Seasonal nonlinear controls on semidiurnal tides at the southern high latitudes of Mars

Abstract

Thermal tides are a fundamental component of Martian atmospheric variability and play a key role in the vertical coupling between the lower and middle atmosphere. Semidiurnal tides are of particular interest at high latitudes, where background wind conditions favor their vertical propagation and polar-orbiting spacecraft provide enhanced local-time sampling. These combined physical and observational advantages make the southern high latitudes a unique region for constraining the seasonal evolution, vertical structure, and dynamical interactions of semidiurnal tides. Here we exploit multi-local-time measurements from the Mars Climate Sounder (MCS) to provide observational constraints on the seasonal evolution and vertical structure of semidiurnal tides in the southern high latitudes. The aim of this study is to investigate the seasonal evolution and vertical structure of thermal semidiurnal tides at southern high latitudes (60--65̧ircS), with a focus on the underlying dynamical processes shaping their variability. We analyzed multi-local-time temperature and aerosol extinction measurements from MCS to derive the amplitudes and phases of thermal semidiurnal tides, stationary planetary waves, and dust-related diurnal variability at southern high latitudes (60--65̧ircS). During the southern winter, the coexistence and phase relationships among the migrating semidiurnal tide with zonal wavenumber 2 (SW2), the stationary planetary wave with zonal wavenumber 1 (SPW1), and the non-migrating semidiurnal tides with zonal wavenumbers 1 and 3 (SW1 and SW3) are consistent with nonlinear interaction between SW2 and SPW1, particularly for SW3. During regional dust storms, the enhanced diurnal variability of dust may contribute to an effective semidiurnal thermal response through its interaction with the diurnal cycle of solar radiation. Southern high-latitude semidiurnal tides on Mars exhibit seasonally distinct nonlinear controls, reflecting the interplay between nonlinear wave--wave interaction during the southern winter and dust--radiation interaction during the dusty season.