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Дата изменения: Unknown Дата индексирования: Sat Dec 22 10:16:22 2007 Кодировка: Поисковые слова: south pole |
(S-1B)   Global Climate, Global Wind Flow
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Part of a high school course on astronomy, Newtonian mechanics and spaceflight
by David P. Stern
This lesson plan is a continuation of (S-1) Sunlight and the Earth,
with lesson plan at Lsun1lit.htm. and of #S1-A Weather and the Atmosphere with lesson plan at Lsun1litA.htm. This lesson plan supplements #S1-B Global Climate, Global Wind Flow.
"From Stargazers to Starships" home page ....stargaze/Sintro.htm |
Goals:
The student continues following the main thread: weather and wind are parts of the process by which the atmosphere disposes heat absorbed from the ground, which is warmed by sunlight. This section is qualitative, and much of it can be viewed as optional.
Terms: tropic of cancer, tropic of Capricorn, tropical region, polar region, "Hadley cell" flow, Coriolis force, jet stream, belt of deserts [optional: Rossby wave, El Niño]. ------------ Starting the lesson:In thunderstorms and other convection, the driving motion is up and down: hot, humid air rises, cooler, dry air returns. The source of energy which drives all that is the heating of the ground by sunlight.However, most winds we know are horizontal. We know that they are part of large systems, as we can see on weather maps. How can the heating due to sunlight drive horizontal winds?
Hadley in 1735 was the first to propose a process for such spreading of heat. What did he propose?
Suppose this happens: the flow would be in the north-south direction. Yet actual winds flow mostly east-west, and we understand this is caused by the rotation of the Earth around its axis. What causes the shift in direction?
This is an example of motion appearing different when viewed in a rotating frame of reference. Not only is a "centrifugal force" added there, but motions of an object from one rotation radius to another seem to get an extra push in a perpendicular direction. What is this called?
And what about air returning equatorwards?
[Optional] Suppose you have a region of low pressure, say, above the middle of USA. Air rushes in from all sides to fill it. The Coriolis force causes that air to swirl. Will it swirl clockwise or counterclockwise?
Does the "Hadley Cell" circulation exist?
Hadley's prediction was that the circulation is between high and low altitudes. Instead, in middle latitudes, the motions are mostly horizontal: warm air flows poleward at one location, equatorward at neighboring ones. The Coriolis force still makes the air moving poleward add an eastward motion, which is why most winds in the continental US come from the west. But the flow is horizontal, and includes large waves ["Rossby waves"], extending appreciably north south. At what altitudes is this flow fastest?
And it is called there...
(Because of the jet stream, a flight from California to New York may be noticeably shorter than one from New York to California.) Moving air may lose some of its eastward flow, say, to friction with the ground. As it returns equatorward (even in Rossby waves), it rotates more slowly than the ground below. What is the result?
...Called what?
What is "El Niño"?
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Author and Curator: Dr. David P. Stern
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Last updated: 11-12-2004