Figure 3.20

GEO-GRAPHIC: Latent heat release over mountain ranges. A parcel of air undergoes adiabatic temperature changes as it flows over a mountain range. 1. At the base of the mountain range, this air parcel’s temperature is 22°C. As the parcel ascends the windward side, it expands and cools at the dry adiabatic rate (10°C/1,000 m). 2. At 1,000 m altitude, the air parcel has cooled to its dew point of 12°C. Above 1,000 m, it cools at a moist adiabatic rate of 6°C/1,000 m. 3. The parcel’s temperature decreases to 0°C as it reaches the mountain peak. 4. On the leeward side, the descending parcel is compressed and warms at the dry adiabatic rate of 10°C/1,000 m. As the temperature increases, the relative humidity decreases, so the leeward side of the range is dry. 5. On the windward side, the parcel’s temperature began at 22°C. At the same elevation on the leeward side, the parcel’s temperature has increased to 30°C due to the release of latent heat.