rainfall Flashcards
cloud formation
-heat cause water to evaporate into water vapour
-warm air containing water vapour starts to rise
-air is cooled rapidly as it rises because temp decreases with altitude
-as parcel of air rises up the atmosphere, temp falls, RH rises (cool air holds less water vapour)
-when RH reaches 100% at high altitudes, air becomes saturated
-excess water vapour ceases to exist as gas and changes back to water (condensation)
-water droplets condense on dust particles which act as condensation nuclei
-tiny water droplets form around these particles
-water droplets collide with each other and merge into larger water droplets (coalescence)
-clouds are formed
convectional rain
-surface of earth heated intensely, warms air near the surface
-air expands and rises as it is heated, capacity to hold water vapour also increases
-as warm air rises, it cools gradually and can no longer hold as much water vapour
-RH of parcel of air increases
-at certain altitude, RH of air reaches 100%
-condensation occurs, tiny droplets of water condenses around dust particles in air to form clouds
-high evaporation and rapid condensation result in cumulonimbus clouds forming, leading to convectional rain
relief/orographic rain
-parcel of air blows across water body and picks up moisture
-as parcel of air approaches mountain, the moist air is forced to rise up the slope
-as warm air rises, it cools gradually and can no longer hold as much water vapour
-RH of parcel of air increases
-at certain altitude, RH of air reaches 100%
-condensation occurs, tiny droplets of water condenses around dust particles in air
-tiny water droplets merge to form clouds
-when droplets are heavy enough, they fall as rain on the windward side
-other side of mountain (leeward side) is usually dry because as parcel of air decreases in altitude, it warms up and can hold more water vapour
