Variability In The Kuroshio Region And Its Effects On The East China Sea

The variability of the temperature, salinity and volume transport in Kuroshio andTaiwan Strait in24°section east of Taiwan were analyzed based on the SODA data.We obtained that the Kuroshio volume transport (KVT) had a rising tendency and hadincreased about2.75Sv in recent50years. Accompany with the increase of the KVT,the volume transport of the Taiwan Strait Current (TSC) increased as well. Thetemperature of the Taiwan Strait and the upper100m area in Kuroshio increasedobviously in the recent50years and the warming rates could reach0.0030°C/monthand0.0011°C/month, respectively. Moreover, the salinity of these two areas had adecrease tendency and the rates were-3.1470e-4/month and-2.5733e-4/month,respectively.Based on the ROMS model, using the5’×5’ spatial resolution grids and takingSODA assimilation data as the forcing boundary, we simulated the circulation,temperature and salinity in the East China Sea. And then we analyzed the effects onthe physical environment of the East China Sea (ECS) by altering the open boundary.After comparing the sensitive experiments with the control run, we obtained the mainconclusions shown as following.Firstly, the changing of the KVT could contribute to variations of the volumetransport across the main transects in ECS. When the KVT increase, the volumetransport of the Tokara Strait (TS) increase as well, and that the increment of the TSwas even larger than that of the KVT. At the same time, the volume transport acrossthe Tsushima Strait (TUS) decreased apparently. In contrary, with the decrease of theKVT, the volume transport of the TS decrease in a larger degree, accompany with theincrement in TUS.The intrusion of the Kuroshio along the200m isobaths varied in three locations when the KVT changed, which were northeast of Taiwan, around122.7~124.3°Eand124.4~124.7°E, respectively. The intrusion northeast of Taiwan was influencedmore by the TSC than by the Kuroshio. When the KVT increase, it accompanied withthe strengthen of the TSC and the increase of the TSC volume transport would restrictthe intrusion of the Kuroshio northeast of Taiwan in turn. As the same, along with thedecrease of the KVT it would be a low volume transport of the TSC, which furtherlead to an increment of the Kuroshio intrusion. The Kuroshio onshore intrusionaround122.7~124.3°E varied the opposite way as the intrusion northeast of Taiwan,which means that the increase of the KVT will accompany with the increase intrusionat this location. The Kuroshio onshore intrusion around122.7~124.3°E varied thesame way as the intrusion northeast of Taiwan. When the KVT increase, the intrusiondecreased at this location. In conclusion, we find out that with the increase of theKVT, the whole intrusion along200m isobaths will weaken. The variations of thevolume transport in those transects due to the change of the KVT could also be seenclearly in the variation of the current velocity.The large KVTA corresponded with the warming in the Kuroshio upper100marea and the Taiwan Strait area, which leaded to the warming of the Donghai Sea. Incontrary, the temperature of the two areas was cold in the low KVTA year andcontributed to the cooling of the Donghai Sea. But when the KVTA decrease, it wouldbenefit to the onshore intrusion of the Kuroshio, which would further cause thewarming of these areas, especially in the bottom of the intrusion area. By the way, theother areas would be cooling with the relatively low temperature of the Kuroshio andTSC. The increase of the KVT and the TSC would weaken the intrusion of theKuroshio, which would further induce the extension of the cool water tongue in theYellow Sea and lead to the cooling. In the contrary, the decrease of the KVT wouldcontribute to the warming of the cool water tongue areas in the Yellow Sea.The salinity of the Kuroshio upper100m area and the Taiwan Strait area variedin an opposite way to the KVT. Their decrease in salinity leaded to most areas in theECS, both surface and bottom, lower their salinities. At the same time, when the KVT decrease, the salinities of the Kuroshio main axis area and the Taiwan Strait increase,which would increase the salinity of the ECS. Whereas, the salinity of the TaiwanStrait was mainly influenced by the Minzhe Coastal Current and it could only exhibitincreasing salinity in summer and autumn. Otherwise, the salinity in the surfaceshowed high correlation with the expansion of the Changjiang diluted water. Insummer, when the KVT increase, the range of the Changjiang diluted water could berestricted due to the increase of the TSC and then the north boundary of the dilutedwater and the Tokara Strait area increase salinity. In the contrary, the decrease of theKVT would lead to the decrease of the TSC, which would extend the coverage of theChangjiang diluted water and caused the salinity decrease. The variation of thebottom salinity was relatively small compared to the surface salinity.