Monday, 27 January 2014 | Weather
We hoped back at the beginning of February that the sudden stratospheric warming event (SSW) that commenced early in January, and has been responsible for rendering this winter one of the 15 coldest on record, would begin to relent as March approached. Eight weeks on, we’re still waiting. Six weeks is a typical duration of temperate-zone cooling after an SSW event, but this one looks to effect us for quite a while longer.
This cross-sectional view of the arctic over the past three months shows the tropospheric (lower-level) warming (orange “flame” signature around the 5th of January) that appears to be the causal trigger of the stratospheric warming, which can be seen near the top of the graphic in the change in color from dark blue to white in the time-frame from late December to about the 10th of January, then from white to orange in early February. (Pressure / height is represented on the Y-axis of the graphic, with the stratosphere near the top.) There are several competing views of the SSW mechanism; one of the more commonly advanced is that SSW is causally initiated from intrusions of warm air at lower levels into the arctic which more or less flex the tropopause quickly upward into much faster winds aloft, with ensuing frictional deceleration and production of heat. Other more “top-down” mechanisms involving planetary waves are also well-subscribed.
This link contains a pretty good layman’s explanation of the phenomenon, and contains links to other work which goes into more detail.
This link gives an alternative view which is quite interesting.
This graphic, sent to me by a regular listener, has a wonderful depiction of winds on a full-disc image of the earth. The word “Earth” in the lower left is the key which allows manipulation of the image; click it, and you can turn the earth in any direction, and view winds at different levels of the atmosphere. It can be quite useful at getting the quick, larger scale view of why the weather in any given location is as it is.