| 研究実績の概要 |
a. Intra-Annual Albedo Variability
I studied how changing albedo patterns on Venus are related to the dynamics and chemistry of the atmosphere. I used Venus dayside images from Akatsuki's UV Imager. Each dataset was subjected to a principal component analysis to find the most important modes of variability. The spatial patterns and the timescales of some of these modes correspond to known physical processes in the atmosphere of Venus such as the 4-day Kelvin wave, 5-day Rossby waves, and the overturning circulation, while some others defy a simple explanation. I have thus been able to breakdown the albedo variability into known and unknown dynamics and estimated what fraction of variability can be attributed to each dynamical mode.
b. Decadal Trace Gas Variability
Sulfur dioxide abundances at the cloud-top of Venus have been observed to oscillate on interannual to decadal timescales but the causes are unknown. I am proposing a new conceptual model to explain this occurrence. The water abundance at the base of the clouds, has a strong influence on the cloud-base heating and cloud level convection. The cloud level convective mixing in turn determines the gradient of water abundance in the atmosphere, and thereby the cloud-base water abundance. Thus, the convection and water abundance form a coupled system which oscillates on interannual to decadal timescales, which can explain the timescale of variability in the transport of sulfur dioxide to the cloud tops. This model will represent a fundamental advance of our understanding of long-term atmospheric variability on Venus.
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