Long-term changes of mesospheric summer echoes at polar and middle latitudes

Details Long-term changes of mesospheric summer echoes at polar and middle latitudes Long-term changes of mesospheric summer echoes at polar and middle latitudes

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006jastp..68.1940b&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 68, Issue 17, p. 1940-1951.

Physics

17

Scientific paper

Strong mesospheric VHF radar echoes can be observed during summer months mainly at polar latitudes (polar mesosphere summer echoes, PMSE) but with a reduced echo power also at middle latitudes (mesosphere summer echoes, MSE). This phenomenon of unexpected strong radar echoes is closely connected with the existence of small ice particles in the upper mesosphere and mesopause region. Therefore, these echoes contain information about the mesospheric temperature and water vapour content. But the strength of (P)MSE also depends on the level of ionisation due to incident solar wave radiation and precipitating high energetic particle fluxes. Using observations with VHF radars at Andenes (69.3°N, 16.0°E) since 1994 and at Kühlungsborn (54.6°N, 11.8°E) since 1998, the dependence of the strength of the (P)MSE on the solar and geomagnetic activity has been analysed and, in addition, possible long-term variations were derived. The special behaviour of the year 2002 is discussed in connection with an interhemispheric coupling due to enhanced planetary wave activity at the southern hemisphere winter season. There are some hints of small trends with increasing radar echo power and duration of the (P)MSE season in qualitative agreement with some changes of the observed occurrences rate of noctilucent clouds (NLC) and of the brightness of polar mesospheric clouds (PMC). However, the significance levels of the derived trends are low, and in most cases the trends are not significantly different from zero.

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