heat transfer due to atmospheric motion
DESCRIPTION
Heat Transfer Due to Atmospheric Motion. Page 224 to 228. Wind is the horizontal movement of air in the atmospheric system Winds result from differences in air pressure. Differences in air pressure are caused by differences in temperature & gravity E.g. pressure falls rapidly with height. - PowerPoint PPT PresentationTRANSCRIPT
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Heat Transfer Due to Atmospheric Motion
Page 224 to 228
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What causes wind?
• Wind is the horizontal movement of air in the atmospheric system
• Winds result from differences in air pressure
• Differences in air pressure are caused by differences in temperature & gravity
• E.g. pressure falls rapidly with height
Low pressure area
High pressure area
wind
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Average pressure at sea level is 1013mbLOW v HIGH
• Increased temperatures
• Air heats & expands
• Less dense & rises
• Creates low pressure below
• Drop in temperature
• Air cools & contracts
• More dense & sinks
• Creates high pressure below
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• HIGH
• Out-blowing
• Descending
• Clockwise
• Gentle winds – gentle pressure gradient
Draw 2 diagrams to show facts below
• LOW
• Blows inwards
• Rising
• Anticlockwise
• Strong winds –steep pressure gradient
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Air movement on a rotation free earth
• If earth did not rotate
• If earth was entirely either land or water
• There would be just one large cell
• Wind would move directly from high to low pressure
• HOW EVER EARTH IS NOT LIKE THIS
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Tricellular Model• 1686 – Halley – one
cell
• 1735 – Hadley – expanded one cell theory
• 1856 – Ferrel – discovered three cells
• 1941 – Rossby – refined the 3 cell theory
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Doldrums – gentle, variable winds
Horse latitudes – calm seas slowed sailors, no food for animals, dead horses thrown overboard
Mid-latitude depressions form
Towering cumulonimbus clouds typical of equatorial climate
Latent heat & moisture picked up from tropical oceans
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Cumulonimbus clouds at ITCZ Mid-latitude depressions at the polar front
Clear skies due to high pressure
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The Coriolis Force
• It is a deflecting motion or force• Suggested by G.G. de Coriolis in 1835• Developed by W. Ferrel in 1855• The rotation of the earth causes a body
moving across its surface to be deflected to the right in the N hemisphere and to the left in the S hemisphere
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Coriolis Force3 controls on wind:
-Pressure gradient
-Coriolis Force
-Friction with land surface
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ROSSBY WAVES = a belt of upper air westerlies which often follow a meandering path.
• Evidence: pilots in WW 2 noticed:- eastwards flights faster than westwards
- N-S flights often blown off course
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Seasonal change in number of meanders – 4 to 6 in summer, 3 in winter
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Jet streams = narrow bands of extremely fast moving air found within the Rossby Waves
• Their purpose is the rapid transfer of energy• Speeds can exceed 230km/hr• Can carry volcanic ash around earth in 1-2 weeks• 5 recognised jet streams:
2 significant - POLAR FRONT JET STREAM - SUBTROPICAL JET STREAM
1 seasonal – EASTERLY EQUATORIAL J.S.
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Normal path of J.S. over Britain is to NE so frequent wet & windy weather as warm air moves north
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Polar Front Jet Stream(divides Ferral & Polar cells)
• Where J.S. moves south:
- Cold air- Descends- Clockwise- Dry- Stable- High pressure- Anticyclones
• Where J.S. moves north:
- Warm air- Rises- Anticlockwise- Strong winds- Heavy rain- Low pressure- Depressions
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• SUBTROPICAL J.S.• 25-30 degrees• Divides Hadley &
Ferral Cells• Meanders less than
PFJS• Lower wind velocities• Similar west to east
path
• EASTERLY EQUATORIAL J.S.
• Seasonal• Associated with
summer monsoons• Indian subcontinent
• MONSOON = a seasonal reversal of wind direction in S.E. Asia
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Balloon uses jet stream to orbit the earth
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