Study on the Coupling between the Ionosphere and Thermosphere at Different Heights on Mars

Solar-driven thermal tides are an important factor driving spatiotemporal variations in the Martian upper atmosphere and ionosphere. Based on radio occultation data from the Mars Global Surveyor, this study systematically investigates the longitudinal variations of the peak electron density, peak height, and neutral scale height for the main ionospheric peak (M2 layer) and the secondary peak (M1 layer). The results reveal that the peak density of the M2 layer is negatively correlated with the neutral scale height, whereas that of the M1 layer exhibits a positive correlation. Moreover, the peak height of the M2 layer exhibits a distinct phase offset relative to the neutral scale height, while the M1 layer displays an in-phase relationship. These differences suggest that the vertical propagation of nonmigrating tides modifies their phase, leading to distinct coupling between the ionosphere and thermosphere at different heights. Fourier decomposition identifies a dominant wave-3 component, whose variations exhibit clear a seasonal dependence, with the M1 layer showing larger amplitudes than the M2 layer. The observed differences between the M1 and M2 layers likely arise from the vertical propagation and dissipation of nonmigrating tides and their interaction with the background atmosphere. These findings provide new insights into the ionosphere–thermosphere coupling processes on Mars and offer theoretical support for improving future models of Martian atmospheric and ionospheric evolution.