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Föreläsare: Prof. Sheila Kirkwood (IRF-K)
Datum och tid: 2004-12-06 00:00
Plats:
Polar Mesosphere Winter Echoes - new results from statistics and from radar interferometry.
Polar mesosphere Winter Echoes (PMWE) is the name we have given to thin layers of enhanced radar echoes observed by the ESRAD 52 MHz and EISCAT 224 MHz radars from mesospheric heights during winter. Earlier observations of radar echoes from the winter mesosphere were made by the Poker Flat radar and the Alomar Sousy 50 MHz radars during the 1980s. At that time, it was assumed that the echoes were due to layers of turbulence in the neutral atmosphere. Our studies have shown that the radar echo strengths are too high for this explanation to be reasonable. We have further found that they appear at heights where no turbulence is expected (according to co-located meteorological rockets) and where lidars see anomalies in the light-scatter profile. A new statistical analysis of PMWE since 1997 will be reported which shows a substantial increase in PMWE ocurrence. Further, exceptionally strong echoes from 29 October 2003 have been analysed using interferometric methods. Those results show will also be presented.
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