UPSC Mains 2024 GS1 Q16: model answer

A twister, or tornado, is a violently rotating column of air extending from a thunderstorm cloud to the ground. It is small (usually tens to hundreds of metres wide) but can have wind speeds above 300 km/h. Intensity is rated on the Enhanced Fujita (EF) scale.

Formation

• Warm, moist air near the surface and cool, dry air above make the atmosphere unstable.
• Wind shear (winds changing speed and direction with height) creates horizontal spinning.
• Strong updrafts in a supercell thunderstorm tilt the spin upright into a mesocyclone.
• A funnel descends and touches the ground as a tornado.

Why most occur around the Gulf of Mexico and the US plains

• Moisture source: the Gulf sends warm, humid air northwards.
• Dry air from the west: hot, dry air from the Mexican plateau and the Rockies flows above it.
• Cold air from Canada: polar air moves south with no east-west mountain barrier to stop it.
• Flat Great Plains: allow these air masses to collide freely.
• Jet stream: provides strong shear in spring.

This is why 'Tornado Alley' (Texas, Oklahoma, Kansas) and 'Dixie Alley' see the most tornadoes; the US records over a thousand a year, the highest in the world.

India and Bangladesh also see tornadoes in the pre-monsoon (nor'westers zone), such as the deadly Daulatpur–Saturia tornado in Bangladesh (1989).

Doppler radar and warnings have cut deaths, but tornadoes remain hard to predict precisely.