southeastern Pacific. The model generated vertically integrated current velocity from surface to the 7th layer (ca.500m depth) showed that the basin-scale mass transport from the southern to the northern hemisphere takes place at the western equatorial region of Pacific (i.e. east of New Guinea Fig.4), and the water accumulated at the western North Pacific ocean by North equatorial current is transported northward, eastward and to the Indian ocean by advection effects of Kuroshio, North equatorial countercurrent, and the Indonesian throughflow respectively.
Ramanathan et.al.,(1995)(9) emphasized that short wave forcing at presence of cloud may not be negligible. Using an ocean-atmosphere coupled general circulation model, Schneider et.al. (l996)(10) showed that the seasonal migration of the warmpool is largely a result of the seasonal variability of the net surface heat flux and that advection is of secondary importance.
Moreover they showed that clouds have little impact on SST in the Pacific portion of the warm pool while clouds limit the maximum SST in the Indian ocean. It is interesting to examine how the barrier layer and short wave forcing influence the ocean mixed layer structure of the warm pool. From coupled ocean-atmosphere numerical experiments and ocean general circulation experiments, it was reported that the temperature of the ocean mixed layer is controled mainly by surface heat flux, buoyancy fluxes, because the effect of the diffusion and advection are small (Schneider et.al.1996(10) and Nakamoto et.al.l996(11)). It is also reported that solar radiation and precipitation provide significant influence on the ocean mixed layer structure (White et.al. 1996(12)).
Fine et.nl.(13) emphasized that the western equatorial Pacific is a cross road of major currents and that their variablities are also large (Fig.5). Bingham and Lukas(l995)(7) showed that a tongue of low salinity intermediate water in the western equatorial Pacific plays a part in exchange of waler at intermediate density between the tropical and subtropical gyres. They emphasized the role of fresh water tongue in the regional, basin-scale and global circulation.
We have been deploying ADCPs at the equatorial region to observe Equatorial undercurrent, Southequatorial current, the NewGuinea coastal current, and the NewGuinea coastal undercurrent. ADCP data at the equator,147E from May 1994 to December 1994 by Jamstec tropical ocean climate study expedition (Muneynma and Kuroda,1996(14)) showed that Southequatorial current was stronger on October to November and Equtorial undercurrent was stronger on June to July in1994(Fig.6). From CTD data analysis we noticed that the New Guinea coastal undercurrent was stronger in July 1995 than in February 1996 (Fig.7a, 7b). Current directions at surface and subsurface in that region are often opposite, indicating that a current shear is larger and a mixing due to shear instability may play a dominant role in the diapycnal mixing.
An observed vertical profile of salinity from surface to 500m depth at the equator between 130E and 150E and a simulation using OPYC model indicate that high salinity water transported from the southern hemisphere; distributed from ca.80m to 300m depth vertically (Fig.8).
