Frontiers of Science

Understanding the Earth’s Atmosphere with the Aid of a Giant Radar

SATO Kaoru

Professor, Department of Earth and Planetary Science

November 1, 2022


Overcoming Challenges and Obstacles, Tackle the Topic you Find ‘Most Interesting’

This is easy to say, but difficult to put into practice. Everyone experiences the difficulty of battling the harshness of reality to achieve their goals. Atmospheric scientist Professor Kaoru Sato is a woman who has done just that. Correction: she hasn’t stopped achieving yet; she continues to tackle her goals today. “My main research interest is atmospheric gravity waves, a concept in meteorology defined as “waves with periods of several minutes to ten-plus hours whose restoring force is the buoyancy in the atmosphere.” This phenomenon used to be difficult to study because the waves are such tiny disturbances in the motion of the atmosphere, but I’ve been studying them since I was in graduate school.” How has she followed her passion for research from the time she found her main interest to the present?

The Road to Meteorology was Paved with a Love of Science Subjects

In elementary school, Sato enjoyed and excelled in math and science. Her love of science subjects continued through junior and senior high school, and when she entered the University of Tokyo, she opted for meteorology. Why did she choose meteorology? “Of the various subjects available, geophysics seemed the most interesting, and I chose meteorology because I thought it was the most physics-focused area of the geophysical sciences.” She found the lectures by the atmospheric scientist Dr. Taro Matsuno (a former professor in Sato’s current laboratory) to be very interesting, becoming absorbed in the physics-rich environment of the field. And in the process of putting together her master’s thesis, Sato discovered her interest in research. However, she didn’t go on to a doctoral program straightaway; instead she found a job at a company (NEC) where she was assigned to a research institute. Although her work there was fulfilling in its own way, she couldn’t give up her longing for natural science research, and left the company after getting married, starting a doctoral program at Kyoto University.

“NEC was a great working environment for women, so it was quite a big decision for me to leave the company I had been welcomed to join. Having made such a momentous decision, I was fully committed to becoming a researcher. I studied hard at Kyoto University, did a lot of research and also had a load of fun. I’d had a vague idea that I wanted to be a researcher since junior high school and senior high school, so I was happy to be getting closer to that goal.”

As noted above, atmospheric gravity waves are tiny oscillations. Not only then, but even today, they defy adequate resolution with our weather forecast models. However, the momentum carried by atmospheric gravity waves plays an important role in atmospheric circulations. In the 1980s, when the action of atmospheric gravity waves was first parameterized and incorporated into weather forecast models, the models became much more accurate than before, despite the lack of resolution. Subsequent improvements in observation and supercomputer technologies led to the start of the full-scale study of atmospheric gravity waves. During her graduate and post-doctoral years, Sato had focused on research into atmospheric gravity waves over mid-latitude regions using the MU radar (a large radar for atmospheric observation installed in Shigaraki by the current Research Institute for Sustainable Humanosphere, Kyoto University), but on becoming an assistant professor at Kyoto University, she extended her focus to other latitude regions.

“I published about 10 papers that focused on the mid-latitudes, after which I began studying atmospheric gravity waves above the equator. This study of the equatorial region generated considerable international interest and contributed to a major shift in our understanding of the climatologically important large-scale oscillation known as the Quasi-Biennial Oscillation. After the mid-latitude and equatorial regions, it was then the turn of the polar regions, so I began studying atmospheric gravity waves in the Arctic and Antarctic. I was then invited to apply for an open position as an associate professor at the National Institute of Polar Research (NIPR). I took up the invitation because I thought that if I went to the NIPR, I might actually be able to go to Antarctica to perform observations.”

Thus, Sato was hired as only the second female associate professor at the NIPR.

A Giant Atmospheric Radar in Antarctica

“Most of the associate and full professors at the NIPR are men, so naturally, female associate professors get a lot of attention. Knowing that first impressions are crucial, I decided to make a splash at my first research seminar where I introduced myself. I suggested that it would be nice to build a large atmospheric radar in Antarctica (laughs).” It was certainly a bold statement. She was initially being mischievous when she said this with the intention of “making a splash” (laughs). But for Sato, it was a serious matter. Since Antarctica didn’t have a well-developed infrastructure for atmospheric observations, researchers had to date been groping in the dark. The installation of a large atmospheric radar was an ambitious proposal to develop Antarctic atmospheric observations into a robust and precise science.

“After the seminar, a senior scientist (at deputy director level) came to my office and asked me to give more thought to what I’d said earlier about the radar. He said, ‘I’ll back you up.’ I was impressed by the generosity of spirit to say such a thing to a female associate professor who’d just arrived on base. This was the birth of the project to establish the Program of the Antarctic Syowa MST/IS Radar (PANSY), the first large atmospheric radar based in Antarctica.”

It took 10 long years to realize the PANSY radar project in Antarctica. Naturally it took time to build because it was a large facility, but even so, it proved to be quite a difficult job. “We were faced with a triple whammy. The first of the three challenges was technical.” These technical challenges were overcome in several ways. First, there was the problem of power. A large atmospheric radar requires about 230 kilowatts (kW) to operate. However, the power needed to run the entire base at Syowa Station in Antarctica was about 200 kW. In other words, even if the power to the base was entirely diverted to run the radar, it still wouldn’t be enough. Naturally, technical innovations were required to reduce the power consumption of the radar. The next challenges were the weight and shape of the antennae. A large atmospheric radar was composed of approximately one thousand 3-meter-tall antennas, each antenna weighing 50 kilograms. In Antarctica, researchers would have to install them all by themselves, but it would be tough to transport and install 1,000 of them, weighing as much as they do. Therefore, weight reduction was essential. “We tried out a lot of different ideas. To solve the power consumption problem, we decided to use the high-efficiency Class E amplifiers used in cellular phones at the time and developed low-loss cables to reduce the operating power consumption to a goal of 85 kW. With various other strategies, we were able to create a system that operates at just under 60 kW. In addition, the base in the Antarctic experiences typhoon-strength winds once or twice each year and is continually buffeted by a constant and strong wind that flows down the Antarctic slopes known as the katabatic wind. So we developed antennas that are not only light and strong, but also shaped specifically to prevent resonance effects. The result was a 12.6 kg antenna that even I could easily carry.”

Furthermore, each antenna had to be able to be assembled quickly so that approximately 1,000 antennas could be installed in the summer period, lasting a little over a month, when construction is possible in Antarctica. “At first, I took a 50 kg antenna provided by Kyoto University to Antarctica to try it out, but it took two days to assemble. We worked with the manufacturer to develop an antenna that even two people who don’t get along can assemble in 10 minutes (laughs).” The outcome of these technological innovations is a ‘human-friendly radar’ that’s easy to assemble with almost all parts weighing less than 20 kg. From outside, it seems that it was quite an achievement to manage such a thoroughgoing development program in 10 years.

Ten Years from Dream to Reality

“The second of the three hurdles was that of gaining inclusion in the mid-term program for the Japanese Antarctic Research Expedition. Initially, there was strong opposition, and it appeared that we might fail. At the same time, we had to deal with the third part of the triple whammy, budgeting. We needed a supplemental budget to build a large atmospheric radar, but at that time it was very rare to secure such significant funding for science and technology projects. I visited the Ministry of Education, Culture, Sports, Science and Technology (MEXT) many times to seek their advice, and I made presentations to international academic organizations, receiving endorsement of the importance of our plan. We could develop the radar technology through our own efforts, but the second and third challenges were dependent on our program partners. We also ran out of things to do in about the seventh year of technical development.” What did she do when she got to that point? “We played dead (laughs).”

In other words, she pretended to give up. She stopped all work on PANSY and focused her research attention on atmospheric gravity wave research using a high-resolution, atmospheric general circulation model, on which she had made a little headway while she was an assistant professor at Kyoto University. Since she had been spending most of her time on PANSY for seven years, she had a sense of crisis that this might not be a good move for her research.

“After we’d played dead for a while, people started asking, ‘Hey, what’s up with PANSY, the activity was so vigorous before?’ The tide began to turn in our favor, we gradually accumulated allies, and finally we were able to secure a budget. Once the budget was set, it was time to say, ‘Let’s include it in the mid-term plan. ...... Ms. Takako Doi, former chairperson of the Japan Socialist Party, had a saying ‘the mountain has moved,’ and that’s exactly how it was for us.

What a dramatic development! The world is not without its complications, and to achieve your aims, you really need a variety of approaches. The installation of PANSY was thus about to become a reality, but for two consecutive years, 2012 and 2013, the icebreaker Shirase was unable to berth to bring in the radar equipment. “Even so, we started observations with a partial system in April 2012 using the equipment we were able to bring in. It took 10 years to complete the installation, and when I saw the wind observation data for the first time, I was absolutely thrilled that the PANSY radar had finally become a reality.” Eventually, all the equipment was brought to Antarctica and observations with the entire system could begin in March 2015.

Seeking to Understand the Effects of Sudden Stratospheric Warming

Antarctica was once the only continent without a large atmospheric radar. Professor Sato overcame this handicap by making PANSY happen. The Earth’s atmosphere is composed of four major layers from the surface upward: troposphere, stratosphere, mesosphere, and thermosphere. Professor Sato’s research focuses on ‘atmospheric gravity waves propagating through these four layers.’ “In the Arctic stratosphere in winter (at an altitude of around 30 km), we occasionally see a phenomenon called ‘sudden warming,’ in which the temperature abruptly rises by several tens of degrees. This sudden warming affects surface air temperatures extensively in the Northern Hemisphere but has also recently been found to affect the upper Antarctic mesosphere at an altitude of around 90 km. I’m continuing my research to understand the mechanism behind this phenomenon.”

There are only several atmospheric radars of the scale of PANSY in the world because they are large and costly to install. Nevertheless, large atmospheric radars have been established in the polar, mid-latitude, and equatorial regions. Professor Sato therefore called on researchers in countries with large atmospheric radars to jointly observe how atmospheric gravity waves in each latitude region change when sudden stratospheric warming occurs. This international collaboration is already in its seventh year. “Now we finally have all the tools we need, including PANSY and an atmospheric general circulation model that can resolve gravity waves. I plan to use these tools to develop my research in the future.”

In recent years, the issue of global warming has drawn much attention, and research on the Earth’s systems, including the atmosphere, impinges directly on this very issue. “Yes, that’s right. I believe that global climate issues must be studied with all atmospheric regions in mind. A well-mixed atmosphere with a ratio of four parts of nitrogen to one part of oxygen extends to the troposphere, stratosphere, mesosphere, and lower thermosphere. In other words, these four layers are connected by atmospheric motion (wind). If we can get an adequate grasp of how phenomena develop through these layers, we can make a good prediction of the impact of the atmosphere on the ground.”

Applying the Theory of the Earth’s Atmosphere to Mars

The more you hear of her story, the more the great adventure of the atmosphierc scientist makes for a fascinating tale. What then is in the pipleine for Professor Sato’s future research? “I want to continue to understand the atmosphere as a whole using the tools we have available. More recently, I’ve also started studying the Martian atmosphere with my students.” Mars? How so? “Atmospheric theory has been developed through studies of the Earth’s atmosphere, and in fact it can be applied directly to the atmosphere of Mars. In particular, the stratospheric and mesospheric theories can be applied almost directly to the Martian atmosphere.” This is amazing. Professor Sato’s ‘most interesting topic’ includes not only the Earth but also extends to the universe. The story goes on and on.

Let’s conclude by asking Professor Sato for her message to the high school students and undergraduates reading this article. “Meteorology is the familiar branch of science that investigates phenomena and general circulation in the Earth’s atmosphere. How can it not be interesting when the subject of fascinating research is right there in front of you (laughs)? Then again, climate and weather are closely connected to society. It’s a science that naturally contributes to society as it pursues what is genuinely most interesting. Come and join us in this fascinating field!”

An atmospheric scientist who has done what she finds most interesting is cheerful, as if the difficulties she overcame in the past had never existed. Today, she continues her favorite research, with her thoughts firmly focused on the Antarctic skies.

Kaoru Sato's Laboratory:https://www-aos.eps.s.u-tokyo.ac.jp/~sato-lab/en/

※Year of interview:2022
Interview/Text: Osamu Shimizu
Photography: Junichi Kaizuka

SATO Kaoru
Professor, Department of Earth and Planetary Science
Professor, Department of Earth and Planetary Science In 1991, completed her doctoral studies in geophysics at the Graduate School of Science, Kyoto University. Ph. D. In 1995, she joined Kyoto University as an Assistant Professor and began researching atmospheric gravity waves and their role in global-scale atmospheric phenomena, and studying the physics of the hierarchical structure embedded in the atmosphere, using large atmospheric radars, radiosondes, and a high-resolution general circulation model for the atmosphere. In 1999, she was appointed Associate Professor at the National Institute of Polar Research, where she initiated a project of the first large-scale atmospheric radar (PANSY) in Antarctica. Installation of the PANSY radar at Syowa Station began in 2011, and continuous observations with the full system are currently being collected. She was a member of the winter party of the 44th Japan Antarctic Research Expedition (JARE) (2002-04) and the summer party of the 60th expedition (2018-19). She has been in her current position since 2005.


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