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Solar cycle variation of the electron density in the topside ionosphere at local nighttime observed by DEMETER during 2006–2008
Author(s) -
Zhang Xuemin,
Qian Jiadong,
Shen Xuhui
Publication year - 2014
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2013ja019463
Subject(s) - ionosphere , solstice , atmospheric sciences , latitude , solar cycle , electron density , northern hemisphere , equator , middle latitudes , southern hemisphere , solar minimum , local time , atmosphere (unit) , physics , environmental science , geology , electron , climatology , meteorology , geophysics , astronomy , plasma , solar wind , statistics , mathematics , quantum mechanics
The solar cycle variations of electron density (Ne) in the topside ionosphere are presented by observations around local time 22:30 from Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite during 2006–2008 in the low solar activity, in which the revisited orbits are selected to construct Ne time sequences at different points. The results show that electron density (Ne) reduced 50–100% since 2006 to 2008 at equatorial area and middle latitudes, with much bigger maximal Ne in 2006 but even no yearly peak in 2007 and 2008 around 30° latitude. The seasonal asymmetry is revealed by the yearly maxima of Ne in December over Southern Hemisphere always being larger than those in June over Northern Hemisphere. Furthermore, the equinoctial asymmetry is found around the magnetic equator and high northern latitudes under the low solar activity, and the latter one has not been revealed in other research. Ne from IRI2012 is close to the actual observation by DEMETER in 2008, even better than those in 2006 and 2007, indicating the great improvement of this empirical ionospheric model in this extremely low solar minimum. After comparison with the fitted results by indices of F 10.7 and EUV combined with the first five periods in Ne, EUV is a little better to describe the variations in Ne during this solar minimum. By discussing the relationship among nighttime Ne and molecules in upper atmosphere, the [O/N 2 ] density ratio is the key factor at high latitude, while [O] density plays a certain role to electron density around the equator.