Abstract
Abstract. From global soundings of ionospheric electron density made with FORMOSAT 3/COSMIC satellites for September 2006–August 2009, day-night variations in vertical and longitudinal structures of the electron densities in equatorial E- and F-regions for different seasons are investigated for the first time. The results reveal that the wavenumber-3 and wavenumber-4 patterns dominated the nighttime (22:00–04:00 LT) F-region longitudinal structures in solstice and in equinox seasons, respectively. In daytime (08:00–18:00 LT) F-region, the wavenumber-4 patterns governed the longitudinal structures in the September equinox and December solstice, and wavenumber-3 in March equinox and June solstice respectively. A comparison of the daytime and nighttime longitudinal electron density structures indicates that they are approximately 180° out of phase with each other. It is believed that this out of phase relation is very likely the result of the opposite phase relation between daytime and nighttime nonmigrating diurnal tidal winds that modulate background E-region dynamo electric field at different places, leading to the day-night change in the locations of the equatorial plasma fountains that are responsible for the formation of the F-region longitudinal structures. Further, a good consistency between the locations of the density structures in the same seasons of the different years for both daytime and nighttime epochs has been noticed indicating that the source mechanism for these structures could be the same.
Highlights
Reported longitudinal four-wave structures in the low latitude ionospheric density distributions as observed by a number of satellite measurements have been attributed to the eastward propagating non-migrating diurnal tides with wavenumber-3 (DE3) (Sagawa et al, 2005; Immel et al, 2006; England et al, 2006a, b; Lin et al, 2007), which are believed to be originated from the convective activities in the troposphere and propagating upward (Hagan and Forbes, 2002)
The global soundings of the radio-occultated electron density retrieved by the F3/C satellites allow for the first time a detailed analysis of the day-night and seasonal variations in the vertical and longitudinal electron density structures in equatorial E- and F-regions
On the whole, the wavenumber-3 and 4 patterns govern the longitudinal structures in F-region in the March equinox, and June solstice and in September equinox and December solstice, respectively
Summary
Reported longitudinal four-wave structures in the low latitude ionospheric density distributions as observed by a number of satellite measurements have been attributed to the eastward propagating non-migrating diurnal tides with wavenumber-3 (DE3) (Sagawa et al, 2005; Immel et al, 2006; England et al, 2006a, b; Lin et al, 2007), which are believed to be originated from the convective activities in the troposphere and propagating upward (Hagan and Forbes, 2002). Owing to the wavenumber-4 longitudinal structure of DE3, when viewed in the local-time fixed reference, the longitudinal four-wave structures will be produced in the overlying ionosphere by these DE3 tidal waves at their four peaks.
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