Thermosphere Density Response to High Speed Solar Wind Streams

Details Thermosphere Density Response to High Speed Solar Wind Streams Thermosphere Density Response to High Speed Solar Wind Streams

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsa24a..03l&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SA24A-03

Physics

0355 Thermosphere: Composition And Chemistry, 0358 Thermosphere: Energy Deposition (3369), 7511 Coronal Holes, 7969 Satellite Drag (1241)

Scientific paper

Thermosphere densities at 400 km altitude from accelerometer measurements on the CHAMP satellite are used to investigate oscillations at periods of less than 13 days during the declining phase of solar cycle 23 (2002-2007). Density spectra reveal the presence of prominent periods around 5 days, 7 days and 9 days. Specifically, a pronounced 9-day periodicity is obtained in the years from 2004 to 2007, and a strong periodicity of about 7 days occurred in 2006 and 2007. The 5-day periodic oscillations were also seen during 2004-2007, but their powers are smaller than those of 7-day or 9-day oscillations. These periodic oscillations in neutral density tend to occur during the latter part of the declining solar cycle when periodic fast streams in the solar wind modulate the level of geomagnetic activity in the geospace environment. In fact, the periodic oscillations seen in neutral densities are simultaneously present in the solar wind and geomagnetic activity index Kp, whereas not in the SOHO solar EUV irradiance data. The periods of 5, 7 and 9 days apparently reflect subharmonics of the 27-day rotation, and may be related to the longitudinal distribution of coronal holes. The periodic oscillations in neutral density are felt globally, and are proportional to the periodic Kp perturbations at the same frequency. The neutral density data thus suggest that these oscillations are related to the solar wind, and not to the influences of planetary waves at similar periods originating in the lower atmosphere.

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