Bestowed with a flower’s name, PANSY is a large atmospheric radar project ongoing at Syowa Station in the Antarctic. It all began when a researcher, newly assigned to the National Institute of Polar Research in January 2000, shared her dream of collecting data in a remote location such as Antarctica. In May of that year, a designer of the MU radars and members of National Institute of Polar Research met and designed a core plan based on Kyoto University’s MU radar, the most advanced of the time. In 2002, the project attracted global attention and was featured in the Asahi Shinbun. The project was also the subject of an interview in the scientific journal Nature. After a delay of about 10 years, the project actually began with the planned first measurement conducted in 2011. Shortly afterward, however, Syowa Station experienced record-breaking snowfall, and to make matters worse, the icebreaker Shirase was unable to dock Syowa Station for two consecutive years, in 2011 and 2012. “PANSY was interesting,” said Kaoru Sato, Professor at the University of Tokyo, despite the difficulties. Professor Sato proposed PANSY in 2000 as a newly appointed associate professor and became the project’s representative in 2005. We interviewed her in 2015 on topics related to the Global Environment Data Project at Research Commons.

Mind-boggling results from a radar station

Geophysics is largely different from, for example, particle physics, in which phenomena are mainly analyzed by advanced mathematics, and theories are tested by highly accurate experiments. On some occasions, discussions were conducted based solely on one or two sets of collected data. However, PANSY is that can produce data that puts theories to the test. With a vertical resolution of 150 meters and a time resolution of 1 minute, this installation can reveal atmospheric expressions that can boggle the mind. Assumptions are no longer required because this installation can produce all the data needed for sound results.

The dance of high-resolution observations, models, and theories

Numerical models are also used to understand atmospheric phenomena. In atmospheric physics, large-scale simulations are performed by supercomputers, which include weather forecasting models. However, it is impossible to directly compare simulation data with observational data because both these types of data take up large volume. Moreover, if clarification of a phenomenon from highly precise data is expected, basic atmospheric theories must often be created. Unlike identifying the physical laws from a large amount of data, this pen-and-paper method requires theory building upon Newton’s first law of motion to find such theories. Applying these theories to various data can largely advance the analysis results. Present-day high-resolution observation data makes it possible to enhance data-centric scientific studies when combined with models and simulation data. Data-centric science is currently the main focus of Professor Sato’s research group at The University of Tokyo.

Gravity waves: misunderstood gems

Around April of 2006, Professor Sato’s research group used the Earth Simulator supercomputer in collaboration with researchers from Japan Agency for Marine–Earth Science and Technology and commenced a global three-year model simulation in accordance with PANSY specifications. The calculations took two years to complete. However, the simulation, which continued for seven to eight years, reproduced various fine atmospheric structures in an imaginary space with a vertical span of 80 km and a vertical resolution of 300 m. This simulation was the best worldwide because of its high-resolution and extensive height coverage. Among the examination targets are very small phenomena in the atmosphere known as gravity waves. Prior to the mid-1980s, these phenomena were considered to be weather noise. However, the inclusion of this effect in the calculation of weather forecasts after that time significantly improved their precision, and the importance of gravity waves became widely known. The research group’s study of these phenomena included simulation data analysis, which revealed their unexpected features. It was determined that gravity waves concentrate at a particular location along their propagation paths, which turned out to be right above Syowa Station.

Beautiful menace: dangerous clouds peculiar to polar regions

PANSY was built at latitude 69.0°S and longitude 39.6°E, which is a suitable location for observations of the atmosphere in the high latitude southern hemisphere. The full system with 1045 antennas has been in operation since March 2015. Built with a focus on power conservation, the radar system has the distinguishing feature of being able to continuously collect observation data from respective atmospheric regions of the troposphere, stratosphere, mesosphere and ionosphere for an extended period of time. The key research topics currently pursued through PANSY include gravity waves, ozone holes, Antarctica’s distinctive katabatic winds, auroras related to energy and material flows from space, and two types of clouds particular to polar regions. One such type of cloud is polar stratospheric cloud (PSC), which forms in the winter stratosphere at altitudes of around 20 km. Although they shine beautifully in pink and orange colors, substances related to Freon undergo chemical reactions on the cloud surface that destroy the ozone layer in that location. Thus, the sizes of these clouds determine the sizes of holes in the ozone layer. The other type is the polar mesospheric cloud (PMC; noctilucent cloud), which appears at a quite high altitude of 90 km in the summer sky. PMC is said to be manmade cloud because it is absent in records before 1885. It is understood that the formations of this cloud reacts acutely to temperature and give rise to climate change. Based on PANSY and linked data generated by optical and radio wave observation instruments such as medium frequency radar, millimeter-wave spectroscopic radiometer, and lidars at Syowa Station, Professor Sato’s research group is improving the scientific understandings of atmospheric phenomena in the Antarctic by simultaneously capturing wind and temperature data and clarifying both vertical and horizontal structures of the gravity waves.

Arctic and Antarctic connection

Clarifying atmospheric phenomena in the Antarctic is important because global atmospheric circulations begin and end there. Furthermore, recent studies have gradually revealed that the mechanism of atmospheric phenomena in the Antarctic can be applied to the phenomena in the Arctic and that the atmospheric conditions in the Arctic and Antarctica are connected through the mesosphere. The goal of Professor Sato’s research group is to connect large atmospheric radars globally to conduct simultaneous observations in all locations. Because the phenomena are very small, it was first believed that they would appear only locally and that simultaneous observation would thus be meaningless. However, if it is possible to connect the global observation data and reproduce the atmospheric conditions from the ground to the mesosphere based on the global model her group developed in 2006, such simulation would be ground-breaking. Furthermore, the research group is examining the rare, well-known phenomenon of sudden warming that occurs when the temperature rises by more than 50° in a few days in the stratosphere above the Arctic. Although this phenomenon occurs only twice every three years, it is responsible for changes in the conditions at mid-latitudes, the Equator, and Antarctica. Professor Sato’s research group aims to simultaneously capture such dynamic global atmospheric circulations for further understanding of climate change factors on the global level.

(Text in Japanese: Kaoru Sato, Rue Ikeya. Photographs: Mitsuru Mizutani. Published: June 10, 2015)