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STRATOSPHERIC WARMINGS
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Stratospheric Warmings (All ftp)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 Center (SEC). The alerts here were obtained from SEC. The annual files contain all the alerts received and issued by SEC. The issue date of the alert is on the first line in YYMMDD form, followed by the associated text. Stratwarm messages received by NOAA Space Environment Center 1987 - 2004NOTE -- Termination of the STRATALERT Reports
Termination of the STRATALERT Reports(from Karin Labitzke, Freie Universitat Berlin) In the 1960s the stratospheric midwinter warmings were regarded as an exciting and interesting research problem. The observations taken during a warming were scarce but in great demand, and a much desired aim was to launch meteorological rockets when a warming was developing above a station. For this purpose an advisory system was necessary, such as had been established in the international geophysical community for other phenomena, the so-called GEOALERT. Charged by WMO (World Meteorological Organisation) the Stratospheric Research Group of the Freie Universitat in Berlin got together with their colleagues of the American Weather Bureau and developed a warning system which was named STRATALERT. It was introduced in 1964 when the IQSY (International Year of the Quiet Sun) began. The Berlin group was at first responsible for the European space, later for the whole Northern Hemisphere, and issued a STRATALERT report every day during winter, and when needed also a GEOALERT. The alerts were disseminated through the German Weather Services international net and reached all interested parties everywhere. The STRATALERT reports were an essential source of information about what was going on in the stratosphere, information which at that time would not otherwise have been available to many scientists interested in current conditions. Because of this information it was possible to time experiments, for instance with meteorological rockets, to take place under desired conditions, and local observations could be fitted into and interpreted on the background of a wider field. This information system has served as a basis for decisions made in many large-scale field experiments. A review and classification of stratospheric warmings can be found in SPARC Newsletter No. 15, Labitzke and Naujokat, 2000. The last winter, 2003/2004, was the last STRATALERT winter. After 41 years we are sorry to announce that we cannot continue this timely warning system in its old format and we could not find a successor. But those interested in the daily development of the stratospheric circulation can find on the FUB web site analyses and different stratospheric parameters based on the ECMWF-data. The general evaluation is, however, left to the user. Additional data links are (amongst others) available: |
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