Intraseasonal eddies in Sulawesi Sea and their impact on the Indonesian throughflow
Yukio Masumoto, Takashi Kagimoto, Toshio Yamagata
Institute for Global Change Research, Frontier Research System for Global Change, Seavans N 7F, 1-2-1, Shibaura, Minato-ku, Tokyo 105-6791, Japan
Abstract
Intraseasonal variability in the Indonesian archipelago, especially in Sulawesi Sea, simulated in a high resolution ocean general circulation model is described and compared with available observations in detail. The global model is developed based on the Princeton Ocean Model, with 1/6 degrees horizontal grid resolutions. The model is driven for 16 years by smooth, climatological daily wind stresses calculated from NCEP reanalysis data. This forcing field for the model does not include the intraseasonal variation associated with Madden-Julian oscillations.
The annual mean upper-layer velocity field indicates an anti-clockwise circulation fitted into the Sulawesi Sea, which constitutes one of the routes connecting the Mindanao Current to the North Equatorial Countercurrent in the western Pacific Ocean. This is consistent with a view inferred from available observations. Unlike this annual mean image, the Sulawesi Sea is occupied by a chain of eddies, with typical horizontal scale of about 300 km, in the snapshot field. Those eddies are generated in a region south of Mindanao Island with about 40 days interval, and they propagate to the west into the Sulawesi Sea with the phase speed of 19 cm/s. The frequency of the eddy generation is consistent with recent analysis of the current meter data obtained from two moorings north of Halmahera Island. Those strong intraseasonal variability in the Sulawesi Sea is highly damped as they move through the Indonesian archipelago in this model, and the upper-layer velocity variation at the Timor passage does not show the intense intraseasonal signal.
The net transport through Makassar Strait, Molucca Sea, and Halmahera Sea indicate significant intraseasonal oscillations with a typical amplitude of about 5 Sv associated with the above eddy activity.
