9:00 AM - 9:15 AM
[PCG21-07] Ground-based observations of the formation and periodical rotation of the global scale UV-feature on Venus cloud top
Keywords:Venus, Y-feature, Ground-based telescope
We newly conducted ground-based Venus imaging observations at 365 nm, which consists of six periods covering over half or one month from mid-August 2013 to the end of June 2014 and one continuous periods from mid-April to end of July 2015. Distributions of the relative brightness were obtained from the equatorial to mid-latitudinal regions in both hemispheres, and from the cyclical variations of these distributions we deduced the rotation periods of the UV features of the cloud tops albedo. The relative brightness exhibited periods of 5.2 and 3.5 days above 90% of significance. The relative intensities of these two significant components also seemed subject to temporal variations.
In 2013 and 2014, although the 3.5-day component persisted throughout the observation periods, its dominance over the longer period varied in a cyclic fashion. The prevailing period seems to change from 5.2 to 3.5 days in about nine months, what is clearly not-coincident with the Venusian year (224 days). The amplitude of relative brightness variation is weak during the transition periods of dominant-wave changing. It was indicated that the stability of the planetary scale UV-feature were observed only in the presence of single longer or shorter periodic waves. In 2015, 3.5-days and 5.2-days wave periods could be observed. We success to obtain the change of the first significant mode from 3.5-day wave to 5.2-day wave continuously. As the former observation results, Venus experienced the absence of dominant-wave mode during the transition periods, and the time scale of the transition is estimated about one month in that period.