The Jetstream and weather in the Arctic

 More Extreme Weather

Sam Carana

Arctic News,

3 February, 2021

As temperatures rise, the weather is getting more extreme. Around the globe, extreme weather events are striking with ever greater frequency and intensity. 

In 2020, in the U.S. alone, a record number of 22 climate and weather disasters took place that each caused damage of more than 1 billion dollar, while jointly causing the deaths of 262 people. 

Rising temperatures cause stronger storms, droughts, heatwaves and forest fires. Rising temperatures are also behind the cold weather that is currently hitting large parts of North America. Two mechanisms that, by distorting the Jet Stream, are contributing to more extreme weather are described below. 

Distortion of the Jet Streams - two mechanisms

The Jet Streams used to circumnavigate the globe in narrow bands. World climate zones used to be kept well apart by stable Jet Streams. 

On the Northern Hemisphere, the coldest point used to be the North Pole, so wind used to flow from the tropics to the North Pole, while the wind was moved to the side due to Earth's turning. 

Polar Jet Stream and Subtropical Jet Stream - NOAA image

This resulted in two Jet Streams forming, circum-navigating the globe in relatively narrow and straight bands, i.e. the Polar Jet Stream at 60°N and the Subtropical Jet Stream at about 30°N. 

 

Polar Jet Stream (blue) and Subtropical
Jet Stream (red) - NOAA image

First mechanism distorting the Jet Stream

The first mechanism distorting the Jet Stream is that, as the Arctic gets hit much harder by temperature rises, the difference in temperature decreases between the North Pole and the Equator.

This slows down the speed at which wind travels from the Tropics to the North Pole, in turn making the Jet Stream more wavy, just like a slow-moving river over flat land will take a winding route and meander.

This slowing of the Jet Stream is compensated to some extent by the fact that overall, the wind has increased in strength due to the global rise in temperature.

Second mechanism distorting the Jet Stream

Due to the rapid temperature rise of the Arctic Ocean, the North Pole is increasingly not the 

coldest place on the Northern Hemisphere. 

Instead, the air over Greenland, North Canada and Siberia is increasingly more cold than before, and can be much colder than the North Pole, as illustrated by the ClimateReanalyzer image on the right.

This creates temperature and pressure conditions over the East Pacific and over North America that make the Jet Stream branch out.

On the next image on the right, the Jet Stream can be seen running over the West Pacific at speeds as high as 387 km/h or 241 mph (green circle) and moving within a relatively narrow band.

The Jet Stream is then confronted with much different conditions over North America that make the Jet Stream branch out widely (white arrows), with one branch moving north and going circular over the Arctic Ocean, while at the other end a branch can be seen dipping below the Equator.

As a result of these two distortion mechanisms, cold air that used to stay contained over the North Pole, can descend more easily over Siberia and North America, causing more extreme weather, while also taking away opportunities for the sea ice to build up to the strength and depth than it used to have. 

The combination image below shows forecasts for February 6, 2021.

On the above combination image, the left panel shows that, not far apart from each other and at the same time, temperature anomalies over North America are forecast to approach the top end and the bottom end of the scale. The right panel shows that temperatures over North America and Siberia are forecast to be much lower than over the Arctic Ocean.

As the temperature difference between land and ocean gets stronger on the Northern Hemisphere in Winter, the transfer of water vapor and heat to the atmosphere increases (#25 on the feedbacks page, image right). Storms and clouds forming over the North Atlantic trap heat and move much heat toward the North Pole.

 
The combination image below shows in the left panel how a branch of the Jet Stream is forecast to be moving over the North Pole at speeds as high as 107 km/h or 67 mph on February 16, 2021.

Hours later that day, as the globe in the right panel shows, the surface temperature on the North Pole is forecast to be -18°C, i.e. warmer than the white-blue color (about -20°C) that covers most of North America.

As the globe in the left panel of the combination image below shows, temperature anomalies in Texas were approaching the bottom end of the scale on February 15, 2021, i.e. 32°C below 1979-2000, while the globe in the right panel shows that on February 16, 2021, temperature anomalies in between Greenland and the North Pole were forecast to approach the top end of the scale, i.e. 32°C above 1979-2000.



Above freezing at North Pole?

As the combination image below shows, the temperature at the North Pole is forecast to be 0°C or 32°F, panel right, on February 22, 2021, 18:00 UTC, while temperature anomalies at the North Pole are forecast to be at the top end of the scale, i.e. 32°C above 1979-2000. 

The light-blue color over the North Atlantic on the globe on the left is a cold anomaly resulting from cold air moving from North America over the Atlantic Ocean.

Conclusion

The situation is dire and calls for immediate, comprehensive and effective action as described in the Climate Plan.


Links

• 2020: Hottest Year On Record
https://arctic-news.blogspot.com/2021/01/2020-hottest-year-on-record.html

• NOAA - U.S. Billion-Dollar Weather and Climate Disasters: Overview
https://www.ncdc.noaa.gov/billions/overview

• Climate Reanalyzer
https://climatereanalyzer.org

Nullschool

https://earth.nullschool.net

• Feedbacks in the Arctic

https://arctic-news.blogspot.com/p/feedbacks.html

• Polar jet stream appears hugely deformed
https://arctic-news.blogspot.com/2012/12/polar-jet-stream-appears-hugely-deformed.html

• Climate Plan
https://arctic-news.blogspot.com/p/climateplan.html