Effect of atmospheric tides on the morphology of the quiet time, postsunset equatorial ionospheric anomaly

Abstract

[1] Recent global-scale observations of the postsunset equatorial O + airglow bands in the F region ionosphere using the IMAGE FUV and TIMED GUVI have revealed a longitudinal wave number four pattern in the magnetic latitude and concentration of the F region peak ion density when measured at a fixed local time. In a new comparison of two data sets with observations made by the OGO 4 satellite, this pattern is seen to be persistent over many days around equinox during magnetically quiet conditions close to solar maximum but can be dominated by other processes such as cross-equator winds during other periods. It is found that the longitudinal variability is created by a processes occurring in the dayside ionosphere. A longitudinal modulation of the dayside equatorial fountain is the most likely driving mechanism. Through comparison with GWSM-02 model, it is shown that the predicted modulation of the dayside thermospheric winds and temperatures at E region altitudes created by non-migrating diurnal tides can explain the modulation in the dayside equatorial fountain. This result highlights the importance of understanding the temporal variability of tropospheric weather systems on our understanding and possible predictability of the development of the F region ionosphere. It may also provide a possible further means of testing our understanding of atmospheric tides on a global scale.

Vertical and longitudinal electron density structures of equatorial E- and F-regions

“…The present results suggest that in nighttime F-region above 250 km the longitudinal wavenumber-4 patterns prevail in equinox and the wavenumber-3 structures dominate the longitudinal electron density variations in boreal solstice. The appearance of the nighttime F-region wavenumber-4 structures in equinox presented here is generally consistent with that obtained by previous investigations (England et al, 2006a, b;Immel et al, 2006;Lin et al, 2007;Ren et al, 2008;Scherliess et al, 2008). However, appreciable differences between present and other experimental results in the daynight/seasonal variations in the longitudinal structures are also found.…”

“…Recently 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.…”

“…When viewed at one fixed local time from satellite, this feature exhibits as a four-peak structure, which was noted as wavenumber-4 component in the overlying F-region by the above workers. However, the aforementioned studies (for example, Immel et al, 2006;England et al, 2006a, b;and Lin et al, 2007) pertained to either vernal or autumnal equinox months in one year, during these periods the DE3 is characterized with significantly enhanced amplitude (Forbes et al, 2008). Hence, it was generally conceived that the eastward propagating non-migrating diurnal tide could play a 82 P. S. Brahmanandam et al: Electron density structures of equatorial E-and F-regions role in the four-wave structures in electron densities via the E-region dynamo mechanism.…”

Observations of thermosphere and ionosphere changes due to the dissipative 6.5-day wave in the lower thermosphere

“…The planetary-scale wave signals with the same period and zonal wavenumber as those in the lower atmosphere are often observed in the IT system, which are thought to be the result of either the direct vertical propagation of the planetary-scale waves into the upper thermosphere or via the wave modulation on the neutral wind and dynamo electric fields in the ionosphere E region (Laštovička and Sauli, 1999;Pancheva et al, 2002;England et al, 2006).…”

Vertical connection from the tropospheric activities to the ionospheric longitudinal structure simulated by a new Earth's whole atmosphere-ionosphere coupled model

“…A prominent four-peak longitudinal structure of the equatorial ionization anomaly (EIA) has been discovered by global satellite observations [e.g., Sagawa et al, 2005;England et al, 2006a;Immel et al, 2006;Lin et al, 2007]. In addition, according to modeling works, the longitudinal dependence of tropospheric convection has been shown to be an important source for the excitation of solar nonmigrating (non-Sun-synchronous) tides that propagate upward to the thermosphere, including the diurnal eastward-propagating tide with zonal wave number 3 (DE3), which has four peaks in the local-time fixed frame [e.g., Forbes, 2002, 2003;Miyoshi, 2006].…”