2018 Fiscal Year Annual Research Report
Oscillations of the Venus Climate System
| Project/Area Number |
18F18316
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| Research Institution | The University of Tokyo |
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Principal Investigator |
今村 剛 東京大学, 大学院新領域創成科学研究科, 教授 (40311170)
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| Co-Investigator(Kenkyū-buntansha) |
KOPPARLA PUSHKAR 東京大学, 新領域創成科学研究科, 外国人特別研究員
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| Project Period (FY) |
2018-10-12 – 2020-03-31
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| Keywords | Venus / atmospheric oscillations / Akatsuki data analysis |
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| Outline of Annual Research Achievements |
We want to explore the fundamental question: What are the dominant modes of variability in the climate of Venus? We propose to answer this using the multiwavelength and high temporal and spatial resolution observations collected by JAXA's Venus orbiter Akatsuki. The first part of this study was recently completed by analyzing data from the Ultraviolet Imager (UVI) of Akatsuki for a period of 1.5 years. The study was able to identify several short-term oscillations that corresponded to well known atmospheric phenomena such as Kelvin and Rossby waves and the meridional overturning circulation. However, some other oscillations found in the study, such as the hemispheric asymmetry mode, are yet to be explained fully. Several follow-up studies are now in progress. For example, a decadal timescale study to identify long-term oscillations using combined data from two missions: Venus Express and Akatsuki is underway. Also, some extensions to these studies using the Longwave Infrared camera on Akatsuki are being explored.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
A preliminary study explored 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 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.
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| Strategy for Future Research Activity |
The techniques developed in the preliminary study described above are being refined and extended to other datasets. The first application is to study the long-term oscillations in Venus albedo at 365-nm using data over 10 years by combining the observations of the European mission, Venus Express with the Japanese mission, Akatsuki. However, the varying spatial coverages between the two datasets will require careful consideration. Furthermore, another application will be to study data from the longwave infrared camera (LIR) of Akatsuki using principal component analysis. The idea will be to understand the nature of atmospheric oscillations using outgoing radiative fluxes. But before this can be done, the effects of limb darkening will need to be corrected in the LIR images, which is a problem being tackled by other researchers. Some simple box modeling of climate oscillations is also being attempted.
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