Cyclonic rain
Also called: Frontal rain · Topic: Water in the Atmosphere: Humidity, Condensation, Clouds and Precipitation · NCERT: Class 11, Ch 9 "Atmospheric Circulation and Weather Systems"; Class 11, Ch 10 "Water in the Atmosphere"
Meaning
Cyclonic rain, also called frontal rain, falls when air is lifted inside a cyclone (a low-pressure weather system). In extra-tropical cyclones, warm air rises over cold air along a front, which is the boundary between two air masses. The rising air cools, its vapour condenses, and rain falls. Warm fronts give long, widespread, steady rain from nimbostratus clouds. Cold fronts give short, heavy showers. Tropical cyclones also give cyclonic rain, and it is very heavy around the eye and in the rain bands.
Example
Western disturbances are low-pressure systems that come from the Mediterranean region. In winter they bring rain to north-west India, in Punjab and Haryana, and this rain helps the rabi wheat crop. In the same way, frontal rain gives north-western Europe its winter rain.
Don't confuse with
- Convectional rain: Here the sun heats the ground and the warm air rises on its own. This rain is short, heavy and local, like the afternoon rain of equatorial regions. Cyclonic rain covers wide areas and can last for days.
- Orographic rain: Here a mountain forces the air to rise, so rain falls on the windward slope (the side facing the wind). In cyclonic rain, the air is lifted by fronts or by a low-pressure system.