Context images for Venus Express radio occultation measurements: A search for a correlation between temperature structure and UV contrasts in the clouds of Venus

TL;DR

This study explores the relationship between UV brightness and temperature in Venus's clouds using Venus Express data, finding a potential anti-correlation at certain altitudes that supports radiative forcing predictions.

Contribution

It provides the first observational evidence linking UV-brightness to atmospheric temperature variations in Venus's cloud layer.

Findings

Possible anti-correlation between UV-brightness and temperature at 65-70 km altitude.

No correlation found between UV-brightness and static stability.

Observations support radiative forcing predictions about UV-absorber effects.

Abstract

Venus exhibits strong and changing contrasts at ultraviolet wavelengths apparently related to the clouds and the dynamics in the cloud layer, but to date their origin continues to be unknown. We investigate the nature of the UV contrasts exhibited by Venus clouds by examining possible correlations between the thermal structure inferred from radio occultation data and UV brightness from imagery data, both observed with Venus Express. We analyse Venus Express images obtained from 11 hours before to a few hours after the time of radio occultation measurements of the same area. We account for the advection of clouds by zonal and meridional winds and apply a phase angle correction to compensate for the changing viewing geometry. We find a possible anti-correlation between UV-brightness and atmospheric temperature in the 65-70 km altitude range for low latitudes. Heating in this altitude and latitude region due to an increase in the UV-absorber has been predicted by radiative forcing studies. The predictions roughly match our observed temperature amplitude between UV-dark and UV-bright regions. We find no evidence for any correlation between UV-brightness and static stability in the atmosphere in the 50-80 km altitude region. This could be the first observational evidence for a direct link between UV-brightness and atmospheric temperature in the 65-70km altitude region in the clouds of Venus.