Variability of Cross-shelf Penetrating Fronts in the East China Sea

Images of 8-day mean chlorophyll-a concentrations of the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard of Aqua Satellite from 2002 to 2007 and of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite from 1998 to 2007 are used to study the variability of the cross-shelf penetrating fronts (CPFs) in the East China Sea. The analysis suggests that the generation of the CPFs has strong seasonal-to-interannual variations, with more CPFs in summer and winter than in spring and fall. Each CPF lasts for a few days to a month. The majority of the fronts are triangle-shaped with their broad bases nearby the coast and their sharp heads penetrating into the middle shelf. There are over 40 CPFs with penetrating distances exceeding 100 km over the East China Sea during the past 10 years of the satellite era, with the maximum ones reaching the Kuroshio at the edge of the continental shelf. Of all the low cloud scenes of the satellite images, more than 25% contain at least one CPF. The high-frequency occurrence of the CPFs suggests that the CPFs play an important role in cross-shelf transport of heat, effluent, and land-derived materials in the East China Sea.The generation of the CPF is found to be influenced by winds and by intrinsic oceanic variability. In particular, the collision of wind-forced coastal jet with the Taiwan Warm Current is suggested as one of the mechanisms that generate the CPFs in the East China Sea.