Rotational/divergent flow and energy conversion of thermal tides in a Venus general circulation model

Abstract

Venusian thermal tides are discussed as a three-dimensional response to solar heating, which is strongly modified by both barotropic and baroclinic energy conversions in a fully developed super-rotation. Thermal tides such as gravity waves propagate upward and downward from the cloud top (∼65 km) at low latitudes, while tidal gyres such as Rossby waves appear at high latitudes according to the general circulation model (GCM) developed at Atmosphere and Ocean Research Institute (AORI), The University of Tokyo. Around the cloud-top heating maximum, strong poleward/equatorward tidal flows are formed by both divergent and rotational flows that are in phase, and equatorial super-rotation is accelerated by the equatorward and vertical momentum fluxes of the diurnal tides and the vertical flux of the semidiurnal tides. These thermal tides are a result of solar heating as well as energy conversions from the zonal-mean jet and its related temperature gradient. The gravity wave is thermally forced in the cloud-top heating maximum where diabatic heating produces eddy available potential energy. The Rossby waves are formed in mid- and high-latitudinal regions where diurnal barotropic energy conversion occurs around the zonal-mean jet core and semidiurnal baroclinic energy conversion occurs below the cloud layer far from the solar heating region.