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

Abstract

Abstract. In this paper, the ten-year (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(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.

Solar activity effects of the ionosphere: A brief review

“…The former shows an amplification feature [75]. Moreover, the seasonal variation of the plasma density at 800 km is dominated by the annual component.…”

“…Zhao et al [74] examined the seasonal and solar activity variations of the plasma compositions at 800 km and developed an empirical model for the DMSP plasma density using empirical orthogonal functions. Liu et al [75,76] further studied the topside plasma density of the DMSP observations and found interesting climatological features: in the topside ionosphere there is strong annual asymmetry in the yearly variations, and an amplification effect in the solar activity dependence of the plasma density was reported for the first time.…”

“…Liu et al [48,75] and Chen et al [67] proposed an explanation for the three kinds of solar activity dependencies of the TEC and electron densities at different altitudes. The complicated solar activity effects of the ionosphere can be understood if the variations of the key parameters (N m F2, h m F2 and scale height) are known.…”

Further study on the solar activity variation of daytime NmF2

“…Many works showed the nonlinearity appearing in the variations of the ionospheric electron density with solar indices [e.g., Balan et al, 1994aBalan et al, , 1996Belehaki et al, 2001;Chen et al, 2008Chen et al, , 2009Gupta and Singh, 2000;Kouris et al, 1998;Liu et al, 2003Liu et al, , 2004aLiu et al, , 2006Liu et al, , 2007Liu and Chen, 2009;Ma et al, 2009;Park et al, 2008;Richards, 2001;Sethi et al, 2002;Su et al, 1999]. An important nonlinear character is the saturation effect that was found in the variations of N m F 2 (maximum electron density of the F 2 layer) or TEC (total electron content) with solar indices; namely, N m F 2 (TEC) increases linearly with solar indices with a higher rate at lower solar activity levels, whereas the increase rate decreases, or even N m F 2 (TEC) does not obviously increase, at higher solar activity levels.…”

NmF2 and hmF2 measurements at 95° E and 127° E around the EIA northern crest during 2010–2014

“…The diurnal variation of solar activity effect on daily NmF2 and hmF2 measured over Dibrugarh and Okinawa from August 2010 till July 2014 and its seasonal variation is studied using solar activity proxies. The widely reported non-linear variation of NmF2 with solar activity (Bhuyan et al 1983;Balan et al 1993Balan et al , 1994Liu et al 2006Liu et al , 2007a is shown to exhibit a diurnal variation. The correlation of Dibrugarh NmF2 and hmF2 with solar activity as well as EEJ is compared with that of Okinawa.…”