139736eo.pdf (20MB) - Japan Oceanographic Data Center

PROBLEMS IN THE PHYSICAL OCEANOGRAPHYOF THE INDIAN OCEANERIC B. KRAUSUniversity of Colorado/CIRESCampus Box 409Boulder, Colorado 80309, U.S.A.ABSTRACTThe singular features of the large-scale water circulation in the Indian Ocean are brieflydescribed, followed by a list of research problems that can be expected to be of regional or globalinterest.INTRODUCTIONThis note was presented in the framework of a workshop to provide the scientific backgroundfor the subsequent First Conference on Economic, Scientific and Technical Cooperation in the IndianOcean. In this context it seemed appropriate to describe briefly the peculiar features of the large scaleIndian Ocean dynamics. The singular nature of the water circulation there determines some of themore important problems that need to be elucidated before changes in the physical environment can beunderstood or predicted. The actual selection of particular research projects, which was one of theindicated objectives of the workshop, depends, of course, not only upon the physical problems, butalso upon the specific interests of the scientific community, upon personnel, finance and materialresources, and upon political or administrative considerations.The Indian Ocean represents a rather unique dynamic environment because of the followingfeatures:(1) The Indian Monsoon produces a stronger annual variation in wind forcing than isexperienced by any of the other main Ocean basins. The semi-annual forcing is also verypronounced. This causes seasonal variations of the near-surface zonal currents along theequator (Fig. 1).(2) The mean westerly wind component at the 500 m b level in winter is stronger over theIndian Ocean than over the Atlantic or the Pacific (Fig. 2). The core of maximum wind speedis also somewhat further south in the same region. This suggests strong cyclonic activity atrelatively high latitudes.(3) The annual variation in wind forcing causes exceptionally large annual sea surfacetemperature changes near the Somali coast. Large surface temperature changes also occur inthe 30'-40'S latitude belt (Fig. 3).(4) Being closed in the north, the Indian Ocean experiences a large net southward transportof heat across the equator.(5) The surface current along the equator tends to be convergent and not divergent as in theAtlantic or Pacific.(6) An unusual thermohaline structure results from the intrusion of dense, highly salinewater from the Red Sea and from the Gulf of Oman on the one hand and from the inflow ofwarm low salinity water through the Indonesian Archipelago on the other hand.(7) The mid-latitude circulation is divided into two separate parts: a subtropical, anticyclonicgyre east of Madagascar and the Agulhas current system in the southwestern area ofthe basin.(8) The Leuwin current along the coast of Australia represents the only known polewardeastern boundary current in the subtropics.43