捍片睡汩楈桧牥畤惯楴汤潩虑-Weatherand.pptVIP

Clouds and Precipitation Introduction Hydrological Cycle – 4 main parts Evaporation of water from the oceans Transport of water vapor in the atmosphere Condensation and precipitation Return of water to ocean by rivers and streams The main events of the hydrologic cycle are: (1) The evaporation of water from the ocean, (2) the transport of water vapor through the atmosphere, (3) condensation and precipitation of water on the land, and (4) return of water to the ocean by rivers and streams. Cloud-forming Processes Upward Air Movement Convection resulting from differences in temperature Barriers such as mountain ranges which provide lift to air masses Meeting of moving air masses with different densities. Adiabatic Cooling Decrease in temperature of an expanding gas Adiabatic Heating Heating of a gas as it undergoes compression Dry Adiabatic Lapse Rate Rate of cooling in the absence of condensation About 10 OC for each increase or decrease of 1 km (5.5OF/1,000 ft) As a parcel of dry air is moved upward, it expands and cools according to the dry adiabatic lapse rate. This graph compares the temperature of a rising and adiabatically cooling parcel of dry air with the average temperatures of the surrounding atmosphere when the temperature at the surface is 30OC (86O F). Atmospheric Stability Stability When the atmospheric lapse rate is less that the dry adiabatic lapse rate Instability When the atmospheric lapse rate is greater than the dry adiabatic lapse rate. If a parcel of air is moved up or down, it will cool or warm according to the dry adiabatic lapse rate. In a state of atmospheric stability, the parcel of air will always be cooler, and therefore more dense, than the surrounding air at any altitude. It will, therefore, return to the original level when the upward force is removed. In a state of atmospheric instability, a parcel of air will always be warmer, and therefore less dense, than the surrounding air at any altitude. The parcel will, therefore, continue on