Diagnostic Requirements for the Superrotation on Venus

Abstract

For the solar heating and zonal wind profiles observed in the Venus atmosphere (below 80 km) we have calculated the eddy source pattern required to maintain the zonally averaged circulation. In the cloud-top region (45-75 km) the calculated residual meridional circulation corresponds to multiple direct and indirect cells in the vertical, whose depths are controlled by the scales of solar heating and eddy sources. For the amount of small-scale diffusion suggested by in situ measurements, the circulation is close to the nearly inviscid limit, and advections by the mean circulation must be balanced by eddy sources. In the presence of mean meridional transports, the observed zonal superrotation can be supported by alternating layers of eddy sources and sinks (i.e., Eliassen-Palm flux divergences or convergences), which may possibly be caused by thermal tides. Below the cloud decks, the effect of meridional motions is small, and eddy sources are required to balance diffusion (if diffusion is as large as measurements indicate). Near the lower model boundary, differential solar heating forces a shallow Hadley cell which controls surface winds and ensures that the net surface torque vanishes in a steady state.