At least thirteen people have been killed by lightning in West Bengal during the last week, and over twenty more have been injured as the annual kalboishakhi storms swept across the state. Most of those who have died were farm workers caught in the open in the Murshidabad, Burdwan and North Parganas Districts. The kalboishaki storms occur around the beginning of the monsoon season each year, as cool dry air masses moving southwest from Iran and Turkmenistan interact with warmer wetter air sweeping up from the Indian Ocean.
The location of West Bengal. Google Maps.
Thunderstorms occur when warm, moist bodies of air encounter cooler, drier air packages. The warm air rises over the cooler air until it rises above its dew point (the point where it cools to far to retain its water content as vapor), and the water precipitates out, falling as rain, sleet or hail.
Warm moist air passing over the surface of the Earth acts as an electrical generator, creating a negative charge in the cloud tops and a positive charge at the ground (or occasionally in a second cloud layer). The atmosphere acts as an electrical insulator, allowing this potential to build up, until water begins to precipitate out. This allows a channel of ionized air to form, carrying a current between the clouds and the ground, which we perceive as lightning.
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