How much do tides affect earth's rotational velocity? Many of us are familiar with an exaggerated picture of the Moon's effect on Earth's tides:
Since the Earth is not uniformly covered with water, however, I imagine that the tidal effect will depend on which part of the Earth is facing the Moon (for simplicity, ignore the Sun's contribution).  I'm sure that the tidal effect still affects the Earth's landmasses, but I'm guessing that it would be to a lesser degree (i.e.: the landmasses would bulge out less than the oceans in the image above).  Now, by conservation of angular momentum, if the landmasses bulge out less, the Earth should rotate more quickly, hence this question's title.
How does the tidal effect of the Moon's gravity affect the Earth's landmasses differently from its oceans?  And how big is this difference?

This question is handeled pretty throughly in Physics site;
https://physics.stackexchange.com/questions/214042/earths-kinetic-energy-change

Your question; "How big is the difference?"

Body Tides Summarize
0.3 ms for a 14 day period.
0.16 ms for a 28 day period
0.14 ms for 1/2 year period
0.02 ms for a year period.
0.126 ms for Lunar node period; (18.6 years)

Ocean Tides
Max 0.05 ms for a 14 days period
0.026 ms for a Years period
0.024 ms for lunar node period


Accurately Measuring Indoor/Outdoor Air Temperature & Relative Humidity I’m conducting an independent study as a concerned citizen on the indoor temperature at an animal shelter to support the need of improved air conditioning by documenting how hot it can reach during summer that would exceed veterinary standards. I’ve bought an electronic hygrometer and have also obtained the building floor plans.

My current data collection process would be the following:

conduct measurements during a high temperature, high humidity, and low cloud cover day.

best mimics the extreme conditions that the animals would be exposed to.
record the date/time and measure or record current outdoor conditions:

temp (shade and direct sun), relative humidity, cloud cover, wind speed.

record the current facility’s AC temperature setting.

take relative humidity (RH) and temperature measurements throughout the facility at 5ft spacing.
(Please advise if my distance is too large or too small)
gently wave hygrometer from side to side for approximately 15 seconds to adjust sensors to current position’s environment.
take all indoor measurements from a 1ft height (approximate mid-height of a dog) using a pole.
take measurements from one end of the facility and walk forwards/sideways in a grid pattern to prevent my body heat and humidity from influencing the reading, and also to limit air circulation from my movements.
wear latex gloves so hand sweat does not increase the RH value.
take measurements within each animal enclosure as there will be additional humidity from water
bowls, urine, etc.

this would be done after the main isles are measured to reduce air movement from opening and closing the enclosures from influencing the aisle measurements.

mark each measurement point on the floor plan and log the data in a spreadsheet.

My data analysis will consist of the following:

floor plan heat map overlays for the following:

air temperature
relative humidity
heat index (HI)

calculate the following values:

animal enclosures

average/min/max temperature
average/min/max RH
average/min/max HI

shelter facility

average/min/max temperature
average/min/max RH
average/min/max HI

Am I missing anything that could potentially invalidate my results and result in inaccurate measurements, or am I lacking any specific data which I should be collecting or calculating? I want this to be as accurate as possible and provide credible evidence that current conditions are not within veterinary standards.

I had asked if this type of question was on-topic here, but overall if it is not please do not close it. Just leave a comment and I'll delete it so as not to ding me negatively in the system. Thank you.

Looking at the source you provided in the comment, there is some other information you may be able to accumulate to help your study.

Control or Baseline.  You need an the same actual set of data from a facility in the area that is meeting the above-mentioned standards.  This needs to be as close to your target facility in size, structure and regional conditions as you can find so you can demonstrate that under the same Temperature and Humidity proper conditions can be maintained.
More Data.  You haven't mentioned Time in your question. Most building temperature studies show conditions throughout the day. The duration that the animals are exposed to extreme conditions may be relevant.  There are data-logging thermometer type devices available , or you may need to perform your tests once an hour during the day to collect enough relevant data to make your case.
More Data. You talk of taking measurements on an extreme day. Gather data on a variety of days, and you may find the care standards are exceeded more (or less) often then you expect.  This way you may find the lower limit of conditions which cause problems. Which brings us to...
More Data.  Once you have a measured example of the problem temperature and humidity reading, for a given day, you can collect data from local weather sources and you can present a graphic showing the number of days, or perhaps hours per year the animals are exposed to these conditions.

You mention Heat Index. According to NOAA,  Heat Index

  is what the temperature feels like to the human body when relative
  humidity is combined with the air temperature...

You might have to prove the relevance of this data to animals which do not react the same way to humidity. If you can find an external source supporting your use of that index, then by all means continue to use it. You may even be able to find a study showing that the animals feel the effects of humidity more then humans do. Look for, more data. The link above mentions a possible place to begin.

Personally I believe the main argument you will face would be the amount of time the proper conditions are exceeded. Like the people who leave the dog in the car, 'but it was just for a minute...'.

Good luck, no matter what results you find.


Why don't all living beings die at night due to lack of oxygen? During the day plants photosynthesize and give out oxygen through stomata. But during the night, when half of the planet is dark, half of the earth's trees/plants consumes oxygen to survive. At that time when an entire hemisphere is producing only $\ce{CO_2}$ and there is no source of $\ce{O_2}$, why don't half of the life forms die? And 12 hours later, the other half when they are in darkness?

The rates at which plants consume CO$_2$ and animals consume O$_2$ is minuscule compared to the vast amounts of CO$_2$ and O$_2$ in the atmosphere. The amount of change overnight is not even measurable, unless the plants are in an enclosed structure.

Interestingly, there is a variation in CO$_2$ concentraion over the course of a year as the Northern Hemisphere (where most of the land vegetation is) goes through its seasons. Here is a plot of CO$_2$ over several decades. It shows an annual cycle superimposed on the general upward trend from the accumulation of man-made CO$_2$.

The red trace is the actual data, and the black trace is the time averaged fit to the data.


Earth Science Search Engine After scirus is closed, which search engine do you all use?

I know of Arxiv, and ADS, which only partially overlaps with Earth Science related issues. Any other recommendations would be appreciated.

I normally use Google Scholar, but Elsevier also has the non-public Scopus (which means I have to use a campus proxy). Also CiteSeerX but the semantic side is not as rich.


What is the relationship between Ekman transport and Ekman pumping? Ekman transport is the integrated horizontal flow in the boundary layer resulting from the balance between frictional forces (at the surface or bottom) and Coriolis. Meanwhile, Ekman pumping is a vertical motion at the base of the boundary layer resulting from the curl of the wind.

What is the relationship between Ekman transport and Ekman pumping?

The link is the conservation of mass equation: $$ \frac{\partial u}{\partial x} + \frac{\partial v}{\partial y} + \frac{\partial w}{\partial z} = 0. $$
Briefly, Ekman pumping is the horizontal divergence of the Ekman transport.

If we integrate this expression over the Ekman layer,
$$ \int_{-D}^0 \frac{\partial u}{\partial x} dz + \int_{-D}^0 \frac{\partial v}{\partial y} dz + \int_{-D}^0 \frac{\partial w}{\partial z} dz = 0$$
where $D$ is the height of the Ekman layer we take $z=0$ to be the surface.  This gives
$$ \frac{\partial}{\partial x} \int_{-D}^0  u dz +  \frac{\partial }{\partial y} \int_{-D}^0 v dz + w_{z=0} - w_{z=-D} = 0$$ or,
$$ \frac{\partial}{\partial x} U +  \frac{\partial }{\partial y} V + w_{z=0} - w_{z=-D} = 0$$
where $U$ and $V$ are the horizontal volume (Ekman) transports.  As a boundary condition we take $w_{z=0} = 0$ leaving
$$ w_{z=-D} = \frac{\partial}{\partial x} U +  \frac{\partial }{\partial y} V. $$
So, the Ekman pumping velocity is the horizontal divergence of the Ekman transport (and thus also proportional to the curl of the wind stress).


Is this what is meant by a phenological season? I’ve often thought there were three ways to define the seasons. I’ll use spring as an example. The first are the astronomical seasons, which is what calendars show and in my example would be the date of the spring equinox. The second is the meteorological seasons, which where I live says spring are the months of March, April, and May.

I’ve always said there was a third way to define spring (and other seasons), it’s spring when it starts to look and feel like spring. For example I like to watch for the first crocus or tree buds. While I’m not being precise, is this in general what would be meant by a phenological season?

The seasons used by indigenous Australians could be classified as a phenological season system.

Depending on the "home range" of each grouping, the year is divided into three to six seasons which are defined by weather and activity by flora and fauna - ecological knowledge.

The CSIRO in Australia has more extensive information about indigenous seasons.

The indigenous seasons in the State of Victoria.

A useful video giving a limited explanation of the some the complexity of the season recognized by different indigenous groups.

The six seasons of the Kakadu region and seasonal ‘calendars’ of Indigenous Australia.


Volcanic eruption force From my research, some volcanic eruptions can produce enough force to turn a 10-tonne rock into a projectile.

Could a supervolcano produce enough force to turn a 35,000 tonne rock into a projectile?

Could a supervolcano produce enough force to project a 35,000 tonne rock ~2000km away from the source?

For visualization purposes, if the $35,000$ tonne rock was composed of something similar to basalt, with a density of $3 g/cm^3$ (also $3 t/m^3$), it would be a sphere with a diameter of $28.1$ m, or a cube with sides of $22.7$ m.

Using a ballistic trajectory calculator, to move anything $2000$ km down range, the object needs an initial velocity of $4430$ m/s ($15,948$ km/h, or Mach $12.9$ - hyper sonic speed), assuming a projection angle of $45$ degrees to the horizon. The rock would reach height of $500$ km.

The kinetic energy of such an object would be $3.434(10)^{14}$ J, using the equation $E_k = 0.5mv^2$.

When Mount St. Helens erupted in 1980, it released $24$ megatons of thermal energy. Using a converter, this is equivalent to $1.004(10)^{17}$ J. This is 292 times the energy required to move a $35,000$ tonne rock $2000$ km.

Now, the energy released by Mount St. Helens was the overall energy released, not the energy given to one lump of rock and Mount St. Helens was not a supervolcano. So, could a supervolcano shoot a $35,000$ tonne rock $2000$ km away? Potentially, but unlikely. Energy always takes the path of least resistance so instead of moving a $35,000$ tonne rock $2000$ km away it will more likely move significantly more material that is in the form of dust or ash.


Analytical solution for seismic wavefield in MATLAB I have been trying to evaluate the analytical solution for a wave travelling in a homogeneous, infinite media. For a given source $S(t)$, the wave-field can be calculated at a distance $r$, for a given velocity $v$

$$W(r)=F^{-1} [-i \pi S(\omega)H_0^{(2)} (kr) ]$$

Here $F^{-1}$ represent inverse Fourier transform.

$S(\omega)$ is the frequency domain representation of $S(t)$

$H_0^{(2)} (kr)$ is the Hankel function of zero order and second kind.

and $k$ is the wave number $(=\frac{\omega}{v})$.

I followed this link which demonstrate code in Python, however, I couldn't implement same in MATLAB. I also had doubts how it works. Since the fourier transform have positive as well as negative frequencies (i.e. $-f_{max}/2<f<f_{max}/2$) but the code in link takes frequencies between $0<f<f_{max}$ for calculating Hankal function.

I wrote following MATLAB code but got the wave-field  all entries as NaN..!

Edit1

As a little modification, I forced the first term of the Hankel function to be zero (since it was containing a NaN in the real part). Now it is working nicely but it produced two peaks.  I thought it to be similar to frequency shift effect, as observed after FFT for positive and negative frequencies, but it is not.  In this case amplitudes are reversed. Can anyone explain it?

Edit2

If I assume that the only the first peak in the solution is correct one and second arises because of some effect (which I don' know). Problem comes when I change the dt (e.g. $dt \in 10^{-4}[1, 2, 3, 4,....,10]$) the shape and amplitude of the solution changes.

Any help is appreciated.

clc;    clear all;      close all;

%% Parameter Setting
vel=2000;   % velocity of medium
r=1000;     % distance at which wavefield will be observed
% the final wavelet should appear at time, t=r/vel=0.5sec

T=1;        % Total time
dt=.0001;   % time step
f0=25;      % central freq

%% Create Source Wavelet
N = round(T/dt);        % No of samples
t0 = 5/(sqrt(2)*pi*f0);     % Zero time shift
t = dt*(0:N-1);             % time vector
tau = t-t0;     % time vector shifted by t0
src = (1 -2* tau.*tau * f0^2 * pi^2).*exp(-tau.^2 * pi^2 * f0^2);  %source     wavelet

%%FT of signal
nfft=2^nextpow2(N);     % no of fft points
fmax=1/dt;              % max frequency
freq= fmax*(-nfft/2:nfft/2-1)/nfft;    % Freq vector:  -Fmax/2 < f < +Fmax/2

sw=fft(src,nfft)/nfft;                % fourier transform of wavelet, S(w)
sw_shift=fftshift(sw);      % shifting to make S(w) amplitude corrosponding to above "freq" vector
amp= abs(sw_shift);         % amplitude of the S(w)

%% Green Function
%(I have taken only positive freq. since hankel func defined only for positive numbers.
% Suggestions please..May be I am wrong..!)
freq_new= fmax*(0:nfft/2-1)/nfft;
w=2*pi*freq_new;
const = -1i*pi;
H02 = besselh(0,2,w*r/vel);
H02(1)=eps;
GF = const*H02;

%% Calculating Wavefield
%I have made Green Function (GF) symmetric and then multipled with source spectrum.
GF_new=[fliplr(GF),GF];
WF= ifft(GF_new.*sw);
t_new=dt*(0:length(WF)-1);

%% Plot
figure();

% Wavelet
subplot(2,2,1);
plot(t,src);     title('\bf{Source wavelet}');
xlabel('Time(sec)');    ylabel('Amplitude ')

% Frequencies
subplot(2,2,2);
plot(freq,amp);    title('\bf{Source freq spec}');
xlabel('Frequencies(Hz)');  ylabel('Amplitude ')

% Gneens Fkt
subplot(2,2,3);
plot(freq_new,abs(GF));   title('\bf{Green Function}');
xlabel('Frequencies(Hz)'); ylabel('Amplitude ')

% Wafefield
subplot(2,2,4);
plot(t_new,real(WF));    title('\bf{Trace}');
xlabel('Time(sec)');  ylabel('Amplitude')

So, I know this question was asked a long time ago. But in the spirit of Stack Exchange, I will post my answer for future users perhaps.

The Greens functions (i.e., analytical solutions)

The first thing to be aware of are the various solutions to the wave equations change for the (1) source type and (2) the dimension.

The source type

Assuming acoustic waves in a homogeneous domain, that means you are either solving:
$$ \frac{\partial^2 p(x,t)}{\partial t^2} = c^2(x)\left(\nabla^2 p(x,t) +f(x,t) \right)  , \tag{1}$$
(where $p$ is pressure, $c$ the compressional velocity and $f$ the source function), or you are solving:
$$ \left\{ \begin{array}{rl} \frac{\partial p(x,t)}{\partial t} & =  -c^2(x)\bigg( \nabla\cdot v(x,t) + g(x,t) \bigg), \\ \frac{\partial v(x,t)}{\partial t} & = -\nabla p(x,t). \end{array} \right. \tag{2} $$
The difference between (1) and (2) is a time differentiation:
$$ f(x,t) = \frac{\partial}{\partial t}g(x,t). $$
This is an important difference in source functions!

The Greens function equation

It is standard to restate equation (1) in the following form:
$$ \left( \frac{1}{c^2(x)}\frac{\partial^2}{\partial t^2} - \nabla^2 \right)p(x,t) = f(x,t). \tag{3a}$$
Transforming this equation to the frequency domain, for which $\partial^2/\partial t^2 \to -\omega^2$, and where $\omega^2/c^2=k^2$ we obtain:
$$ \left( -k^2 - \nabla^2 \right)p(x,\omega) = f(x,\omega), \tag{3b}$$
or
$$ \left( k^2 + \nabla^2 \right)p(x,\omega) = -f(x,\omega), \tag{3c}$$
We can consult, e.g., https://www3.nd.edu/~atassi/Teaching/AME%2060633/Notes/greens.pdf to find the Greens functions (for which $f(x,\omega)=\delta(x-x_s)$ with $x_s$ the source location).

The Greens functions

I'll just copy the results. For equations of type (1) we have the Green's functions $G$:
$$
\begin{array}{lrl}
\text{1-D:} & G & = −\frac{i}{2k}e^{−ik\lvert x−x_s \rvert}, \\
\text{2-D:} & G & = −\frac{i}{4}H_0^{(2)}(k \lvert x−x_s \rvert),\\
\text{3-D:} & G & = \frac{1}{4\pi}\frac{e^{−ik\lvert x−x_s \rvert} }{\lvert x−x_s \rvert}.
\end{array}
$$
Indeed, $H_0^{(2)}$ is the Hankel function, in MATLAB we simply write that with besselh(0,2, k*r).

The MATLAB implentation

I made the following changes w.r.t. your code:

The frequency vector can be defined from $f_1\in(0,\frac{1}{\Delta t})$ rather than how you did it, which is $f_2\in(-\frac{1}{2\Delta t},\frac{1}{2\Delta t})$. In this way, the Hankel function only receives positive frequencies. Moreover, it is exactly the order in which the FFT produces its output. I thus also removed the fftshift operations.
I changed the Green's function to the 2-D case, i.e., I changed const=-1i*pi to const=-1i/4.
I changed the nfft, to just using the FFT of the size of the wavelet or time vector. This made it easier to obtain results of similar amplitudes... Also, I don't divide the source function by nfft, to make the results relatively independent of the chosen dt.

Thus, the final code, having made only small changes compared to yours, becomes:

clc;    clear all;

%% Parameter Setting
vel=2000;   % velocity of medium
r=1000;     % distance at which wavefield will be observed
% the final wavelet should appear at time, t=r/vel=0.5sec

T=1;        % Total time
dt=.0025;   % time step
f0=25;      % central freq

%% Create Source Wavelet
N = round(T/dt);        % No of samples
t0 = 5/(sqrt(2)*pi*f0);     % Zero time shift
t = dt*(0:N-1);             % time vector
tau = t-t0+1*dt;     % time vector shifted by t0
src = (1 -2* tau.*tau * f0^2 * pi^2).*exp(-tau.^2 * pi^2 * f0^2);  % source wavelet

%%FT of signal
fmax=1/dt; % max frequency
freq= linspace(0,fmax,N);    % Freq vector:   0 <= f <= Fmax
sw=fft(src);      % fourier transform of wavelet, S(w)

%% 2-D Greens Function
w=2*pi*freq;
const = -1i/4;
H02 = besselh(0,2,w/vel*r);
H02(1)=0;
GF = const*H02;

%% Calculating the Wavefield
WF= ifft(GF.*sw);

%% Plot
% Wavelet
subplot(2,2,1);
plot(t,src);     title('\bf{Source wavelet}');
xlabel('Time(sec)');    ylabel('Amplitude ')

% Frequencies
subplot(2,2,2);
plot(freq,abs(sw));    title('\bf{Source freq spec}');
xlabel('Frequencies(Hz)');  ylabel('Amplitude ')
xlim([0 fmax/2])

% Gneens Fkt
subplot(2,2,3);
plot(freq,abs(GF));   title('\bf{Green Function}');
xlabel('Frequencies(Hz)'); ylabel('Amplitude ')
xlim([0 fmax/2])

% Wafefield
subplot(2,2,4);
hold on
plot(t,real(WF));    title('\bf{Trace}');
xlabel('Time(sec)');  ylabel('Amplitude')

Provided that the signal is sampled to the Nyquist frequency, this should give good results:


Geothermal gradient near surface? Is there a good chart of the geothermal gradient but near the surface? I haven't been able to find one because they are primarily studied at larger depths, but I would like to know the equilibria at different depths within 1 kilometer.

The trouble with geothermal gradients is they are not the same everywhere. It is generally accepted that the geothermal gradient is 25-30 °C/km but there can be local variations. In South Australia the gradient is generally 30° C/km, but in the deeper parts of the Cooper Basin the gradient is 55-60 °C/km. Elsewhere, at a depth of 200 ft the temp is 11 C. In the UK the average geothermal gradient is 26 °C/km, but locally it can be in excess of 35°C/km.
With near surface depths, the ground temperature will vary with depth according to the time of day.

So to get an accurate geothermal map for your region would require localized data.


Is the Yellowstone National Park unique for its geysers? The Yellowstone National Park in Wyoming is unique for its large number of "thermal occurrences, of which there are some 30 geysers. This, in turn, appears to be the result of the presence of large quantities of molten rock, and the thinness of the earth's crust there, compared to the other spots on the earth.

To the best of my knowledge, there is no other (known) place on earth where so much thermal power is contained in a relatively small area. Is this in fact the case? If so, what made Yellowstone, Wyoming so unique in this regard?

Yellowstone is thought to be above a mantle plume, of with there are tens to hundreds on our planet, although there is plenty of debate on this matter. The exact nature of mantle plumes is a huge area of hotly contested research, but generally the are thought to be large melts originally sourced from the D'' layer (core / mantle boundary). Below the park, the plume is theorized to have resulted in magmatic intrusions overlain by a hydrothermal system. The intrusions can also be considered as magma chambers of a supervolcano, which has had several ultraplinean caldera-forming events.

The Yellowstone hotspot is the only obvious expression of a mantle plume beneath the continental United States, which may be why you consider it "unique." The other major plume / hotspot in the US is Hawaii.

Yellowstone is certainly not the only major geothermal area in the world; geothermal areas in New Zealand, Italy, Japan and Antarctica are comparable in terms of heat flow. It's unclear what you mean by "thermal power" but Yellowstone park does not have any geothermal electric power generation plants. New Zealand, on the other hand, generates 13% of their national power needs geothermally.


How was the Marinoan Glaciation triggered? The Marinoan Glaciation (a.k.a. Elatina Glaciation) was a glaciation that is thought to have occurred towards the end of the aptly-named Cryogenian period at ca. 650Ma. It is particularly known as one of the glaciations that may or may not have been a Snowball Earth.

Whether or not this glaciation was truly global, there is evidence that this glaciation existed. But what are the current hypotheses on how this glaciation was triggered?

Several articles suggest that the mechanisms involved with the weathering and/or the breakup of supercontinents as being a mechanism for this kind of glaciation, in the timeframe pertinent to your question, Rodinia.

According to the article Precambrian supercontinents, glaciations, atmospheric oxygenation, metazoan evolution and an impact that may have changed the second half of Earth history (Young, 2013), a suggested mechanism of the onset of glaciation is the formation of the supercontinent, specifically, the author postulates:

  Enhanced weathering on the orogenically and thermally buoyed supercontinents would have stripped $CO_2$ from the atmosphere, initiating a cooling trend that resulted in continental glaciation.

The Polarisbreen Formation is touted in the article The Marinoan glaciation (Neoproterozoic) in
northeast Svalbard (Halverson et al. 2004) suggests that weathering as being one of the main factors for the sustained glaciation.

An alternative hypothesis is proposed in the article From Volcanic Winter to Snowball Earth: An Alternative Explanation for Neoproterozoic Biosphere Stress (Stern et al. 2008), where the authors suggest that increased global volcanism from the breakup of the supercontinent.


What percentage of cumulonimbus clouds create lightning? I understand that cumulonimbus clouds can create lightning, but do not understand how many of them create lightning.  I would assume that most multi-cell systems would have lightning, while single cell systems would have less of a chance at creating lightning.
 Is that right?  What percentage of cumulonimbus clouds create lightning?

I've done some research studies about the flash rate in various storms. My paper is now in review, but here is some info from this paper:

We have computed measurements for supercell and moderate thunderstorms, counting CG+ discharges. There are 24 times more discharges in supercells than in moderate thunderstorms. Supercells on average had better thermodynamic conditions to develop into a huge storm cluster.

The only help to answering your question is that Cb clouds are not similar to each other. But what I can tell you is that Cb lightning in my studies for CG+ discharges occurred once a minute, whereas for a supercell this number is equal to 24 per minute.

I studied thunderstorms from 19th of July 2015 and 17th of April 2016 over Poland.


how are the global effects of local environmental disasters? Are there any local environmental catastrophes that affected another places in the world?

There is a huge list of environmental disasters on Wikipedia that I have found: https://en.wikipedia.org/wiki/List_of_environmental_disasters

I would really appreciate if there are some academic or non academic references that point out the global effects of local environmental disasters?

Edit: To be more specific, for example, can a catastrophe that occurred in a Latin American country affect the environmental quality (pollution level) in another place in the world (Asia, Africa or another place)?

Let's say that the pollution level increased in USA and resulted in a catastrophe. Could we say that higher level of pollution and catastrophe occurred in USA can cause another catastrophe in somewhere else?

An excellent example of this would be the Mount Pinatubo eruption in 1991. The specific nature of this eruption features massive amounts of aerosols and ash put into the atmosphere. When Mount Pinatubo erupted, the amount of dust and ash it injected into the atmosphere was responsible for a worldwide reduction in temperature of 0.5–0.6 °C in the northern hemisphere over the next year, as well as a massive increase in ozone depletion.


The river or the hills; which came first? On the upper Mississippi in Illinois and southern Wisconsin, the river is bounded by hills and bluffs which  define the outer edges of the flood plain. There are similar configurations for some of  its tributaries, specifically the Illinois, the Rock and the Wisconsin Rivers.

My question is whether the hills preexisted the  course of the river or did the river in some way cause the hills  to "appear".

Are the hills all glacial deposits which guided the course of river?

I understand  erosion   formed the bluffs  at Wisconsin Dells and Starved Rock, but why did the river flow there in the first place?

This is a kind of chicken or egg question, since there was never really a point at which there was no river flowing, or no hills to flow around.

  My question is whether the hills preexisted the course of the river or did the river in some way cause the hills to "appear".

Most of the area which you describe along the Mississippi is formed of sand, gravel and till deposited by glaciers in the previous two glaciations. Though there would have been solid bedrock beneath it all before that, complete with hills and rivers flowing across the landscape.

Rivers flow along the path of least resistance over the landscape under the influence of gravity. This means that, in general, they will take the route with the steepest downhill gradient from their source to the sea.

  Are the hills all glacial deposits which guided the course of river?

The hills formed by glacial deposits would indeed have influenced the course of river after de-glaciation occurred. Though the flowing glacier will have shaped the hills in the first place.

At the same time, the river will be eroding the material through which it flows, so it is constantly (but very slowly) carving out new formations in the landscape. Fluvial landscapes tend to produce very dendritic landscapes – that is, comprising of a dense network of channels with many small tributaries – in comparison to landscapes formed by glaciers. In this sense, the river will be causing new hills to 'appear' as it carves out new valleys and tributaries into the glacial material. Some of the smaller hills in the area may well have been formed entirely post-glacially.

Summary:

A mixture of both really. River courses are influenced by existing topography, but they also have the power to carve out new features into the landscape.

Afterthought:
If you go back far enough in Earth history, before the formation of water at the surface, there would have been some sort of topography (hills). So you could argue that ultimately the hills came first.

Sources: Bennett and Glasser (2009) Glacial Geology; Anderson and Anderson (2010) Geomorphology


What are the domains of Earth Science? Increasingly confused by all the "spheres" and agreed relationships between them. As a result, I am looking for a singular answer that clearly states at the very least what the top-level and secondary domains of Earth Science are and if possible, the domains relationships.

Spheres I have run across include, but are not limited to: biosphere, atmosphere, pedosphere, lithosphere, hydrosphere, geosphere, cryosphere, exosphere, and more.

Diagram Request: While not required, a visual, such as a venn diagram would likely be of use.

Regarding subdomains - I expect that there may be hundreds or thousands of subdomain *spheres.

For example, I've studied soil for many years and had never heard of the "drillosphere", "porosphere", "aggregatusphere", or "detritusphere".

  “drilosphere” (the portion of the soil volume influenced by secretions
  of earthworms), the porosphere (the total pore space), detritusphere
  (dead plant and soil biota), aggregatusphere (the sum of aggregates)
  and the rhizosphere.

from fig 4 in the same Nature Education article that provided the macro-view venn diagram in @blunders' answer.

(source: nature.com)


What would be the depth variation of a "water ellipsoid" above a reference ellipsoid Earth? The question If the Earth was a smooth spheroid how deep would be the ocean? has an excellent answer which explains the shape and surface area of an oblate spheroid before calculating the average depth of the Earth's surface water (about 2.7 km). The difference in radius, and surface area compared to a sphere look to be of the order of parts-per-thousand compared to a sphere.

But even within the approximation of an ellipsoid, the Earth's gravity is not uniform in direction nor magnitude, and so the assumption of a constant water depth from pole to equator may also require some correction of the order of parts-per-thousand.

How would one calculate the variation of depth of the water from pole to equator taking into account some kind of first order variation of gravitational force and rotational effects (centrifugal force) to get the shape of the "water ellipsoid"? Does it turn out that the thickness would end up being uniform because the Earth ellipsoid is already a response to rotational effects, or would there be a pole-to-equator variation in depth of order parts-per-thousand?

A complicating factor will be the change in density with temperature. So for this I will assume a constant density of water.
As the thickness of the water layer is quite small compared to the size of Earth (given as 2.6 km by the answer to the other question) I think an approximation with a constant g at any particular location should give a fairly reasonable answer.
Water naturally finds its level based upon pressure. So if we have a constant pressure at the top of the surface, the pressure at the bottom must also be constant. And this should work as a reasonable approximation for any number of layers.
Noting that for any column of water, the pressure increase will be given by:
$P=\rho \cdot g \cdot h$
Taking the values of g from Wikipedia:
At the equator, g, due to Earth being an oblate spheroid and rotating is ~$9.78 \frac{\mathrm{m}}{\mathrm{s}^2}$
At the poles, g is ~$9.83 \frac{\mathrm{m}}{\mathrm{s}^2}$
Equating the 2 we end up with:
$P=\rho \cdot 9.78 \frac{\mathrm{m}}{\mathrm{s}^2} \cdot h_e=\rho \cdot 9.83 \frac{\mathrm{m}}{\mathrm{s}^2} \cdot h_p$
Factoring out common terms leaves us with:
$h_e = \frac{9.83}{9.78} h_p$
So the equator will have water that is roughly 0.5% deeper than the poles.
For 2.6 km, that works out to be roughly 13 m.


Sea Level Rise due to Climate Change I've been trying to make sense of the argument surrounding sea level rise and not getting very far.

Those who claim that Sea Level Rise is insignificant generally assert that we have been unable to statistically link rising Greenhouse Gas levels to rising sea levels. I assume that this is incorrect, but I do not have the knowledge to analyze this and have not heard the claim refuted before.

I would like to know whether Sea Level Rise is linked to Greenhouse Gas emissions and what the mechanisms are behind it.

The first part of the association is that increasing levels of greenhouse gases in the atmosphere will cause rising temperatures on earth. Here is some information on why that is so, if you are interested. Now assuming that temperatures are currently going up (they are), there are two mechanisms that will connect this to rising sea level, melting of ice on land, and thermal expansion of water

Land Ice

As climate lawyers are quick to point out, if floating sea ice melts, it doesn't really change the level of the ocean (much) because floating ice displaces a volume equal to an equivalent mass of water. As we will see in the next part, the temperature change from ice melting and then warming will cause some changes.

Meanwhile, there is about 2.8 million cubic km of ice locked in Greenland's ice cap and 26 million in Antarctica. These two sheets, if fully melted would cause about 7m and 58m of sea level rise, respectively. They will not melt immediately; while the topic is under debate, Greenland will probably take a millennium to melt completely. Antarctica is larger, colder and more isolated from world temperatures fluctuations due to the circumpolar currents, and would probably take a much longer time to melt fully.

Thermal Expansion of water

The density of seawater changes with temperature. Using data from this chart (Data-Table 9), the density of seawater (at 35000 ppm salinity) at 10 C is $1.0270 \frac{\text{g}}{\text{cm}^3}$ and at 15 C is at $1.0260 \frac{\text{g}}{\text{cm}^3}$. Therefore, there is an estimated $\frac{1.027-1.026}{5} = .001 \frac{\text{g}}{\text{cm}^3}$ change per degree C, or a $\frac{.001}{1.027} = .097 \% $ increase in volume for a one degree C increase in temperature from 10 C to 11 C.

Not all the earth's ocean's are at 10 C, but using this as an estimator, the $1.35 \times10^9 \text{ km}^3$ will increase by $1.31 \times10^6 \text{ km}^3$ with a 1 C increase in temperature. If you divide that by the surface area of the ocean, 510 million $\text{ km}^2$, you get an approximately 2.5 meter increase in sea level.

That calculation is not at all rigorous; deep ocean water is colder than 10 C and at lower temperatures thermal expansion is much less (just look at the linked chart to see), but it does demonstrate that there will be a detectable rise in sea level from thermal expansion of seawater as the planet heats up.


Historical isobaric charts? I am looking for a small-scale isobaric chart, which encompasses central Africa. I am interested in the time span of the past few months.

Do you know where to find it?

Thanks

I have found an archive of small-scale charts encompassing part of Africa here.


How does the subsurface earth temperature vary around the world? In the US, when constructing a geothermal heat pump, common knowledge holds that anywhere in the country the subsurface ground temperature at a depth of 5 m will be around 10 to 15 C, which is a good temperature to provide cooling in summer and heating in winter.

I was trying to find information on subsurface temperatures at various depths around the world -- I had assumed that this value would be fairly consistent, but I am unable to confirm.

How does subsurface temperature vary around the world (say at a depth of 5 to 10 m), and what does this depend on? I am not concerned about the effect of local phenomenon such as volcanic activity.

I'd be particularly interested in a map (static or interactive) presenting this information.

The subsurface temperature will vary due to the soil type: sand, clay, loam, silt and the degree of saturation of the soil, soil thickness, the thermal conductivity of the soil, the surface temperature (time of the year) and the albedo of the surface.

Temperature changes within soil become less variable with depth.

So far I have only found information for two regions: the US-Virgina and Cyprus. Following is a series of curves for the US. A similar diagram is available for Cyprus, but its locked in a pdf file.

In Cyprus, the soil temperature at 3 m depth varies between 18 °C and 20 °C. In the US, at a depth of 12 feet (3.6 m) the temperature varies between 60 °F and 65 °F (15.5 °C and 18.3 °C).

These results are similar, but it needs to be noted both locations are in temperate climate zones. The latitudinal extent of Virginia is between 36.5° and 39.5° North and Cyprus is 35° North.

From research undertaken in Australia, the temperature at depth in a soil is also dependent on the air temperature and hence the latitude. At a depth of 1 m the soil temperature is 35 °C at latitude 10° South and 12 °C at latitude 45° South. There will be a corresponding difference at 5 to 10 m depth.

The British Geological Survey states:

  About half of the solar radiation received by the Earth is absorbed at the surface. As a result, the ground temperature shows seasonal fluctuations to depths of about 15 m where the temperature is approximately equal to the mean annual air temperature(8 - 11° C in the UK). Below this the ground temperature increases at, on average, 2.6 °C per 100 m due to heat flowing from the interior of the Earth. Mean temperatures at 100 m depth in the UK vary between about 7 - 15°C.


Why does lightning strike from the ground-up? The enlightening image below is of a lightning strike slowed down at 10,000 frames per second.   It can be seen that the most intense flash produced from the lightening occurs in the direction from the ground up.  Why does this final "ground-up" strike occur and why is it so much brighter and faster than the initial part of strike heading towards the ground?

Does lightning strike from the sky down, or the ground up?

  The answer is both. Cloud-to-ground lightning comes from the sky down,
  but the part you see comes from the ground up. A typical
  cloud-to-ground flash lowers a path of negative electricity (that we
  cannot see) towards the ground in a series of spurts. Objects on the
  ground generally have a positive charge. Since opposites attract, an
  upward streamer is sent out from the object about to be struck. When
  these two paths meet, a return stroke zips back up to the sky. It is
  the return stroke that produces the visible flash, but it all happens
  so fast - in about one-millionth of a second - so the human eye
  doesn't see the actual formation of the stroke.

  Source: National Severe Storms Laboratory

The reason is that when cloud-to-ground strike approaches the ground, the presence of opposite charges on the ground enhances the strength of the electric field and the "downward leader" strike creates bridge for the "return stroke"; this per the wiki page for Lightning.

Cloud to cloud and Intra-Cloud Lightning

Might be worth also noting that cloud-to-ground is not as common as Cloud to cloud (CC) and Intra-Cloud (IC):

  Lightning discharges may occur between areas of cloud without
  contacting the ground. When it occurs between two separate clouds it
  is known as inter-cloud lightning, and when it occurs between areas of
  differing electric potential within a single cloud it is known as
  intra-cloud lightning. Intra-cloud lightning is the most frequently
  occurring type.

Ground-to-Cloud

Appears that ground-to-cloud is possible, though normally only a result of a man-made object creating "unnatural" electric potential, and is the least common type of lightning.


Why are clouds outlining the southeastern United States? While watching the Starlink 25 launch earlier this month, I noticed that the Florida peninsula seemed to be nicely outlined by clouds.  Pulling up satellite imagery from that time showed that my impression was correct: virtually the entire southeastern United States was covered with small, puffy clouds, neatly cut off at the coastline, with clear skies over the ocean.
What causes this?

The small puffy clouds over Florida are cumulus clouds ('fair weather clouds' accompanying the launch). The sun heats the ground and the ground composition is not evenly distributed, where air is warmed more quickly it starts to rise until the moisture it contains condensates, forming clouds, while colder air in between sinks. This is called convection, in this case limited to the lower atmosphere over Florida.
The ocean is mostly free of them because it isn't heated as much as the land and warming is more uniformly distributed, so that in that specific weather situation (high pressure it seems) no convection did develop over water.


To stop anthropogenic climate change, is it necessary to stop extracting petroleum and start pumping carbon under ground? The amount of carbon (C) on Earth is constants.  As far as i understand, all carbon that is not found in the atmosphere or the oceans in the form of CO2 or CO is stored either in the biomass (plants, animals, including humans, bacteria, mushrooms, etc.), or in fossils and fossil fuels (coal, petroleum, natural gases), or in non-organic form as graphite and diamonds.  Is this correct?  Does it follow that the only way to stop anthropogenic climate change and decrease the amount on CO2 in the atmosphere is to stop extracting fossil fuels and to start converting CO2 from the atmosphere into graphite or diamonds or into some form of petroleum and pump it back under ground?

I have asked a related question about carbon distribution on Earth.

Summary
Most of the remaining stocks of hydrocarbons (coal, natural gas, oil) will have to remain unburnt. In almost all cases, that will mean leaving them in the ground. We already have proven technology to prevent new emissions of anthropogenic greenhouse gas emissions, and in most cases, the technical and economic barriers are solved: the remaining problem is purely political.
Let's make sure we're talking about the same thing
Let's get our terminology straight first. The big issue is rapid climate change; and we can do something about that, because the current rapid climate change we are starting to experience, is anthropogenic - it is human-caused.  So, "climate change" here refers not to historic natural processes over thousands to millions of years, but the present anthropocentric-induced processes that are happening over decades. That is the most common usage of the phrase these days, but it still can be useful to state it explicitly once in a while so that we know we are discussing the same thing.
Stocks and flows
Climate change is a result of changes in the stock of greenhouse gases in the atmosphere.
Those stocks have increased a lot over the last 180 years or so, and are continuing to change, because we've messed about with the flows. In particular, we've increased the rate of emissions from sources, without increasing the rate of take-up of sinks.
The bathtub analogy: we've opened the bath taps further, so water's flowing in faster. But we haven't widened the drain, so the level of water in the bath is rising, and soon will overflow and flood the house. It's not the rate at which water enters the bath that's the problem in and of itself: it's the level of water in the bath, and that's rising quickly because the inflow is much faster than the outflow. Similarly, what matters for climate and climate change is the level of greenhouse gases in the atmosphere, and the level of CO2 absorbed into the oceans.
Even if new net emissions went to zero this year (technically impossible without the collapse of human civilisation, which would rather defeat the whole exercise), we'd still see increasing heat content of the Earth over the next few years, as things move towards equilibrium, based on the current levels of greenhouse gases which represent a historic increase over the levels that prevailed over the last few thousand years during which human civilisation has developed.
So, to prevent further climate change, we have to balance out sources and sinks. So we can do either, or a combination, of two things: we can decrease the rate of emissions from sources down to the level where existing sinks can absorb them; and we can increase the rate at which sinks absorb.
Reducing sources
Stopping burning fossil fuels is the easiest and simplest way to decrease the rate of emissions. To the best of my knowledge, we now have alternatives for almost all of the major emissions sources, with the possible exception of methane emissions from livestock farming. Some are very well-established, like hydro and onshore wind electricity generation. Some are maturing quickly, like PV, offshore wind. Some are successful in the lab, and ready to move to commercial-scale prototypes, such as decarbonised production of steel, clinker, and liquid hydrocarbons.
Increasing sinks
Carbon sequestration is one way to increase the sinks. It's been trialled at small scale, and remains problematic. The way that's been done so far is to pump the carbon dioxide underground. At the moment, no business has been willing to accept the open-ended liability that is posed by the risk of leakage. So at the moment, the market is saying that this is not a viable technology. That might change. It's also worth noting that at the moment, the market also wants to use CO2 sequestration as a means of extracting even more oil (Enhanced Oil Recovery, EOR), which just makes the whole problem worse.
One way that is fast, effective and affordable is increasing the amount of carbon in biomass. Reforestation and afforestation are two ways to do this, and would help reverse a lot of the human-caused loss of forest ecosystems, if done well.


Is there a lake whose sole source of water is rain and has a hole at the bottom draining it? Oregon lake has a drain hole at the bottom but also has water flowing into it. Pingualuit crater has no water flowing into it but probably has no drain hole at the bottom either.

I'm wondering if there's also a lake that has no water flowing into it but has a drain hole at the bottom. If such a lake exists, would the water in it be very pure because the slightest bit of impurities in it move to the drain hole and flow out? I think that for such a lake to exist, the land around it would have to be higher than the land further away like Pingualuit crater.

I think there is some misunderstanding of the water balance of a lake, or to put it differently, why some holes in the ground are dry while some are filled with water (known as lakes). The linked articles contain lists of closed lakes, but I'll also try to explain how lakes are formed.

Fresh water comes from the rainfall (and snow and moisture) that falls on the ground, and if it does not evaporate, it will eventually seep down into the groundwater when it reaches the groundwater table.

The groundwater flows towards lower elevation, known as hydrostatic head, and eventually, it reaches the sea level. If you would dig a number of holes from the sea towards the mountains, you'll see that if the holes are deep enough to reach groundwater (wells), the elevation of the groundwater surface will form a slope. If the geology is such that the water only flows slowly through the ground and the precipitation is high, the slope can be steep, but if you have e.g. a sandy ground and low precipitation, the groundwater table is subhorizontal. Indeed, in areas with high evaporation, the slope can face away from the ocean, towards a local depression as e.g. the Dead Sea or Death Valley.

If the groundwater table crosses the ground so that the elevation of ground is lower than the hydrostatic pressure of the groundwater, the groundwater will be exposed and form a lake or enter a river. The lakes and rivers are manifestations of the groundwater level. Sometimes there is a delayed response time as water flows much quicker in a river than in the ground. This causes flash floods to flow above the ground if there is not enough time for surface water to penetrate the surface. Like a coffee filter overflooding if one pour water in it too fast. Given enough time, the surface water will enter the groundwater and flow towards the ocean or evaporate.

Sometimes there are features that speed up the flow, e.g. karsts or gravel lenses that have a very high hydraulic conductivity so that water can flow rather fast through. Interesting phenomena can occur that control this kind of quick drains if e.g. the drainage gets frozen and clogged in winter or there are some other seasonal variations. This is maybe what you describe as a drain hole, but usually, lakes without outlets just adjust the water back into the groundwater by penetration and by evaporation of the surface.

Dissolved salt is concentrated in lakes without an outlet and they are called closed lakes or endorheic basin. If the climate is changing, an open lake can become a closed lake and vice versa.

A lake is always a temporary feature. They fill up with sediments over time and becomes a part of the river path. As you noticed, there is always a special reason for a lake to form, e.g. rapid post-glacial rebound, rifting or an impact crater.

Ponds and tarns without a visible outlet are rather common, at least in post-glacial areas as Canada or Scandinavia, but if a lake has enough inflow, its level will rise until it gets a visible outlet. Depressions without a visible outlet are called sinks.

How pure the water in the lake is depends on a number of factors. Silt and clay come from fast-flowing inlet rivers or wind. The residual time and current for the water in the lake defines how much of the sediments that have time to settle. The bathymetry is also an important factor as local depocenters can take care of most of the sediments. Fine sediments can take a long time to settle. Finally, the biology of the lake is naturally very important.


Can tides at night by consistently higher than in the daytime? Can the tides at night be consistently higher than in the daytime in southwest Australia in the port of Fremantle?
Also, what is the explanation for the tides being significant during a part of the year, and then disappear.

I find the statement in the question difficult to believe.Tides have a pretty cyclical period and I doubt the resulting effect is a day-night difference unless only S1 and S2 tidal constituents are important in that location, which I find very unlikely.

In fact, the portal
https://www.tide-forecast.com/locations/Fremantle-Australia/tides/latest
shows the high tide being larger during the day for the rest of the month of May 2018.
That behavior changes in time as one would expect. The dominant frequencies at this location are diurnal tides (mostly a single high tide and low tide per day). The main diurnal tides have a period around 24 hours and in this case the dominant periods are slightly larger than 24 hours.

You can download the hourly data from: http://uhslc.soest.hawaii.edu/data/netcdf/fast/hourly/h175.nc
and the resulting time series goes from 1984 to now. Here is the time series for the year 2017. There is no time at which the tide "dissappears".

The resulting harmonic analysis (using t_tide) shows that the tidal constituents with amplitudes over about 5 cm are:

Constituent  Period (h)  Magnitude (m)
   O1         25.82      0.1206
   K1         23.93      0.1667
   M2         12.42      0.0525
   S2         12.00      0.0465

The dominant constituents are K1 and O1, with comparable amplitudes. The resulting effect of the two main diurnal frequencies is a period slightly over 24 hours. The effect of the semidiurnal constituents (M2, S2) is smaller and can be seen in the first time series as slight humps in May 24-27.

T_tide: Pawlowicz, R., B. Beardsley, and S. Lentz, "Classical Tidal
"Harmonic Analysis Including Error Estimates in MATLAB
 using t_tide", Computers and Geosciences, 28, 929-937 (2002).


In an Earth-like planet with no history of carbon-based life forms, would there be limestone? The extent of my understanding of limestone is about what Wikipedia says at the very top of the page:

  Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).

What catches my curiosity is the word "mainly" there... I can't tell if it means "the main part of all limestone" is [skeletal fragments of organisms]" or if it means "part of limestone (in the usual cases) is [skeletal fragments of organisms]".

Phrased in the most general and interesting way (to me):

Given an Earth-like planet with all the right ingredients (e.g. large bodies of liquid water, iron-nickel partially-liquid core, etc.) with one exception—no history of carbon-based life forms—would we find significant amounts of limestone like we have on Earth today?

I'd have to say, yes. Once life evolved in the world's oceans, the vast majority of limestone formation has been through the organic process. However, before life did evolve, limestone formed through an inorganic process where rain water falling through a CO2-rich atmosphere reacted to form a weak carbonic acid solution that then reacted with calcium-containing minerals to form calcites. This then washed into the world's oceans to form limestone deposits.From gsu.edu:

  Limestone may form inorganically or by biochemical processes.
  Another form of limestone of inorganic origin is oolitic limestone, limestone formed from small spherical grains called ooids.

In an paper from Stanford.edu:

  Carbonic acid dissociated to form hydrogen ions, which found their way into the structures of weathering minerals, and bicarbonate, which was carried down rivers and streams to be deposited as limestone and other minerals in ocean sediments.

So even in a world devoid of carbon-based life, limestone could still form if it had a CO2-rich atmosphere, water (and thus rain), and calcium-containing crustal deposits. Though the paper from Stanford is theoretical, note that this does not mean hypothetical and is (I believe) based on solid science.


How do I interpret this "sky cover" chart? The image below is a screenshot of forecasted sky cover in percentage for various parts of Arizona. Is the sky cover percentage the percentage of each pixel that has cloud, or is it the percentage of a circle with a certain radius where a certain pixel is the center? Not sure how to word it more clearly.

The "sky cover" represents the percentage of sky obscured by clouds, as would be visible to an observer (or weather instrument) at the Earth's surface.

The most direct reference I could find to this quantity was in this archived presentation from the American Meteorological Society's 2014 Annual Meeting: "The United States Federal Meteorological Handbook (FMH) No. 1 defines sky cover as “the amount of the celestial dome hidden by clouds and/or obscurations”. User @MikeChristianson also identified a direct definition for this exact National Digital Forecast Database (NDFD) product here, confirming this interpretation: "Sky cover is the expected amount of opaque clouds (in percent) covering the sky valid for the indicated hour."

There is also supporting evidence with some additional detail in the NWS Products and Services Reference Guidebook, specifically Section 9, Tables and Abbreviations: The “sky condition” describes the average percentage of the sky that is covered by opaque clouds (not transparent to light) at a given time, followed by a tabular description of the percentile sky cover forecast interpolated to the forecast image in question:

Slight differences in terminology aside, both of these descriptions equivalently refer to the portion of sky obscured by clouds. For typical weather forecasts (as in the example in question), either would be interpreted as describing the sky as it would be visible to an observer at a given point on the Earth's surface - the visible "celestial dome". See also the definition quoted here from the 2nd edition of the American Meteorology Society's glossary, defining cloud cover as "observed from a particular location," in this case the Earth's surface.

Additionally, as noted in the comments, the definitions are vague enough that the observer could be a person or a weather instrument - naturally, the exact details of what would be visible and quantified depend on the observer, but for a simple use of this forecast parameter, the FMH & NDFD definitions support this interpretation of sky cover.


At what altitude stalagmite/stalactite caves are located? What kind of rocks are needed to form them? I know that there are many kinds of such caves, but I am looking for ones (if they exist, and I don't know) that contain stalagmite and stalactites and are located at high altitude inside a mountain. I also need to know in what kind of mountains they are, and what kind of rocks must be present.
Also, can you suggest me a reference book about the topic?
I know nearly nothing about geology.

The classic text has long been "Karst Hydrology and Physical Speleology" by Alfred Bogli, - which I highly recommend.

Karstic dissolution and precipitation (to form stalactites, helictites, etc.) are basically hydrologic processes in which groundwater seeks to attain thermodynamic equilibrium with the carbonate rocks with which it is in contact. Water flows downhill towards the base-level of erosion - generally sea level. But bear in mind that during the last glaciation sea level was about -120 metres compared to modern sea level. To get very high mountain karst the system has to develop and then be lofted by other tectonic processes of uplift. In the Jebel Akhdar of Oman there are caves up to about 2 km elevation, but I guess that some limestone massifs have been elevated higher than that.


Is there a simple temperature prediction model? I'm working on piecing together a game that involve sea trading, loosely based on historical conditions. As a part of making the game, I'm creating a map. From that map, I'm trying to determine what the temperature is, at least on average, for a number of reasons. I'm also going to include a seasonal model to it. What I'm trying to do is to find a first order estimate of the average temperature by day and by latitude, at sea level. I know that this varies tremendously based on a number of factors, but it seems to me that assuming equal distance to the sun, a perfectly spherical Earth with a known axial tilt, and some other reasonable assumptions, there should be a model that will work, which I can add to some noise to cover some of the other sources of error.

Bottom line, is there a relatively simple model of latitude and time of year vs average temperature at sea level? Bonus points if it includes a difference by altitude. Thanks!

Simple? Depends upon the level of accuracy you are looking for. Insolation alone is a rough indicator of sea surface temperatures.

image from http://www.ospo.noaa.gov/Products/ocean/sst/contour/

In more detail SSTs around the globe are significantly influenced by oceanic currents which, in turn, are very strongly influenced by the distribution of continents.


Are 60C heat waves predicted by 5C of global heating? (The worst consequence of global heating) It seems to be the case that 1C of global heating caused the whole global temperature bell curve to shift two standard deviations to the right. (see below)

To anyone knowing much about statistics and bell curves this would seem to make the 80 years BAU 5C temperature anomaly have the drastically lethal consequence of much more frequent heat waves greatly exceeding the 44C maximum human survival limit.

My own projections of the current trend are a little more pessimistic than IPCC RCP8.5 projections. They simply extrapolate the current exponential increase of atmospheric CO2 and project 877 PPM by 2100 then apply the current IPCC equilibrium CO2 sensitivity formula

3C ± 1.5C for every doubling of atmospheric CO2
log2(877/280) * 1.5 = 2.47
log2(877/280) * 3.0 = 4.94   // Business as usual for 80 more years
log2(877/280) * 4.5 = 7.41

https://www.giss.nasa.gov/research/briefs/hansen_17/
When we examine this graph we see that a single degree of temperature anomaly is associated with a shift of the whole temperature bell curve two standard deviations to the right.

If we hypothesize that a single degree of temperature anomaly directly caused the entire bell curve to shift the right two standard deviations then the consequences of a 5C would seem to be quite lethal.

Once we numerically quantify the relationship between temperature anomaly and shifts of the bell curve then we would be able to apply this to historical geographical  temperature extremes and predict the frequency, geographic and temporal extent of heat waves that would kill everything within their boundaries.

This relationship seems to predict that the 5C temperature anomaly projected from "business as usual" for 80 more years could reasonably result in 60C (140F) killer heat waves. A 60C heat wave will kill everything in its path very quickly. Apparently humans cannot survive 44C for very long.

Neither an answer, just common sense.

Not sure if anybody can give exact numbers for temperatures of future heat waves in their projections. Predictions are difficult, especially those regarding the future. But there is consensus and now observation that heatwaves become more frequent and hotter not only on land. One could perform a search for publications that deal with the impact of land heatwaves, e.g. on agriculture (wheat for example), desertification, loss of habitable space, flooding, loss of resources like potable water, etc. There is a lot of published work around.

We went past the 1°C warming compared to pre industrial levels in 2015, after [https://www.ncdc.noaa.gov/cag/global/time-series] and many publications. Current estimations range between 0.9 and 1.6°C for 2019. Several islands have been devastated in the past years, damage still not totally repaired. Jakarta is drowning, catastrophic fires in California, Australia and elsewhere, fed by drought, heat and mismanagement, cost lives and property.

The effect of past and current heatwaves on the health of the population is pretty well visible, western European countrie's and the US health departments have published their estimations of fatalities attributed to heat.


How is Karst topography formed on land? I read that the source of Karst topography is coral reefs, when coral reefs are found in water bodies, how is karst topography formed on land?

Karst topography on land is characterized by sinkholes, springs, losing streams, and caves.  They are formed by the dissolution of easily dissolved carbonate rock such as limestone and dolomite.  The rock is dissolved by carbonic acid in rain.

From Wikipedia:

  The carbonic acid that causes karstic features is formed as rain
  passes through the atmosphere picking up carbon dioxide (CO2), which
  dissolves in the water. Once the rain reaches the ground, it may pass
  through soil that can provide much more CO2 to form a weak carbonic
  acid solution, which dissolves calcium carbonate.

Here is an illustration of karst topography:

Source:  //www.wandelgek.nl/?p=18828&lang=en

Here is an illustration of karst formation:

Source:  http://slideplayer.com/slide/3400196/


Why is potential vorticity so emphasized in technical work, but often neglected in maps on weather websites? When I was first introduced to potential vorticity, I was told that it is a very important tool for meteorologists to learn. Sure, it solved a simple problem in dynamics, but it wasn't apparent to me at the time on why it was important.

As I progress, I find that it becomes more and more useful in finding notable features, such as tropical cyclones and fronts. That being said, why isn't it plotted more often? I don't find plots of potential vorticity often, but when I do, it is often plotted for higher in the troposphere, and not where features are commonly found.

This one has not been answered for a long time and I am going to summarize what I wrote in the comments. If I understood OP's question correctly I believe it is asking why Potential Vorticity  is not shown in weather maps in a operational sense.

From this old(but still very useful reference) Isentropic Potential Vorticity presuming isentropic surface are available operationally(AFAIK GFS provides isobaric PV surfaces Warning: You need to register to access the GFS link) and you need to interpolate from isobaric to isentropic.

  Generally, as in constant pressure analyses, one would like to use at least two or three isentropic surfaces to analyze. However, unlike constant pressure analyses, one has to choose different isentropic levels depending upon the time of year.

| Season     |   Low Level Potential Temperature  |

| Winter     |       290-295 K

| Spring     |      295-300 K

| Summer     |      310-315 K

|Fall         |      300-305 K

As one can see the correct isentropic surface to choose for a particular day can be quite a challenge. Also each part of the world may have it's own low level potential temperature complicating the problem.

  Isentropic surfaces tend to intersect the ground at steep angles causing analyses near where they intersect the ground to be suspect. One must be careful about over-interpreting analyses made near where the isentropic surface intersects the earth. One would do best to choose isentropic levels which never reach the ground. However, to depict moist/dry tongues associated with synoptic scale systems one tries to go as low as possible without hitting the ground. So there are trade-offs; as usual, there are no quick-fixes!

In my part of the world(tropics) an all season isentropic surface that does not intersect with the earth's surface globally is the 370 K isentropic level. From a isobaric perspective this turns out to be around 200 hPa from a perspective of climatology.

As one can note this is at a very high level and corresponds to the level of the jet stream. As one analyzes lower isentropic levels one can see maps (you need 3-D to plot PV on an isentropic surface) that intersect the earth's surface and when that happens you need sophisticated extrapolation methods to calculate PV especially along orography(and these turn to be generally inaccurate). Over the tropics generally at lower isentropic levels PV surfaces tend to be perpendicular and their utility is restricted to as OP puts it to the inside of tropical cyclones and mesoscale convective systems.

An example of using PV at lower levels of the atmosphere can be seen in this youtube video Sandy PV filaments


Topography & physiography What is the difference between physiography & topography? I can't understand the context in which to use both. Please explain by giving suitable examples.

Physiography explains the physical characteristics of the area more generally describing the physical processes or forces that formed the landscape, while topography describes particular features, typically associated with elevations. For example in geomorphology (as your post is tagged) the physiography of Canadian prairies may describe deep fertile soils, ancient lake bed remnants, multiple sloughs or ditches that fill with water, etc. The topography would describe the extreme flatness with many depressions in the landscape. In practice, physiography is quite broad and topography refers to elevation data (I.e. a topographic map would have elevation points or contours).

Take a look here at WikiDiff as well.


Seismic wavefield theory: velocity anisotropy Does the reciprocity principle hold true in an anisotropic subsurface environment?

Yes, or at least certainly in theory. If you look up any derivation of the elastodynamic representation theorem you're bound to find that it holds for the most general version of the elastic wave equation:
\begin{align}\rho \frac{\partial^2 u_i(x,t)}{\partial t^2}& = \frac{\partial \sigma_{ij}}{\partial x_j} \\ \sigma_{ij}(x,t) & = c_{ijkl}(x)\varepsilon_{kl}(x,t)\end{align}
with $u$ the displacement, $\sigma$ the stress, $\rho$ the density and $c_{ijkl}$ Hooke's tensor. You'll have run into this tensor whenever you researched anisotropy, because it is how one describes anisotropy.

The main reference is a book by Aki & Richards (1982): https://www.ldeo.columbia.edu/~richards/Aki_Richards.html , but it is also derived in these handouts, see the bottom of page 15: http://www.geo.uu.nl/~paulssen/Theoreticalseismology/handout.pdf .

The notation $G_{nm}(\xi_2,\tau|\xi_1,t)= G_{mn}(\xi_1,\tau|\xi_2,t)$ is the reciprocity relation. $G_{nm}(\xi_2,\tau|\xi_1,t)$ is the measured displacement due to a point source in direction $m$ at time $t$ at location $\xi_1$ as measured at time $\tau$ at $\xi_2$ in direction $n$. The reciprocity relation says that this recorded signal is identical to an experiment where a source in direction $n$ at time $t$ at location $\xi_2$ is measured at time $\tau$ at $\xi_1$ in direction $m$. Hence, you can interchange source and receiver when you interchange source and receiver dirctions too.


What supports the Rockies? What supports the Rocky Mountains in North America? Or put another way, Why are they there? and Why are they still there?

It might be tempting to think of compression, especially in an east-west direction. However at the south end, New Mexico is experiencing east-west extension (grabens including Rio Grande Rift Valley, plus associated volcanism).

Hot spot and/or mantle plume uplift doesn't appear to explain them either. Yes there's the Yellowstone Hotspot under NW Wyoming. Regardless of whether this is really caused by a mantle plume or not, the related volcanism does not correlate with the mountains.

Part of the current topography might be due to a hot upper mantle below the Rocky mountains. This can be determined by seismic tomography. The hot mantle creates isostatic uplift.

Just one of many pictures I found:

http://srl.geoscienceworld.org/content/83/1/23/F2.large.jpg


Radiometric dating data sets I am in the process of learning what sort of data is collected with radiometric dating techniques, used for absolute dating. It sounds like there are two primary ones:

Radiocarbon dating (~50k year scale)
Potassium-argon dating (billion year scale)

Then in between is tree ring dating, but that is a separate thing. And for completeness, there is also a sort of luminescence dating technique which I have never heard of. In this question I am just wondering about the Radiometric techniques. There is also Uranium-lead dating, but I don't see much info on that one, so focusing here just on carbon and potassium-argon.

First, I am wondering if there are any data formats used for storing the data (which will help with search). I searched around a bit but didn't find anything. Second, I'm wondering if there are any data repositories containing radiometric datasets, just to get started. And third, if there's not any "centralized repositories" of this sort of data, and instead it is by individual author in their own style, that might be good to know, just so I don't think I'm missing something obvious.

At first I found this from here:

GEOGRAPHIC REGION: Tropical Pacific

DESCRIPTION:
Pacific Bomb Radiocarbon Coral Data.

Uva island, Gulf of Chiriqui, Panama (7°48'N, 81°45'W),

CUVA; Uva island, Gulf of Chir(7°48'N, 81°45'W)
                              Druffel, ERM(1987). JMR, 45:667-698
Gardinesoseris planulata
collected July 1980 Collected by: P. Glynn

   WH#       YEAR      ¯14C   ERROR
    42    1950-1951    -64       ±3-4‰   for the whole
    43    1952-1953    -59     data set
    68    1952-1954    -58
    69       1955      -51
    70       1956      -46
    71       1957      -47
    72       1958      -45
    73       1959      -37
    74       1960      -42
    75       1961      -24
   115       1962      -26
   109       1963      -22
   110       1964      -23
   106       1965       29
   112       1966       46
   108       1967       34
   111       1968       66
   113       1969       74
   114       1970       70
    96       1972       75
    94       1973       67
    99       1974       70
    92       1975       56
    95       1976       43
    93       1977       54
    91       1978       52
    97       1979       74
    98       1980       73

But that doesn't look like much, basically some sort of in integer value for each year. I'm wondering if there is a lot more data typically, such as like you would find in mass spectrometry or crystallography or something. Or if it is literally just an integer or decimal number without anything else (like probability of correctness or other things). Like I'm wondering if the data is much more complicated and would look along the lines of this:

I also found this which I haven't looked too much into yet. And this (which unfortunately is a PDF), which has a bunch of maps. So it seems like the data would be some sort of GIS shapefile or something perhaps.

If it matters, I am interested in particular in fossil radiometric data.

It sounds like there are two primary ones:

No, these are not the two "primary ones". The method used depends on what you are dating, and what age you expect it to be.

Radiocarbon dating is relevant to things younger than a few tens of thousands of years, and it's only relevant for things that were living (or growing), and incorporated atmospheric carbon.

Other methods such as U–Pb (the "gold standard" when dating igneous rocks), Rb–Sr, Re–Os, Sm–Nd, K(Ar)–Ar, Lu–Hf, and many more, are used for older things in the millions to billions of years. The one used depends on what you're analysing (Re–Os for sulfide minerals, U–Pb for zircons, Rb–Sr for micas, Sm–-Nd or Lu–Hf for garnets), and what is present in the rock, and what has textural evidence for being preserved.

You might call U–Pb on zircon the "primary" one, because most of the dating is done on zircon. It's robust, easy, gives good ages, quick and relatively cheap.

  First, I am wondering if there are any data formats used for storing the data (which will help with search).

Most U–Pb data is reduced using IsoPlot, so the data will look like something that came out of that software. But in general, no. There is no standardised  data format for geochronology, unfortunately.

  And third, if there's not any "centralized repositories" of this sort of data

There are several of those. You can search EarthChem, that has some geochronological data. Australian government agencies also have some geochronology data in them, for example GA or NTGS.

  If it matters, I am interested in particular in fossil radiometric data.

Fossils are among the hardest thing to date. If the fossils are relatively young (few thousands of years), there's radiocarbon. Anything older than that, and it becomes much harder. There's U–Th disequilibrium series which may work for some slightly older fossils (~1 million years). Anything older than that in deep geological time has to be dated with indirect methods. Finding a database of that is probably wishful thinking, and to understand their dates you need to have some geological background to understand the geological relations and considerations that allow the indirect dating.


Where can I find the original scientific articles on Heat index (published by either Larry P. Rothfusz or Steadman)? I'm curious to learn more about the research and thought that went into calculating the heat index. In particular I want to understand how Steadman or Rothfusz managed to fit a model (in terms of relative humidity and temperature) on data with variables related to human physiology.

After having a look at the references of a few papers about heat index (like this one). It looks like the original publications you are looking for are

The Heat Index "Equation" (or, More Than You Ever Wanted to Know About Heat Index) by Lans P. Rothfusz available here, and
The Assessment of Sultriness. Part I: A Temperature-Humidity Index Based on Human Physiology and Clothing Science, by R. G. Steadman available here.

As a general suggestion, looking at the references in related papers is always a great way to find the original research articles on any topic.


How much change has there been to the shape of plate boundaries over geological time? This is a question that has bothered me for many years.  As a new teacher I was asked this question by a 12 year old in our plate tectonics class.  I said I would go away and find out.  I would really appreciate some help!

I have some understanding of plate tectonics but I struggle with understanding how the plate boundaries have changed in terms of their actual spatial positions over long periods of time.  For example, what would the 'jigsaw pattern' of plates at the time of Pangea have looked like?  At plate margins, does the pressure of compression or expansion actually change the spatial position of the margin?  Anderson comments...
"The definition of a plate and a plate boundary is subjective. Things are constantly changing. It is improbable that there is a steady state or equilibrium configuration of plates because both ridges and trenches migrate and only a few of the 16 kinds of triple junctions are stable."

This serves to confuse me further unfortunately.  I have no issues understanding how continents move around, it is the potential change to the size, shape, orientation and position of plates that baffles me!

This probably relates to the potential for new plate boundaries to be formed...and existing ones to close up.  Is this possible?  Sorry if this is an overly simple question.  If this is possible it could explain a lot.  A geologist friend told me that the East African Rift Valley is an example of a weakness in the crust that could turn into a plate margin.  If that's true that could explain a lot.  If new plates can form and existing ones disappear this would go a long way to solving my dilemma.

Any views would be much appreciated and I can then give my 12 year old pupil a decent answer!
Many thanks all.

PS. Just about every geography text book out there suggests plate tectonics is a result of convection currents in the mantle.  Many teachers teach this because that's what they've been taught.  I appreciate the science has moved on and now involved slab-pull and several other potential forces!  Without making it too complex, what should we be teaching 12+ year olds?

I am not sure if you are actually asking about Tectonic Plate boundaries, or the boundaries of continents, which are often described a puzzle pieces when teaching continental drift due to the way continents like South America and Africa fit together. I'm going to try and address both possibilities.

Tectonic Plate boundaries are constantly changing. Many of the edges of tectonic boundaries are thin freshly-formed oceanic crust which isn't going to put up much of a fight. You know about subduction so you understand that oceanic crust is constantly 'recycled'.

The present day amount of continental crust on earth hasn't existed for all of earth's history. Current thinking is that it has been been accumulated overtime (theories differ as to how quickly), through a number of processes which have built up the present level of continental crust that is more buoyant that the mantel and oceanic crust and thus resistant to subduction. As a result the size and shape of the continents have been slowly changing and growing over earth's history as they gain new bits, join and split.

  For example, what would the 'jigsaw pattern' of plates at the time of Pangea have looked like?

this video shows continents moving around, growing and joining and how they change over time, at least for the last 1.5 billion years of earth's 4.5 billion history. Pangea was around from 335Ma to 175Ma, you can see it form and break up in the video.

https://www.youtube.com/watch?v=IlnwyAbczog

  This probably relates to the potential for new plate boundaries to be
  formed...and existing ones to close up. Is this possible?

In this video blue and red lines show active tectonic plate boundaries.
you can see that they change. They move around, old ones stop and new ones start. They even change from divergent to convergent or consume each other.

  At plate margins, does the pressure of compression or expansion actually change the spatial position of the margin?

Absolutely. at the end of the video watch India slam into Asia and create the Himalayas as a result.

I'm not an education specialist, but i have seen videos like these be used to explain the processes to kids.


How to better understand the RIP-nomenclature used in the CMIP5 project? I am a statistician working on a climatological downscaling project in the Caribbean Sea.

I am just starting to learn about the CMIP5 GCM data project. I plan to download CMIP5 data from 6 climate centers and examine 3 scenarios: historical, RCP4.5, and RCP8.5 I was hoping that someone could further explain the CMIP5 ensemble RIP-nomenclature to me:

R: realization

I: initialization

P: physics

More specifically, if I were to use the same ensemble number (say r1i1p1) across all 6 centers - would I have the exact same data for each scenario (historical, RCP4.5, and RCP8.5)?  If not, should I keep the ensemble number consistent across models or should I vary it somewhat?

I guess the main question here: is it more common in geography to examine the variance between climate center projections or the variance between runs within a single ensemble?

The RIP-nomenclature is used to distinguish between different runs of the same scenario within a modeling center rather than to indicate any similarity across modeling centers.  Strictly it's within and across models not centers, because some centers have more than one model, e.g., the MIROC center submitted models MIROC5, MIROC4h, MIROC-ESM, etc.  So r1i1p1 for some scenario is typically just the ensemble member that happened to be run first for each model.  One caveat is that whichever historial ensemble member you pick for each model, you should use the same member from the corresponding RCP scenario, e.g., historical r3i1p1 should join seamlessly with rcp8.5 r3i1p1:

  A  recommendation  for  CMIP5  is  that  each  so-called  RCP  (future  scenario)  simulation  should when  possible  be  assigned  the  same  realization  integer  as  the  historical  run  from  which  it  was initiated.

  From Taylor et al (2012) CMIP5 Data Reference Syntax (DRS) and Controlled Vocabularies (pdf)

There's loads more detail in that Data Reference Syntax doc that I've linked to, and a summary of it on the IPSL website.  Karl Taylor gave a presentation that summarised it even more succinctly:

  r = “realization”: simulations started from equally likely initial conditions
  that lead to equally likely realizations of the true climate trajectory
  i = “initialization”: only used in decadal predictions, to distinguish among
  different initialization procedures
  p = “physics”: to identify simulations that are very closely related (e.g.,
  “perturbed physics” ensemble members or simulations forced by slightly
  modified parameterizations)

In practice, the "initialization" and "physics" ensemble members are a bit specialist and the vast majority of CMIP5 users just stick to the rNi1p1 members, and most of them probably just stick to r1i1p1 from each model (e.g, Peng et al, 2019) for simplicity.  You should feel free to use any of the "realisation" members from each model, and you could pick r1i1p1 from one model and r10i1p1 from another.  I'd advise sticking to one ensemble member from each model though, to avoid your analysis over-representing the forced responses of models that submitted more realizations to the CMIP5 database.

To address your final question, it's more common to look at the variance across the models for a given scenario.  But there are also plenty of studies that use the variance within each model ensemble to estimate the uncertainty of a model property due to internal variability, e.g., emergent constraints on climate sensitivity.  It really depends what you're investigating.


On the light difference between morning and afternoon It is long time that I am looking for what physical reason(s) explains this observation:

the sun ambient light between sunrise and midday is crispy, somehow whiter than that of the afternoon hours. In other words it is like that morning outdoor light is more similar to that of a white lamp, and that of afternoon more yellow and incandescent bulb -'like.

Even in more physics term, it seems that the morning light has a higher Temperature than that of afternoon. Note that I refer to the T of an emitting black body, not the temperature as colloquially used in fashion, art, etc that goes right the other way around.

For those just a bit familiar with photography, is as the golden hours of morning and afternoon are not identical (the obvious opposite casting of shadow is obviously not part of the matter), like if the source of lighting changes (obviously the sun doesn't, so it is an atmospheric phenomenon or so).

Everything I came up would have a basically symmetric behaviour around midday so can't explain this.

The only asymmetry I can see is that " morning is light through a night chilled atmosphere", while "afternoon is light going around in an already warmed up atmosphere". However "this explanation" - as a ground where to plug optical phenomena of refraction or Mie scattering - would require about the same temperatures of the air, in summer as in winter,  or day after day.

Another possible asymmetry is due to our long scale adaptation to luminosity or brightness, but the change I refer to is relatively abrupt around noon.

A possibility might be related to temperature of the atmosphere perhaps via refraction between layers of it..... it is the last idea that came to my mind. In this case same layering might occur independent of seasons.

Please note that I am not asking for Rayleigh scattering alone and why yellow and red are dominant near horizon at sunrise or sunset.

I am asking why the light of a clear day is not symmetrically changing centered at noon.

Please also note that before telling me that the difference I am asking about does not exist, ask yourself if you feel able to tell if it is morning or afternoon without knowing anything else but looking at the environmental light in a clear day. Most persons I've talked to about this, didn't realise it before (again a big surprise).

I am asking why the light of a clear day is not symmetrically changing centered at noon.

Trying to attribute this to a single cause misses the point. There are multiple causes. Other than lighting itself (i.e., the Sun angle), most aspects of the atmosphere are not symmetric about noon.

The low on a clear day typically occurs right around sunrise (not midnight), while the high typically occurs hours after noon. Assuming a front is not passing through, relative humidity is typically highest in the hours around sunrise, lowest a few hours before sunset, roughly coinciding with the low and high temperatures. Atmospheric stability is high in the early morning on a clear calm day, low in the afternoon and evening. During weekdays, pollution oftentimes is at a minimum around 6 to 8 AM and a peak around 5 to 7 PM.

All of these can contribute to the effects you are seeing, plus other factors I did not list.


Has Earth's geological activity calmed down in the past 250 million years? In the past, the Earth's ecosystem has experienced catastrophic mass extinctions as a result of large-scale volcanic eruptions. One example is the event known as the "Great Dying", 252 million years ago. According to a New York Times article, massive volcanic eruptions in Siberia ignited fossil fuel deposits. The released CO2 led to a warmer climate and acidic oceans, triggering the mass extinction.
252 million years is not that long ago in the overall history of the Earth; it's only 5.6% of the 4.5 billion years Earth has been around.
Hence my question: Is the Earth geological much calmer today than 250 million years ago, or are such events simply rare enough that higher mammals and humanity could evolve during one of the lucky lulls?

The large-scale volcanic eruptions you mention are called Large Igneous Provinces (LIPs) and are probably linked to mantle plumes. They have been investigated for quite some time now. Ernst & Buchan (2001) built a database of 300+ LIPs and used it to analyse their temporal distribution, among other things. Here is the age spectrum they obtained:

... ‘well-established’ and ‘probable’ plume head events occur
throughout the geological record since at least 3500 Ma, and probably
since 3800 Ma, with no plume-free intervals greater than about 200 Myr
since 3500 Ma. Plume head arrival does not follow any obvious
periodicity...

If you look at the cumulative frequency diagram, there seems to be a increase in event frequency over the last 150 Ma:

There are periods when plume activity appears to be more intense than
at other times. These intervals are identified by steeper slopes on a
cumulative plot of LIP frequency. The most prominent are at
2800–2700, 2200–1800, 150–0 Ma and more speculatively at 1300–1100 Ma.

But as the authors explain, this is a bias due to the fact that the recent record preserves both oceanic and continental LIPs. However, the oceanic crust is consistently recycled (it's nowhere older than ~200 Ma), thus older events are continental LIPs only. If corrected to include only continental LIPs in the recent (< 150 Ma) record, the trend seems "normal" (dotted line).


'Late Veneer' on other planets Is there any evidence of external material source events, like the 'Late Veneer' on other planets?

Or is this theory specific just for Earth?

Note, that this question may be related to How and why did the oceans form on Earth but not on other planets?

But this is question is not water specific, or chondrite specific.

This is an important and pertinent question to help understand the 'late veneer' process on Earth.  To do so, understanding how it may have occurred, if at all, on the other terrestrial planets (Mercury, Venus, Mars and possibly the Moon, even possibly the rocky moons of other planets).  If there is no evidence, then that sheds light on another aspect of the uniqueness of Earth.

For practical reasons, my answer will focus on Mars and Venus, as according to an article specific on the topic, Dynamical and collisional constraints on a stochastic
late veneer on the terrestrial planets (Raymond et al. 2013), that asserts that the late veneer was

  an accretionary phase for Venus, Earth and Mars but an
  erosive phase for Mercury and the Moon.

There are obvious difficulties in fully answering this question; however, Raymond et al. assert that evidence exists of 'late veneer' like activity for not only the Earth, but for the Moon and Mars, from the article:

  Evidence for the late veneer comes from the existence of highly-siderophile
  elements (HSEs) in the mantles of Earth, Mars and the Moon. Simply put,
  HSEs are “iron-loving” elements that tend to partition into metal and should
  thus be removed from a planet’s mantle during core formation.

Mantle samples are taken from Martian meteorites that have landed on the Earth and are detailed in the paper Evolution of the martian mantle inferred from the $^{187}Re$–$^{187}Os$ isotope and highly siderophile element abundance systematics of shergottite meteorites (Brandon et al. 2012) who observe the observations made by Raymond et al. as

  The
  measured concentration of HSEs in the Martian mantle is similar to the
  Earth’s (Walker, 2009; Brandon et al., 2012).

Based on a conclusion made by Brandon et al. that

  The relatively high HSE abundances in both planetary mantles likely cannot be accounted for by high pressure–temperature metal–silicate partitioning at the bases of magma oceans, as has been suggested for Earth. If the HSE were instead supplied by late accretion, this event must have occurred prior to the crystallization of the last martian magma ocean.

According to Raymond et al. the situation for for Venus and Mercury, the late veneer is modeled to have possibly affected their retrograde motion, but the authors admit that this is is speculative.

In the absence of sufficient samples from Mercury and Venus, it is modeling rather than sampling that the authors use to hypothesise the possible effect of the Late Veneer on them.  Given Venus' size, it is likely that it, alongside Earth were the 'primary targets' of the late veneer bombardment.

  Additional references:

  Walker, R. J. 2009. Highly siderophile elements in the Earth, Moon and
  Mars: Update and implications for planetary accretion and
  differentiation. Chemie der Erde / Geochemistry 69, 101–125.

  Walker, R. J., M. F. Horan, C. K. Shearer, and J. J. Papike 2004. Low
  abundances of highly siderophile elements in the lunar mantle:
  evidence for prolonged late accretion. Earth and Planetary Science
  Letters 224, 399–413.


Heat at High Altitudes Why does the temperature of let’s say 85 degrees Fahrenheit in southern California feel hotter at 7,500 ft elevation than it does at sea level?

How things feel is partly psychological and often doesn't have a purely physical explanation. If you run a hot bath and the water from the tap starts to feel tepid, plunge your hand into the very hot water with which the bath is filled. Hold it there for a minute or two, then put it under the tepid tap. The water will feel stone cold, though when tested with the other hand it still feels tepid.

If 85F at 7,500 ft feels hotter to you than 85F at sea level, it could be due to a number of things. On a sunny day you will get more solar radiation at high altitude, especially around mid day, and that will be in addition to the shade temperature which weather forecasters use. When walking from A to B in the mountains, we usually exert ourselves more than we would at sea level, and therefore we feel hotter.

The day you have in mind might have been especially humid in your mountain location, so that would make it feel warmer as well. Maybe your walk was when the sun was at its highest and you are comparing it to walks in the lowlands where, although the shade temperature was the same, the sun was lower in the sky or maybe there was even some cloud. And always there is the psychological aspect to consider. Our minds like to play tricks on us.


Which clouds can produce lighting and thunder? There are several number of cloud types, but I only know that cumulonimbus clouds discharge electricity, which in turn produces thunder and lightning. Is this type of cloud (cumulonimbus) the only cloud that can produce an electrical discharge or are there other clouds that can produce an electrical discharge?

Why are cumulus the only basic cloud type to favor lightning?
Because the speed of rising in the updraft is fundamental to lightning formation, as shown by this example plot from Total lightning activity as an indicator of updraft characteristics by Deierling and Petersen:

The faster the air rises, the more lightning in makes.  Only rapid updrafts can separate charges fast enough to overcome dissipation and build up the hundreds of millions of Volts (related ESE question) needed for lightning.  Out of the three standard cloud categories, only cumulus involves significant vertical motion.

Other cloud types?
First off, nearby clouds of other types can mask the cumulus structure responsible for the lightning.  Very commonly in strong storm environments, the broad widespread rising motion, especially near the warm front, can cause a thick low-level stratus deck to form.  And sometimes, in situations where dynamic forcing is dominant (such as with upper-level storm systems), or where storms move into a new environments (such as lake effect snow storms), fog can be thick, such that basically nothing can be seen!  So in those situations, its hard to truly attribute the lightning to the cumulonimbus, despite that being the cause.

Plus, full storm cells often develop fairly complex structures:

(Wikipedia, credit Kelvinsong)

Due to their shape and motions, some parts of storms might reasonably be categorized as stratus or altostratus, though they stem from a larger (past or present) cumulonimbus structure. These stratus-like components include arcus, incus, and velum.  And mammatus clouds that can occur as part of strong storms are actually a unique example of clouds with sinking air.  Even though air in these regions isn't rising much, leftover charge from nearby (or past) updrafts can still bring about lightning.  Anvil crawlers are a common lightning seen in the fairly flat upper regions of storms.

Also, while more precise cloud classifications do now set the stages of growing thunderstorms clouds into the cumulonimbus genus, the nimbus prefix classically meant precipitating (raining/hailing/snowing).  Precipitation reaching the ground is not an absolute requirement for a storm cloud to produce lightning.  So in a loose sense, a cloud doesn't truly have to be a cumulonimbus, at least historically.

And of course, as it can do with just about any non-insulating material, lightning can pass through inactive clouds on the journey to the ground.

But while these situations may technically satisfy your search for lightning in other clouds types, you're fundamentally right, standard lightning generally derives from cumuloform cloud origins.