Observational Research of Large-Scale Hydrological Cycle and Processes Centered on the Indonesian Maritime Continent

Observational Research of Large-Scale Hydrological Cycle and Processes Centered
on the Indonesian Maritime Continent

Shuichi MORI ( Researcher, Hydrological Cycle Observational Research Program, FORSGC )

The Indonesian maritime continent is one of the regions that experience the most rainfall in the world. Atmosphere over this region drives the global circulations, i.e., the east-west Walker circulation and the south-north Hadley circulation, through the frequent convective cloud activity.

Regardless of the extremely important position this region holds in terms of climate mechanisms, including the Asian Monsoon System, as an "aerial crossroads" of water and energy circulations, remarkably limited surface meteorological and aerological observation data is available. Therefore, continuous in situ observation and analysis of meteorological data in this region are being counted on not only in view of climate change prediction research, but also towards improving cumulus parameterization techniques, validation of satellite observation data, and so on.

Fig. 1 Diurnal variation of rainfall around Sumatra Island observed by TRMM satellite (The upper figure). Distinct contrast of rainfall characteristics is shown between over the land and its adjacent sea area. Rawinsonde data at Kototabang observatory (indicated by the cross (+): 0.2S, 100.3E) shows clear diurnal variations of wind and humidity suggesting close relation with that of rainfall.

Currently, our research group has established the Kototabang observatory in Sumatra Island (Fig. 1) as a base station to develop high-accuracy meteorological observations that can resolve the diurnal variation predominant in the tropical equatorial region. Particularly, for the first time in this region, we have been conducting Global Positioning System (GPS) rawinsonde observations (Fig. 2) that take measurements every 3 to 6 hours during campaigns, totaling more than 100 days over a one-year period.

Based on these observations, we are investigating the interaction between the detailed variations in the atmospheric structure and mesoscale phenomena, such as the torrential rainfall peculiar to tropical regions, and their relationship with ENSO and other large-scale climate change systems. Furthermore, we have adopted advanced methods using GPS for observations of short-term variations in precipitable water and stable isotope studies of water, and have been simultaneously conducting investigations into the recycling process and water vapor transport across the wide area covering Thailand, Nepal, Tibet, and Siberia.


	Fig 2. Prior to launching the GPS rawinsonde observation balloon at the Kototabang observatory by local stuff (The upper figure), and precise profiles of observed data in November 2001 with 10m resolution in height (left panel).

Indonesia is subject to many natural disasters, such as large-scale forest fires during El Nino periods, and severe rain-fall and floods during La Nina periods. Indonesian government thus has high expectations of Japan's observational research activities. Our goal is not only to serve important meteorological process studies that will improve climate change prediction research, but also to produce scientific output, such as disaster-pre-venting information, that can benefit the local community as a part of Japan's international cooperation.

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