ch08 - Jon Ahlquist 10/18/2006 Chapter 8: Air pressure,...

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Jon Ahlquist 10/18/2006 MET1010 Intro to the Atmosphere 1 Chapter 8: Air pressure, Forces, and Winds Cause of pressure and how it varies with height Mercury and aneroid barometers Surface pressure (i.e., station pressure) Adjusting surface pressure readings to sea level Surface and upper level weather maps Newton’s laws of motion Pressure gradient force Coriolis force. Example: Foucault pendulum Geostrophic and curved winds Flow near surface and effect of friction Vertical motion Atmospheric pressure (pp. 192-193) ± Air pressure is due to the weight of the air above a point ± Pressure at upper levels depends on how warm the air is, because that determines how expanded the column is. ² Upper level low if column is cold ² Upper level high if column is warm Fig. 8.2c, p. 193 Example: Hurricane has upper-level high pressure due to warmth in eye wall Fig. 15.8, p. 411: Latent heat release gives a hurricane a warm core. This is responsible for an upper level high, as in the previous figure. The upper level high pushes air out at the top, reducing the amount of air in the column, H means high compared to same level, not higher than surface. Mercury barometer (pp. 195-196) ± Invented by Toricelli, student of Galileo, in 1643 ± Air pressure pushes mercury up glass tube. Height of mercury is proportional to pressure ± Mercury used instead of water because it is so much denser. Height of mercury column: 30 in Height of water column: 30 ft ± Same principle for drinking straw: lower pressure in straw, so fluid pushed up tube ± Mercury barometer not so popular because mercury is a hazardous material. Fig. 8.5, p. 196 Aneroid barometer (pp. 195-196) ± Aneroid barometer: sealed can (“aneroid” is from Greek “without liquid”) ± Used in: ² home barometers ² weather balloons ² automated weather stations Fig. 8.6, p. 196 Examples of pressure at sea level (Fig. 8.4, p. 196) ± 1084 mb (hPa) (32.01 in): highest recorded sea level pressure (Siberia, December 1968) ± 1064 mb: highest recorded sea level pressure in US (Miles City, MT, December 1983) ± 1013 mb: AVERAGE SEA LEVEL PRESSURE ± 980 mb: Deep mid-latitude low pressure system ± 926 mb: Lowest sea level pressure in Hurricane Andrew (Miami, August 1992) ± 882 mb: Lowest recorded sea level pressure over the Atlantic Ocean (Hurricane Wilma, October 2005) ± 870 mb: Lowest recorded sea level pressure anywhere (Typhoon Tip, October 1979) ± Horizontally, pressure changes only a few %!
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Jon Ahlquist 10/18/2006
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This note was uploaded on 07/21/2011 for the course MET 1010 taught by Professor Staff during the Fall '08 term at FSU.

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ch08 - Jon Ahlquist 10/18/2006 Chapter 8: Air pressure,...

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