Abstract
The circulation structure surrounding the Qingdao cold water mass in 2019 was investigated using three-dimensional ensembles of numerical simulations. This study reveals that a cold pool appears in early spring and reaches its peak in late May, and this pool is accompanied by local seasonal anticyclonic circulation. Momentum diagnostics reveal that vertical friction cannot be ignored because of the shallow topography and surface wind stress; as a result, the geostrophic balance is inapplicable in the Qingdao cold water mass region. Seasonal circulation mostly results from the balance of the pressure gradient, Coriolis, and vertical friction forces. The no-tide and no-wind numerical simulation results suggest that when the tidal forcing is turned off, unrealistically strong currents appear and are caused by the decrease in vertical friction in the no-tide simulation. Moreover, the direction of the eastern side of the anticyclonic circulation is reversed. Furthermore, the seasonal southwesterly monsoon contributes to the magnitude of the anticyclonic circulation, especially in the western portion of the anticyclonic circulation, by piling up the surface water eastward and further changing barotropic pressure gradient force. Additionally, upwelling occurs vertically around the Qingdao cold water mass and is influenced by tidal and wind forcings. The wind forcing affects upwelling (especially in the western part), which can be explained by Ekman pumping; the tides contribute to upwelling in the eastern part by reshaping the thermocline and further changing the barotropic and baroclinic pressure gradient force. Ensemble simulations are used, and a t test reveals that 51 % (90 %) of points, difference between the control run and the ensemble experiments without tidal forcing (and without wind forcing) is statistically significant.