The analysis of large-scale turbulence characteristics in the Indonesian seas derived from a regional model based on the Princeton OceanModel

[摘要] Turbulence characteristics in the Indonesian seas on the horizontal scale oforder of 100 km were calculated with a regional model of the Indonesian seascirculation in the area based on the Princeton Ocean Model (POM). As is wellknown, the POM incorporates the Mellor–Yamada turbulence closure scheme. Thecalculated characteristics are: twice the turbulence kinetic energy per unitmass, q²; the turbulence master scale, ℓ; mixing coefficients ofmomentum, K_M; and temperature and salinity, K_H; etc. The analyzedturbulence has been generated essentially by the shear of large-scale oceancurrents and by the large-scale wind turbulence. We focused on the analysisof turbulence around important topographic features, such as the LifamatolaSill, the North Sangihe Ridge, the Dewakang Sill, and the North and SouthHalmahera Sea Sills. In general, the structure of turbulence characteristicsin these regions turned out to be similar. For this reason, we have carriedout a detailed analysis of the Lifamatola Sill region because dynamicallythis region is very important and some estimates of mixing coefficients inthis area are available.

Briefly, the main results are as follows. The distribution of q² is quiteadequately reproduced by the model. To the north of the Lifamatola Sill (inthe Maluku Sea) and to the south of the Sill (in the Seram Sea), large valuesof q² occur in the deep layer extending several hundred meters above thebottom. The observed increase of q² near the very bottom is probably dueto the increase of velocity shear and the corresponding shear production ofq² very close to the bottom. The turbulence master scale, ℓ, wasfound to be constant in the main depth of the ocean, while ℓ rapidlydecreases close to the bottom, as one would expect. However, in deep profilesaway from the sill, the effect of topography results in the ℓ structurebeing unreasonably complicated as one moves towards the bottom. Values of 15to 20 × 10⁻⁴ m² s⁻¹ were obtained for K_M and K_H in deepwater in the vicinity of the Lifamatola Sill. These estimates agree well withbasin-scale averaged values of 13.3 × 10⁻⁴ m² s⁻¹ founddiagnostically for K_H in the deep Banda and Seram Seas(Gordon et al., 2003) and a value of 9.0 × 10⁻⁴ m² s⁻¹ founddiagnostically for K_H for the deep Banda Sea system(van Aken et al., 1988). The somewhat higher simulated values can beexplained by the presence of steep topography around the sill.

[学科分类] 海洋学与技术