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The Rigakubu News
The Rigakubu News, Nov. 2025.
Research Student Communicates to Faculty >
Climate Change on Venus Approached by the Himawari Satellite
Gaku Nishiyama(Visiting Co-Researcher/ Department of Earth and Planetary Science),Takeshi Imamura(Graduate School of Frontier Sciences / Professor (also serving as Professor in the Department of Earth and Planetary Sciences)
Venus, often described as Earth’s “twin planet” because of its similar size and mass, nevertheless possesses an atmospheric environment strikingly different from our own. Its dense carbon dioxide atmosphere produces an extreme greenhouse effect, its surface is shrouded entirely by clouds of sulfuric acid, and its atmosphere exhibits rapid super-rotation—features that make Venus an essential target for understanding planetary atmospheres in a universal context. Observations by Venus orbiters such as Akatsuki have advanced our knowledge of its atmospheric structure. However, many mysteries remain, particularly regarding the stability of Venus’s climate—whether it has remained constant over time or undergoes variations comparable to those on Earth. In this study, we used images of Venus that occasionally appear in data from the geostationary meteorological satellite Himawari to clarify long-term variations in the planet’s atmospheric temperature structure, thereby gaining new insights into Venusian climate change.
Recent observations by the Venus orbiter Akatsuki have steadily advanced our understanding of the Venusian atmosphere. One well-known feature is the “super-rotation,” a global atmospheric circulation in which the winds blow westward at speeds about sixty times faster than the planet’s rotation. It has become increasingly clear that this super-rotation is maintained in part by atmospheric waves called thermal tides, which are excited when solar radiation is absorbed by Venus’s cloud layers and causes them to heat up.
However, even Akatsuki has not resolved all mysteries. One major unsolved problem is the mechanism driving the long-term variability of Venus’s atmosphere. Observations show that the wind speeds of the super-rotation can fluctuate by as much as 30% over a span of only a few years, but the cause of this variation remains elusive. To address this, long-term monitoring of atmospheric temperature—which should be strongly linked to wind speed—as well as long-term observations of thermal tides, a key factor in super-rotation, is essential. Yet due to limitations such as spacecraft lifetimes, continuous temperature measurements extending beyond a decade have not been feasible.
To complement spacecraft observations, our study turned to long-term Venus monitoring using data from Japan’s geostationary meteorological satellite Himawari. The satellite’s Earth images, familiar from weather forecasts on television, actually capture the surrounding space at the time of imaging. This space occasionally includes stars and Solar System objects—and Venus is no exception. Although the Venus image is extremely small, the observations are free from the influence of Earth’s atmosphere. Moreover, Himawari observes in nine infrared wavelengths, each with different atmospheric transmission properties, making it possible to extract temperature information from multiple altitudes within Venus’s atmosphere.
By analyzing these infrared images of Venus taken by Himawari, we successfully detected nearly ten years of temperature variations across multiple atmospheric layers. For the first time, we identified long-term changes in atmospheric temperature and in planetary-scale wave structures such as thermal tides, as well as their altitude dependence. This represents a significant step toward understanding climate variability on Venus.
Research that utilizes meteorological satellites in this way will become increasingly important. Unfortunately, Akatsuki’s operation came to an end in September 2025. Although next-generation Venus missions are being planned, there will be no orbiting spacecraft around Venus until they are launched. During this interim period, Himawari will continue to serve as a space telescope capable of monitoring the Venusian atmosphere and collecting valuable observational data. The new Venus revealed through these observations will be something to watch closely in the years ahead.
The results of this study were published as G. Nishiyama et al., Earth, Planets and Space 77, 91 (2025).
Venus captured in images taken by the Himawari weather satellite