Seasonal variation of volume transport in the major inflow region of the Taiwan Strait: the Penghu Channel

Eight cruises of current measurements along a zonal transect (∼31.84 km) across the major inflow region of the Taiwan Strait, the Penghu Channel, were carried out using the shipboard Acoustic Doppler Current Profiler during 1999–2001. On each cruise, the measurement was repeated twice along the transect with a time lag of 6 h and 12 min, and the repeated data were averaged to eliminate the dominant semidiurnal tidal currents. Velocities, after removing semidiurnal tides, suggest a strong northward flow in the channel, with a speed of about 100 cm/s in the upper 50 m in summer. The northward flow becomes much weaker in winter. The calculated throughflow transports vary seasonally and are correlated with the change of the East Asia monsoon. The estimated transport is around 0 during the peak northeast monsoon in winter, increases from 0.5 to 1 Sv (1 Sv=106 m3/s) as the northeast monsoon weakens in spring, peaks to 1.5 Sv at the end of southwest monsoon in summer, and decreases rapidly from 1.5 to 0 Sv when the northeast monsoon intensifies in fall. The error, mostly induced by unfiltered diurnal tidal currents, is estimated to be±0.20 Sv in the transport calculation.