The solar cycle variation of plasma parameters in equatorial and mid latitudinal areas during 2005–2010

The asymmetrical features in electron density during extreme solar minimum

“…Therefore, the comparison between June Ne and December Ne in 2005 contains the effect of satellite altitude adjustment, and the results in 2005 only can be taken as a reference. Another problem is about the ISL data quality, which was often argued on the photoelectron contamination and data processing techniques (Lebreton et al, 2006;Zhang et al, 2013). According to the study of Kakinami et al (2013), DEMETER Ne was about 70% lower than those of IRI in daytime and its solar irradiance dependency is consistent with the reference data in nighttime.…”

“…Therefore the special feature of enhanced solstitial asymmetry during 2008-2009 needs further study. Compared with the solar cycle variations in Ne at different latitudes (Zhang et al, 2013(Zhang et al, ), during 2008(Zhang et al, -2009, the amplitude of annual variation differed intensively at Southern and Northern Hemisphere at middle and high latitudes. This phenomenon demonstrates that under this extreme low solar activity, the solstitial asymmetry at both hemispheres becomes enhanced, rather than weakened.…”

“…In previous research (Zhang et al, 2013), the solar cycle variation features in Ne have been studied in local daytime and nighttime respectively from DEMETER satellite during 2005-2010, and the results showed globe Ne decreased with the reducing solar flux since 2005 to 2009. While there exhibited phase shift at middle latitudes and even reversed annual variations at high latitudes over Southern and Northern Hemisphere, and the annual variation amplitudes were asymmetrical over two hemispheres.…”

Seismo‐ionospheric coupling appearing as equatorial electron density enhancements observed via DEMETER electron density measurements

“…The electron density is higher in the geomagnetic equator region than in the midlatitude region, and the longitudinal structure appears along the geomagnetic equator region. The detailed description on the behavior of the electron density measured by ISL according to the season and solar cycle can be found in the studies of Zhang et al [] and Zhang []. It is clear that only one peak region exists near the equator, in general, so the EIA intensity index derived using two density peaks in the Northern and Southern Hemispheres is not applicable to the altitude and local time of DEMETER during normal conditions.…”

New understanding achieved from 2 years of Chinese ionospheric investigations

“…Based on the DEMETER satellite observations, Zhang et al [33,34] studied the solar cycle variations in the electron density in the topside ionosphere (660-710 km) during low solar activity years in 2005-2010, in which the electron density Ne reduced by more than 50 % in 3 years, from 2006 to 2008, at the equatorial and middle latitudes. Zhang [35] revealed the overestimation of Ne by the IRI model.…”