The Analysis Of Summer Circulation Of The Bohai Sea

On the basis of a thermohaline data set obtained during the summer of 2006, the summer circulation of the Bohai Sea is analyzed with the consideration of the shallow water correction when calculating geostrophic current. Also the first baroclinic Rossby radius are calculated by using both WKB approximation and numerical method for further verification.The results indicate that, currents enter into the Bohai Sea though the north of the Bohai Strait and trun toward north in the middle of the central Bohai, finally form in a clockwise circulation with central location 120.5°E 39°N and radii about 50~60km, velocity about 10cm/s. In Liaodong bay, there is an anticlockwise circulation to the west Changxing island, with central location 120.8°E 39.7°N and radii about 50~60km. A flow goes toward the north along the east side of the Liaodong bay and turn to west in the north, mix with the coast current of the Liaodong bay and match down south. Beyond the Yellow River estuary, a flow towards to the northeast inflows into the high salinity current entering from the northern Bohai strait, when reaching Luan River estuary nearby turns aroud and forms an anticlockwise circulation. In Laizhou bay, there exists a weak clockwise circulation.The spatial distribution of the baroclinic Rossby radius and the baroclinic phase speed estimated by the two methods are nearly the same, which are both almost consistent with the distribution of the isobath of the Bohai Sea. The results of numerical method shows that, the maximum first baroclinic Rossby radius reaches up to 4.72 km in surrounding waters of the Beidaihe and the Changxing island, and the corresponding maximum baroclinic phase speed reaches to 0.44 m/s. The minimum baroclinic Rossby radius and phase speed are found in the Laizhou bay, which are 1.76 km and 0.16 m/s. In the central of the Bohai Sea, a minimum Rossby radius appeared near the inner Bohai strait and a maximum value appeared in the westward of the central Bohai Sea, which leads to the contour lines of the Rossby radius presenting a ‘S’ shape in NE-SW-direction. The result of the WKB approximation estimation is lower than the numerical estimation, mainly because that the WKB approximation is depended on weakly variation of the Buoyancy frequency, which is inappropriate when taken into the estimation of the first baroclinic Rossby radius and the first baroclinic phase speed in the summer of the Bohai Sea.Comparing the value and the distribution of the first baroclinic Rossby radius, it is mostly assured that the result is reliable for the radius of the summer circulation is far more larger than the corresponding baroclinic Rossby radius.