Heat Transfer Due to Atmospheric Motion Page 224 to 228

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

Average pressure at sea level is 1013mb LOW 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

Draw 2 diagrams to show facts below Blows inwards Rising Anticlockwise Strong winds –steep pressure gradient HIGH Out-blowing Descending Clockwise Gentle winds – gentle pressure gradient

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

Tricellular Model 1686 – Halley – one cell 1735 – Hadley – expanded one cell theory 1856 – Ferrel – discovered three cells 1941 – Rossby – refined the 3 cell theory

Latent heat & moisture picked up from tropical oceans Towering cumulonimbus clouds typical of equatorial climate Mid-latitude depressions form Horse latitudes – calm seas slowed sailors, no food for animals, dead horses thrown overboard Doldrums – gentle, variable winds

Mid-latitude depressions at the polar front Cumulonimbus clouds at ITCZ Mid-latitude depressions at the polar front Clear skies due to high pressure

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

Coriolis Force 3 controls on wind: Pressure gradient Coriolis Force Friction with land surface Coriolis Force

- eastwards flights faster than westwards 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

Seasonal change in number of meanders – 4 to 6 in summer, 3 in winter

Their purpose is the rapid transfer of energy 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.

Normal path of J.S. over Britain is to NE so frequent wet & windy weather as warm air moves north

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

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

Balloon uses jet stream to orbit the earth