Long‐Term Variability of the Thermal Structure in Venus's Low‐Latitude Atmosphere Investigated Using Venus Express and Akatsuki Radio Occultations

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Abstract
Despite decades of exploration, Venus's climate system governing the atmosphere beneath the cloud top (70 km altitude) remains poorly understood due to the persistent thick cloud cover. Here, we present the first detailed characterization of temporal variability in the thermal structure of Venus's low‐latitude atmosphere from the sub‐cloud region to the mesosphere (45–80 km), using 257 vertical temperature profiles obtained from Venus Express and Akatsuki radio occultation measurements in 2006–2024. Remarkable decadal temperature variations of 10 K were observed below 55 km, far exceeding those of 2 K seen at comparable pressure levels in Earth's tropics. In terms of the relative variation, the change on Venus over a decade is 1.4%, which is larger than the corresponding value of 0.6% in Earth's tropical region, indicating that the variability on Venus is more pronounced. The variation in temperature partly correlates with that in the ultraviolet albedo of Venus's cloud, suggesting potential links to the solar heating, cloud physics, and photochemistry. Furthermore, the variations in temperature and geopotential height are nearly in phase with those in zonal wind speed at the cloud top, indicating a strong coupling between the atmospheric dynamics in the upper cloud and the underlying thermal structure. While the mechanisms behind the observed variations remain elusive, our findings reveal that Venus has a more pronounced intrinsic climate variability than Earth. To elucidate Venus's climate system, we need long‐term and continuous observations by successive future missions.
Funding Information
  • Japan Society for the Promotion of Science (20K01450)
  • Japan Society for the Promotion of Science (25K01071)
  • Japan Society for the Promotion of Science (23H00150)
  • Japan Society for the Promotion of Science (24H00021)
  • Institute for Basic Science (IBS‐R035‐C1)

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