Wind

Pressure, Wind and Weather Systems � � WINDS are horizontal flows of air; winds blow from areas of high pressure to areas of low pressure (nature tries to equalise pressure) Air heated by contact with ground expands; becomes less dense and rises Sun heats up ground Insolation LOW PRESSURE Denser air drawn in at low level to replace rising, less dense air Air stops rising when it meets air of equal density, then diverges at high level to produce more wind which eventually sinks elsewhere to complete the circulation cell

Land and Sea Breezes

Land & Sea Breezes Land Breeze (cool land/warm sea)  Cool air over land moves out toward the water and takes the place of rising air.  Warm air over the water rises. Sea Breeze (warm land/cool sea)  Warm air over the land rises.  Cool air over the water moves toward land and takes the place of the warmer air that has risen.

A. water throughout the day, air starts to rise and air from A.As the land heats faster than the water throughout the day, air starts to rise and air from over the sea will come in to replace it. This is a sea breeze circulation (takes place during the day). B. B.As the land cools faster than the water throughout the day, the air begins to sink over land and rise over water. This is a land breeze circulation (takes place during the night)

Land/Sea breeze  The temperature differences between land and water occur because water has a much higher heat capacity than land. This means more heat is required to raise the temperature (or drop the temperature) of water than that of land.  These temperature differences cause pressure gradient forces that force the breezes  satellite satellite  Animation Animation

Cyclones and Anticyclones

Northern Hemisphere: Cyclone Anticyclone Cyclone: Low pressure, Counterclockwise winds, cloudy and rainy weather Anticyclone: High Pressure, Clockwise winds, sunny weather

Southern Hemisphere: Cyclone Anticyclone Cyclone: Low Pressure, clockwise, cloudy or rainy weather Anticyclone: High Pressure, counterclockwise, sunny weather

How High and Low Pressure Works   ow/whighlow.htm ow/whighlow.htm

How Low Pressure Areas Work   es/wlowpres.htm es/wlowpres.htm

How High Pressure Areas Work   /whighp.htm /whighp.htm

Highs have sinking air above them, lows have rising air. Sinking air over highs causes dry weather, Rising air above lows can condense and form clouds or rain or both.

Strong winds also occur in low latitudes due to stronger heating and steeper presure gradients. Hurricanes and tornadoes are both tropical phenomena. WIND DIRECTION & STRENGTH � � Wind strength depends on the difference in pressure between the high and low pressure systems, and the distance between them. � � This is called the PRESSURE GRADIENT; it is a similar concept to the physical slope between two places, shown on a contour map. Pressure is shown by ISOBARS on a weather map. � � Pressure difference essentially depends on the temperature difference between the two places. Locally, wind is channelled down streets (wind canyons). Beach windbreaks reduce windsped by increasing friction Strong polar winds due to low friction Farmers plant trees to protect orchards, houses, stock or prevent soil erosion Hurricane in Florida A steep pressure gradient results from a large pressure difference or short distance between places and causes strong wind. Tornado in USA

Wind Speeds down a Pressure Gradient

Weather map

Coriolis

Types of Surface winds: 1. 1.Trade winds- occurs between 30 o N and 30 o S latitude. 2. Prevailing Westerly- occur between 30 o to 60 o in both hemispheres. They blow west to east. 3. Polar Easterlies- occurs between 60 o and the poles in both hemispheres. They blow east to west.

Ocean Currents Ocean Currents: movement of ocean water   The main cause is the Coriolis Effect Coriolis Effect: the rotation of the Earth causes the oceans water to circle away from the equator   Currents generally help to control climate and are useful in moving nutrients throughout the oceans   Northern Hemisphere currents move clockwise; while currents in the Southern Hemisphere move counter- clockwise.

Earth Science Reference Table Earth Science Reference Table