and heavy snow on the side of the Japan sea. She has also been making observations along 137｡? since 1967. JMA has four Marine Observatories, each of which is operating one research vessel. As shown in Fig. 1, these vessels have been regularly operating fixed observation lines around Japan five or more times in a year. The Agency has been making good use of the accumulated data for better understanding of inter-annual oceanic variabilities, especially variation of Kuroshio and Oyashio in the seas adjacent to Japan. Recently, for the purpose of better usage of altimeter data of TOPEX/POSEIDON, the JMA's research vessels have been making observations along its groundtracks.
2.1.2 Ryofu Maru
The Ryofu Maru II built in 1966 as one of the six JMA vessels carried out numerous oceanographic and marine meteorological observations including international cooperative surveys over 28 years. Her years of observation along 137｡? helped clarify the role of the western equatorial Pacific in El Nino events. In addition, the vessel later made observations of greenhouse gases such as CO2 and methane in and over the western Pacific. Among these cruises of the Ryofu Maru II, the most extensive one was the highly precise oceanographic survey along 137｡? from the south of Japan to the equator conducted in 1994 as part of the World Ocean Circulation Experiment (WOCE) to depict detailed oceanographic structure. The cruise has successfully provided geographical distribution of greenhouse gases in the oceans, as well as description of precise physical and chemical oceanographic structure. Almost three decades after its construction, the capabilities of the vessel recently became insufficient for comprehensive observation demands, in particular, to cope with global issues on climate and environment. To meet such demands, a new Ryofu Maru was built and started observation cruise in July 1995. The new 1,380 ton Ryofu Maru III is fully equipped with state-of-the-art observation systems, such as a CTD profiler with rosette samplers, an Acoustic Doppler Current Profiler, greenhouse gases (CO2, CH4, CFCs, N2O) measuring system, an automatic shipboard rawinsonde system, an integrated marine meteorological observation system, a shipboard wave recorder, and a sea surface flux observation system.The vessel will carry out marine meteorological and oceanographical observations to obtain data which are required for the development and verification of coupled ocean-atmosphere circulation models, and measurement of greenhouse gases which are closely related to global warming. She is anticipated to play a bigger role in monitoring marine environment and revealing the oceans functions in climate change and other global environmental issues.
2.1.3 ENSO and warm water pool
ENSO, one of typical climate variabilities, has been a major concern related to abnormal weather events in the world. JMA has been making oceanographic observations along 137｡? from the south coast of Japan to the equatorial region by Ryofu Maru and Keifu Maru in winter since 1966 and in summer since 1972. These observations have contributed to understanding the roles of the western North Pacific in the climate system.
High quality data collected along 1370E in the tropical pacific show a relationship between variabilities of warm water pool in the western Pacific and ENSO. Figure 2 shows geopotential anomalies in winter from 1967 to 1996. Variabilities in accordance with El Nino can be seen around 7｡? and those in accordance with variation of Kuroshio current are also found north of 30｡?.
