Principal Modes of Thermospheric Density Variability: Empirical Orthogonal Function Analysis of CHAMP 2001-2007 Data

Details Principal Modes of Thermospheric Density Variability: Empirical Orthogonal Function Analysis of CHAMP 2001-2007 Data Principal Modes of Thermospheric Density Variability: Empirical Orthogonal Function Analysis of CHAMP 2001-2007 Data

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsa21b1544m&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SA21B-1544

Physics

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

Scientific paper

In this paper we characterize dominant modes of global density variability as empirical orthogonal functions (EOFs) using densities obtained from the accelerometer experiment on board the CHAMP satellite during 2001-2007. From a sequential non-linear regression analysis of sparse observations of the density along satellite trajectories, we obtain EOFs in latitude/local-time coordinates and its orbit-time dependent amplitude. The analysis unravels not only the importance of each mode to the overall density variability but also underlying drivers of the primary modes of the density variability. The primary mode of the variability takes form of the diurnal variation. It correlates highly with daily F10.7 index and moderately with geomagnetic indices (Kp and Dst). It underscores that solar EUV is far the strongest driver of the overall thermospheric density variability. The secondary mode has a latitudinally asymmetric structure, and represents the summer-to-winter annual density variation. In contrast to this annual variation of the secondary mode, the primary mode indicates semiannual variation with peaks at around equinoxes. The quaternary mode reflects effects of the high-latitude forcing.

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