Variations of electron density and temperature in ionosphere based on the DEMETER ISL data
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Abstract
Observations of the Langmuir Probe Instrument (ISL, Instrument Sonde de Langmuir) onboard the DEMETER satellite during four years from 2006 to 2009 were used to analyze the tempo-spatial variations of electron density (<i<N</i<<sub<e</sub<) and temperature (<i<T</i<<sub<e</sub<) in the ionosphere. Twenty four research bins with each covering an area with 10° in longitude and 2° in latitude were selected to study the spatial distributions of <i<N</i<<sub<e</sub< and <i<T</i<<sub<e</sub<. The results indicate that both <i<N</i<<sub<e</sub< and <i<T</i<<sub<e</sub< have strong annual variations in the topside ionosphere at 660 km altitude. The semiannual anomaly and equinoctial asymmetry which are usually well known as the features of F-layer also exist in the topside ionosphere at low- and mid-latitudes. The yearly variation of <i<N</i<<sub<e</sub< is opposite to the peak electron density of the F2-layer (NmF2) at higher latitudes in daytime and both are similar in nighttime. Also the yearly variations of <i<T</i<<sub<e</sub< at low-latitude are contrary to that at 600 km in daytime and similar in nighttime. An interesting feature of nighttime <i<T</i<<sub<e</sub< at low-latitude is an obvious annual variation in the northern hemisphere and semiannual variation in the southern hemisphere. The yearly variations of <i<T</i<<sub<e</sub< in daytime have negative and positive correlation with <i<N</i<<sub<e</sub< at mid- and high-latitudes, respectively. Both <i<N</i<<sub<e</sub< and <i<T</i<<sub<e</sub< in the neighborhood bins at the same latitude have a high correlation. In ionospheric events analyzing, this information may help to understand the characteristics of the variation and to distinguish the reliable abnormality from the normal background map.
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