Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 23, 3615-3631, 2005
http://www.ann-geophys.net/23/3615/2005/
doi:10.5194/angeo-23-3615-2005
© Author(s) 2005. This work is distributed
under the Creative Commons Attribution 3.0 License.
 
23 Dec 2005
Statistical characteristics of the total ion density in the topside ionosphere during the period 1996-2004 using empirical orthogonal function (EOF) analysis
B. Zhao1,2,3, W. Wan1, L. Liu1, X. Yue1,2,3, and S. Venkatraman4 1Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
2Wuhan Institute of Physics and Mathematics, CAS, Wuhan 430071, China
3Graduate School of Chinese Academy of Sciences, Beijing, China
4William B. Hanson Center for Space Sciences, University of Texas at Dallas, Richardson, USA
Abstract. We have applied the empirical orthogonal function (EOF) analysis to examine the climatology of the total ion density Ni at 840 km during the period 1996-2004, obtained from the Defense Meteorological Satellite Program (DMSP) spacecraft. The data set for each of the local time (09:30 LT and 21:30 LT) is decomposed into a time mean plus the sum of EOF bases Ei of space, multiplied by time-varying EOF coefficients Ai. Physical explanations are made on the first three EOFs, which together can capture more than 95% of the total variance of the original data set. Results show that the dominant mode that controls the Ni variability is the solar EUV flux, which is consistent with the results of Rich et al. (2003). The second EOF, associated with the solar declination, presents an annual (summer to winter) asymmetry that is caused by the transequatorial winds. The semiannual variation that appears in the third EOF for the evening sector is interpreted as both the effects of the equatorial electric fields and the wind patterns. Both the annual and semiannual variations are modulated by the solar flux, which has a close relationship with the O+ composition. The quick convergence of the EOF expansion makes it very convenient to construct an empirical model for the original data set. The modeled results show that the accuracy of the prediction depends mainly on the first principal component which has a close relationship with the solar EUV flux.

Citation: Zhao, B., Wan, W., Liu, L., Yue, X., and Venkatraman, S.: Statistical characteristics of the total ion density in the topside ionosphere during the period 1996-2004 using empirical orthogonal function (EOF) analysis, Ann. Geophys., 23, 3615-3631, doi:10.5194/angeo-23-3615-2005, 2005.
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