INTRO TO WEATHER
INTRO TO WEATHER MET 1010
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This 6 page Class Notes was uploaded by Maureen Ledner on Friday September 18, 2015. The Class Notes belongs to MET 1010 at University of Florida taught by Staff in Fall. Since its upload, it has received 22 views. For similar materials see /class/206629/met-1010-university-of-florida in Meteorology at University of Florida.
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Date Created: 09/18/15
Chapter 11 Global Wind Systems Review When do clouds form Low Pressure High Pressure Upper Level Surface The important criterion is rising air not pressure Clear skies Clouds Sinking air Rising air L Wind gt gt gt gt E gt V l 2103 Wind speeds up Less dense More dense Here a surface low gives fair weather Often a surface low gives clouds and rain See Fig 713 In all cases rising air gives clouds regardless of pressure Fig 112 represents a model of atmospheric circulation assuming 1 No land 2 No tilt of the Earth s axis however the Earth does rotate This is a depiction of surface pressures and wind directions General Features 1 Heat at equator causes air to rise Surface low forms clouds and rain Surface air ows in from higher latitudes Coriolis force causes NE winds in the Northern hemisphere and SE winds in the Southern hemisphere respectively 2 Cold at poles causes sinking air Winds ow away from the poles on surface Coriolis de ects these winds eastward 3 Another cell forms between 30 and 60 latitude that opposes the polar and Hadley subtropical cells This Ferrel cell has northward owing surface winds in the Northern Hemisphere Southward winds in the Southern Hemisphere and Coriolis causes westerlies in the Northern and Southern Hemispheres Easterlies above and below equator are called trade winds Winds are light near equator and subtropical high 30 doldrurns and horse latitudes ITCZ trade winds converge Fig 113 The real world Average sealevel pressures and winds Observations l Semipennanent highs and lows 2 Thermal seasonal cyclones lows and anticyclones highs 3 Seasonal movement of ITCZ and other features 4 Sinking stable air near 30 associated with clear weather shifts with seasons AM Why are winds light near highs and lows U tdv lo c J KL distance a AP Generally 7 is small near highs and lows and largest in between highs and lows Fig 118 Upper level pressure and wind 1 Semipermanent lows moved westward Why 7 Coriolis 2 Mostly westerlies aloft 7 small easterly flow equatorward of highs 3 Contours closer in winter p steeper pressure gradients higher winds Also recall from Chapter 9 m AP PGF 7 7 p d As you go higher in altitude air density decreases 2 PGF increases so wind blows faster at higher altitudes N Westerly winds have v gt 1000 knots Easterly winds have v lt 1000 knots Equator on surface v 1000 knots As viewed by stationary observer above ear Calm air would be fixed relative to the surface of earth so to the stationary observer would be moving at 1000 knots Note Speed at surface of earth gets smaller toward the poles because you go less far in 24 hours Example Standing 1foot from the North Pole you would move 21 feet in 24 hours However westerly winds move faster towards the east than the earth s surface does and so appear to us on earth to move toward the east Winds that appear to us to move towards the west are actually moving toward the east to a stationary observer Jet Stream Fast moving air currents long and thin Rising air attens out at the tropopause because the atmosphere in the stratosphere is very stable an inversion Jet streams are caused by steep pressure gradients aloft See Fig 1110 At locations where adjacent cells meet Hadley Ferrel warm air meets cold air and strong temperature and pressure gradients develop Jet streams are also helped by angular momentum L mvr Smaller r gt largerv As air aloft moves from the equator to the poles and is de ected ist by coriolis force r is also decreasing which speeds wind up Why do winds follow curvature the curvature of the earth as they blow over long distances N PGF wind equator As the earth curves away from the wind PGF decreases so FG gt PGF and FG PGF provides the centripetal force required curving the wind in an arc It is northward and southward blowing winds that are responsible for pumping momentum away from the equator These north and south winds are generally associated with highs and lows Winds blowing away from the equator are turned into westerlies by coriolis force 0 Equator Winds blowing toward the equator are turned into easterlies by coriolis force lt9 lt Equator Ocean currents tend to follow air currents Closed ocean current loops are called gyres the same root as gyration Large high pressure cells dominate the world s major bodies of water Winds blow clockwise and outward in the northern hemisphere and counterclockwise and outward in the southern hemisphere around these highs Air K Isobars Northern Hemisphere Southern Hemisphere Water responds to these moreorless constant winds through the frictional force Air f aw A L V gt f wa Water Surface Newton s 3rd Law For every action there is an equal and opposite reaction Result Water is pushed in direction of air However coriolis force is around too in northern hemisphere water de ects to the right and in the southern hemisphere water de ects to the Q
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