Context: Large swathes of Canada and the USA were hit by a massive winter storm. At least five people have died in the United States over the weekend and the storm has led to mass school closures, dangerous road conditions and power cuts. The extreme weather has been caused by the expansion of the polar vortex southwards.
Relevance of the Topic:Prelims: Key facts about Polar Vortex.
What is Polar Vortex?
- Polar vortex is a circulation of strong, upper-level winds that normally surround the Northern Pole, moving in a counter-clockwise direction, i.e., a polar low-pressure system.
- These winds tend to keep the bitter cold air locked in Arctic regions of the Northern Hemisphere. On occasion, this vortex can become distorted and dip much farther South, allowing the cold air to spill Southwards.
- There are two types of Polar Vortex: Tropospheric and Stratospheric:
- Tropospheric polar vortex occurs at the lowest layer of the atmosphere — it extends from the surface up to about 10 km to 15 km — where most weather phenomena occur.
- Stratospheric polar vortex occurs at around 15 km to 50 km high. Unlike the tropospheric polar vortex, the stratospheric polar vortex disappears during the summer and is the strongest during the autumn.
Formation of Polar Vortex:
- Polar Vortex forms every winter because of the temperature difference between Equator and Poles.
- In the polar stratosphere, sunlight basically gets cut off during the late fall and early winter—and that makes it cold, while the equator remains quite warm.
- A jet forms to balance this temperature difference. This jet is what we call the Polar Vortex or Polar Night Jet.
Distortion of Polar Vortex:
- When the pressure difference gets lower, the jet streams get weakened and follow a much wavier path. This change in intensity allows the dense Arctic cold wind to spill down to the lower latitudes and lead to major cold air outbreak in the US, parts of Europe, and Asia.
- This oscillation is known as the Arctic Oscillation, and it can switch from a positive phase to negative phase a few times per year. This oscillation -- namely the Negative phase, where the polar winds are weaker, tends to lead to major cold air outbreaks in one or more regions of the planet.
Climate Change and Polar Vortex
- Scientists are still researching the precise impact of climate change on the polar vortex. Some researchers believe that as the poles are getting warmer at a faster rate than the rest of the Earth, the polar vortex and jet stream are becoming weaker. Warmer temperatures make it easier for the polar vortex and jet stream to get disrupted.
- This can be understood through following:
- Jet streams are propelled forward by temperature differences and the Earth's rotation. Warm air is less dense than cold air and rushes to fill in low-pressure regions. Wider temperature differences create faster moving winds.
- Earth is warming more quickly at the poles than at the mid-latitude regions, meaning the temperature contrast that drives jet streams has decreased.
- Complex sequence of events involving sea ice, which is rapidly diminishing in the Arctic. As ice retreats, summertime heat is absorbed by the dark ocean that lies underneath. This heat is released into the atmosphere during winter, spurring winds that can disrupt the polar vortex.