The role of global thermospheric zonal winds on the variability of equatorial ionospheric irregularities

Abstract

We analyze the role of thermospheric winds on the variability of ionospheric plasma density irregularities for solar maximum periods using ionospheric plasma density profiles from the three Swarm satellites and zonal wind data from the Horizontal Wind Model 14 (HWM14). The results show that the plasma density irregularities are strongest during post-midnight hours compared to pre-midnight hours in the African – American longitude sector and this is associated with an enhancement in eastward zonal wind after midnight. In addition, the occurrence of plasma irregularities are observed to show a westward shift. The zonal wind reversal from westward to eastward during post-sunset hours is found to be very important for the generation and variability of plasma irregularities. In the African – American longitudinal sector, where plasma irregularities are the most intense, the eastward wind is strongest in December solstice than for the other seasons. Moreover, plasma irregularity during the December solstice is comparable to the Rayleigh-Taylor Instability mechanism (RTI) favored equinox seasons. But, plasma irregularities are weakest in the June solstice where the zonal eastward wind over geomagnetic equatorial region is weakest as compared to the other seasons. Zonal wind reversal from westward to eastward around post-sunset hours occurred early for seasons with stronger ionospheric irregularity activity whereas the reversal is delayed for the season with weakest ionospheric irregularity activity in the African – American sector. Our results are confirmations of the theoretical prediction on the role of eastward zonal wind in plasma instability growth rate by Kudeki et al. (2007).