Stratospheric Warmings

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A stratwarm is a major disturbance of the winter, polar, middle atmosphere (heights from the troposphere to the D-region of the ionosphere). It lasts for several days at a time and is most recognized by a warming of the stratosphere by some 10's of degrees. This anomaly results from a breakdown of the polar vortex (i.e. a polar night time jet stream flowing around the polar cap) into two cells. Air which has been trapped in the middle of the vortex is now mixed by the new meridional flow and its constituents can become exposed to sunlight. In particular, the solar lyman-alpha radiation ionizes the nitric oxide, enhancing the electron density and producing strong HF absorption (for transpolar paths).

Four to five stratwarms occur per winter season with the last (and largest) occurring in March (for the northern hemisphere) as daylight returns to the pole.

There is no evidence stratwarms affect the lower atmosphere; in fact, the disturbance may itself be generated by tropospheric conditions.

The stratwarm alerts are issued by the Free University of Berlin and sent to the NOAA's Space Environment Services Center (SESC). The alerts on this disk were obtained from SESC.

The files are annual with all the alerts received and issued by SESC for the year. The date the alert was issued in on the first line of the alert followed by the associated text.