A LAGRANGIAN APPROACH TO THE SEASONAL-VARIATION OF SALINITY IN THE MIXED-LAYER OF THE INDONESIAN SEAS

We have investigated the seasonal variation of the salinity in the mix ed layer of the Indonesian Seas from a Lagrangian viewpoint using the ''particle-tracking method.'' Numerous labeled particles are tracked i n a velocity field obtained using the robust diagnostic general circul ation model with seasonal forcing. Salinities tagged to these particle s are subsequently changed by freshwater flux through sea surface duri ng their transit. Finally, the salinity in the ''mured layer'' (upper 50 m) of each basin comprising the Indonesian Seas is calculated by mo nthly averaging the salinities of all particles located in the mixed l ayer of each basin. The seasonal salinity variation in the mixed layer obtained with this method shows similar features to that observed. Si nce this method has the advantage of clarifying the origins and histor ies of waters affecting the salinity variation in the mixed layer, a c lose examination of the: result by the particle-tracking method reveal ed the major factors causing seasonal salinity variation In each basin of the Indonesian Seas. Seasonal variation of the salinity in the mix ed layer of the Indonesian Seas is determined by the seasonal variatio ns of net air-sea freshwater flux, three-dimensional velocity field, a nd their combined effect.