![]() The stratospheric polar vortex is often bombarded with waves from the troposphere with little impact. However, note that this requirement means the waves can’t go into the stratosphere in summer, when the winds blow from east-to-west instead, or right after a major warming, when the winds reverse direction. In general these wind conditions are met in the Arctic winter months. The biggest atmospheric waves have a particular requirement: they can only travel vertically if the winds through which they are traveling are blowing from west-to-east and also not too fast. A dash of the perfect west-to-east wind speed in the stratosphere (not too fast, not too slow!).NOAA image, adapted from original by Amy Butler. But the pattern lacked the high pressure (red areas) across Greenland and the eastern Arctic. The configuration in late December had low pressure over the North Pacific (gray), which is part of the "wave-1" pattern that often precedes the polar vortex getting displaced off the pole. When planetary waves in the troposphere adopt either of the configurations shown in the middle and right-hand globes, their energy is amplified, enabling them to push upward and break into the stratosphere. The location of these patterns are in just the right place to amplify existing non-moving (or “stationary”) wave patterns that form in response to mountain ranges and land-sea temperature contrasts, especially the largest atmospheric waves, helping them to reach the stratosphere.Ītmospheric conditions in the troposphere in late December 2023 (left globe) did not match either of the two patterns (center and right) that usually precede major disruptions of the polar vortex. There are two types of persistent weather patterns that typically precede sudden warmings: either unusually low pressure over the Aleutian Islands and high pressure (or blocking) over the North Atlantic, or else simultaneous high-pressure/blocking over both the Aleutian and Ural regions. This is analogous to how ocean waves break on a beach, but in the atmosphere, the waves instead break in the stratosphere which can slow the polar vortex winds. If these waves sit in just the right place for long enough, they can grow and amplify enough in the vertical direction to reach the stratosphere, where the waves can break. In the troposphere, planetary-scale atmospheric waves arise from air blowing over mountain ranges, temperature differences between the land and the ocean, and even from far away tropical thunderstorms that drive persistent wave patterns called teleconnections. Yes, the atmosphere, like the ocean, has waves! And waves are key to how the stratosphere and troposphere communicate. A pulse of planetary-size atmospheric waves.Ingredients for a sudden stratospheric warming ![]() ![]() So what happened? Though we certainly don’t have a definitive answer yet, we can start to understand possible reasons by delving into how the stratosphere and the troposphere come together to bake up these sudden warming events, using a few key ingredients. NOAA image, adapted form original by Laura Ciasto. Individual forecasts for temperature (bottom graph, light red lines) average out to just below normal temperatures (thick pink line). For the GEFSv12 forecast issued on January 7, only a few model runs predict a reversal of the vortex winds (top, thin magenta lines), and the average of all the runs (thick magenta line) predicts wind speed and direction will be near normal. ![]() Observed and forecasted (NOAA GEFSv12) wind speed (top) and temperature (bottom) in the polar vortex compared to the natural range of variability (faint shading).
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