We explore the dominant modes of variability in the observed albedo at the
cloud tops of Venus using the Akatsuki UVI 283-nm and 365-nm observations,
which are sensitive to SO2 and unknown UV absorber distributions respectively,
over the period Dec 2016 to May 2018. The observations consist of images of the
dayside of Venus, most often observed at intervals of 2 hours, but interspersed
with longer gaps. The orbit of the spacecraft does not allow for continuous
observation of the full dayside, and the unobserved regions cause significant
gaps in the datasets. Each dataset is subdivided into three subsets for three
observing periods, the unobserved data are interpolated and each subset is then
subjected to a principal component analysis (PCA) to find six oscillating
patterns in the albedo. Principal components in all three periods show similar
morphologies at 283-nm but are much more variable at 365-nm. Some spatial
patterns and the time scales of these modes correspond to well known physical
processes in the atmosphere of Venus such as the ~4 day Kelvin wave, 5 day
Rossby waves and the overturning circulation, while others defy a simple
explanation. We also a find a hemispheric mode that is not well understood and
discuss its implications.Comment: 9 pages, 6 figures, accepted in A&
