chapter  7
45 Pages

Planetary-scale motions in the atmosphere and ocean A Variation of pressure and wind

The air pressure at the surface, or at any level in the atmosphere, depends on the weight of the overlying air column. In Chapter 2B, we noted that air pressure is proportional to air density and that density varies inversely with air temperature. Accordingly, increasing the temperature of an air column between the surface and, say, 3km will reduce the air density in the column and therefore lower the air pressure at the surface without affecting the pressure at 3km altitude (the weight of the atmospheric column above 3km remains the same). Correspondingly, if we compare the heights of the 1000 and 700mb pressure surfaces, warming of the air column will lower the height of the 1000mb surface but will not affect the height of the 700mb surface (i.e., the thickness of the 1000-700mb layer increases).