Eddy-Resolving Simulations for the Asian Marginal Seas Using ROMS

Tony Song JPL, California Institute of Technology Tao Tang Hong Kong Baptist University

EQ

10°S

10°N

20°N

30°N

40°N

100°E 120°E 140°E

ASIA

Sea of Japan

South China Sea

East China Sea

Celebes Sea

Flores Sea

PACIFIC

NEC

NECC

MC

KC

Importance:

• Water Exchange

• Indonesian throughflow

• Warm pool & El Nino

Characteristics:

• Complex geometry

• Sleep topography

• Monsoon winds

• Strong currents

Observations: A detached warm eddy from Kuroshio was observed near the Luzon Strait (Li et al. 1998).

warm ring centerAug. 1994

Previous Studies

Fang, G. H. (1995): The structure of the Taiwan-Tsushima-Trugaru Current System and its relation to the Kuroshio. Marine Sciences. 4, 43-48.

Hsueh, Y., J. R. Schults, and W. R. Holland (1997): The Kuroshio flow-through in the East China Sea: A numerical model, Prog. Oceanog. 39, 79-108.

Pohlmann, T. (1987): A three-dimensional circulation model of the South China Sea, in Three-Dimensional Models of Marine and Estuarine Dynamics, edited by J.C.J. Nihoul and B.M. Jamart, pp. 245-268, Elsevier, New York

Metzger, E. J. and H. E. Hurlburt (1996): Coupled dynamics of the South China Sea, the Sulu Sea, and the Pacific Ocean, J. Geophys. Res. 101, 12331-12352.

Model Description

The model uses curvilinear grid with a variable resolution from 10x10 km for the complex geometry of the Asian marginal seas and 30x30 km grid for the eastern Pacific.

Initialized with Levitus T and S; forced by the monthly mean air-sea fluxes of momentum, heat, and freshwater from COADS.

Closed in the north and west, open in the south and east by combining the radiation scheme with nudging technique (Marchesielo et al. 2001)

The challenge is the topographic representation from shallow (e.g. ECS, 60 m) to deep region (Pacific, 5 km) without losing the resolution in the surface layer.

Z = (1+s) + hs + (H-h)c(s), the s-coordinate (Song&Haidvogel 1994)

shallow deep

5000m

10mh

Model Results

Surface layer circulation Deep layer circulation Vertical structure Water exchanges between AMS and Pacific

Kuroshio eddy

Cyclonic circulation

Tsushima Current

Mindanao Current

Strong Kuroshio intrusion

Weak TSWC

cyclones

Deep Western Boundary Current

To SCS

To Selebes

Kuroshio warm rings

Cold and fresh

Upwelling Downwelling

Selebes Sea Luzon Strait

Vertical Structure

Conclusions and Discussion

High-resolution and low-viscosity are key factors for a better representation of the exchange of waters through narrow straits and passages.

The detached eddies near the Luzon Strait play a role in transporting warm and salty water into the SCS, while the cyclonic circulation in the Celebes Sea play a role in contributing cold water to the throughflow.

The WDBC of the Pacific Ocean is found to provide fresher waters to the SCS and the Celebes Sea.

However, it is not clear how much they contribute to the water mass of the SCS water and the throughflow. Future study will focus on model-data comparisons.

Dinner Time