A simulation study for the couplings between DE3 tide and longitudinal WN4 structure in the thermosphere and ionosphere

Abstract

In this study we numerically investigated the couplings between the non-migrating atmospheric tide in the mesosphere and low thermosphere (MLT) and the response wave in the upper thermosphere and ionosphere. The diurnal eastward wavenumber-3 (DE3) tidal mode was considered as the lower boundary perturbation in the simulation based on the Global Coupled Ionosphere–Thermosphere-Electrodynamics Model, developed by the Institute of Geology and Geophysics, Chinese Academy of Sciences (GCITEM-IGGCAS). We then obtained the longitudinal wavenumber-4 (WN4) structure in the upper thermosphere and ionosphere by running GCITEM-IGGCAS with some devised control conditions. The simulated results are treated as the contribution of the two mechanisms: the upward tidal wave propagation and the electro-dynamical coupling. As examples, we analyzed in detail the WN4 structure of both neutral mass density and electron number density in the upper thermosphere and ionospheric F2-region (∼400km altitude) at an afternoon time (15:00). The model simulation shows that both the upward wave propagation and the electro-dynamical coupling can produce the thermospheric and ionospheric WN4 structure. The thermospheric WN4 waves are directly produced by the wave propagation mechanism; they are also indirectly created by the mechanism of electro-dynamical coupling combined with ion-neutral collision. Correspondingly, the ionospheric WN4 waves are directly produced by the electro-dynamical coupling; and they can also be indirectly excited by the mechanisms of upward wave propagation combined with neutral-ion collision. It is found that the solar activity seriously affects the DE3-WN4 coupling process. As the solar activity increases, rapid decrease occurs for both the thermospheric and ionospheric WN4 intensity related to the wave propagation mechanism, while only little change is found for that corresponding to the electro-dynamical coupling. Further quantitative analysis lead to the conclusion that the electro-dynamical coupling mechanism is responsible for almost all the ionospheric and thermospheric WN4 waves, and the upward tidal wave propagation mechanism is important only for the thermospheric WN4 waves under low and moderate solar activity conditions.