A model simulation on the circulation in the Sea of Okhotsk and the East Sakhalin Current

Abstract

Numerical model experiments have been conducted to clarify the circulation in the Sea of Okhotsk. The Princeton Ocean Model, which uses a vertical sigma coordinate, is adopted with the realistic topography. The East Sakhalin Current (ESC) is reproduced in the experiment forced by the annual mean wind stress. The ESC in the model consists of two components: a nearshore component on the shelf and an offshore one over the shelf slope, which is consistent with the drifter observations. The offshore component is interpreted as the western boundary current of the cyclonic circulation driven by the positive wind stress curl. The nearshore component is driven by the alongshore wind, regarded as an “arrested topographic wave” (ATW). The seasonal and interannual variations of the ESC transport are examined with the experiments forced by the daily wind stress for the period of 1985–1999. The model well reproduces the variabilities of the transport and structure of the ESC observed with the mooring array. Although a precise Sverdrup balance does not hold in the interior region, the amplitude of the monthly mean ESC transport corresponds roughly to one third of the Sverdrup transport with a phase lag of about a month. The transport variation of the nearshore component is explained well by integration of the onshore Ekman flux, which is consistent with the ATW theory. The circulation of the Okhotsk Sea and the transport of the ESC are affected only slightly by surface heat flux.