Unformatted text preview: Fall 2009 Atmospheric Pressure & Wind
Chapter4 - FIRST TOPIC: ATMOSPHERIC PRESSURE Recall from Chapter 1:
Pressure 1s deﬁned as the force per unit area. ' The ressure at any level 1n the atmosphere depends on the amount of air (or mass)
‘ that level.
Pressure always ' ' with height. .--u-—._-_--_--__-_-_-__---_-___---- ........................... Pressure Change How can the pressure at some place in the atmosphere change?
To understand how, let’s look at the equation of state (also known as the ideal gas law)
(you won’t have to memorize this equatiOn) P = pR—T where P = pressure, p = density, R is a constant and T = temperature ‘. What this equation says is pressure will change if the a ( If t ‘3] ‘5 changes . or the 'thV‘PWTMV—O changes hiTTC.I'T., For a given volume, pressure will change if the amount of in that volume changes. In other words, if density changes. How does temperature affect density and pressure?
The average (or mean) temperature in an air column affects the way pressure decreases with height. Consider two columns of air Both contain the same amount of mass but column A . . , .
is colder than column B. (We re talking about the average temperature in each column)_ '
A muonmuse, E) TWRWL *
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goon. 0H WM!“ U63 «gm; :
f‘SUD . _ A I 1
.M. 35' t _ _ 3.», i
mg m; l 53"— - ' \mamw ' . _ .3
Which column has the hi her densi ?
Answer: g ty ‘HWQ. 'i'QWP‘i VCGALV C, Wt“ LV W \Gje, ‘Hﬂe mm, on— wwcm QYQIfiAYC dQCVﬂtSe 3 A w \th vﬂng WES/wt, Nut cletvmge, 0““ 0t warm" more, wit-tn comer CKW YCVWCV WOW NCW men mﬁ-—uv;'m__ . :__._. ...
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- Fall '08