Evaluation of Global Ocean Models on Simulating the Deep Western Boundary Current in the Pacific

Abstract

ABSTRACT Although it is an important branch of the global overturning circulation, the deep western boundary current (DWBC) in the Pacific was poorly understood because of sparse observations. Six state-of-the-art global ocean model outputs were used herein to evaluate their performance in simulating the DWBC in the Melanesian Basin (MB) and the Central Pacific Basin (CPB). These model outputs were compared with historical observations, in terms of water-mass characteristics, spatial structure, and meridional volume transport of the DWBC, as well as seasonal variation. The results showed that most of the models reproduced the DWBC well in the two basins. Except for the Ocean General Circulation Model for the Earth Simulator (OFES) with its obvious cold and salty biases, the models had minor deviations in temperature and salinity in the deep layer. These models can reconstruct the spatial structure of the DWBC in detail and simulate appropriate transports of the eastern branch of the DWBC, ranging from 6.36 Sv to 8.55 Sv (1 Sv = 106 m3 s−1). The western branch of the DWBC was underestimated by all the models except the Hybrid Coordinate Ocean Model (HYCOM), which simulated a transport of 4.48 Sv. For the DWBC, HYCOM performed best with a total transport of 12.84 Sv. Analysis of the temperature and salinity from Levitus data demonstrated the existence of annual and semi-annual cycles in the deep water of the MB and CPB, respectively, with a warmer and saltier water mass in summer and autumn. Overall, the six models were able to simulate the seasonal variations of temperature and volume transport of the DWBC in the Pacific. The seasonal signals probably originated from the DWBC upstream and propagated along its pathway.