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

L Liu,M.-L Zhang,B Zhao,X Yue,W Wan,B Ning

doi:10.5194/angeo-25-1337-2007

Abstract

Abstract. In this paper, the ten-year (1996–2005) total ion density Ni 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 Ni 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 Ni becomes greater with increasing solar EUV. This is quite different from the dependence of Ni near the F-Region peak (NmF2), at which the rate of change of NmF2 decreases with increasing solar EUV. The rate of change of Ni at the DMSP altitude is greatest in the latitude range where Ni is greatest during high solar activity. We suggest that this greater rate of change (or amplification effect) of Ni 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 (hmF2) and the density NmF2 play a secondary role.

Highlights

It is well known that the temporal variations of the Earth’s ionosphere are linked to those of solar activity, because the main source of the ionospheric plasma is photoionization of neutrals by solar extreme ultraviolet (EUV) and X-ray radiations
In this paper the dependence of plasma densities in the topside ionosphere on solar activity level has been investigated by analyzing the Defense Meteorological Satellite Program (DMSP) total ion density, the Solar EUV Monitor (SEM)/Solar Heliospheric Observatory (SOHO) EUV, and solar proxy F107 from 1996 to 2005
The present investigation reveals that DMSP Ni at 848 km is rather sensitive to solar EUV flux, which has latitudinal and seasonal features

Summary

Introduction

It is well known that the temporal variations of the Earth’s ionosphere are linked to those of solar activity, because the main source of the ionospheric plasma is photoionization of neutrals by solar extreme ultraviolet (EUV) and X-ray radiations. Previous studies have shown that electron density in the ionosphere varies with solar activity in a rather complicated way Kane, 2003; Lei et al, 2005; Liu et al, 2006b; Sethi et al, 2002), while limited analyses have been applied to the topside ionosphere Evidence indicates that ionospheric variations have altitude dependencies (Rich et al, 2003; Su et al, 1999). Su et al (1999) found strong altitude dependencies in the solar activity variations of electron densities, which were observed with the Japanese incoherent scatter radar. Rich et al (2003) revealed that the 27-day effect is much more pronounced in the topside plasma density than that in the total electron content (TEC)

Results

Discussion

Conclusion