| As the thermal fronts and upwelling-related lower SST zones being detected by four years of AVHRR-derived SST images, a three-dimensional primitive equation numerical model has been applied to study the physical mechanisms for the formation of fronts in the Taiwan Strait. Summertime mean AVHRR-derived SST image indicates that there exist lower SST zones along the northwestern and southwestern coasts of the Taiwan Strait and in the sea area between the Taiwan Bank and the Penghu Islands. The thermal fronts with large SST gradient are thus formed narrowly adjacent to the lower SST zones. The numerical modeling of seven major tidal constituents (M2, S2, K1, O1, P1, N2 and K2) demonstrates a belt with high kinetic energy of tidal current between the Taiwan Bank and the Penghu Islands. The value of lg[h/(u*u*u)], where h is the depth in meter and u is the vertical mean tidal current amplitude in m/s, is calculated to examine the frontal position. It is shown that the contour lines with the value of lg[h/(u*u*u)] less than 3.5 exist in the sea area between the Taiwan Bank and the Penghu Islands. These small lg[h/(u*u*u)] areas are well-mixed by tides. The locations of contour lines lg[h/(u*u*u)] =3.0~3.5 are in good agreement with the thermal fronts detected by the satellite observations. As for the southwestern and northwestern coasts of the Taiwan Strait, the value of lg[h/(u*u*u)] is mostly less than 3.5 in the near shore areas. Therefore, it is suggested that the tidal mixing may play an important role on the formation of the fronts between the Taiwan Bank and the Penghu Islands, but the coastal upwelling may be a principal factor for the fronts along the southwestern and northwestern coasts of the Taiwan Strait while the tidal mixing may be another important factor if the front appears in the near shore areas. |
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