Abstract
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.
Highlights
Besides the usual diurnal variation, periodic trends are often observed in the ionospheric parameters
By using the data set of the Defense Meteorological Satellite Program (DMSP) that covers the 11-year solar cycle, Rich et al (2003) revealed that plasma density in the mid-latitude to low-latitude ionosphere at 840 km varies with a period of 27 days, synchronized with the same variation in the F10.7 index
After comparing the predicted results with the original data set, we found that the predictions can well reproduce the 27-day seasonal and semiannual variations
Summary
Besides the usual diurnal variation, periodic trends are often observed in the ionospheric parameters. Rich et al (2003) by parameterizing the latitude distribution and a Scintillation Meter (SM) This instrument package has of plasma density in the topside ionosphere over 9 years by been described by Rich (1994), Greenspan et al (1994), and using the empirical orthogonal function (EOF) method. Time series from any one set of the DMSP data are unaffected by local time variations (especially at low and equatorial latitudes) which can dramatically affect plasma characteristics. This constancy in LT allows other drivers of the plasma characteristics to be more noticeable. We adopt the adjusted flux to remove the 7% annual variation that arises from the changing Sun-Earth distance with respect to the observed value
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
