Time variations of O2(a1Δ) nightglow spots on the Venus nightside and dynamics of the upper mesosphere

Nadir observations have also been divided into time series, allowing generating animations to follow the intensity and the displacement of bright patches over time. Apparent wind velocities and characteristic decay/rise times and have been deduced from these time series. The speed of the displacements varies from ∼0 up to 213 m s−1, with a mean value of 54 m s−1. Owing to the high variability of the direction of the displacements both in the short and the long terms, no clear trend of a global motion at ∼96 km can be deduced from these observations. The mean decay time is ∼750 min while the mean rise time is ∼1550 min. The decay time can be explained as a combination of radiative decay and atomic oxygen transport.