Our Research

Kaoru Sato's Lab in Atmospheric and Oceanic Science Group at Department of Earth and Planetary Science conducts research in the area of atmospheric dynamics. Atmospheric motion can be divided into balanced and unbalanced flows, depending on whether or not a balance between horizontal forces (primarily a balance between Coriolis and pressure gradient forces) is established. You may be familiar with extratropical cyclones and typhoons from weather forecasts - these are examples of phenomena resulting from balanced flows. In comparison, the cap clouds that sometimes appear over Mt. Fuji are an example of a visual manifestation of atmospheric gravity waves, which are unbalanced flows.

These phenomena which are familiar to people are visible by their associated clouds, but they are only a small fraction of all atmospheric phenomena. Horizontal scales of atmospheric phenomena range from a few hundred meters to a global scale (a few tens of thousands of kilometers). These individual phenomena coexist to form an atmospheric system with a continuous hierarchical structure. Within this system, unbalanced flows tend to occur on a smaller scale than balanced flows, which has traditionally made unbalanced flows difficult to observe or simulate; however, with the recent development of high-resolution atmospheric radar and supercomputing technology, we can now see these smaller scale phenomena unfold before our eyes, allowing us to piece together a complete picture of the atmosphere's hierarchical structure.

Our lab's research takes place at the forefront of these new developments in meteorology. Our most recent efforts have focused on the middle atmosphere, which extends from the stratosphere to the lower thermosphere, and is where global-scale general circulation takes place. General circulation in the middle atmosphere not only transports minor but important chemical species such as ozone and carbon dioxide, but it also significantly affects the temperature structure of the atmosphere due to the adiabatic heating or cooling with vertical motions; this is driven by the momentum deposit by Rossby waves (a typical balanced flow) and gravity waves (a typical unbalanced flow) originating from the troposphere. Our studies in this area are currently in a very exciting phase, as we are steadily elucidating the interesting relationship governing the coexistence of these two waves.

The main topics of our research are: 1) atmospheric hierarchical structure; 2) atmospheric gravity waves, Rossby waves, and equatorial waves; 3) stratospheric polar vortex (a low pressure vortex) and Asian monsoon anticyclone (a high pressure vortex); 4) three-dimensional middle atmosphere general circulation (most studies until now have been limited to two dimensions); and 5) teleconnections between the Northern and Southern Hemispheres. In addition to theoretical and modeling studies, our lab is unique in that we also place a strong emphasis on observational studies; notably, we have access to the PANSY radar in the Antarctic, one of the world's few high-power atmospheric radar currently in operation, and we are collaborating with scientists from around the world to conduct observations and model simulations using this facility, as well as analyzing the acquired data and developing related theories. Just recently, our research interests have also expanded into data assimilation, where observational data are integrated into models, and into novel data analysis studies that take advantage of new methods in the field of information science.