Global structure of thermal tides in the upper cloud layer of Venus revealed by LIR onboard Akatsuki

TL;DR

This study uses data from Akatsuki's LIR instrument to map the global thermal tide structure in Venus's upper clouds, identifying wave modes and their vertical profiles over multiple years.

Contribution

It provides the first comprehensive analysis of Venusian thermal tides using long-term infrared observations, revealing wave modes and vertical structures in the planet's atmosphere.

Findings

Diurnal tide mainly consists of Rossby and gravity waves

Semidiurnal tide mainly consists of gravity waves

Vertical structures roughly match wave mode predictions

Abstract

Longwave Infrared Camera (LIR) onboard Akatsuki first revealed the global structure of the thermal tides in the upper cloud layer of Venus. The data were acquired over three Venusian years, and the analysis was done over the areas from the equator to the mid-latitudes in both hemispheres and over the whole local time. Thermal tides at two vertical levels were analyzed by comparing data at two different emission angles. Dynamical wave modes consisting of tides were identified; the diurnal tide consisted mainly of Rossby-wave and gravity-wave modes, while the semidiurnal tide predominantly consisted of a gravity-wave mode. The revealed vertical structures were roughly consistent with the above wave modes, but some discrepancy remained if the waves were supposed to be monochromatic. In turn, the heating profile that excites the tidal waves can be constrained to match this discrepancy, which would greatly advance the understanding of the Venusian atmosphere.