Sudden Stratospheric Warming Arctic Region YouTube Lecture Handouts

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Heavy Rains in South India in due to Arctic? Know the Reason - Sudden Stratospheric Warming

Sudden Stratospheric Warming Arctic Region

What Triggers SSW?

Illustration: What Triggers SSW?

What Triggers an SSW Event and What is Its Impact?

  • The stratosphere is an atmospheric layer about 10 - 50 km above the Earth՚s surface. During winter, the pole is tilted away from the sun and is in 24-hour darkness; whereas at the equator, the stratosphere receives sunlight. There is therefore a large difference in the stratosphere temperature between the high and low latitudes (a strong temperature gradient) .
  • This results in strong winds blowing in a westerly direction around the cold air over the pole. This arrangement is known as the stratospheric polar vortex, and it forms every winter. On occasions, this vortex can be disturbed, the temperature can rise by up to and the winds can weaken, or vice versa. The reversal of the winds is called SSW.
  • It occurs around six times in a decade in the northern hemisphere, but only one has ever been observed in the southern hemisphere. This is because of the different arrangement of land and sea in the two hemispheres. The northern hemisphere has more regions with land-sea temperature contrast, which can set up atmospheric waves that disturb the vortex. The southern hemisphere sees more of the sea, continuous around Antarctica.
Illustration: What Triggers an SSW Event and What is Its Impact?
  • Southern India was deluged by unusually heavy rainfall in the first 17 days of the New Year. Tamil Nadu received almost 10 times more rainfall than normal. All its 38 districts experienced large excess rainfall — 60 per cent over normal as by IMD. 1 million hectare crops was submerged
  • In Kerala, Kasargod and Malappuram, where the rainfall was 100 times the normal
  • On January 5, the Arctic region recorded a Sudden Stratospheric Warming (SSW) event that takes place in the stratosphere, the second major layer of our atmosphere that starts roughly 50 km from the Earth՚s surface. During such events the temperature of the stratosphere can increase by up to 50 degree C within 10 days
  • The last SSW event happened in 2019 during which the polar vortex split into three smaller vortices releasing cold winds into the southern regions – it causes circulation anomalies in troposphere where weather is generated.
  • After SSW, one sees meandering and southward shifted jet stream in the troposphere, causing colder winter weather in Northern Eurasia and the northeastern United States, as well as increased storminess and precipitation in the Mediterranean region.
  • No SSW event was seen between 2013 to 2018.
  • Jet streams are some of the strongest winds in the atmosphere. Their speeds usually range from 129 to 225 kilometers per hour (80 to 140 miles per hour) , but they can reach more than 443 kilometers per hour (275 miles per hour) . They are faster in winter when the temperature differences between tropical, temperate, and polar air currents are greater.
Illustration: What Triggers an SSW Event and What is Its Impact?
  • SSW occurs in two phases — easterly and westerly — based on the direction of the planet it impacts.
  • Easterly SSWs have a stronger cooling effect over north India than its westerly phase. It adds that an easterly SSW event increases the speed of the western disturbances, an extra tropical storm originating in the Mediterranean region that brings sudden winter rain to the northwestern parts of the subcontinent. This translates into intense winters in North India
  • 5 to 6 days prior to the peaking of polar SSW (January 5 in the case of the current event) , there is a change in the wind patterns in Kochi՚s troposphere along with unusual rainfall in the city. First week of January 2021, Delhi received three times more rain than the normal for the entire month. While the primary reason is the western disturbance over central Pakistan.
Illustration: What Triggers an SSW Event and What is Its Impact?
  • Sea ice loss in the Barents and Kara seas in the Arctic weaken the polar vortex.
  • If the polar vortex strengthens, in the future (which means less SSWs) the drying of the Mediterranean region will be faster and extreme storminess in northern Europe will increase. In this scenario, it would result in milder winters for northern Eurasia.
  • If the vortex weakens (which means more SSWs) , opposite patterns would be the case and the cooling effects of SSWs in northern Eurasia could partly dilute the expected effects of global warming in winter in these regions.

Manishika