Colder Times Up High? Japanese Team Identifies Polar Noctilucent Clouds in Lower Latitudes


Noctilucent clouds are thin, streaky clouds that frequently appear in the summer. These noctilucent clouds are far higher than ordinary clouds, at an altitude of approximately 85 kilometers, and have so far been observed exclusively in the Arctic and Antarctic. However, in recent years, these noctilucent clouds can be seen in places as far from the poles as Hokkaidō and Paris as well.

Noctilucent clouds appearing over Paris in July 2009. (Courtesy of
Noctilucent clouds appearing over Paris in July 2009. (Courtesy of

According to Tsutsumi Masaki of the National Institute of Polar Research, who specializes in atmospheric physics and has experience as the captain of the sixtieth Japanese Antarctic Research Expedition, noctilucent clouds have become more frequent in lower latitudes because they are believed to be closely related to global warming.

Tsutsumi Masaki at far left during the Antarctic expedition. (Courtesy of the National Institute of Polar Research)
Tsutsumi Masaki at far left during the Antarctic expedition. (Courtesy of the National Institute of Polar Research)

“As the phenomenon of global warming progresses, places where people live will get hotter. Due to an effect called radiation balance, this causes places high in the sky to become colder. We think that as the air temperature at high altitudes has decreased, noctilucent clouds, which were previously only seen in the Arctic and Antarctic, have formed in various other places. In other words, we can read from the noctilucent clouds that global warming is progressing.”

Upper-Atmosphere Temperatures Plunge

Furthermore, Tsutsumi’s colleagues have observed surprising trends from observations of the Arctic upper atmosphere.

“In a continuous study of temperature changes at an altitude of 320 kilometers, which is even higher than that of the noctilucent clouds, found that the temperature is decreasing at a rate of 1.4 degrees per year.”

In other words, the effects of global warming are felt throughout the earth’s atmosphere, far above the surface of the planet.

Japan’s High Performance Radar “PANSY”

However, changes in weather cannot be captured without continuous recording of proper observation data. Therefore, the PANSY large atmosphere radar array was installed at Japan’s Shōwa Station in Antarctica.

Atmospheric observation facilities are scarce in Antarctica, and Shōwa Station is the only research facility in Antarctica that has a large atmospheric radar array. PANSY, built in 2012, includes more than 1,000 antennas are set up in an area about 300 meters across.

“This is a high-performance radar that Japan can be proud of,” says Tsutsumi, “with more than 1,000 antennas working as one large antenna that can measure wind from altitudes of 1 kilometer to 500 kilometers.”

Some of the antennas in the PANSY array. (Courtesy of the National Institute of Polar Research)
Some of the antennas in the PANSY array. (Courtesy of the National Institute of Polar Research)

Observations by PANSY are mainly conducted by researchers from the University of Tokyo, the NIPR, and Kyoto University. They are investigating how the atmosphere flows from the surface to high altitudes, and what kinds of changes occur in each layer. The sixty-fourth Antarctic Research Expedition, which starts this November, will continue observations from the ground to the upper atmosphere with PANSY.

PANSY’s Role in International Collaborative Work

Since 2015, at the request of Professor Satō Kaoru of the University of Tokyo, a PANSY project representative, an initiative called ICSOM (Interhemispheric Coupling Study by Observations and Modeling) has been underway. In this project, PANSY and other atmospheric radars around the world simultaneously observe the atmosphere. Hopes are high for the research using the data obtained from this cooperative observation.

In addition, since it is difficult to capture all atmospheric phenomena through observation alone, research that combines captured data with atmospheric simulations using computers is also being planned. The importance of this sort of research is demonstrated by the results of Syukuro Manabe (Manabe Shukurō), who won the Nobel Prize in Physics for his climate change simulation research.

PANSY is an exceptionally large project for an Antarctic expedition, and it is expected to be scaled back in the future due to its high maintenance and operational costs. Professor Tsutsumi says that the most important thing is to observe clean data for more than 10 years and then to preserve valuable data for the future.

(Originally published in Japanese. Banner photo: The Antarctic observation ship Shirase breaking through sea ice. Courtesy of the National Institute of Polar Research.)

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