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| Titel |
A new method for studying the thermospheric density variability derived from CHAMP/STAR accelerometer data for magnetically active conditions |
| VerfasserIn |
M. Menvielle, C. Lathuillere, S. Bruinsma, R. Viereck |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 25, no. 9 ; Nr. 25, no. 9 (2007-10-02), S.1949-1958 |
| Datensatznummer |
250015909
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| Publikation (Nr.) |
 copernicus.org/angeo-25-1949-2007.pdf |
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| Zusammenfassung |
Thermospheric densities deduced from STAR accelerometer measurements onboard
the CHAMP satellite are used to characterize the thermosphere and its
response to space weather events. The STAR thermospheric density estimates
are analysed using a Singular Value Decomposition (SVD) approach allowing
one to decouple large scale spatial and temporal variations from fast and
local transients. Because SVD achieves such decomposition by using the
reproducibility of orbital variations, it provides more meaningful results
than any method based upon data smoothing or filtering.
SVD analysis enables us to propose a new thermosphere proxy, based on the
projection coefficient of the CHAMP densities on the first singular vector.
The large scale spatial variations in the density, mostly related to
altitude/latitude variations are captured by the first singular vector; time
variations are captured by the associated projection coefficient.
The study presented here is focused on time dependent global scale
variations in the thermospheric density between 50 N and 50 S geographic
latitudes. We show that the time variations in the projection coefficient do
in fact represent those in the global density that are associated with
magnetic activity as well as with solar EUV radiations. We also show that
the NRLMSISE-00 empirical model better accounts for the density forcing by
Solar radiations when tuned using Mg II indices. Using the so modified model
with an additional geomagnetic parameterization corresponding to quiet
geomagnetic situation enables one to define time reference values which are
then used to evaluate the impact of geomagnetic activity. The ratio of CHAMP
density projection coefficient to the quiet model projection coefficient is
a global quantity, independent of altitude and latitude, which quantifies
the thermospheric density response to auroral energy deposition. It will
serve as a proxy of the response of thermospheric density to geomagnetic
activity forcing. |
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