ch12 - Jon Ahlquist Chapter 12 Middle-Latitude Cyclones...

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Jon Ahlquist 11/13/2006 MET1010 Intro to the Atmosphere 1 Chapter 12: Middle-Latitude Cyclones Definition Examples from history Polar front theory Life cycle Typical paths of lows and highs Where and why storms start Vertical structure of storms Conveyor belt model Nor’easters Polar lows Mid-latitude Cyclones Cyclone = low pressure area, hundreds of miles in size, with “cyclonic” circulation, i.e., counterclockwise (CCW) in the Northern Hemisphere, clockwise (CW) circulation in the Southern Hemisphere. Synonym: storm. Either mid-latitude or tropical This chapter focuses on mid-latitude cyclones. Older meaning of cyclone is tornado, as in Iowa State Cyclones, named in 1895. We are not using this sense here. Anticyclone = high pressure area with “anti-cyclonic” circulation (CW/CCW in N/S Hem) Examples of Important Mid-latitude Storms in History (not in book) 1588: Spanish Armada defeated partly by English navy with superior armaments and tactics and later by bad storm. 150 Spanish ships started, only 65 returned. March 1776: Storm caused British to cancel assault on US troops under Washington at Dorchester Heights. 6 June 1944: D-Day invasion of France in WW II: Allied forecasters correctly forecasted break in storm, allowing invasion, when Germans thought storm would continue. Development of concept of a front Basic concepts developed by Norwegian team, published in 1919 & 1922. Team members: Vilhelm Bjerknes (leader, physics professor) Jakob (Jacob, Jack) Bjerknes, son of Vilhelm and chief author. (22 years old in 1919. 30 years later, he did fundamental El Nino research at UCLA.) Halvor Solberg Tor Bergeron (Swedish pioneer of ice crystal process of rain formation, p. 193 of Ahrens.) Don’t memorize their names, but these guys had good ideas in several areas of meteorology!
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