Cyclonic Rainfall (Frontal Rainfall)

GS 1 – GEOGRAPHY

 

Cyclonic rainfall occurs due to the convergence of contrasting air masses (warm and cold) that results in the formation of a low-pressure system, leading to cloud formation and precipitation. This type of rainfall is associated with cyclones, particularly temperate cyclones (mid-latitude cyclones) and sometimes tropical cyclones.

Types of Cyclonic Rainfall:

1. Frontal or Temperate Cyclonic Rainfall (Mid-latitude Cyclones):

• Occurs when warm air mass meets a cold air mass at the fronts.
• The warm air, being lighter, rises above the cold air, cools adiabatically, and causes condensation and rainfall.
• Found in the temperate zones (30° – 60° latitudes).
• Associated with depressions and fronts (warm front, cold front, occluded front).
• Rainfall is moderate to heavy and lasts for several days.

2. Tropical Cyclonic Rainfall:

• Occurs in tropical cyclones (also called hurricanes, typhoons).
• Caused by intense low-pressure systems over warm ocean waters.
• Leads to heavy rainfall, thunderstorms, and violent winds.
• Rainfall is intense but short-lived, mostly around the eye wall of the cyclone.

Mechanism:

1. Formation of a Front: Warm and cold air masses meet.
2. Lifting of Warm Air: The lighter warm air rises over denser cold air.
3. Cooling and Condensation: Rising air cools and condenses to form clouds.
4. Precipitation: Continuous condensation results in rainfall.

Characteristics:

Feature	Temperate Cyclonic Rainfall	Tropical Cyclonic Rainfall
Origin	Frontal convergence	Warm ocean surfaces (ITCZ)
Air Masses Involved	Cold and warm air masses	Moist air over warm oceans
Region	Mid-latitudes	Tropical and subtropical regions
Rainfall Intensity	Moderate to heavy	Heavy to torrential
Duration	Several hours to days	Few hours to 1-2 days
Associated Weather	Cloudiness, rain, drizzle, wind	Thunderstorms, lightning, gales

Relevance to India

• Tropical cyclones from Bay of Bengal and Arabian Sea affect Eastern and Western coasts of India (e.g., Odisha, Andhra Pradesh, Tamil Nadu, Gujarat).
• Cyclones bring destructive winds, floods, and storm surges, but also contribute to rainfall, especially in post-monsoon (Oct-Dec) season.
• Part of Northeast Monsoon (Retreating Monsoon) rainfall is due to cyclonic depressions over the Bay of Bengal.
• Temperate cyclones (Western Disturbances) bring cyclonic rainfall to North and Northwest India, especially in winter, crucial for rabi crops like wheat.