Effects of mesoscale phenomena on water mass formation and transportation in the subtropical/subpolar frontal region
H.Mitsudera and Y. Yoshikawa
Japan Marine Science and Technology Center
1. Introduction
It has been found in the last decade that there are significant decadal time scale signals in the north Pacific (e.g. Tanimoto et al, 1993). Ocean must be responsible for this long-time-scale climate variability because of its huge heat storage. The Kuroshio and its extension current carries the vast amount of heat, so that it should play an important role in such climate variability. It is not well understood, however, how the sea surface temperature (SST) is determined in the presence of the strong current, and how the SST interacts with the atmosphere above. In other words, we should explore more thoroughly the three dimensional processes of ocean mixed layers such as advection of heat by currents and eddies.
Another important phenomenon in the northwestern Pacific is the extensive distribution of the North Pacific Intermediate water on the isopycnal surface of σθ=26.8. The water mass originates from the subarctic ocean, and somehow transported into the subtropical gyre. Yasuda et al (1996) showed some evidences of North Pacific Intermediate water occasionally crossing over the Kuroshio Extension, which is likely to occur through meanders. This isopycnal surface can reach 800m in the central subtropics, and shallows in the equatorward and poleword, implying the formation of a shallow thermohaline circulation. The time scale of the overturning is thought to be interdecadal so that its variability is probably important for the climate variation of this time scale.
In JAMSTEC, it is planned to deploy two surface mooring buoys in the midlatitude as a part of the TRITON (TRIangle Trans-Ocean buoy Network) program. Although it is aimed to elucidate decadal to interdecadal climate variability here, we would use the surface buoy for a process-oriented study, rather than long term monitoring; as for a climate study, results derived from this experiment will serve mainly for improving model parameters and their validation. It is also hoped to serve for designing the simplest possible monitoring system, particularly linking with satellite measurements. Conidering the above we shall place our purposes as follows:
(1) Elucidation of the mixed layer processes when the advection of heat due to currents and eddies is very large.
