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Why does Earth's tilt produce summers and winters?

Why does Earth's tilt produce summers and winters? - Physics Forum

Why does Earth's tilt produce summers and winters? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #41  
Old 11-06-2006, 05:27 AM
John Popelish
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Default Why are poles colder than the Equator?

Peter Webb wrote:

But isn't the more energy deposited in that overhead air
subtracted from that deposited onto the ground, and isn't
the energy deposited in the air radiated into space more
efficiently than that deposited on the ground?


It seems that you are arguing both sides of the case.
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  #42  
Old 11-06-2006, 06:48 AM
The Chief Instigator
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Default Why are poles colder than the Equator?

"Peter Webb" <[Only registered users see links. ].au> writes:









I left out the detail of the energy distribution of sunlight on a surface at
such latitudes, which is the primary determinant of the amount of heating.

--
Patrick "The Chief Instigator" Humphrey ([Only registered users see links. ]) Houston, Texas
chiefinstigator.us.tt/aeros.php (TCI's 2006-07 Houston Aeros)
LAST GAME: Houston 3, Hamilton 2 (SO) (November 4)
NEXT GAME: Thursday, November 9 at Iowa, 7:05
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  #43  
Old 11-06-2006, 07:10 AM
Peter Webb
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Default Why are poles colder than the Equator?


"John Popelish" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ] ...

100% of the energy deposited into the air goes into warming the air; only a
percentage of light deposited on the ground eventually warms the air (as
some is reflected, and some warms the ground).

The argument about heat radiation is a furphy - its true that the warmer the
air, the more it radiates back into space (as black body radiation), but
that already presumes the air is warmer.


No. Direct warming by the Sun of the air is not a major contributor. To the
limittted extent that it does make a contribution, having the Sun shine
through more air would increase the air temperature, not decrease it -
contrary to what you suggested.

The overwhelming consideration is the angle of invidence to the ground, as
very well illustrated by your football ground analogy.



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  #44  
Old 11-06-2006, 10:52 AM
Sue...
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Default Why are poles colder than the Equator?


Sorcerer wrote:

[...] <snip> SNIP! )

At the lunar poles, path geometry accounts for nearly 100 percent
of the attenuation.

At the terrestial equator, the atmospheric path accounts for
nearly 100 percent of the attenuation. (About 75 percent)

....then ya draw two smooth curves.

Sue...


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  #45  
Old 11-07-2006, 01:14 AM
Father Haskell
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Default Why does Earth's tilt produce summers and winters?


AlexZ wrote:

Not mentioned is that days get longer as the sun climbs higher
with the ecliptic. Much of the sun's heat is accumulated and
reradiated by the ground. More daytime = more heat stored in
soil, water, paving, etc.

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  #46  
Old 11-08-2006, 05:33 AM
Peter Webb
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Default Why are poles colder than the Equator?


"Sorcerer" <Headmaster@hogwarts.physics_e> wrote in message
news:fID3h.136979$[Only registered users see links. ].blueyonder.co .uk...

Refraction, mostly, as I said.


Greenland is colder than any of those places. It is further from the
equator, and the angle of incidence effect causes less flux per sqm. Nothing
to do with the amount of air the sun's rays go through.

Greenaland is also colder at altitude than it is at sea level. Funnily
enough, the light goes through less air at altitude, so by your "logic" the
air tempertaure should be higher. At the top of Mount Everest, the sun goes
througnway less air than at the equator, but its still colder.

The decrease in temperature with altititude is largely a result of Boyle's
Law (PV=nRT), nothing very much to do with warming be the Sun - but that is
an altitude related effect, not a latitude related effect (as we were
discussing).

HTH


Peter Webb



Infra red radiation is no more "heat radiation" than is visible light (in
fact rather less so).


Coorect.


Partially correct, but off-topic


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  #47  
Old 11-08-2006, 08:46 AM
Peter Webb
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Default Why are poles colder than the Equator?


"Sorcerer" <Headmaster@hogwarts.physics_e> wrote in message
news:6df4h.140934$[Only registered users see links. ].blueyonder.co .uk...

I am not an educator, but I have do have an Honours degree in theoretical
physics. However, the subject of why the sky is blue is no what we are
discussing.


Yes, the air does absorb energy before it hits the ground. This warms the
atmosphere. The more distance the light has to go through the air, the more
energy it loses to the air, and the more energy (heat) is transferred to the
air, warming it more. This should make the equator air temperature lower
than at higher latitudes, because there is less air for the light to have to
warm before it hits the ground (remember, when we measure temperature at a
place, we are measuring air temperature).

The reason that the Poles are colder is because the ground is at a low angle
to the radiation, so the energy flux per square metre of light hitting the
ground is less. Has nothing to do with the light going through more
atmosphere; that would make the Polar air temperature warmer, not colder.







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  #48  
Old 11-08-2006, 11:07 AM
Ben Newsam
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Default Why are poles colder than the Equator?

On Wed, 8 Nov 2006 16:33:27 +1100, "Peter Webb"
<[Only registered users see links. ].au> wrote:

That's interesting. So, if I moved a bit I would see a different
colour?

It would seem that red sky at night isn't shepherd's delight after
all. :-(
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  #49  
Old 11-08-2006, 01:06 PM
N:dlzc D:aol T:com \(dlzc\)
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Default Why are poles colder than the Equator?

Dear Peter Webb:

"Peter Webb" <[Only registered users see links. ].au> wrote in
message news:45516c2c$0$23136$[Only registered users see links. ].a u...
....

Rayleigh scattering, not refraction.
[Only registered users see links. ]

....

"Nothing" is too strong a word. "Little" or "Very little" are
more correct. Ambient conditions have more to do with local
sensible temperature than dissipation of insolation over the path
*to* the local area.

You won't convince Androcles, by the way.

David A. Smith


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  #50  
Old 11-09-2006, 01:59 AM
Peter Webb
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Default Why are poles colder than the Equator?


"Sorcerer" <Headmaster@hogwarts.physics_e> wrote in message
news:CAp4h.177377$[Only registered users see links. ].blueyonder.c o.uk...

I studied Snell's law, and indeed studied optics as part of my degree.

But as this is now an ad-hominem discussion, what are your qualifications on
the subject?



No, by your "illogic", which presupposes that energy loss to the atmosphere
is the reason the air temperature is lower at the Poles. I am simply
demonstrating that if this was the cause (and it isn't) it would increase
Polar air temperature, not decrease it.



No. Which is why we know that direct heating of the air by the Sun is not
the cause of the temperature differential between the Poles and the equator,
as you claimed.



The mechanism for warming the air is primarily driven by surface
temperatures. Not warming of the air directly by the sun (as I have said
before). If absorption of air by the Sun was the difference (as you claim),
then places where the sun loses more of its energy to the air (such as at
higher latitudes) would have warmer air temperatures. This is clearly not
so.



Because your mechanism - the sun loses more of its energy to the atmosphere
at higher latitudes - is complete bullshit.


I have tried to explain this as simply as I could ... what part don't you
understand?


No, that is not the direct reason that your car tires get hot. The equation
is PV=nRT; in this case P is higher because n is higher. It is however the
reason that the pump gets hot when you try and inflate tires manually. Its
also the mechanism used by fridges, air conditioners, and Carnot cycle heat
engines. Its pretty fundamental to thermodynamics, but hell what would I
know; my degree is in physics.





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