Sudden stratospheric warming refers to a rapid rise (by more than 50°C over a matter of days) in the temperature high up in the stratosphere. It is common and occurs every second year on average in the northern hemisphere, however, in the southern hemisphere it is a rarity. However, this phenomenon is now witnessed
with increasing frequency in southern hemisphere as well.
It usually occurs when at altitudes of less than 10 kilometers above Earth’s surface, planetary-scale waves form and propagate upward into the stratosphere, where they dissipate.
Sudden stratospheric warming occurrence mechanism Every winter, strong westerly winds develop in the stratosphere high above the South Pole and circulate around the polar region due to the difference in temperature over the pole (high pressure and low temperature) and the Southern Ocean (low pressure
and high temperature). This leads to the formation of the stratospheric polar vortex.
Later, as the sun shifts southward during spring of Southern Hemisphere, the polar region comes under the sun rays and starts to warm. The air waves from the lower atmosphere propagate upward into the stratosphere
and warm the stratosphere above the South Pole. This leads to weakening of the stratospheric polar vortex and reversing the direction of the westerly winds (if waves rapidly break down the polar vortex). It causes the temperature in the stratosphere to rise very rapidly; hence result in sudden stratospheric warming.
Effect on ozone hole formation over Antarctica
The Antarctic ozone hole forms during the Southern Hemisphere’s late winter as the returning Sun’s rays start ozone-depleting reactions. These reactions involve chemically active forms of chlorine and bromine derived from man-made compounds and occur on the surfaces of cloud particles that form in cold stratospheric layers. However, the rapid rise of temperatures due to sudden stratospheric warming restricts the formation of
polar stratospheric clouds. The life cycle of the polar stratospheric clouds is also reduced, therefore limiting the ozone depletion process.
Further, the breakdown of polar vortex leads to increasing the mixing of air between mid-latitudes and the polar region. The disrupted winds from the tropics carry more ozone-rich air to the polar region, helping repair the ozone hole.
