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16 Nov 2018 14:41

Question about the little ice age- is it possible there was some sort of connection between volcanic eruptions and changes in the solar cycle?  This also happened around the time the dinosaurs died out (and of course the big asteroid impact.)

Also, since we are in the process of switching magnetic poles, how will this impact the aurora?
 
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16 Nov 2018 14:43

We talk about SSW frequently in weather forums, basically when the stratosphere warms the lower atmosphere temps cool down and vice versa.  There is a lag effect but SSW lead to severe winter events a few weeks later.
 
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16 Nov 2018 20:12

Watsisname wrote:
Source of the post Yes, seriously.  As we saw a little bit ago, the altitude of the different aurora colors is determined by the average time between collisions of the excited atoms or molecules.  If the collisions happen too frequently, then colors associated with slower transitions won't have a chance to be emitted.

Isn't auroral activity caused by magnetic processes that occur far higher then the stratosphere, in the magnetosphere with the excited protons and electrons precipitating into the thermo/exosphere? Wouldn't this place it beyond atmospheric temperature influences? While I'd agree that there is a connection between solar-activity and global temperatures (there is a lot of evidence for this), it would be considered a parallel affect to our particular greenhouse effect, which is of course caused by multiple sources of industrialization and agriculture.  As midtskogen stated, attributing all the causes for something as complex as GLOBAL weather is very messy business. I'm honestly surprised meteorology can be presented on the morning news - even if that is just local weather.

A-L-E-X wrote:
Source of the post Question about the little ice age- is it possible there was some sort of connection between volcanic eruptions and changes in the solar cycle? 



Erm, no. Solar activity like sun-spots or even solar-flares could not influence volcanism on Earth. While there are SOME tentative conclusions as to their connection, it generally doubted, or could have some coincidental cause, or might be a bit more complicated then just solar minimum=volcanic activity. An interesting question of course, since both phenomena, including earth-quakes, can influence the ionosphere in many ways.


A-L-E-X wrote:
Source of the post This also happened around the time the dinosaurs died out (and of course the big asteroid impact.)

Indeed, the Deccan Traps lava beds in India were a contributing blow to the non-avian dinosaurs extinction, though I think they could have survived a supervolcanic explosion, were it not for the Yucatan asteroid.  The Traps would have spewed great amounts of CO2, CO and SO2, and large concentrations of sulfur dioxide in the atmosphere form aerosols, and in turn can cause drastic atmospheric changes like a global cooling (the climate cooled 2 degrees Celsius during the eruptions - and had already been cooling due to sea-level changes) and acid rain. The Traps erupted at 66.20 million years, the asteroid hit at 66.04 million years ago, give or take ten thousand years. These two blows were cumulative enough to kill off the dinos obviously, but if only the Traps erupted, there is plenty of evidence that many dinosaurs could survive in fairly hostile and cold environments. There is a very interesting article HERE discussing what may have happened if the K-T had gone differently.
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16 Nov 2018 22:07

Stellarator wrote:
Source of the post Isn't auroral activity caused by magnetic processes that occur far higher then the stratosphere, in the magnetosphere with the excited protons and electrons precipitating into the thermo/exosphere?

That's right, but as I explained, the greenhouse effect also cools the upper atmosphere, including at the altitudes where the aurora occur.  It even affects the decay of orbital debris, by reducing the atmospheric drag on them.  This isn't very obvious or well known -- there is more to the greenhouse effect than just "trapping heat" and warming the surface as it is commonly described. :)

The key insight to why it works this way is that a good absorber of radiation is also a good emitter.  The greenhouse effect warms the surface by absorbing the heat it radiates, and re-emitting some of it back downward.  So for the lower altitudes the greenhouse effect is just like adding an insulating blanket.  But at higher altitudes, increasing the concentration of greenhouse gases allows those layers to radiate more efficiently to space, cooling them.

The aurora are produced by charged particles (mostly electrons) being accelerated by magnetic fields and slamming into the upper atmosphere, exciting the atoms or molecules there.  When those excited atoms relax back down, they re-emit that energy as light, some in the visible spectrum which we see as aurora.  But that emission doesn't happen instantly -- it takes different amounts of time for the different colors.  A competing effect is that collisions of the atoms with one another can transfer that excess energy away, preventing the aurora from being emitted.  Aurora colors that take a long time to be emitted cannot occur at low altitudes, because the collisions with other atoms are too frequent.  That's why the base of the aurora happens at a specific altitude, like ~100km for the green aurora.

So, with a warming world, the conditions for which the aurora can glow should be met at lower altitudes, because the upper atmosphere is cooling and collapsing downward, giving excited atoms at a given altitude more time to emit that glow.
 
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16 Nov 2018 22:17

A-L-E-X wrote:
Source of the post Question about the little ice age- is it possible there was some sort of connection between volcanic eruptions and changes in the solar cycle?  This also happened around the time the dinosaurs died out (and of course the big asteroid impact.)

I agree with Stellarator -- I can't think of any plausible way in which one could care about the other.  What might be possible is that large asteroid impacts may be connected with volcanic eruptions on the opposite side of the planet.  I have heard some conjecture about such a link, but I do not know if this is well supported or even widely accepted as plausible by the geologic community.  Something to look into, maybe. 

At the very least, I can imagine how it could be true a lot more easily than how eruptions could be connected to solar activity. :)
 
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16 Nov 2018 23:03

There's a lot of different fascinating connections at play here, even if it isn't causal, it could be that both are linked to some third, heretofore unknown factor.  I'm looking for a Nature article I read a few years ago, talking about how earthquakes had been linked to unusual weather, unusual cloud formations, etc.  Another fascinating thing about the K-T event is the chance that it might not have been just one impact, but a series of impacts that occurred near the same time, perhaps a larger asteroid that broke apart into two or more pieces or maybe a small "family" of asteroids that travel together.  And the idea of periodic mass extinctions when the sun's orbit around the center of the galaxy enters a particularly vulnerable spot to make such collisions more likely.  Some scary thoughts- because we still dont have a real idea how many of these things are out there, where they are, or how to stop them.
 
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17 Nov 2018 03:01

Watsisname wrote:
Source of the post As for climate, the link is fairly well understood, with lower sunspot number related to decreased solar irradiance which cools the planet.

The trouble is that the variation only changes the irradiance by 0.1%, which is pretty insignificant alone for any cooling.  It would require secondary effects, which is much less understood.
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17 Nov 2018 03:08

Another thing is other animals being able to know in advance that an earthquake (or tsunami) might be coming. During the August 2011 quake that hit the east coast, some animals (particularly orangutans) began acting very weirdly about 30 min prior to the quake at the National Zoo in DC.  It was documented on video and zoogoers were talking about how eery and odd the behavior of the animals was.
 
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17 Nov 2018 03:26

A-L-E-X wrote:
Source of the post  some animals (particularly orangutans) began acting very weirdly about 30 min prior to the quake at the National Zoo in DC. 

It is possible that some animals can feel the initial waves, and humans will only notice later waves arriving minutes later.  But that would only be the case for fairly distant quakes.  Another explanation could be that the animals feel smaller quakes prior to the main quake, and that can be verified by instruments.  Yet another explanation, which I think is more probably in many cases, is that animals occasionally act weirdly, but only when something unusual happens shortly after will we remember the weird behaviour.
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17 Nov 2018 11:50

midtskogen wrote:
Source of the post The trouble is that the variation only changes the irradiance by 0.1%, which is pretty insignificant alone for any cooling.  It would require secondary effects, which is much less understood.

Using the formula for the temperature of a planet,

Image


a 0.1% change in solar insolation directly produces a 0.07°C change in Earth's surface temperature.  This is already within an order of magnitude of the observed change.


This directly forced change in temperature is then amplified through internal climate feedbacks, which are pretty well understood.  It's the same reason the negative radiative forcing due to volcanoes cools the planet as much as it does.
 
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17 Nov 2018 13:38

I don't think I've shown the derivation of the above formulas on this forum.  If anyone was curious where they come from, it's a pretty neat application of radiation laws and geometry.


The temperature of a planet, or any object in thermal equilibrium with its environment, is determined by a balance of energy flowing into it and energy flowing out of it.  

Image

If the majority of the energy received by a planet is from sunlight, then we can relate it to the solar luminosity, L*.  The sunlight is spread evenly over a sphere whose radius is the planet's orbital distance a.  The surface area of that sphere is 4πa2.  

The planet intersects some of the sunlight, with a cross sectional area of πRp2, and absorbs a fraction of it which is 1 minus the albedo, AB.  So the energy flowing into the planet is

Image

By radiation laws, an object with temperature T radiates thermally with a luminosity proportional to its surface area and its temperature to the 4th power.  The proportionality constant is the Stefan-Boltzmann constant, σSB.  So the energy flowing out of the planet is 

Image

There is also an "emissivity" factor, ε, representing how efficiently it emits. (ε=1 for a blackbody, or between 0 and 1 for a "grey" body).  For most materials, ε is between 0.9 and 1.  It is much lower for metals (because they are good reflectors, and a good reflector is a poor absorber is a poor emitter).  Earth with its atmosphere is well approximated has having ε=0.61 due to the greenhouse effect (otherwise, as we will see shortly, Earth would be frozen!).

Finally, set these energy flows equal to each other and solve for the temperature T.   After some algebra,

Image


We can also identify the flux F (watts per square meter) of sunlight to be L/(4πa2), in which case this simplifies to

Image


Setting a = 1AU = 1.5x1011m
A= 0.3, 
L* = 3.85x1026W,
σSB = 5.67x10-8 W/m2/K4,
and ε = 1,

then this predicts the Earth's equilibrium temperature if it were a perfect emitter to be 255 Kelvin, or -18C!  Earth clearly cannot be a perfect emitter, or it would be an uninhabitable frozen wasteland.  We owe our existence to the greenhouse effect.

The greenhouse effect warms the surface to about 288K, corresponding to ε=0.61.  It also cools the upper atmosphere, both by reducing the outgoing thermal radiation (what we call Eout in this derivation) that reaches it, and also by making those layers radiate to space more efficiently (increasing ε).  The greenhouse effect can essentially be thought of as a change in ε with respect to altitude in the atmosphere, decreasing the effectiveness by which the surface can cool by radiating to space, and increasing it at higher altitude.  

Of course the actual details of radiation absorption and emission through an atmosphere are very complex, and this simple derivation just treated it as a single layer that is doing the absorbing and emitting.  Still, the simple derivation does provide the correct and useful intuitions for understanding, and even calculating, the temperature of a planet from first principles.  The same formulas are used in astronomy and Space Engine.  They can also be used to estimate the magnitude of the greenhouse effect on other planets (or anti-greenhouse in some cases like Titan).
 
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17 Nov 2018 16:46

midtskogen wrote:
A-L-E-X wrote:
Source of the post  some animals (particularly orangutans) began acting very weirdly about 30 min prior to the quake at the National Zoo in DC. 

It is possible that some animals can feel the initial waves, and humans will only notice later waves arriving minutes later.  But that would only be the case for fairly distant quakes.  Another explanation could be that the animals feel smaller quakes prior to the main quake, and that can be verified by instruments.  Yet another explanation, which I think is more probably in many cases, is that animals occasionally act weirdly, but only when something unusual happens shortly after will we remember the weird behaviour.

It's certainly very possible but in this case all the animals at the zoo were behaving weirdly all at the same time a few minutes prior to the quake.  They might have been sensing something lower than the threshold of what we can sense, since animals do seem to have keener senses than we do.
 
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18 Nov 2018 01:05

A-L-E-X wrote:
Source of the post Another fascinating thing about the K-T event is the chance that it might not have been just one impact, but a series of impacts that occurred near the same time, perhaps a larger asteroid that broke apart into two or more pieces or maybe a small "family" of asteroids that travel together.

I find this to be unlikely, though still plausible. There has been a lot of debate over this, obviously, but the general consensus is that the K-T "mover and shaker" was a fairly solitary and random asteroid. Yes asteroid impacts are considered cyclic due to there solar-system origins - but this is only roughly so. There is also some research suggesting that mass extinctions are on a cycle of some type, but it would take a bit more investigating to see if asteroids or asteroid showers operate on a similar schedule.  A key bit of information here are the exact details and position of the K-T asteroid impact. It is tricky to say, because the pieces of a broken-up asteroid would fall roughly in the same area, resulting in a sole crater. Still, one would still expect other craters present, but so far few have made the cut. The closest we've come to occurring near the time of the Chicxulub impact the Boltysh crater in eastern Ukraine. It's age was an uncertain 105 million to 88 million years old, but recent argon-argon dating has placed from being made within 600'000 years of the K-T.  It's impact wouldn't have been enough to trigger an extinction though.

The other detail to consider is WHERE the main K-T asteroid hit. It struck shallow water, unfortunately right on top of sulfurous sedimentary deposits. The resulting dust, sulfur aerosols and vaporized water had plenty of effect on the extinction, but also severe earthquakes and tsunamis were present. I say this as a rather unnecessary recap because the thought here is, that if the K-T impactor had not hit the sediments and shallow water, and instead hit the deeper waters of the Atlantic, or bare rock, it's impact effects would have been much less severe, resulting in no or a very reduced extinction. Hence, we can make a tentative conclusion that the Chicxulub was the sole impact of the time.
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18 Nov 2018 03:49

Some asteroids are binaries, and there are even a few claimed binary impact structures on the Earth (though some commonly-believed binary craters have later been proven unrelated to each other, like the Clearwater Lakes).  Probably the most compelling case of a binary impact, at least that I am aware of, is the Lockne crater and its neighbor Målingen in Sweden.  Their ages are well determined and consistent with one another, and the parent asteroid was also tied to a known main-belt asteroid breakup event 470 million years ago.  


Good review of the K-T extinction, Stellarator.  I also have not seen any convincing evidence of multiple impacts being responsible for it.  As you say, the Boltysh crater is fairly small (perhaps ~105 Megatons of energy vs ~108 Megatons for Chicxulub), and from the size-frequency relation of terrestrial impacts,

Image


we expect an impact of that energy to happen on average once every few million years.  So it is both statistically likely to see such an impact that close in time with Chicxulub but be completely unrelated to it, and we don't get K-T level mass extinctions from this magnitude event anyway.
 
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18 Nov 2018 12:37

The chart is a bit misleading suggesting that size can be mapped to energy.  Speed has a lot to say, since the kinetic energy is ½mv².  So an asteroid hitting at 72 km/s has 43 times the energy of an equal asteroid hitting at 11 km/s.  Then, the density could be anything from a comet of 0.5 g/cm³ to an iron body of 7 g/cm³, so the same size can have 1 unit of energy or 600 units.
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