The solar cycle variations of plasma parameters and their correlations at topside ionosphere from DEMETER during 2005–2010

Abstract

Based on the IAP (Instrument d’Analyse du Plasma) observing data onboard DEMETER satellite, the solar cycle variations in ion density (Ni), ion composition [O+,H+,He+] and ion temperature (Ti) were analyzed respectively in local daytime 10:30 and nighttime 22:30 during 2005–2010 during the 23rd/24th solar cycles, which would greatly contribute to the research of the topside ionospheric physics during this extremely low solar minimum. Based on analyzing the solar cycle variations of these plasma parameters, it was found that longitude-averaged Ni, [O+] and daytime Ti presented positive correlation with solar flux, while [H+], nighttime Ti and [He+] varied negatively to reach their maxima at the solar minimum. Furthermore, [O+], as the main composition at the altitude of DEMETER of 660km, showed typical seasonal variation and close relationship with sub-solar dynamics. Daytime [He+] was the most complex component, showing negative variation with solar activity at low latitudes over Southern Hemisphere and positive correlation at middle latitudes over Northern Hemisphere. The correlation of Ni and Ti in local daytime was dependent on season over two hemispheres, and the results illustrated negative correlation at low latitudes, and positive correlation at middle latitudes especially over Southern Hemisphere in solstitial seasons. While [H+] presented anti-correlation, especially the peak values with Ti valleys at 0–20°N in each year, which all might be related to the thermal diffusion and relative drift among different ions. Furthermore, the asymmetrical features of Ni over two hemispheres in solar minimum were widely revealed at different longitude sectors, latitudes and local times, which might be explained by the concentration of neutral oxygen, neutral winds, and also the lower atmospheric dynamics.