THE STRATOSPHERIC POLAR VORTEX

December 23, 2023

NOAA Climate.gov launched a new blog to focus on the stratospheric polar vortex, a weather phenomenon that has gained widespread attention in recent years.
Meteorologists closely monitor the polar vortex because it plays a pivotal role in shaping weather patterns across the Northern Hemisphere. Changes in the strength and position of the vortex can lead to significant weather anomalies, including extreme cold outbreaks, winter storms, and shifts in the jet stream
The Arctic polar vortex is a band of strong westerly winds that forms in the stratosphere between about 10 and 30 miles above the North Pole every winter. The winds enclose a large pool of extremely cold air. It forms in late summer, when when the amount of sunlight reaching the pole begins to decrease. Because the North Pole, which is completely dark for several months in the winter, receives less of the Sun’s rays than the tropics, the polar stratosphere air becomes colder than the tropical stratosphere air. To eliminate that temperature difference, the warm tropical air flows north toward the cold polar air. Earth’s west-to-east rotation nudges the wind to the right in the Northern Hemisphere, and the winds become primarily westerly (air moves from west to east). These winds are associated with the strength of the polar vortex, and they are strong enough to act as a barrier between the midlatitude and polar air, reinforcing the cold stratospheric air within the vortex.
The polar vortex doesn’t always influence winter weather in the mid-latitudes. When it does, however, the effects can be extreme.
A weakened polar vortex is probably the cause of the bitterly cold air that recently surged into China and set new seasonal records for low temperatures. There is a possible weakening in the barrier of swift air currents that typically serves as a buffer against Arctic blasts. Accompanied by winds prompting the highest gale warnings from Chinese authorities, a potent cold wave made its way into China through Xinjiang on December 13. Swiftly advancing eastward, it enveloped the Chinese capital, Beijing, in icy conditions.
Channel News Asia reported that, “Temperatures will drop to below minus 40 degrees Celsius in parts of the northeastern province of Heilongjiang and in the region of Xinjiang in the northwest, along with Inner Mongolia and the provinces of Gansu and Qinghai, according to forecasts from China’s National Meteorological Centre.”
(Source: NOAA/NOAA Polar Vortex Blog/CNA/Reuters – Image: Winter in Hegang City, northeast China’s Heilongjiang Province/Xinhua)