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Cold wave in north India

Date: 28 November 2020 Tags: Geography & Environment

Issue

Northern India is bracing for a cold winter with sharp drop in night time temperatures. This is expected to bring a new cold wave.

 

Background

One of the main reasons for cold wave is snowfall in J&K, Himachal Pradesh, and Uttarakhand that has pushed cold waves towards Ganges plains.

 

Details

  • The snowfall occurred under the influence of Western Disturbance. It is a phenomenon associated with rainfall, fog, and snow.

  • When skies are cloudy, there is comparatively lower radiation during day time. This lowers maximum temperatures.

  • A reason behind this temperature drop is explained by climate pattern La Nina, which has developed this year.

  • Polar vortex has also weakened, leading to pushing of cold waves deeper towards equator from the northern pole.

 

Polar vortex

  • A polar vortex is a persistent, large-scale, upper-level low-pressure area that rotates counter-clockwise at the North Pole and clockwise at the South Pole (called a cyclone in both cases), i.e., both polar vortices rotate eastward around the poles.

  • The vortices weaken and strengthen from year to year. As with other cyclones, their rotation is driven by the Coriolis effect.

  • Polar vortices are weakest during summer and strongest during winter. Ozone depletion occurs within the polar vortices – particularly over the Southern Hemisphere – reaching a maximum depletion in the spring.

  • When the vortex of the Arctic is strong, it is well defined, there is a single vortex, and the Arctic air is well contained.

  • When weaker, it will break into two or more vortices. The flow of Arctic air becomes more disorganized, and masses of cold Arctic air can push equatorward, bringing with them a rapid and sharp temperature drop.

  • Sudden stratospheric warming events are associated with weaker polar vortices. This warming of stratospheric air can reverse the circulation in the Arctic Polar Vortex from counter-clockwise to clockwise.

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