Surface Thermal Tides and Radiative Adjustment in Venus's Deep Atmosphere

Abstract

Thermal tides on Venus have been extensively studied near the cloud tops, where their three-dimensional structure and contribution to the atmospheric momentum budget have been characterized from temperature and wind fields. However, their downward propagation and influence within the deep atmosphere remain uncertain, and their behavior in the deep atmosphere, particularly near the surface, remains poorly constrained. Using the LMD Venus Planetary Climate Model, we investigate the near-surface thermal tides and their governing timescales. The simulations show that these tides are generated by heat transfer from the surface to the planetary boundary layer and produce a diurnal pressure response with a phase lag of about $30°$ corresponding to a radiative adjustment timescale of about 10 Earth days. In addition, a 35-day oscillation appears within the stably stratified 10–20 km layer, consistent with a planetary-scale internal gravity wave. These results suggest that coherent oscillations beyond the diurnal tide can develop in the deep atmosphere, with the surface pressure variability dominated by a superposition of three modes: the diurnal and semidiurnal tides and the 35-day oscillation. Together, these components account for about 70$\%$ of the total surface pressure variance, with potential implications for gravity measurements by forthcoming missions such as VERITAS and EnVision.