Spatial and Temporal Variability of the 365-nm Albedo of Venus Observed by the Camera on Board Venus Express

Abstract

We mapped the distribution of the 365-nm albedo of the Venus atmosphere over the years 2006-2014, using images acquired by the Venus Monitoring Camera (VMC) on board Venus Express. We selected all images with a global view of Venus to investigate how the albedo depends on longitude. Bertaux et al. (2016, https://doi.org/10.1002/2015JE004958) reported a peak in albedo around 100° longitude and speculated on an association with the Aphrodite Terra mountains. We show that this peak is most likely an artifact, resulting from long-term albedo variations coupled with considerable temporal gaps in data sampling over longitude. We also used a subset of images to investigate how the albedo depends on local time, selecting only south pole viewing images of the dayside (local times 7-17 hr). Akatsuki observed mountain-induced waves in the late afternoon at 283 nm and 10 micrometer (Fukuhara et al., 2017, https://doi.org/10.1038/ngeo2873). We expect that the presence of such waves may introduce 365-nm albedo variations with a periodicity of one solar day (116.75 Earth days). We searched for such a periodicity peak at 15:30-16:00 local time and low latitudes but did not find it. In conclusion, we find that temporal albedo variations, both short and long term, dominate any systematic variations with longitude and local time. The nature of VMC dayside observations limits regular data sampling along longitudes, so longitudinal variations, if they exist, are difficult to extract. We conclude that any influence by the Venus surface on 365-nm albedo is negligible within this data set.