The dependence of plasma density in the topside ionosphere on the solar activity level

【摘要】：正In this paper,the ten-year(1996-2005) total ion density N_i measurements from the Defense Meteorological Satellite Program(DMSP) spacecraft in the morning and evening(09:30 and 21:30 LT) sectors have been analyzed to explore the dependence of plasma densities in the topside ionosphere at middle and low latitudes on the solar activity level.Results indicate that there is a strong solar activity dependence of DMSP N_i at 848 km altitude,which has latitudinal and seasonal features.The plasma density in the topside ionosphere has an approximately linear dependence on daily F107 and a strongly nonlinear dependence on SEM/SOHO EUV,such that the change rate of N_i becomes greater with increasing solar EUV.This is quite different from the dependence of N_i near the F-Region peak(NmF2),at which the rate of change of NmF2 decreases with increasing solar EUV.The rate of change of N_i at the DMSP altitude is greatest in the latitude range where N_i is greatest during high solar activity.We suggest that this greater rate of change(or amplification effect) of N_i at the DMSP altitude is mainly a consequence of the solar activity variations of the topside scale height.The changes in the height of the F-Region peak (hmF_2) and the density NmF2 play a secondary role.