|Posted by Conspiracy Cafe on November 25, 2019 at 8:45 AM|
GFS temperature and height analysis of the stratospheric polar vortex. Image by: SWE
By Andrej Flis | Global weather | 05 November 2019
We often hear the term “polar vortex” as we head closer to winter. But this season, we will talk about it earlier than expected. We recommend you read our tutorial article, on what is the polar vortex and why is it so significant for our weather?
WHAT IS THE POLAR VORTEX, AND WHY IS IT IMPORTANT?
Currently, the stratospheric polar vortex is strengthening, almost reaching near 40-year record high strength for this time of year at the 10mb (~30 km) level in the next few days.
November and early December, are periods when the polar vortex undergoes maximum intensification. Days are getting shorter, the pole is cooling and the pressure is dropping. If the polar vortex intensifies during this period to high power, it is very likely that it will help to create or boost a positive NAO pattern, meaning a milder winter. That is exactly what the model forecasts are currently indicating for winter. A strong stratospheric polar vortex also increases the polar circulation in the lower levels, which can lock the cold air in the polar circle, resulting in a boring winter.
But weather is always dynamic. It goes through changes on a daily and hourly basis all around the world, interconnected on multiple levels. Sometimes we have a more dynamic and active weather pattern across the Northern Hemisphere. More dynamic global circulation patterns (higher number of strong high&low pressure systems), can exhibit a lot of energy in various forms. If the dynamics are in the right place, they can radiate/deflect some of that energy upwards into the higher levels of the atmosphere. When/if that energy reaches higher atmospheric levels (and strong enough), it can cause warming and pressure on the stratospheric polar vortex, in the form of waves. They help slowing it down, weakening it and in some cases when the disruption/warming is strong enough, we can completely destroy/displace the polar vortex, and warm up the polar stratosphere. That is called a Sudden Stratospheric Warming event (SSW). The criteria for designating such an event, is the wind reversal in the polar stratosphere, which means that the polar vortex has lost its strength, and the polar high (“anti-vortex” is dominating. So not every warming is an SSW event, because we also need to remove the polar vortex from its frozen throne. With some time delay, as the polar vortex weakens, the pressure also usually rises on the surface over the Arctic, which means the cold polar air can move more easily down south towards Europe or USA.
GFS model forecast of the polar vortex and the minor warming event at 10mb level. Image by: SWE