Winter-spring fronts in Taiwan Strait

摘要

Fine structures of surface fronts during winter-spring in the Taiwan Strait and their evolution over time are studied using satellite and in situ data. At times, different water masses are interleaved into each other. The northward intruding warm water bifurcates into several branches, causing complicated multiple cross strait fronts with maximum surface temperature gradients at the fronts to be greater than 2°C/km. The mean surface velocity of the fronts estimated from a sequence of satellite images is between 0.15 and 0.3 m/s during the February–March 2001 frontal event. The speed appears to have accelerated during the latter stages from 0.2 m/s during March 2–4 to 0.3 m/s during March 4–6. The total northward transport associated with the passage of the fronts is estimated to be 0.6–1 Sv between February 16 and March 6, 2001. The timescale of the passage of the fronts through the entire Taiwan Strait is therefore at least four weeks. Hydrographic observations in February–March of 1998 and 2000 also demonstrate similar frontal events with strong vertical gradients of water temperature and salinity on the western side of the strait. The 1998 data also show clearly that the low temperature and low salinity Zhemin Coastal Current separates from the coast and enters into the middle of the strait, a feature consistent with the satellite observations.