Can the meteorological satellites Himawari-8/9 be utilized as space telescopes?: Successful observation of long-term temperature variations in Venus's Atmosphere
Jul. 2, 2025 | GATEWAY to Academic Articles
NISHIYAMA Gaku / German Aerospace Center (DLR) and
Department of Earth and Planetary Science, Graduate School of Science,
The University of Tokyo
If you live in Japan, you should have seen images taken by the meteorological satellites Himawari-8 or -9 at least once on a weather forecast on TV or the Internet. Himawari-8 and -9 are Japanese meteorological satellites launched in 2014 and 2016, respectively. After the start of operation, these satellites provide essential images of the Earth from space to support daily weather forecasting, capturing the Earth as frequently as every 10 minutes at multiple wavelengths. Images taken by these satellites also include space adjacent to the Earth, where other celestial bodies, such as the Moon and planets, are captured occasionally. In this study, we utilized such images to explore planetary science, specifically for Venus, and succeeded for the first time in observing long-term temperature variations simultaneously at multiple altitudes in Venus’s atmosphere.
Venus is known for its extremely thick atmosphere and a unique phenomenon called super-rotation, where its atmosphere rotates about 60 times faster than the planet itself. While long-term variations in wind speeds have been observed, the temperature structure of atmospheric waves, which are believed to be closely linked to the mechanism driving super-rotation, has remained unknown. Utilizing infrared observations at multiple bands, this study revealed how temperatures at different altitudes in Venus change over time, shedding light on the vertical structure and temporal variability of these atmospheric waves. Based on the observed variation in this study, future detailed comparison with atmospheric circulation models of Venus would uncover factors driving Venus’s mysterious long-term variations. The observations can also help calibrate instruments onboard planetary exploration missions, expanding the role of meteorological satellites beyond the Earth observation and contributing to future planetary science and space explorations.
Research Summary
One of the most distinctive features of Venus is its super-rotation, a phenomenon where the planet’s thick atmosphere rotates about 60 times faster than the planet itself. This super-rotation has been observed to show long-term variations in wind speed on several-years timescale. Atmospheric waves, such as thermal tides*1 caused by solar heating and planetary-scale*2 waves like Rossby waves*3, are thought to play a crucial role in sustaining this super-rotation. However, whether these wave structures also have long-term variations or not remains an open question. A key to revealing physical mechanisms behind long-term variations and related atmospheric dynamics is long-term temperature monitoring of Venus’s atmosphere, which has not been achieved by any single planetary mission until the present. With no ongoing mission capable of over a decade of continuous observation, alternative approaches are necessary.
This study introduces a novel method: utilizing images of Venus that has been occasionally taken during the Earth observation by the meteorological satellites Himawari-8 and 9*4. These satellites take full-disk images of the Earth every 10 minutes, including space adjacent to the Earth, and occasionally capture celestial bodies, such as Venus, in the image (Figure 1). After analyzing all the data up to date, we found that Venus was captured 437 times between July 2015 and February 2025.
By analyzing these Venus images at infrared bands, this study successfully tracked long-term variations in the brightness temperature*5 (Figure 2). Observation at multiple infrared bands also allowed us to observe dependence of temperature variation on altitudes, based on difference in optical thickness*6 among various infrared bands. Further analysis uncovered time-varying patterns of thermal tides. In addition, we succeeded in identifying, for the first time, the altitude-dependent temperature amplitude and time variability of Rossby waves (Figure 3). These findings provide clues for understanding the long-term variability of Venus’s atmosphere. Future comparison with atmospheric circulation models could help deepen our understanding of the physical processes in Venus’s thick atmosphere.
This study also provides insights to future calibration of infrared radiometers on ongoing planetary missions as well. During the operation of Himawari-8/9, Venus has been observed by two infrared instruments: long-wave infrared camera (LIR) *7 onboard JAXA’s Venus Climate Orbiter Akatsuki and Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) *8 onboard ESA-JAXA’s Mercury mission BepiColombo. Using simultaneous observations from all three instruments, our cross-comparison yields a new quantitative benchmark for recalibrating LIR brightness temperature data in the future.
This pioneering approach of meteorological satellites for planetary science could be extended to other meteorological satellites, founding a new methodology for monitoring Venus’s atmospheric temperature. Since communication with Akatsuki is not established at present, this approach could be the only means of observing Venus at infrared wavelengths from space until the next dedicated Venus mission arrives. The methods developed in this study continuously enriches our understanding of Venus by delivering valuable long-term data on Venus’s atmosphere, as well as contributing to other planetary study and future planetary exploration missions.
Terminologies
- *1 Thermal tides: Global-scale gravity waves excited by solar heating in the cloud layers of Venus. When the atmosphere is stably stratified like Venus (i.e., a warm upper layer atop a cold lower layer), a restoring force acts upon heated air parcels, and the resulting vertical oscillations propagate as gravity waves. Note that this wave is not gravity wave in astrophysics but waves in planetary atmosphere.
- *2 Planetary-scale: This term refers to the scale of atmospheric phenomena and movements that occur across an entire planet, such as atmospheric general circulation.
- *3 Rossby wave: Planetary-scale waves that arise due to variations in the Coriolis force with latitude, caused by a planet’s rotation. Unlike on the Earth, Rossby waves on Venus propagate eastward. When an object moves on a rotating body like the Earth, an apparent force (inertial force) that acts perpendicular to the direction of motion is called the Coriolis force.
- *4 Himawari-8 and -9: Himawari 8 and 9 are Japan’s geostationary meteorological satellites that capture images of Japan, East Asia, and the western Pacific region. They support not only weather forecasting but also the monitoring of typhoons, heavy rainfall, and climate change. Himawari 8, launched in 2014 as the successor to Himawari 7, started to be operated in the summer of 2015. Himawari 9 was launched in 2016 and initially served as a backup, but started to be operated in December 2022, switching the roles with Himawari 8.
- *5 Brightness temperature: The temperature of a hypothetical blackbody that would emit radiation at the same intensity as the observed radiance at a specific wavelength. Radiance refers to the amount of electromagnetic energy emitted in a specific direction, expressed per unit area and per unit solid angle.
- *6 Optical thickness: A measure of how much light is attenuated as it passes through a medium like clouds. Because the attenuation varies with wavelength, measurements at multiple wavelength bands can infer temperature information from different altitudes within Venus’s cloud layers.
- *7 LIR (Longwave Infrared Camera): A single-band infrared camera onboard the Venus Climate Orbiter Akatsuki, designed to observe cloud-top temperatures on Venus at wavelengths of 8-12 micron.
- *8 MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer): An infrared radiometer and spectrometer onboard the BepiColombo mission, capable of measuring emissivity at mid-infrared wavelengths to obtain information on the mineralogical composition, as well as surface temperature.
Information
| Journal Title | Earth, Planets and Space |
|---|---|
| Full title of the paper | Temporal variation in the cloud-top temperature of Venus revealed by meteorological satellites |
| DOI | https://doi.org/10.1186/s40623-025-02223-8 |
| Publish date | 30 June 2025 |
| Author(s) | Gaku Nishiyama, Yudai Suzuki, Shinsuke Uno, Shohei Aoki, Tatsuro Iwanaka, Takeshi Imamura, Yuka Fujii, Thomas G. Müller, Makoto Taguchi, Toru Kouyama, Océane Barraud, Mario D'Amore, Jörn Helbert, Solmaz Adeli, Harald Hiesinger |
| ISAS or JAXA member(s) among author(s) | SUZUKI Yudai (Department of Solar System Science, ISAS, as a Japan Society for the Promotion of Science (JSPS) Research Fellow (PD)) |
Links
- Graduate School of Science, The University of Tokyo, Press Release, “Meteorological satellites observe temperatures on Venus: The forecast is bright for future, long-term multiband monitoring of planets,” 30 June 2025
- National Astronomical Observatory of Japan, Press Release, “Earth Weather Satellites Track Venusian Weather,” 1 July 2025
Author
March 2019: Bachelor of Science, Department of Earth and Planetary Physics, School of Science, The University of Tokyo
March 2021: Master of Science, Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo
March 2022-March 2023: Guest Scientist, German Aerospace Center (DLR)
March 2024: Ph.D., Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo
April 2024-March 2025: Guest Researcher, National Astronomical Observatory of Japan (NAOJ)
April 2024-Present: Guest Researcher, Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo
April 2024-Present: Japan Society for the Promotion of Science (JSPS) Overseas Research Fellow (Host: German Aerospace Center)
A word from the co-author at ISAS (SUZUKI Yudai)
Dr. Nishiyama, working at the German Aerospace Center (DLR), has studied the surface and interior of the Moon and asteroids. At the same time, he has been active in various planetary exploration projects. A Japanese weather satellite, Himawari, observes the Earth, and occasionally other planets such as Venus appear in its field of view. In this study, we focused on Venus and succeeded to obtain long-term observation data in infrared at multiple wavelengths for the first time. JAXA has carried out a lot of planetary exploration projects, but the number is still limited. Our achievements are valuable just for showing long-term temperature variations at multiple altitudes of Venus, but for expanding the possibility of applying satellites, which are not originally intended for planetary observations, to planetary science. Our study also contributed to the calibration of instruments onboard currently operating spacecraft, Akatsuki (Venus orbiter) and BepiColombo (Mercury orbiter). It can be said that this study improves the quality of future infrared observation data of planets.
March 2018: Bachelor of Science, Department of Earth and Planetary Physics, School of Science, The University of Tokyo
March 2023: Ph.D., Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo
April 2023-Present: Working at Department of Solar System Science, Institute of Space and Astronautical Science, as a Japan Society for the Promotion of Science (JSPS) Research Fellow (PD)
May 2023-December 2023: Associate Researcher, Le Laboratoire Atmosphères, Observations Spatiales (LATMOS), France