How does sun heat the air?

At 02:28 20 December 2017, wrote:
The people who really care about this stuff are climatologists (and
climate=
modelers), and increasingly the solar power community. The
issue as far
a=
s the soaring community is concerned is that most of the sunlight
that is
l=
ost to absorption in the atmosphere is mostly-always lost=20

* UV is absorbed in the stratosphere; as far as total energy is
concerned
=
there is not much variability in what gets to the ground. =20

* Chappuis-band O3 absorption (in the visible red) can change the
surface
=
heat flux a few percent, no more

* the big H2O band at 940 nm is very important climatologically ..
but is
p=
erhaps 5% of total energy flux and not as variable as people might
think=20

* H2O and CO2 (and some others) at wavelengths 1.4 microns
lead to
substa=
ntial extinctions in the 1.4 - 3 micron wavelength domains -- but
our
huma=
n eyes don't see that, the sun's solar output is decreasing at longer
wavel=
engths, nor do silicon solar cells get energy from these
wavelengths. =20

When you look at energy balance commonly more than 20% of the
sun's
radiati=
on is absorbed in the atmosphere, and this is very important to the
thermal=
structure of the atmosphere, but it isn't highly variable (as a
fraction
o=
f total energy) so people just don't pay too much attention to it,
for
purp=
oses like soaring.

This energy ends up as heat, distributed non-uniformly through the
atmosphe=
ric column. The most blatantly obvious effect is that we have a
stratosphe=
re; there are also climatically-important consequences to this in
the
trop=
osphere. Most of this heat is deposited at altitudes where we
don't fly.
=
=20

The dominant issues that effect lower-boundary layer heating rates
are
pret=
ty obvious: clouds! Yes, surface-albedo ... and then a very large
factor
n=
ot discussed here is what meteorologists call the "Bowen ratio:"
the ratio
=
of the latent-to-sensible heat flux from the surface ... how much of
the
he=
at is used to evaporate water.

Deserts are good for soaring because most of the captured
radiation does
go=
to sensible heat. =20

A "secret" most western pilots don't know -- the best soaring
season in
th=
e northeast is spring, before the trees leaf out. It's our desert.
After
=
they leaf out ... then every damned tree is a water-sucking
nuisance ...
an=
d a subtle point is that deciduous trees flux more water than
conifers ...
=
there are easily-observable differences in Bowen-ratio from
deciduous vs
co=
nifer forests. =20

More subtly there is a second "good" period in the fall when the
trees
lose=
their leaves, although with the declining sunlight it's not really
great.
=
But since the time of Benjamin Franklin naturalists noted that
stream
flow=
s in the northeast jump after the trees lose their leaves in the fall,
and
=
correctly attributed the reason for this.

One of several reasons "the high ground" is usually better soaring
(everywh=
ere) is that water runs off it; the trees are almost always water-
stress
li=
mited and shifted to species (conifers) that do that better. A
water-stres=
sed tree keeps its stomata closed: doesn't flux water but also
cannot
photo=
synthesize.=20

Plants do change the surface albedo, usually lower it. Plants look
green
b=
ecause they don't use green light, and they want to reflect it to
avoid
its=
heat. They also increase the albedo at longer wavelengths. But
this
eff=
ect on albedo is usually less important that their water flux ... if
they
a=
ren't water stressed.

Soil moisture can be measured (sort-of) by remote sensing in the
microwave,=
and there are very large variations in soil moisture temporally
(ask any
f=
armer), but also spatially across the terrain ... in places (not our
wester=
n deserts) where there's enough water for plants to grow
generously. =20

Hey Eric Greenwell? You still flying around Richland Washington? I
flew
w=
ith you, and towed you years ago when I worked at PNL. It's
pretty arid
ou=
t there ... but nobody finds good thermals coming up off the big
irrigated
=
crop circles. In desert terrains stay away from green like the
plague.

In the northeast the hierarchy is plowed-fields better than conifers,
conif=
ers better than growing hay or corn UNLESS the farmers are
complaining
abou=
t a dry spell, say out of the river bottoms and anywhere with
deciduous
tre=
es, worse yet willows. =20


Thanks for a great post!

RO