Abstract
Abstract Dynamical, electro-dynamical and electrical coupling processes originating from upward propagation of atmospheric waves, and magnetosphere-ionosphere interaction are responsible for the large degree of variabilities observed in the low latitude ionosphere. One of the most outstanding aspects of its phenomenology is related to the sunset electrodynamical processes responsible for the evening enhancements in zonal and vertical electric fields and the associated spread of F/plasma bubble irregularity development. Recent observational results have provided evidence of significant contribution to their quiet time variability arising from thermospheric wind patterns, upward propagating planetary waves and possibly sporadic E layers. This paper provides an overview and some new results on planetary wave coupling with the equatorial F region, the E layer conductivity as key connecting mechanism, a possibly interactive role by sporadic E layers, and the resulting day-to-day variability in the evening prereversal electric field enhancements with consequences on spread F development.
Highlights
Coupling processes involving different external forcing mechanisms are responsible for the major phenomenology and the day-to-day variabilities of the equatorial atmosphere ionosphere system
The influence of the planetary waves (PWs) on the sunset electrodynamics can result in significant modifications in the intensity of the evening prereversal electric field enhancement and the post sunset F layer heights and, play an important role in the widely observed day-to-day variability in the equatorial spread F/plasma bubble irregularity generation, which is primarily driven by the EPE
The upward propagation of these waves to ionospheric height, causing corresponding oscillations in the post-sunset F region densities and heights that are controlled by the EPE, was verified. These results demonstrate the existence of a strong vertical coupling through upward propagating planetary waves leading to day-to-day oscillations in mesospheric winds, EPE and post-sunset F region parameters
Summary
Coupling processes involving different external forcing mechanisms are responsible for the major phenomenology and the day-to-day variabilities of the equatorial atmosphere ionosphere system. The influence of the PWs on the sunset electrodynamics can result in significant modifications in the intensity of the evening prereversal electric field enhancement and the post sunset F layer heights and, play an important role in the widely observed day-to-day variability in the equatorial spread F/plasma bubble irregularity generation, which is primarily driven by the EPE. The degree of scatter in the SF intensity for a given Vzp amplitude indicates additional factors shown in Fig. 1 that control the SF intensity, including (1) the amplitude of the seed perturbation (such as gravity waves) needed for the R-T instability mechanism to operate and (2) field line integrated conductivity depending upon thermospheric meridional/trans-equatorial winds (Maruyama, 1988; Abdu, 1997; Mendillo et al, 2001) of which some recent results have been presented by Abdu et al (2006c, 2007). The statistical association between the Vzp over Cachimbo and the ESF intensity over the same site as well as over two low latitude sites CG and CP are presented in Fig. 8 for the period October to December 2002 (see Abdu et al, 2007).
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