Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jgra..11412314c&link_type=abstract
Journal of Geophysical Research, Volume 114, Issue A12, CiteID A12314
Other
7
Ionosphere: Midlatitude Ionosphere, Ionosphere: Equatorial Ionosphere, Ionosphere: Ionosphere/Atmosphere Interactions (0335), Ionosphere: Electric Fields (2712)
Scientific paper
From global measurements of ionospheric electron density profiles made by the FORMOSAT-3/COSMIC satellites, the morphology of E region electron density is investigated. Seasonal, latitudinal, and diurnal variations in daytime E region electron density are well described by the Chapman theory, and the E layer peak electron density NmE and its peak height hmE are governed by the solar zenith angle χ in accordance with relations NmE $\propto$(cosχ)p and hmE $\propto$ln(secχ), respectively. However, it is revealed that there are three geomagnetic latitude regions where striking enhancements of the E region electron density occur. One of them is located at the geomagnetic equator with relatively narrow latitude extent of about 6°-10°, and the other two with much wider latitude extent of about 10°-20° appear on both sides of the geomagnetic equator in latitude regions ±20°-30°, respectively. The locations of these E region density enhancements are asymmetrical about the geomagnetic equator in solstice seasons, and they have a salient tendency to shift toward (away from) the summer (winter) hemisphere. The off-equator E region electron density enhancements are closely connected with the bottomside of the F region equatorial anomaly crests, where the component of the electron density parallel to the magnetic field line is maximum. It appears that the off-equator E region electron density enhancements are very likely the footprints of the F region equatorial anomaly crests. The morphologies of the exponent n and coefficient K in the power law relation between χ and foE (E region critical frequency) are also examined. There is a tendency for the n and K values to be larger in local winter than in local summer seasons in the latitudinal regions the same as the off-equator electron density enhancements. In addition, it is found that a minor peak in the K values is nearly continuously present in all seasons over the geomagnetic equator. A comparison shows significant discrepancies in the E region electron density morphologies between COSMIC measurement and IRI model prediction. Furthermore, compelling evidence is provided to show the presences of longitudinal wave number 3 and 4 structures of the electron density in the height region 100-200 km, which are in coincident with the longitudinal structures of equatorial electrojet. It is believed that these longitudinal 3- and 4-peak structures are very likely associated with nonmigrating diurnal tides propagating eastward in ionospheric E region.
Chu Y.-H. Y.-H.
Su Ching-Lun
Wu Kong-Hong
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