations during the 30 year span in that plot don't have much to do with the variation over the 200 year span since the early 1800s, and those in turn don't have much to do with the very, very long term variations in length of day due to transfer of angular momentum to the Moon. That very, very long  term trend becomes obvious only over the course of many tens of thousands of years or more. Over the short term (a hundred years is "short term" in this sense), various cyclical effects dominate over this very long term trend. The transfer of angular momentum to the Moon is completely hidden in the 30 year span covered in the plot shown in the question. That's just too short a time span to see that transfer of angular momentum.
So what is that plot showing? The two most notable features are the long stretch between 1900 and 1998 with almost yearly leap second adjustments and the long stretch between 1999 and 2006 with no leap second adjustments.
Short-term Variations in Length of Day
Those leap second adjustments make it a bit hard to see what's going on. Here's a much better portrayal:

Source: https://hpiers.obspm.fr/eop-pc/earthor/ut1lod/UT1.html_nov08
The first thing you should look at in the above plot is the top curve. This is LOD, length of day (better: excess length of day). The length of a day is 86400 seconds and a tiny bit more. LOD is defined to be just that tiny bit more. LOD decreased between 1973 to 1987 and then again between 1993 to 2004. The Earth's rotation rate was very slightly increasing during those intervals.
As mentioned above, angular momentum is being transferred from the Earth to the Moon, but this is a very slow process. What this means is that the Earth's total angular momentum is very nearly constant over the span of years, even decades. Note that it's angular momentum, not angular velocity that is the nearly conserved quantity. Angular velocity can change while angular momentum remains constant. The graph above depicts change in period, and hence change in angular velocity.
The Earth comprises five different rotating systems: The inner core, the outer core, the mantle and crust, the oceans, and the atmosphere. Our terrestrial timescales, UT1 and UTC, are based on the rotation of the mantle and crust only. These five systems do not quite rotate in unison. For example, the inner core is currently rotating slightly faster than one revolution per day while the outer core is rotating slightly slower than one revolution per day. These systems transfer angular momentum amongst themselves.
Some of this transfer is visible in the "Seasonal Variations" plot in the above graph. The mantle and crust transfer angular momentum to and from the oceans and atmosphere on a seasonal basis. What's left after removing those season variations and other high frequency variations (shown as "Irregular Variations" in the above graph) is the white "Trend" line overlaid on top of the blue plot. This white curve shows multi-year variations in the length of day.
Summary
The trend over hundreds of millennia a very gradual increase in length of day due to transfer of angular momentum from the Earth's rotation to the Moon's orbit about the Earth, currently about 2.3 milliseconds per day per century. That's not visible in the plot shown in the question. Over the past several millennia, post-glacial rebound has exchanged less dense ice/water in the polar regions with more dense rock. This reduced the Earth's moment of inertia and thus increased the Earth's rotation rate. Over decades, variations in length of day largely due to interactions between the core and mantle. The inter-annual variations are due to transfers of angular momentum amongst the core, mantle, oceans, and atmosphere. The El Niño–Southern Oscillation and changes in the gravitational field are key drivers in these inter-annual variations.


Origin of Sulphuric Acid in the Atmosphere I often see claims that volcanic emissions of sulphur dioxide, on Earth and on the planet Venus, creates sulphuric acid when it combines with water vapour. It doesn't. Sulphur dioxide creates sulphurous acid, which is less corrosive than sulphuric acid. To make sulphuric acid you need sulphur trioxide. Is there a natural process which converts sulphurous acid into sulphuric acid, or has one  acid been confused with the other?

Oxidation states of sulphur vary between -2 and +6. Sulphur compounds are generally
  emitted in reduced form. They are then oxidised in the Earth’s atmosphere, generally to
  SO2
  , a +4 oxidation state. Around 65% (the remainder is removed by dry deposition) of this
  sulphur dioxide is eventually oxidised to the +6 state of H2SO4
  , where SO2 –
  4
  is the sulphate
  ion. Sulphur is stable in the presence of oxygen in this state. The higher-state compounds
  also generally have a greater affinity to water, meaning they are more readily removed from
  the atmosphere by wet deposition.

The natural atmospheric sulphur cycle and its response to anthropogenic perturbations, Angus J. Ferraro


Why is cold air fast in an occluded front, but slow in an anti-cyclone? I've read that cold air moves faster than hot air, for example in an occluded front. But in case of anti-cyclone encountering a cyclone it appears that the cold air of the anti-cyclone moves very slowly.

So why these differences and what causes this?

I do not think that there is a general relation between the temperature of an airflow and its velocity in meteorology.

There are several physical processes that need to be considered when thinking about the surface winds in occluding cyclones or fronts. A possible mechanism that I could think of explaining the stronger winds in the cold air compared to the warm air is the difference in vertical stability. The colder air is often characterized by steeper lapse rates (a stronger decrease in temperature with height). This leads to more exchange of momentum between the near-surface air layer and the so-called free troposphere air aloft. This exchange accelerates the surface winds compared to a situation where there is less exchange (as is the case for the warm air in an occluding front).

In a (wintertime) anti-cyclone, the cold air establishes itself mainly close to the surface due to radiative cooling. This leads to a very stable vertical profile, meaning that there is not much exchange of momentum between the near-surface layer and the air aloft. In such a situation, one can say that the surface layer is decoupled from the free troposphere. When a front moves in, it will simply move over the cold layer at the surface without disturbing it too much initially. The cold air indeed moves only slowly in this case.

Hope this explains at least a part of your question.


Before the artificial changes of the Aral Sea, what was its average depth and salinity? The Aral Sea was a major lake of the USSR until it suffered artificial changes, which began sometime no later than the 1960s.

I am unfortunately not sure when major artificial changes began. Wikipedia says that canal construction "on a large scale" began in the 40's, but then mentioned "By 1960, between 20 and 60" cubic km of water was being diverted. So it appears the date I'm looking for is somewhere between 1940 and 1960.

Anyway, the two key figures I'm interested in are average depth and salinity. What were these in the Aral Sea before it changed? One reason I ask is I'm especially curious if it was just a smaller version of the Caspian.

From the link provided by Keith McClary, the Aral had a salinity of about 1% and a max depth of 69 m. (Could not find average depth in the article.)

The Caspian Sea, on the other hand, has a salinity of about 1.2%, max depth of 1,025 m, and average depth of 211 m. I think this is enough information to say that the Aral was not just a smaller version of the Caspian, unless your main criteria is salinity.


How does a whirling hygrometer work, how does it differ from static dry/wet bulb thermometer, and how to obtain humidity from its readings? Answers to my previous question How is relative humidity determined from a wet and dry bulb readings? provide equations for converting the two temperature measurements to a relative humidity.
In comments under this question I have heard of a Whirling Hygrometer which seems to be the same basic beast (two thermometers, one with a wet bulb from a cotton sock and small reservoir) but like the name says, this one you have to "whirl" around for most of a minute; presumably the evaporation is more efficient in the blowing air.
But I don't understand if that leads to a lower cold temperature and therefore requires a different equation, nor if the speed that it is whirled makes a difference. And I'm not sure why whirling is used if the static non-whirled kind also can be used, without moving parts.
Question: How does a whirling hygrometer work, how does it differ from static dry/wet bulb thermometer, and how to obtain humidity from its readings?

Related:

How do the pros measure humidity?
What is the second thermometer in the image from the Esperanza Antarctic temperature record?
How is the specific heat of a wet bulb determined?

 click for larger

Instead of «whirling thermometer» you probably refer to «sling psychrometer» consisting of a dry-bulb thermometer and a wet-bulb thermometer.  Yet, different to a static wet-bulb thermometer shown in the question, the constant rotation of the two thermometers permits evaporation from the wet cloth around the web bulb thermometer to «pristine parts» of surrounding air.

(credit)
If the air around the wet-bulb thermometer is less than water saturated, the temperature of shown on the wet-bulb thermometer will be lower than the one read on the dry-bulb thermometer.  The swirling motion aims to expose the wet-bulb thermometer to air which was not yet in contact with the former.  Thus, both recordings allow you to report both (dry) temperature, dew temperature, and humidity of the air.
A beginner's introduction is equally given here, a computation chart relating the temperature difference read (one for the Celsius, an other for the Fahrenheit scale) to the relative humidity here.

Suggested by user @uhoh, it is worth to set the quality of the readings obtained with this instrument into a context.
The 1993 edition of Conserve O Gram 3/1 (accessed from the series' program overview) mentions «These instruments are accurate to $\pm \pu{2\% RH}$ when properly maintained and operated by trained and practiced users.»  Equally, the guide reminds to the Clausius-Clapeyron relation when stating:

«Psychrometers and psychrometric charts are intended for use within a certain range of atmospheric pressure. High altitude, above 900 m (approx. 3,000 ft), will directly affect the accuracy of the RH reading unless a pressure correction formula is applied or a psychrometric chart or slide rule for the appropriate pressure is used. For further information see Ann Hitchcock and Gordon C. Jacoby, “Measurement of Relative Humidity in Museums at High Altitude,” Studies in Conservation 25 (1980): pp. 78-86. (Copies are available to NPS sites from Curatorial Services Division, Harpers Ferry office.»

A study by Wang and Tang /  Singapore's metrology centre published by 2007 mentions:

«... that although the psychrometer coefficient of a particular psychrometer can be quite consistent with long-term stability typically within the range of  ± 1% rh equivalent, there are larger variations (up to 4% rh equivalent) among different psychrometers even of the same type.»


How to cite LandSat 8? I'm wondering how to quote a Landsat mission product. I have seen many ways, but I can't decide which one is the best. Thus, I would like to know if there is a standard for the minimum information that should be quoted such as mission, data, sensor, orbita/ponto. Furthermore, do I have to include a link to access the image?

If anyone has any tips or guess on the subject would be grateful!

Landsat products obtained via various sources (ex the EROS Center) can have their own requirements when using their products. For instance the EROS Data Citation page indicate that they are quite open regarding how their documents are cited and require the following acknowledgement only. For example

Acknowledgement:
Data available from the U.S. Geological Survey.
See USGS Visual Identity System Guidance (link is external) for further details.
Questions concerning the use or redistribution of USGS data should be directed to: ask@usgs.gov (link sends e-mail) or 1-888-ASK-USGS (1-888-275-8747).

Metadata files attached to images are often filled with useful information. Usual relevant information for a technical or scientific paper are the moment of acquisition, the scale, the bands, the name of the sensor, maybe the series of the product, maybe there is a serial number too, possibly a URL.
I have cited in a recent paper the following for Landsat 7, and did not went into much details because it was a reworked product (a special issued mosaic), which was convenient for our scope:
NRCan, Canada Centre for Remote Sensing. A complete orthorectified Landsat-7 mosaic
of the Canadian Arctic archipelago, August 2010. URL http://geogratis.gc.ca/api/en/nrcan-rncan/ess-sst/-/(urn:iso:series)a-complete-orthorectified-landsat-7-mosaic-of-the-canadian-arctic-archipelago


What are the temperature and pressure conditions an ROV design would have to deal with to descend to 4000m? I have looked at a few do it yourself remotely operated vehicles (ROV), and considered making one myself. However my research on the web has turned up a lot of conflicting information about determining what the temperature and pressure ranges to expect at various depths.

I would like to be able to build something that can go to 4000 meters or even 6000 meters depth. My interest is chiefly in being able to carry illumination and cameras.

Can someone direct me to validated resources of temp pressure and perhaps even pH conditions. Has anyone ever heard of using fused silica cylinders to hold camera/lighting/battery packs for an ocean going ROV?

For pressure, you can use something simple like the fact that pressure increases by around 1 atm with each 10 m of water depth. You can also use some very simple calculators that assume a constant density (not a bad assumption) and gives you the different unit conversion.

For temperature, it varies a fair amount depending on where in the ocean. The average vertical profile for mid-latitudes, looks something like:

 (Windows to the Universe).

If you need more detail temperature information for a specific location, you can look into the World Ocean Atlas, which provides observed temperature, salinity (and in some cases other parameters like ph) for the entire world.

My suggestion is that, if you need any specific information, you might ask the people at the Woods Hole Oceanographic Institution (for instance) that deal with this kind of problem on a regular basis.


What are the formulae for calculating the thermal heating effect of back radiation in greenhouse gases? The ability of greenhouse gases to trap heat and re-radiate some of it back to the original heat source looks like a useful thermal property which could possibly be incorporated in things like double glazing, wall insulation, etc. What are the formulae which will enable us to calculate this additional thermal effect on top of the normal conductive heat loss parameters, heat capacity, U values etc ? We would also like to find details of the original experiments which were used to confirm the accuracy of said formulae as all I can find with internet searches are the well know school type experiments with plastic bottles and heat lamps which demonstrate the principle but are not sufficiently quantitatively accurate.
We asked a similar question in Physics Stack Exchange as we considered it a question relating to fundamental physical (thermal) properties of gases but it got little response.

As you have mentioned already, there are several physical phenomena which are responsible for heat and energy transfer. I'll just list them again for completeness, although you already addressed them in your question.

Conduction
Convection
Latent heat of vaporization
Radiation

To get to your question: Radiation is the transport of energy by means of electromagnetic waves emitted from a body of a absoulte temperature uneqal zero Kelvin.

What does that mean? Radiation does not rely on contact or a transporting fluid as do conduction and convection. Instead it is equivalent to the fourth power of its absolute Temperature. This is what we know as "Black Body Radiation".

The equation for this is:

$$ E = \sigma * T^4$$

where σ is the Stefan-Boltzman Constant and T is the absolute Temperature in Kelvin. This law is obtained by integrating Planck's law over the solid angle and wavelength, in order to determinate the energy which is transmitted not only by one particular wavelength, but the whole spectrum and in all directions. Combined with Kirchhoffs Law, which says, that the absorbtivity of an object equals its emissivity, you can calculate the radiated Energy of any object or atmospheric layer.
The emissivity (ε) of a body is a value between zero and one with one being the perfect black body. For most things you can find values in the web. It also explains why aluminum foil is such a good insulator.

$$ E = ε * \sigma * T^4$$

To put all of this in an example:
Everything around you radiates heat. Beginning with the most obvious, the sun. The sun's surface has an approximate temperature of 6000K. This means it emits radiation of the following spectrum:

As you can see, the maximum of the energy of the sun is radiated in the part which we know as visible light. Also a big part of the radiated energy is absorbed in the atmosphere (the difference between yellow and red graphs). Responsible for these are particularly Ozone (O3), Water (H2O) and (CO2) which are also our most important greenhouse gases.

What happens, is that the radiated energy of a particular wavelength "hits" the molecules and excites them into a state of higher kinetic energy. The average random kinetic energy of a substance is what we know as the temperature of this substance. Hence, also the atmosphere acts like a black body and radiates energy
back to space but also back to earth.

Unfortunately I can't really say much about the second part of your question. I don't know about the original experiments. But I suggest a read about Gustav Kirchhoff, who introduced the idea in 1860 which then has been proceeded by Josef Stefan in 1879 and Ludwig Boltzman (1884). Also Planck's works from 1900 could be helpful.

I hope I was able to point you in the right direction with your studies.


Book recommendation for 7 year old By some poorly understood series of events, I have managed to convince my 7 year old daughter that she wants to be a geologist when she's older. Of course I'm aware that this likely won't be the case, but I thought I'd try to seize on the moment and get her a book on geology.
So I am looking for any recommendations for a children's book on geology, perhaps with facts/experiments about stuff that she can find in the garden/in her local area. We live in a reasonably urban part of the world (Surrey).

There are at least 2 books that come to mind:

National Geographic Readers: Rocks and Minerals (2012), a richly illustrated guide for kids.
Ultimate Explorer Field Guide: Rocks and Minerals (2016) by Nancy Honovich, a guide focussed on getting kids outside, looking at rocks in their backyards and on the camping.

Considering you're in the UK, afterwards I'd start with some experiments about limestone. National Geographic used to have rock kits for kids, not sure who else sells them near you. With the keywords "rock kit kids uk" I get some results that may be worth a look at.


Trees cleaning the air Sorry if this is the wrong place...
I have been camping a lot recently and I couldn't help but notice some of the campgrounds I am in are acres and acres of mostly pine trees. These trees have very little greenery on them as opposed to most other species. Does that make, say an Oak a better tree for cleaning the air and/or as a carbon sink than a pine?  If I wanted to plant a native species of tree on my land with the intent of helping to clean the air the most, is there research that exist for that? Or is there a reasoning of 10 pines in the same space of one oak is better?

Evergreen trees grow faster than most hardwood deciduous trees, so their absorption and oxygen emission is greater.
Note that trees do not "clean" air. Plants emit oxygen which is why air in a house with lots of plants will seem more fresh. In the global environment algae and other primitive organics are primarily responsible for converting CO2 to oxygen, not trees.
Particulate pollutants and some compounds with good water solubility, like sulfur dioxide and ammonia, are removed from air by moisture which condenses and falls to earth bringing the particulates with it.


Is there an index that evaluate how even temporal rainfall distribution is? Like some biodiversity indices that account for species evenness (whether it is dominated by a few species), I am wondering do meteorologists use an index to describe how even a temporal rainfall distribution is? (whether most precipitation are dominated by just a few days over a long time span). Thank you.

Try to read something about Köppen climate classification. This classification among other things tries to distinguish between rainy and dry season for many areas. So, scientist needs to know the distribution of precipitation. Another possibility could be indices described in this scientific article on the ResearchGate.


What is the northernmost/southernmost city that receives no snow? What is the northernmost or southernmost city on Earth which receives no snow? The exact definitions are:

City means any settlement with more than 1000 people permanently residing there
"No snow" means the city receives less than 1cm of snow per year on average
Northernmost/southernmost refers to the absolute latitude of the city on either the Northern or Southern hemisphere

Related question.

On the North American west coast, Coos Bay, Oregon is the northernmost place I can find, of any significance, that gets no snow.  Astoria, Oregon gets 2.5 cm of snow per year.  Coos Bay is at 43.4 degrees north latitude.

On the east coast, Boston is of similar latitude and gets significant snow, so that coast is out.

In western Europe, A Coruna seems to be the best candidate, at 43.4 degrees north in Spain.  I had originally thought Guernsey would be a good candidate but it gets a little too much snow, and cities in France seem to get regular snow too, even on the coast.  Venice looks like a tempting alternative, but it seems to get snow consistently, if uncommonly.

So, so far, 43.4 N seems to be the answer on both the North American and European continents.

In the southern hemisphere, Comodoro Ravadavia, Argentina at 45.8 S gets snow, but Trelew, Argentina at 43.3 S does not, so the snow band in eastern South America seems to be quite close to the same latitude as we see in western North America.  There are few significant communities on the western Chilean coast, but Puerto Montt, Chile is snow-free at 41.4 S.  Southern New Zealand is at similar latitudes, but seems prone to heavy snowfalls at times, probably because of its proximity to Antarctic currents and the presence of tall mountains.

There are quite a few southern islands that are candidates, but most seem to get snow, and none have any significant settlements, short of the Falklands, which definitely do get snow.

If you get rid of the people requirement, the McMurdo Dry Valleys at 77.3 S are probably the answer.  They are very cold, but so arid that they are largely snow-free all year long.  Snow that does try to fall often sublimates directly into the atmosphere.


What sort of climate zones would be present if Earth was tilted like Uranus? The three main climate zones on Earth are tropics, temperate and polar. Due to Earth's axial tilt, the three zones experience different seasonal patterns:

The tropics experience 2 or 4 wet/dry seasons depending on how the tropical rain belt passes over it.
The temperate zones experience the 4 seasons.
The polar regions experience sun-less winters and an endless summer day, but due to the angle, receives little sunlight and is cold all-year round.

Of course it can get a lot more complex, but these are the broad types of climate seen on Earth.

Suppose that Earth was extremely inclined, like Uranus - its axis lies parallel to its orbit. The equator would alternate between normal day/night to an endless twilight; the poles will alternate between endless twilight, endless noon, twilight, and endless midnight over the year.

In the same, very broad sense, what types of climate would this result in, and what would they be like?

A paper on this topic just appeared: Multiple Climate States of Habitable Exoplanets: The Role of Obliquity and Irradiance.

In case of 90° obliquity, summer and winter would appear together with day and night, respectively. This means, in summer one hemisphere completely faces the Sun with 24h daylight a day causing extreme hot summers. The temperatures in winter very much depend on the hemisphere. In the Southern Hemisphere, oceans are predominant compared to the continents, having a very low albedo makes it possible to store the heat in summer. Thus, the winters in the Southern Hemisphere are still warm. In contrary, the Northern Hemisphere becomes rather cold in winter due to the small heat storage in the oceans.

The equator region is the coldest region on the planet, since this region has the lowest incoming solar radiation (Fig. 1a,b). This could lead to sea ice building around the equator region and provides an alternative hypothesis to Snowball Earth (Williams, 2008): The High Obliquity, Low-latitude Ice, STrong seasonality (HOLIST) hypothesis for pre-Ediacaran glaciation.

The warm poles and the cold equator significantly change the dominating jets. The mechanism can be explained by the thermal wind equation:
$$
p \dfrac{\partial u_g}{\partial p} = \dfrac{R}{f} \dfrac{\partial T}{\partial y} ~~,
$$
where $p$ is the pressure, $u_g$ the geostrophic zonal wind, $R$ the specific gas constant for air, $f$ the Coriolis parameter, $T$ the temperature, and $y$ the meridional distance in meters. The thermal wind equation shows that the vertical change in zonal wind is proportional to the meridional temperature gradient. Thus, the sign change of the meridional temperature gradient causes a sign change of the zonal wind. This means that the dominating jets turn into easterlies due to the reverse meridional temperature gradient (Fig. 1c,d).

However, the climate also depends on the initial condition of the planet, i.e., multiple climate states are possible for the same parameters. In case of 90° obliquity either a so-called "Uncapped Cryoplanet" or an "Aquaplanet" state exists (for further details see Kilic et al., 2017). An Uncapped Cryoplanet has large areas of sea-ice around the equator and a permanent open ocean at the higher latitudes. This climate type posses a previously unknown meridional atmospheric circulation which is neither a thermally direct nor indirect cell but rather a superposition of both cell types (Fig. 1e).

Figure 1: Uncapped Cryoplanet (left column) and the Aquaplanet (right column) for a planet with 90° obliquity in southern summer: (a), (b) zonal mean air temperature, (c), (d) mass stream function (colour, positive for clockwise overturning) and zonal-mean zonal wind (contour, positive for westerlies), and (e), (f) the poleward energy flux for the eddy and the mean contribution, the total energy flux, and the meridional heat flux in the ocean. Note: The figure shows an aquaplanet configuration, i.e., continents were neglected.