Cloud Patterns, Waves and Convection in the Venus Atmosphere

Abstract

We provide morphological and kinematic desc6ptions of the UV markings seen in the Mariner 10 imagery of Venus: the dark horizontal Y, bow-like waves, circumequatorial belts, subsolar disturbance, spiral streaks and bands, polar ring and polar region. The dark horizontal Y is interpreted as a westward-propagating planetary wave with zonal wavenumber 1 and period ?4.2 days; it may he the superposition of a Rossby-Haurwitz wave dominant at mid-latitudes and a Kelvin wave dominant in equatorial regions. Bow-like waves may be true bow waves formed by the interaction of the rapid zonal flow with internal gravity waves of lower horizontal phase speeds generated by the subsolar disturbance. Circumequatorial belts are interpreted as internal gravity waves with horizontal wavelength ?500 km and zonal extent ?5000 km. They are essentially parallel to latitude circles and propagate southward at about 20 m s?1. Cellular features in the subsolar region undoubtedly imply convection there. The identificatiod of both bright- and dark-rimmed cells, with horizontal scales of about 200 and 500 km, respectively, implies a 15 km deep convective layer, based on an analogy with mesoscale convection in the terrestrial maritime atmosphere. The dark areas of the cells may be regions of downwelling. Variability in the location and intensity of the polar ring may be caused by a zonally propagating disturbance, perhaps related to the planetary wave producing the Y in lower latitudes. Circulation patterns and other atmospheric processes in the polar region may be rather different from elsewhere on the planet; only in the polar region are UV markings also visible in the orange.