Dayside cloud top structure of Venus retrieved from Akatsuki IR2 observations

T. M. Sato, T. Satoh, H. Sagawa, N. Manago, Y. J. Lee, S. Murakami, K. Ogohara, G. L. Hashimoto, Y. Kasaba, A. Yamazaki, M. Yamada, S. Watanabe, T. Imamura, M. Nakamura

Research output: Contribution to journalArticle

Abstract

We describe the dayside cloud top structure of Venus as retrieved from 93 images acquired at a wide variety of solar phase angles (0–120°) using the 2.02-μm channel of the 2-μm camera (IR2) onboard the Venus orbiter, Akatsuki, from April 4 to May 25, 2016. Since the 2.02-μm channel is located in a CO2 absorption band, the sunlight reflected from Venus allowed us to determine the cloud top altitude corresponding to unit aerosol optical depth at 2.02 μm. First, the observed solar phase angle dependence and the center-to-limb variation of the reflected sunlight in the region equatorward of 30° were used to construct a spatially averaged cloud top structure characterized by cloud top altitude zc, Mode 2 modal radius rg, 2, and cloud scale height H, which were 70.4 km, 1.06 μm, and 5.3 km, respectively. Second, cloud top altitudes at individual locations were retrieved on a pixel-by-pixel basis with an assumption that rg, 2 and H were uniform for the entire planet. The latitudinal structure of the cloud top altitude was symmetric with respect to the equator. The average cloud top altitude was 70.5 km in the equatorial region and showed a gradual decrease of ~2 km by the 45° latitude. It rapidly dropped at latitudes of 50–60° and reached 61 km in latitudes of 70–75°. The average cloud top altitude in the region equatorward of 30° showed negligible local time dependence, with changes up to 1 km at most. Local variations in cloud top altitude, including stationary gravity wave features, occurred within several hundreds of meters. Although long zonal or tilted streaky features poleward of ~45° were clearly identifiable, features in the low and middle latitudes were usually subtle. These did not necessarily appear as local variations at the cloud top level, where mottled and patchy UV patterns were observed, suggestive of convection and turbulence at the cloud top level.

Original languageEnglish
Article number113682
JournalIcarus
Volume345
DOIs
Publication statusPublished - Jul 15 2020

Keywords

  • Atmospheres, dynamics
  • Atmospheres, structure
  • Infrared observations
  • Radiative transfer
  • Venus, atmosphere

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Sato, T. M., Satoh, T., Sagawa, H., Manago, N., Lee, Y. J., Murakami, S., Ogohara, K., Hashimoto, G. L., Kasaba, Y., Yamazaki, A., Yamada, M., Watanabe, S., Imamura, T., & Nakamura, M. (2020). Dayside cloud top structure of Venus retrieved from Akatsuki IR2 observations. Icarus, 345, [113682]. https://doi.org/10.1016/j.icarus.2020.113682