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Special Session 5: Ocean-atmosphere interaction, multi-scale climate variability and their implication for biogeochemical processes |
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Variability of the current system in the tropical western Pacific Ocean: Numerical modeling study
Wednesday 11th @ 1130-1150
Room 1
Junlu Li* , The Hong Kong University of Science and Technology
Jianping Gan, The Hong Kong University of Science and Technology
Presenter Email: jliaw@connect.ust.hk
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| In the Western Pacific Ocean (WPO), the North Equatorial Current (NEC), Mindanao Current (MC) and Kuroshio Current (KC) form a circulation system, which is known as NMK. NMK is crucial in determining the ocean circulation and marine ecosystem of the China Seas (CS) through physical and biogeochemical substance transports between the WPO and the CS. However, the process and dynamics in the NMK and thus its linkage with corresponding processes in the CS remain largely unclear due to lacking of observational data and geophysical understanding. By combining remote sensing data, in situ ARGO measurements with results from the China Sea Multi-scale Ocean Modeling System (CMOMS), we conducted comprehensive studies on the spatiotemporal variability of the NMK and its underlying intrinsic physical process and controlling mechanism. The structures and intensities of the NEC, MC and KC, including their undercurrents, exhibited prominent spatiotemporal variabilities. The existence of Luzon Undercurrent (LUC) and Mindanao Undercurrent (MC) below KC and MC respectively were confirmed by model results. The multi-core structure of NEC Undercurrent was also successfully simulated. NEC, KC and MC transports showed prominent seasonality, which were large (small) in summer (winter). The temporal variation of the NEC birucation latitude (NECBL) was controlled by NEC flux center (NECFC) largely in both inter-annual and seasonal time scales, while the wind stress curl in the region contributed partly to its seasonal variability. Through dynamic analyses, we found that the intensity of the NEC, KC and MC were mainly controlled by the cross-stream pressure gradient force (PGF) under mainly geostrophic balance, and frequently modulated by ageostrophic effect arising from wind forcing in winter and from nonlinear advection in summer. Based on depth-integrated vorticity dynamics, we found that the origin of the cross-stream PGF is composed of baroclinicity, sloping effect and bottom PGF. The meridional shifting of the NEC was controlled by the along-stream PGF variation that was formed mainly by beta effect, partly offset by wind induced vertical viscosity, and adjusted by Modified Joint Effect Baroclinicity and Relief. The spatiotemporal variability of NEC, KC and MC was dynamically linked. This study revealed the three-dimensional, time-dependent variability of the NMK and provided new understandings of its underlying forcing mechanisms. |
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