Factors Effecting Precipitation
Mechanism of Cooling
Condensation of Water Vapors
Growth of Droplets
- Mechanism of Cooling
There reduction in pressure when air ascends from the surface of earth to upper levels in the atmosphere is the only mechanism capable of producing the degree and needed to account for heavy rainfall. The capacity of a given volume of air to hold a certain amount of water vapors is lowered due to cooling. Super saturation is known to occur in the atmosphere so the excess moisture over saturation condenses through the cooling process which ultimately results in precipitation.
- Condensation of Water Vapors
It normally occur when there is 100% relative humidity and a condensation, nuclei having an affinity for water is present, Sources of these condensation nuclei are the particles of sea salt , carbon dioxide and the sulfurous and nitrogenous oxides emanating from the surface of the earth anti the atmosphere.
- Growth of Droplets
It is required so that the liquid particles present in the clouds can reach the ground. Coalescence of drops through the collision due to difference in speed of motion between larger and smaller droplets results of which their rate of fall is also increased whereby more collision either other droplets and more growth of droplets takes place. The growth of droplets is also achieved by their co existence with ice crystals. This generally happens in a temperature range of 10oF to 20oF. When ice crystals and water droplets co exist in a cloud, an imbalance is caused due to lower saturation vapor pressure over as compared to water. The results in the evaporation of water droplets and condensation of much of these droplets on ice crystals also causing their growth and ultimate fall through clouds. This effect is known as Bergeron’s theory presented in 1933.