Analysis Of Different Resolutions Of Wind Forcing On Sea Hydrodynamic Simulation

Sea surface wind field is one of the most important drives for the upper layer ocean, meanwhile, the data of the sea surface wind field is critical parameter for the ocean model simulating, especially the resolution of the wind field which will affect the outcome of the simulation. By utilizing FVCOM model and the data of the high resolution wind field as well as different new wind field data translating from the high resolution wind field, we did the numerical simulation of the barotropic flow field of Bohai Sea, so to analyze different resolutions of wind forcing on sea hydrodynamic simulation.The seasonal characteristics of Bohai Sea’s wind field:wind speed during autumn and winter is relatively higher with the average speed of 7-8m/s, mainly northerly winds consistently; However, in Spring and Summer, wind speed slow down to the average speed of 4-5m/s and its directions is Frequent and changeable, but most of the time toward south. Offshore wind speeds are higher than near-shore wind speeds, and this regional difference is more outstanding especially in autumn and winter. The changing pattern of the field wind resolution is consistent which primarily represented as coastal sea surface wind speed rising up, dramatic decreasing of the partial sea surface wind speed in central gulf, larger average changes of the wind directions near shore than off shore. The difference of flow speed increases as the resolution of wind field decreases. The change of temporal-spatial resolution of wind field basically shows that the sea surface wind field would fluctuate with time. The changes of monthly-averaged wind field is the most significant, sea surface wind speed and directions keep the same, but proportion of northerly wind increase over the year.Wind current of barotropic Bohai sea is weak, the depth of average flow speed of spring, summer and winter is less than 4cm/s, but will reach to 6.7 cm/s in autumn. Surface field speed is higher than bottom field speed. Flow speed in Bohai Strait and winding coastline and headland is much stronger than in the open sea area and centers of three gulfs. There is a circulation in the middle of Bohai sea throughout the year, by the effect of wind field, topography and flow field of north Yellow sea, and its size, location, strength and directions is changing within one year. For example, clockwise structure in spring, summer and winter will turn into counter clockwise in autumn, circulating current is becoming strongest in autumn. Influenced by water coming in and out of the bay, structures between single eddy and double eddies are mutually transformed into each other. Bottom flow field struct affected by surface flow field’s Ekman effect as well as water accumulation, therefore, bottom structure differentiated from surface structure greatly.Effects of special-resolution of wind field on flow field:in the same experiment, variation in the wind field has smaller effect on flow field in spring, summer and winter, flow speed lower around 0.1 cm/s primarily, however, some local area’s flow speed will increase. The variation in autumn is the largest. The effect of wind field on flow field increases as the resolution of wind field decreases. The range of the flow field speed changes will gradually expand in different experiments in the same month. The change is dramatic within near-shore area, and the change of outbound flow speed is especially significant in the south part of the Bohai Strait. Driven by the wind stresses, the change of surface flow speed is largely related to the change of wind speed. However, this effect will decrease along with deepening of the sea water; Flow speed change in bottom level is less than that on surface level. Yet change of the spatial-resolution wind field will not alter vertical structure of the flow field in open sea area. Only that the flow speed will decrease while the wind field spatial resolution decrease in the condition that the original flow direction keeps the same. Area of the change in vertical structure gradually expand, meanwhile, water flux through Bohai Strait gradually diminish.Effects of change of temporal-resolution wind field on flow field:compare to the 3 hours average wind field, the variation of 6 hours average driven flow is small. Daily average wind field have prominent influence on barotropic flow field, especially on the surface flow field. Monthly-average wind field have the most significant effect. During August and November, the flow field structure will change in most areas; maximum change of the flow speed will rise up approximately 10cm/s. As for monthly average wind field, the water flux through Bohai strait apparently changed from October to December.