Typhoons enhancing northward transport through the Taiwan Strait

Volume transport in the Taiwan Strait is usually northward for most of the year and varies seasonally because of the adjustment of the East Asian monsoon. Based on model simulations, the influence on this northward transport of every typhoon formed during the period 2005–2009 was examined. The results showed that there were four typhoons which enhanced northward transport during these five years. The current measurements, obtained from a buoy deployed in the Taiwan Strait, matched these events exactly. These typhoons had special moving tracks and life histories. They traveled westward in the area south of the strait or moved northward from the south to the north. Under the influence of such a typhoon, the prophase southward atmospheric forcing in the strait was weak and the anaphase northward atmospheric forcing (mainly along-strait wind stress) was strong, which is necessary and crucial in enhancing the northward transport. The ageostrophic process, another important driving factor in transport change, was generated mainly by local atmospheric forces inside the strait under the typhoon weather conditions and its effect on transport magnitude was comparable to that of direct atmospheric forcing. It first stored some energy from the atmospheric forcing to restrain the transport change, and then released the stored energy to prolong and even to intensify the enhanced northward transport.