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Li P.,Ocean University of China | Fu G.,Physical Interaction Lab | Lu C.,National Science Foundation | Fu D.,Ocean University of China | Wang S.,Ocean University of China
Weather and Forecasting | Year: 2012

In this paper, a dense sea fog event that occurred over the Yellow Sea (YS) on 9 March 2005 is investigated using the Weather Research and Forecasting Model version 3.1.1 (WRF v3.1.1). It is shown that theWRF can reasonably reproduce the main features of this fog case with a newly implemented planetary boundary layer (PBL) scheme developed by Mellor-Yamada-Nakanishi-Niino (MYNN). The low-level jet (LLJ) associated with this fog episode played an important role in triggering the turbulence. During the fog formation, sea fog extended vertically with the aid of turbulence. The mechanical production term resulting from wind shear contributed to the generation of the turbulence. WRFsimulation results showed that the fog layer was thicker in the northeastern part of the YS than that in the southwestern part due to the intensity of the inversion layer and the LLJ. The topography test in which the mountain region in Fujian Province was removed showed that the roles of topography were to prevent the moisture from extending to land, to intensify the inversion layer, and to enhance the intensity of LLJ, as well as to elevate its altitude. © 2012 American Meteorological Society.

Xu L.,Physical Interaction Lab | Xie S.-P.,Physical Interaction Lab | Xie S.-P.,University of Hawaii at Manoa | Liu Q.,Physical Interaction Lab | And 2 more authors.
Journal of Oceanography | Year: 2012

Response of the North Pacific subtropical countercurrent (STCC) and its variability to global warming is examined in a state-of-the-art coupled model that is forced by increasing greenhouse gas concentrations. Compared with the present climate, the upper ocean is more stratified, and the mixed layer depth (MLD) shoals in warmer climate. The maximum change of winter MLD appears in the Kuroshio-Oyashio extension (KOE) region, where the mean MLD is the deepest in the North Pacific. This weakens the MLD front and reduces lateral induction. As a result of the reduced subduction rate and a decrease in sea surface density in KOE, mode waters form on lighter isopycnals with reduced thickness. Advected southward, the weakened mode waters decelerate the STCC. On decadal timescales, the dominant mode of sea surface height in the central subtropical gyre represents STCC variability. This STCC mode decays as CO 2 concentrations double in the twenty-first century, owing both to weakened mode waters in the mean state and to reduced variability in mode waters. The reduced mode-water variability can be traced upstream to reduced variations in winter MLD front and subduction in the KOE region where mode water forms. © 2011 The Oceanographic Society of Japan and Springer.

Lu J.,Physical Interaction Lab | Liu Q.,Physical Interaction Lab
Journal of Geophysical Research: Oceans | Year: 2013

Based on analysis of both observational data and data-assimilation model product, it is shown that there exists a gap-leaping path of the Kuroshio in the Luzon Strait. Numerical results of two sets of Hybrid Coordinate Ocean Model twin experiments indicate that bottom topography and islands in Luzon Strait exert control of Kuroshio's gap-leaping behavior, especially existence of sharp northeast cape of Philippine Island is one of the most important factors for the gap-leaping Kuroshio path in model simulation. Corresponding to the gap-leaping Kuroshio, there is steep westward shoaling of thermocline in Luzon Strait. The enhanced upper-layer stratification in South China Sea due to westward shoaling thermocline results in strong zonal potential vorticity (PV) gradient (one order higher than ß-induced planetary PV gradient), and PV isolines are always parallel to the gap-leaping path of the Kuroshio. This PV front acts as a dynamic barrier in the Luzon Strait, blocking the westward propagating Rossby waves and eddies from Pacific. This blocking effect is verified through sea-surface height anomaly spectrum analysis, Radon Transform based Feature-Tracking method, and eddy identification and tracking method. Numerical twin experiments demonstrate from another point of view that the gap-leaping Kuroshio can efficiently block the westward propagating Rossby wave and eddy energy, while the fluctuating Kuroshio is less efficient for blocking. © 2013. American Geophysical Union. All Rights Reserved.

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