Ch 6 Atmospheric and Oceanic Circulations Wednesday September 24 2014 3 57 PM o o o o o o What is wind Horizontal movement of air What causes wind Four controls on wind speed and direction Earth s gravitational force almost uniform Pressure gradient force from higher barometric pressure more dense air to lower barometric pressure less dense air Horizontal variations in pressure pressure gradient Unequal heating Isobars What causes horizontal pressure variations Thermal Temperature T inversely related to pressure P and density D High T LOW P D Low T HIGH P D Dynamic Rising air LOW P on surface Falling air HIGH P on surface Causes wind to blow from high to low pressure 90 degree angle wind blows perpendicular to the isobars Increased gradient increased wind High pressure fall and spread cold day Low pressure rise and converge hot day Where are the highest winds Coriolis force Due to the rotation W E spin Without rotation surface winds would move in a straight line from areas of higher to lower pressure Affects only the direction of movement Effect increases with increasing speed of the object Airplanes coriolis deflection corrections in the navigational calculations Varies with latitude No deflection vs maximum deflection Friction force On the Earth s surface Global Pressure and Wind Zones 0 to 90 degrees N S Equatorial low ITCQ Subtropical high Subpolar low o Winds o o o o o o o o o o o o o o o Easterlies trades Westerlies Equatorial Low Pressure 10 degrees N to 10 degrees S A lot of energy Constant high angle of incidence Constant day length 12 h Surface air hears up and rises Air rises converges and consequences Hadley Cells Intertropical Convergence zone ITCZ Trae Winds The winds converging on the equatorial trough Easterlies H to L pressure Pick up large quantities of moisture as they return through Hadley Circulation Sub Tropical High Pressure Hot dry desert air 20 degrees to 35 degrees N S High pressure to low pressure Hot low humidity descending air Weather is clear warm calm Migrates 5 10 degrees latitude with seasons Sub Tropical High Pressure Cells The zones of windless hot dry desert air Deadly in the era of sailing ships Horse Latitudes Subpolar Low Pressure Cells Cool and moist air and clouds Near 60 degrees N S Lat