INTRO TO WEATHER
INTRO TO WEATHER MET 1010
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This 5 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 14 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 9 Air Pressure Forces and Wind Air pressure Using a model that assumes a constant air density with altitude L H Pl Pz 1 2 cold hot For the warmer city 2 higher pressure aloft will eventually lead to lower surface pressure because wind blows from high to low pressure in response to the pressure gradient force How can air density be constant with altitude Only approximately true over small heights Ideal Gas Law P p T If P is in millibars mb T is in Kelvins and p is in kgm3 then C E 287 This relation is valid for a parcel of air within which P p and T are constant Example A parcel of air is raised from the ground to a height of 2 km At 0 km P1 1013mb T1 25 C At 2 km P2 800mb Assume lapse rate of 8 C km What is pz p1 EL 13 C2 8MZL p1 CTZ P1 1013 KTZ T125 C4273298K DTMTWCMDWCNamp ampK amp 800 E 083 p1 1013 K282 p2 83 of p1 Note P2 is 79 of P1 so P decreases faster Mercu Barometer A column of mercury Hg of height h 76 cm exerts about 1 atm of pressure Forces of gravity and air pressure are balanced Station Pressure pressure reading at your location corrected for temperature instrument error calibration and variations in gravity Altitude Corrections allow comparisons of atmospheric pressure from one city to another correcting for different altitudes of the cities Sea Level Pressure add lOmb for every 100 meters that your station is above sea level Connect points of equal pressure at sea level and draw them on a map See map with sea level isobars see Fig 99 b Also very useful in predicting weather trends is a 500mb map which shows contours of altitude at which the pressure is 500 mb See Fig 915 b Note On a surface map winds blow counterclockwise CCW and inward around a surface low and across isobars Winds blow parallel to contours on a 500 mb map What determines how the wind blows Forces cause objects to accelerate Acceleration is any change in speed direction of motion Constant Speed 7 V Acceleration a because of a change in direction Newton s Second law F ma F is net external force on object m a is acceleration of object of mass m Forces that in uence wind are 1 Pressure gradient force 7 causes wind to blow 2 Coriolis force 7 de ects moving wind 3 Centripetal force 7 a combination of other forces that acts perpendicular to V and allows circular motion 4 Friction 7 slows wind down near earth 9 Pz latm 1mm 2 34 ft PATM I 3 T Pz 2 I atm E Pz is linear straight line 1 E I because water is incompressible p constant 34 68 2 ft P P Pressure Gradient PGF is directed from high to low pressure perpendicular to isobars and is larger for closely spaced isobars Coriolis Force We live in a rotating reference frame The earth Example Transparency demo Forcefree frictionless motion will cause object to veer to the right in the Northern Hemisphere as viewed in rotating frame veer to left in Southern Hemisphere Fcor 0 at equator large at poles Fcor is larger for high speeds Centripetal Force An object moving in a circle is accelerating even if it moves at constant m Sitting in a car you need a push to accelerate forward brake g move around a curve So if winds move in a circle around a high or low pressure system a force must be acting on the air directed inward toward the center of the low or high A Isobar
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