A Numerical Study Of The Yellow Sea Temperature And Circulation Responses To Different Frequency Wind

The Yellow Sea (YS) is a tidal energetic continental shelf sea, besides the energetic tidal forcing, winds also play an important role in the turbulence and mixing process. Studying the ocean responses to the different wind forcing frequency, especially on the research of the temperature and circulation characteristics under the forcing of the synoptic scale wind field, is the basic requirement of building up the high temporal and spatial resolution three-dimensional marine hydrodynamic forecasting system.In this article, we simulate the YS responses to different wind forcing frequency using the Regional Ocean Modeling System (ROMS), comparing the temporal and spatial distributions and time variations of the temperature and the circulation under the forcing frequency of monthly, daily and 3-hourly, respectively. We mainly talk about the situations in summer because the temperature is vertically uniform in winter. Although the seasonal averaged circulation pattern shows no obvious difference in all experiments, the summer averaged temperature field and the synoptic time scale horizontal and vertical velocity show high sensibility to the wind forcing frequency. When increasing the wind forcing frequency, the temperature of the upper mixed layer decreases while increasing below it due to the enhanced the vertical mixing process generated by the wind induced near inertial internal waves around the temperature thermocline. On the other hand, the near inertial oscillations appear in most areas of the Yellow Sea under the 3-hourly wind forcing frequency, which exist throughout the whole water depths, time intermittent, surfaced intensified and characterized by a first baroclinic mode in the vertical. At the same time, the vertical velocities are strengthened.We choose a typical strong wind event to compare the different characteristics of the YS temperature and current temporal and spatial variations because the strong relationship between the near inertial oscillation strength and the wind stress field. The results indicate that no matter whether there is tidal forcing, the drop of the sea surface temperature and the near inertial oscillations are well simulated. We conclude that the strong background tidal currents could obviously affect the ocean responses to the typhoon Bolaven:because of the tides, a tidal induced temperature front could be developed between the warmer water near the shore and the colder water off the shore. After Bolaven, the warmer water expands offshore, although the upper mixed layer temperature drop is significant right to the track, it is much more obvious of the near shore warmer water expansion west of the YS. On the other hand, the near inertial responses are weakened because of the tides, and the semidiurnal currents are still prominent. The near inertial velocities are characterized by a first baroclinic mode in the vertical. The near inertial energies in the upper mixed layer and below the thermocline are decreased because of the tides. In addition, Bolaven has little influences on the semidiurnal energies, and the near inertial responses to Bolaven are mainly distributed in the central areas of the YS.