POLAR VORTEX AND THEORIES OF ARCTIC AMPLIFICATION

Why in news: Research shows that Arctic is warming four times faster than the rest of the planet  Recently Arctic amplification has led to harsh winters in U.S., Summer heat waves in Europe and Floods in Pakistan.

 Theories of Arctic Amplification

• The different theories of how Arctic amplification could be affecting the mid-latitudes fall broadly into three main categories: those that focus on a “wavier” jet stream, the stratospheric polar vortex and “wave resonance”.

Wavier jet stream

• In the UK , if the jet stream path shifts to the south, it pulls down cold air from the Arctic. When it sways north, it brings warm air up from the tropics.
• The strength of the jet stream is driven by the difference in temperature between the cold air over the Arctic to the north and the milder air to the south.
• As the Arctic is warming more rapidly than the mid-latitudes, the temperature difference is declining, which leads to a weaker jet stream.
• The weaker jet stream with diversions from its path increase the likelihood of a wavier jet stream pattern.
• When the jet stream takes larger north-south meanders – known as “Rossby waves” – warm air can penetrate north and cold air can plunge south.

Polar vortex

• As with the jet stream in the troposphere, the polar night jet forms a boundary between the very cold Arctic air and the warmer air over the mid-latitudes. However, if something disrupts the stratospheric polar vortex it can weaken, reverse direction and even split into two. This can trigger a sudden stratospheric warming (SSW) event where air collapses in over the Arctic, causing a spike in temperatures in the stratosphere – by as much as 50C in just a couple of days.
• This allows the cold air the polar vortex was holding in to spill out into the mid-latitudes during the weeks that follow. This is what brought the “Beast from the East” to the UK in 2018 and is the root cause of the dramatic weather currently hitting the US this winter. 

Wave resonance

• “Wave Resonance” also relates to the jet stream in the troposphere, but only occurs during summer. It is suggested to have played a role in the European heatwave and the Pakistan floods .

• This theory suggests that a weakened jet stream increases the likelihood of it splitting into two distinct jets. One jet then moves north and the other south, potentially trapping weather systems in between. This “quasi-resonance” results in persistent – and often extreme – summer weather.

Where to use?

Paper 1 (Important Geophysical phenomenon, Climate change) Paper 3 (Environment) 

Paper I (Geography Optional : Atmospheric circulation, Jet Streams, Global Climatic Change)