ABSTRACT
― Keynote Address ―
Decadal and Interdecadal Climate Events and Their Impact on the Ocean Circulation in the Indo-Pacific Sector
Toshio Yamagata
Department of Earth and Planetary Physics, Graduate School of Science, The University of Tokyo Also affiliated with Frontier Research System for Global Change, Institute for Global Change Research
With accumulating satellite datasets such as sea surface temperature, surface winds, sea level and drifter tracks as well as in situ observations, decadal / interdecadal climate events (DICES) have been reported in many places of the world oceans. The Indo-Pacific sector is not an exception. Although the satellite datasets, per se, are still too short to capture DICES, recent development of high-resolution ocean general circulation models provides a useful means to combine those various datasets and to clarify interrelations among DICES. For example, long-term hydrographic observations in the western tropical Pacific revealed not only the oceanic thermal variability associated with the ENSO events but also DICES related to the global warming trend from the mid-1970's. Since the background SST is high in the tropical Pacific, even weak SST anomalies may strongly affect the tropical and extratropical atmospheric circulation. The subtropical atmospheric response, in turn, affects the mid-latitude ocean circulation, particularly the Kuroshio transport through the surface wind action and induces corresponding oceanic DICES as observed by the long-term in situ measurement near Okinawa. It is found using such a high-resolution model that recent frequent occurrence of the large meandering path of the Kuroshio south of Japan is closely linked with the decadal / interdecadal increase of the transport. Analyses of long-term SST dataset and tropospheric circulation data suggest that DICES in the subarctic region in the northern North Pacific is different from DICES in the tropics and subtropics. It has turned out that satellite drifter tracks provide a useful means to check the hypothesis. Despite poor observations, the Indonesian throughflow and the surface circulation in the Indian Ocean are also expected to show DICES which are closely linked with Pacific partners. The Indian Ocean is basically much affected by monsoonal winds and brief westerlies during semiannual monsoon breaks; Indian DICES appear as the decadal / interdecadal modulation of the seasonal signals according to analyses focused on specific major events such as the 1994 unusual condition.
