FRONTIER Newsletter No.9 Jan.2000

The age of the Earth is about 4 .6 billion years. The continents, atmosphere and oceans appeared during the long geological time. The atmosphere and ocean general circulations have been influenced by the movements of continents, the variations of greenhouse gases in the atmosphere and the fluctuations of solar radiation. The variations of the general circulations have induced the drastic natural variations of global climate mainly through the variations of meridional heat transports.

The ancestor of human appeared about 3 million years ago in the long terrestrial history. The population explosion of the humanbeing began about just two hundred years ago, 1800's. The sufficient supplies of the energy by burning of the fossilfuel after Industrial Revolution and the food by forest burning for agriculture partially kept rapid increase of population with huge artificial emission of carbon dioxide, which is greenhouse gas, into the atmosphere.

Now, in succeeding to above natural and anthropologic history of the Earth, what is the present conditions of the global climate and how is it expected to vary in the future? n order to answer these questions the studies for understanding the essence and mechanism of the global changes including the global warming in the paleoclimate time scale are going on through numerical experiments by using the global coupled ocean- atmosphere general circulation model.

I joined Atmospheric Composition Research Program on June 1999. As a member of the Greenhouse Gases Modeling Group, I am now working on the analysis of the global cycles of greenhouse gases, such as carbon dioxide.

My ongoing research interests include the investigation of the physical and biogeochemical processes and mechanisms that control the carbon and oxygen isotope compositions of atmospheric carbon dioxide, in order to develop an inverse analysis of model against measurements. I have been developing a two- dimensional multi- box carbon cycle model to elucidate the various exchange processes of isotopic ratios of atmospheric carbon dioxide. Isotopes hold a key to discriminate and identify various sources and sinks of other greenhouse gases (e.g., methane, carbon monoxide), as well as of atmospheric carbon dioxide. For the future, I am interested in the approach using isotope data to other gases, in order to increase our understanding of the global cycles of greenhouse gases.

I encountered the world of oceanic observations near Snake Island in the Black Sea about a quarter century ago while I was a student. It was on board a Stalin's yacht, still decorated with huge mirrors, wool carpets and the red wood. The storm was hell, and the sea gave me a flavour of its frightening beauty. In following two years, I was lucky to be a technician of the hydrographic team in the POLYMODE experiment.

The season-long cruises of the POLYMODE program were an excellent school for physical oceanography and also quite a bit beyond. After that there were field experiments in the tropics of the Atlantic Ocean, in the Barents Sea of the Arctic Ocean, and the California Current region of the Pacific Ocean.For the last several years, I have worked on 'The Ocean in Miniature', the Japan Sea, where we organized and carried out the first multiyear and multinational observational program that uncovered 'Jeddy (the Japan Sea Eddy)'and the change in the deep- sea ventilation.

Our new research project, the Kuroshio Observational Program (KOP), of Frontier, focuses on understanding the barotropic and baroclinic components of the Kuroshio current and then on using this new knowledge to verify and improve our modelling capability, with a major emphasis on predictability the seasonal and interannual components of the Kuroshio variability. A long- term measurement array will be built up on either side of Okinawa and near the Kuroshio entry and exit points of the East China Sea to provide ground- truth- data for assimilation in extensive numerical models of the ocean circulation.

The field experiment will comprise intensive measurements by Acoustic Doppler Current Profiler (ADCP), XBT/XCTD, Inverted Echo Sounder with Pressure Gauge (PIES) that will be combined with satellite altimeter data. The field experiment will provide us with new information on the sea surface height variability, the Kuroshio flow and its baroclinic structure in the East China Sea and the Ryukyu Current east of the Ryukyus with an enhanced regional coverage. The basic surveys will be essentially extensions of existing hydrographic sections across the Kuroshio, near Okinawa, such as the famous PN- line, but with more frequent observations with better spatial resolution and a strong emphasis on the use of oceanic acoustic technique. Two 2 D moored arrays, of up to 60 PIESs, will be set up northwest and southeast of Okinawa, allowing for the first time a production of daily maps of the Kuroshio and the Ryukyu Current with mesoscale resolution.

The field experiment will enable us to determine time- varying mass and heat transports of the Kuroshio and the Ryukyu Current, to observe interactions of the currents with the mesoscale eddies, to better understand the physics of Kuroshio instabilities, and to improve forecasts for the downstream Kuroshio.