ch08 - Jon Ahlquist Chapter 8 Air pressure Forces and Winds...

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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. Upper level low if column is cold 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, so the weight (& pressure) decreases at the surface. 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)