Wave structure in Venusian clouds

This night-side image of the southern hemisphere of Venus was taken by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board Venus Express on 29 July 2006, from a distance of about 64 000 kilometres over the surface (around the orbit apocentre), at a wavelength of 1.7 micrometres. The South pole is visible on the top left of the image.

This image provides a remarkable example of a wave structure, running from the bottom to the top-right, each ‘wave’ extending about 150 kilometres. This peculiar cloud feature is often seen at a latitude of about 55º South.

The picture also shows a part of the polar vortex (top left). Regions of thinner clouds are also present in this image. They are visible as bright spots (top left corner), as they allow more thermal radiation to escape towards deep space from the hotter regions below.

The region between the black stripe around the pole and the wave structure contains the so called ‘cold collar’, a region in which the temperature of the clouds is lower than that of the surrounding area.