WN4 effect on longitudinal distribution of different ion species in the topside ionosphere at low latitudes by means of DEMETER, DMSP-F13 and DMSP-F15 data
Résumé
Plasma probe data from DMSP-F13, DMSP-F15 and DEMETER satellites were used to examine longitudinal structures in the topside equatorial ionosphere during fall equinox conditions of 2004 year. Since the launch of DEME-TER satellite on 29 June 2004, all these satellites operate close together in the topside ionosphere. Here, data taken from Special Sensor-Ion, Electron and Scintillations (SSIES) instruments on board DMSP-F13, F15 and Instrument Anal-yser de Plasma (IAP) on DEMETER, are used. Longitudinal variations in the major ions at two altitudes (∼730 km for DEMETER and ∼840 km for DMSP) are studied to further describe the recently observed " wavenumber-four " (WN4) structures in the equatorial topside ionosphere. Different ion species H + , He + and O + have a rather complex longitudinal behavior. It is shown that WN4 is almost a regular feature in O + the density distribution over all local times covered by these satellites. In the evening local time sector, H + ions follow the O + behavior within WN4 structures up to the pre-midnight hours. Near sunrise H + and later in the daytime, He + longitudinal variations are out of phase with respect to O + ions and effectively reduce the effect of WN4 on total ion density distribution at altitudes 730–840 km. It is shown that both a WN4 E × B drift driver and local F-region winds must be considered to explain the observed ion composition variations.
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