Chapter 7 Global Scale Winds Jet Stream Meridional flow pattern Midlatitude westerlies Monsoon Polar easterlies Polar front Polar front jet stream Rossby wave Short wave Split flow pattern Subtropical highs Subtropical jet stream Thermal lows Trade winds Zonal flow pattern Zonal index Key Terms Angular momentum Blocking pattern Conservation of angular momentum Doldrums Hadley cell Horse latitudes Index cycle Intertropical Convergence Zone ITCZ Summary In this chapter we developed a conceptual model to explain patterns of global circulation and their associated weather and climate Upward vertical motions near the equator explain the ITCZ which can be identified in global satellite imagery and precipitation maps When rising air reaches the tropopause and accelerates poleward it comes close to the Earth s axis of rotation and increases speed while conserving angular momentum This produces the subtropical jet stream Convergence of air near the subtropical jet stream helps cause the subtropical highs This descending air of the Hadley cell is compressed and warms lowering the relative humidity This sinking air explains the large desert of Africa Saudi Arabia and Australia This inking air of the Hadley cell results in nearly calm winds at the surface producing the horse latitudes dreaded by ancient mariners who used wind power to travel Some descending air that reaches the surface moves toward the equator to supply moisture to the ITCZ As air moves toward the equator the Coriolis force acts to produce the steady northeast and southwest trade winds sought by sailors Some of the air associated with the descending branch of the Hadley cell moves poleward and clashes with cold polar air masses that are moving toward the equator Fronts exist where the cold air meets the warm subtropical air producing midlatitude westerlies causing them to move eastward The polar jet stream exists in the vicinity of fronts In our simple conceptual model the globe is covered with water a good approximation because the Earth is 70 water However the differences in land and water are important in weather and climate The Indian monsoon provides and example of ocean land and topography interact to form clouds and precipitation or to bring a dry season A monsoon is a seasonal reversal in wind patterns associated with changing regional energy budgets The change in wind direction results in dry and wet seasons The general circulation of the atmosphere transports hear form the equator to the poles especially in midlatitudes The world s oceans also transport heat
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