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How does sun heat the air?



 
 
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  #11  
Old October 9th 09, 04:34 PM posted to rec.aviation.soaring
T8
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Posts: 429
Default How does sun heat the air?

On Oct 9, 10:47*am, Tim Taylor wrote:


Evan,

While the long wave does have a greater input back into the total
atmosphere and to radiation back into space I think in the boundary
layer conduction and convection are still the primary sources of heat
transfer. * *Since the air is primarily oxygen and nitrogen that are
both opaque to long waves as well it it mostly the other sources that
generate thermals.


Hey Tim,

I think you'll find if you dig into this that it's long wave
radiation, plus convection (thermals + wind) and evaporation/
condensation. Conduction is a bit player.

See second two answers here, though I cannot vouch for numbers
http://www.newton.dep.anl.gov/askasc...0/wea00082.htm -- the first
response given is in error. There must be something better on the
web, but I can't find it quickly.

What's missing here is useful info on absorption coefficients and heat
flux vs wavelength and water vapor content. But what I am given to
understand here is that most of the heat energy that drives thermals
we can use comes from long wave infrared transmitted from the heated
surface and absorbed in the first few feet / tens of feet / hundreds
of feet. I cheerfully admit I don't have the time to go get the
details to back up my case

Best,
Evan Ludeman / T8
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  #12  
Old October 10th 09, 02:37 AM posted to rec.aviation.soaring
Frank[_12_]
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Posts: 100
Default How does sun heat the air?

On Oct 8, 9:59*pm, " wrote:
The sun shines down through the atmosphere, hits things on the ground,
the things on the ground get hot, and then the hot things on the
ground heat the air?

Sun light passing through the air does not heat the air at all? *Heats
the air some but not much?

If the air is transparent to solar energy, how is *the air able to
pick up so much energy from hot objects on the ground?

Bill
6W


Bill,

Solar (electromagnetic) energy in the visible light spectrum doesn't
couple very well to dry air. However, energy in the visible light
spectrum *does* couple nicely to darker objects like a dark farm field
or a parking lot, etc. The visible light energy heats the ground,
thereby converting visible light energy to much lower frequency
(longer wavelength) IR energy, and energy in the IR band *does* couple
to dry air in close contact with the hot objects. However, dry air is
a great insulator, so only the air a few centimeters/meters above the
ground gets heated directly, forming a mat of heated air underneath
colder air above. This is an unstable configuration, and thermals are
nature's mechanism for re-establishing equilibrium. This mechanism is
closely analogous to heating a pot of water on the stove. The water
immediately adjacent to the bottom of the pot gets hot, and this sets
up circulation currents to re-establish equilibrium in the rest of the
pot. If the heating is fast enough, local vaporization takes place
causing bubbles to form (i.e. the pot boils).

Just as an evolutionary side note, eyes evolved to see in the visible
spectrum *because* the air is transparent (i.e. very low coupling
coefficient) to that band of energy. If our atmosphere happened to be
only transparent to what we call infrared, then we'd all see in the
infrared, not the visible range, and thermals would be much easier to
"see" ;-).

Regards,

TA
  #13  
Old October 13th 09, 02:11 AM posted to rec.aviation.soaring
[email protected][_2_]
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Posts: 12
Default How does sun heat the air?

On Oct 9, 8:37*pm, Frank wrote:
On Oct 8, 9:59*pm, " wrote:

The sun shines down through the atmosphere, hits things on the ground,
the things on the ground get hot, and then the hot things on the
ground heat the air?


Sun light passing through the air does not heat the air at all? *Heats
the air some but not much?


If the air is transparent to solar energy, how is *the air able to
pick up so much energy from hot objects on the ground?


Bill
6W


Bill,

Solar (electromagnetic) energy in the visible light spectrum doesn't
couple very well to dry air. *However, energy in the visible light
spectrum *does* couple nicely to darker objects like a dark farm field
or a parking lot, etc. *The visible light energy heats the ground,
thereby converting visible light energy to much lower frequency
(longer wavelength) IR energy, and energy in the IR band *does* couple
to dry air in close contact with the hot objects. *However, dry air is
a great insulator, so only the air a few centimeters/meters above the
ground gets heated directly, forming a mat of heated air underneath
colder air above. *This is an unstable configuration, and thermals are
nature's mechanism for re-establishing equilibrium. *This mechanism is
closely analogous to heating a pot of water on the stove. *The water
immediately adjacent to the bottom of the pot gets hot, and this sets
up circulation currents to re-establish equilibrium in the rest of the
pot. *If the heating is fast enough, local vaporization takes place
causing bubbles to form (i.e. the pot boils).

Just as an evolutionary side note, eyes evolved to see in the visible
spectrum *because* the air is transparent (i.e. very low coupling
coefficient) to that band of energy. *If our atmosphere happened to be
only transparent to what we call infrared, then we'd all see in the
infrared, not the visible range, and thermals would be much easier to
"see" ;-).

Regards,

TA


Still air, like in a double pane window or fiberglass insulation,
seems to block heat tranfer. Moving air, like a car radiator or a
breeze, seems to heat the air and carry away heat. Neither the long
wave radition or conduction seems to explain how air is heated. As
you appoach a hot object with your hand, you feel radiation from the
hot object, not hot air. It seems that air velocity and mixing is the
key to heating air ? Dry air seems to heat much faster than damp
air?

Bill Snead
  #14  
Old October 13th 09, 04:10 PM posted to rec.aviation.soaring
mattm[_2_]
external usenet poster
 
Posts: 167
Default How does sun heat the air?

On Oct 12, 9:11*pm, wrote:
On Oct 9, 8:37*pm, Frank wrote:



On Oct 8, 9:59*pm, " wrote:


The sun shines down through the atmosphere, hits things on the ground,
the things on the ground get hot, and then the hot things on the
ground heat the air?


Sun light passing through the air does not heat the air at all? *Heats
the air some but not much?


If the air is transparent to solar energy, how is *the air able to
pick up so much energy from hot objects on the ground?


Bill
6W


Bill,


Solar (electromagnetic) energy in the visible light spectrum doesn't
couple very well to dry air. *However, energy in the visible light
spectrum *does* couple nicely to darker objects like a dark farm field
or a parking lot, etc. *The visible light energy heats the ground,
thereby converting visible light energy to much lower frequency
(longer wavelength) IR energy, and energy in the IR band *does* couple
to dry air in close contact with the hot objects. *However, dry air is
a great insulator, so only the air a few centimeters/meters above the
ground gets heated directly, forming a mat of heated air underneath
colder air above. *This is an unstable configuration, and thermals are
nature's mechanism for re-establishing equilibrium. *This mechanism is
closely analogous to heating a pot of water on the stove. *The water
immediately adjacent to the bottom of the pot gets hot, and this sets
up circulation currents to re-establish equilibrium in the rest of the
pot. *If the heating is fast enough, local vaporization takes place
causing bubbles to form (i.e. the pot boils).


Just as an evolutionary side note, eyes evolved to see in the visible
spectrum *because* the air is transparent (i.e. very low coupling
coefficient) to that band of energy. *If our atmosphere happened to be
only transparent to what we call infrared, then we'd all see in the
infrared, not the visible range, and thermals would be much easier to
"see" ;-).


Regards,


TA


Still air, like in a double pane window or fiberglass insulation,
seems to block heat tranfer. *Moving air, like a car radiator or a
breeze, *seems to heat the air and carry away heat. *Neither the long
wave radition or conduction seems to explain how air is heated. *As
you appoach a hot object with your hand, you feel radiation from the
hot object, not hot air. *It seems that air velocity and mixing is the
key to heating air ? * Dry air seems to heat much faster than damp
air?

Bill Snead


Think of the shimmer when looking over hot ground in the summer. This
is the heating process in action. The shimmer is caused because the
first foot or two of air adjacent to the ground is much warmer than
the air
above it, and because of the temperature difference it has a different
refractive index (just like the pencil sticking out of a glass of
water looks bent).

Some amount of wind is helpful because
it will push the warmer air up against a wick of some type, which will
break the surface tension and allow the heated air to travel upwards
(e.g. cell phone tower, ridge, line of trees, even a body of water).

I think the issue with damp air is really damp ground. Water has a
much
higher heat content factor, i.e. it takes more energy to raise the
temperature
of water a degree than it does dry ground. Moist air is actually more
buoyant
because H2O molecules are lighter than N2 or O2 molecules but still
take
up the same room. Normally this is only a factor when other lifting
mechanisms are at work (because of damp ground not heating as well)
but it has a huge effect in creating storms.

-- Matt
  #15  
Old October 14th 09, 03:09 AM posted to rec.aviation.soaring
[email protected][_2_]
external usenet poster
 
Posts: 12
Default How does sun heat the air?

On Oct 13, 10:10*am, mattm wrote:
On Oct 12, 9:11*pm, wrote:





On Oct 9, 8:37*pm, Frank wrote:


On Oct 8, 9:59*pm, " wrote:


The sun shines down through the atmosphere, hits things on the ground,
the things on the ground get hot, and then the hot things on the
ground heat the air?


Sun light passing through the air does not heat the air at all? *Heats
the air some but not much?


If the air is transparent to solar energy, how is *the air able to
pick up so much energy from hot objects on the ground?


Bill
6W


Bill,


Solar (electromagnetic) energy in the visible light spectrum doesn't
couple very well to dry air. *However, energy in the visible light
spectrum *does* couple nicely to darker objects like a dark farm field
or a parking lot, etc. *The visible light energy heats the ground,
thereby converting visible light energy to much lower frequency
(longer wavelength) IR energy, and energy in the IR band *does* couple
to dry air in close contact with the hot objects. *However, dry air is
a great insulator, so only the air a few centimeters/meters above the
ground gets heated directly, forming a mat of heated air underneath
colder air above. *This is an unstable configuration, and thermals are
nature's mechanism for re-establishing equilibrium. *This mechanism is
closely analogous to heating a pot of water on the stove. *The water
immediately adjacent to the bottom of the pot gets hot, and this sets
up circulation currents to re-establish equilibrium in the rest of the
pot. *If the heating is fast enough, local vaporization takes place
causing bubbles to form (i.e. the pot boils).


Just as an evolutionary side note, eyes evolved to see in the visible
spectrum *because* the air is transparent (i.e. very low coupling
coefficient) to that band of energy. *If our atmosphere happened to be
only transparent to what we call infrared, then we'd all see in the
infrared, not the visible range, and thermals would be much easier to
"see" ;-).


Regards,


TA


Still air, like in a double pane window or fiberglass insulation,
seems to block heat tranfer. *Moving air, like a car radiator or a
breeze, *seems to heat the air and carry away heat. *Neither the long
wave radition or conduction seems to explain how air is heated. *As
you appoach a hot object with your hand, you feel radiation from the
hot object, not hot air. *It seems that air velocity and mixing is the
key to heating air ? * Dry air seems to heat much faster than damp
air?


Bill Snead


Think of the shimmer when looking over hot ground in the summer. *This
is the heating process in action. *The shimmer is caused because the
first foot or two of air adjacent to the ground is much warmer than
the air
above it, and because of the temperature difference it has a different
refractive index (just like the pencil sticking out of a glass of
water looks bent).

Some amount of wind is helpful because
it will push the warmer air up against a wick of some type, which will
break the surface tension and allow the heated air to travel upwards
(e.g. cell phone tower, ridge, line of trees, even a body of water).

I think the issue with damp air is really damp ground. *Water has a
much
higher heat content factor, i.e. it takes more energy to raise the
temperature
of water a degree than it does dry ground. *Moist air is actually more
buoyant
because H2O molecules are lighter than N2 or O2 molecules but still
take
up the same room. *Normally this is only a factor when other lifting
mechanisms are at work (because of damp ground not heating as well)
but it has a huge effect in creating storms.

-- Matt- Hide quoted text -

- Show quoted text -


Maybe the solar energy primarly reacts with (is absorbed by ) liquid
water. If there is a lot of water (the ocean a big lake), the mass of
water takes the energy but does not heat the air. However, if the
ground is what we think of dry, maybe the limited water grabs the
solar energy in a way that causes the air to heat quickly. In central
Texas in August typically the earth gets dry enough to wilt the
plants. As the plants turn brown, the maximum temperature will jump
from about 95 to maybe 102 F. The thermals will increase in strength
from about 350 feet per minute to over 500 feet per minute. In our
quarry the average moisture content of the crushed rock is about 6
percent. In the dry spells the moisture content of the rock never
falls below about 3 percent. So there is still a lot of water around
even though the place looks dry.

Bill Snead
  #16  
Old October 11th 16, 09:50 PM posted to rec.aviation.soaring
[email protected]
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Posts: 1
Default How does sun heat the air?

I wonder if the sun does do this. right guys? Am i wrong? well the sun brings light down and produces the heat we have now.

  #17  
Old October 13th 16, 07:16 AM posted to rec.aviation.soaring
2G
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Posts: 245
Default How does sun heat the air?

On Thursday, October 8, 2009 at 6:59:55 PM UTC-7, wrote:
The sun shines down through the atmosphere, hits things on the ground,
the things on the ground get hot, and then the hot things on the
ground heat the air?

Sun light passing through the air does not heat the air at all? Heats
the air some but not much?

If the air is transparent to solar energy, how is the air able to
pick up so much energy from hot objects on the ground?

Bill
6W


The atmospheric isn't totally transparent to solar radiation, but absorbs a portion of it before it reaches Earth. Solar irradiance at the troposphere is 1366 W/m^2; by the time it reaches Earth it has decreased to about 1000 W/m^2. The difference of 366 W/m^2 goes into heating the atmosphere. Of course the ground reradiates infrared energy it absorbs back into the atmosphere.

Tom
  #18  
Old March 27th 17, 09:04 PM posted to rec.aviation.soaring
[email protected]
external usenet poster
 
Posts: 1
Default How does sun heat the air?

On Thursday, October 8, 2009 at 7:59:55 PM UTC-6, wrote:
The sun shines down through the atmosphere, hits things on the ground,
the things on the ground get hot, and then the hot things on the
ground heat the air?

Sun light passing through the air does not heat the air at all? Heats
the air some but not much?

If the air is transparent to solar energy, how is the air able to
pick up so much energy from hot objects on the ground?

Bill
6W


  #19  
Old March 27th 17, 09:17 PM posted to rec.aviation.soaring
Duster
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Posts: 161
Default How does sun heat the air?

Not exactly transparent. The sky appears blue because air molecules and suspended particles absorb and scatter certain wavelengths of light. This energy is transduced from photons into heat. However, the majority of advection is due to the previous explanation. Not a physicist, so someone else take a stab.

  #20  
Old March 29th 17, 08:58 AM posted to rec.aviation.soaring
Jim White[_3_]
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Posts: 217
Default How does sun heat the air?

At 20:17 27 March 2017, Duster wrote:
Not exactly transparent. The sky appears blue because air molecules and
sus=
pended particles absorb and scatter certain wavelengths of light. This
ener=
gy is transduced from photons into heat. However, the majority of
advection=
is due to the previous explanation. Not a physicist, so someone else

take
=
a stab.

The downward energy radiated by the sun is short wave and not absorbed by
the atmosphere. The upward energy radiated by the ground is long wave which
is.

 




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