It may surprise readers to learn that the American Geophysical Union has divisions named Atmospheric and Space Electricity, Global Environmental Change, and Atmospheric Sciences. In short, the geosciences world include a very large element of atmospheric science. The following query has several different elements, all of which suggest an awareness of how dynamic our atmosphere really is.
Q: Hello. I wasn't sure which category to inquire within
but this seemed appropriate. Since Earth is not a perfectly spherical object,
nor any other planetary bodies we know of, how does that affect the gaseous
layers of atmosphere surrounding us? My question stems from an uneducated
assumption that our atmosphere is not a perfect bubble around us but must be
dynamic given the amount of energy factors associated with it, the terrain
beneath it and which locations have the greatest gravitational pull. Can the
sphere of air around us ever dissipate into space? Are there higher or lower
points that exist because of geography that make our categories of layers more
ambiguous?
-Joe A
A: As you suggest, the atmosphere is indeed a very
dynamic thing, and yes all rotating solar system bodies are oblate spheroids
because of centrifugal force at the equators (and none at the poles). Jupiter
rotates at a phenomenal rate (it has 9.8 hour days!) and is thus is the most
oblate planet of all.
If you think about oceans, however (the ocean surface is
at the same elevation above the spheroid datum over the Marianas Trench as it
is in Pamlico Sound), then mountain ranges will similarly have little to do
with atmospheric height over the globe (there IS a small amount of isostacy).
The most common exception to this are called storm surges - the low-pressure
cores of hurricanes and typhoons will literally lift up the (warmed and
expanded) ocean water. With Hurricane Katrina, the storm surge reached an
astonishing 8.5 meters (27.8 feet!) at Pass Christian, Mississippi. That's
above the normal tides!
There is atmospheric thinning with altitude, however, and
the upper reaches can still be detected at 100+ kilometers, which is why
satellites must fly at 250+ kilometers. Even at those altitudes there is
measurable drag that over time will bring down low-flying satellites and launch
vehicle debris. Most of the upper atmospheric variation has to do with solar wind
and solar heating activity, however. Because of Earth’s gravity, most of our
original atmosphere remains - unlike Mars, where the original atmosphere and
water were stripped over time by solar winds. When you see clouds over mountain
tops (pretty common over our volcanoes in the Pacific Northwest), it is because
winds trying to get around the mountain send some of their components up and
OVER the mountain. This leads to a drop in temperature with increasing
altitude, which contributes to dissolved moisture precipitating out into what
we call orographic clouds - cloud caps. As the air moves past and back down to
lower elevations the water re-dissolves back into the atmosphere and the clouds
disappear... but the same AMOUNT of water remains.
Q: I had to do a little research to understand a few of
the terms you used but I definitely feel like I came away with a better
understanding. Thank you for your insightful response. I shouldnt be surprised
I guess that avenues of inquiry like this are out there given the ubiquity of
websites, but I never tried something like this before. I had a thought, did
some googling and found you. It's awesome to get answers from professionals as
if I was back in school and could pick the brains of my professors after hours.
So thanks again, despite my questions being kind of convoluted!
- Joe
A: I'm glad I could help. I suppose I am technically a
professional, in that I get paid to do research in geophysics, but I'm just a
very ordinary person with the same level of curiosity that you have. I
personally don't divide the world into professional vs. non-professional, but
instead into interested vs. non-interested. I plumber who asked some really
deep questions about the lithosphere and upper mantle told me he spends a lot
of "windshield time" thinking about the physical world as he drives
from job to job.
THAT meets my definition of a scientist. You and I fit in
there also. That goes for anyone reading this chapter, too.
