Sub-seasonal variability of Luzon Strait Transport in a high resolution global model
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Sub-seasonal variability of Luzon Strait Transport in a high resolution global model ZHANG Zhengguang1 , ZHAO Wei1∗ , LIU Qinyu1 1
Physical Oceanography Laboratory, Ocean University of China Qingdao 266100, China
Received 17 July 2009; accepted 18 December 2009 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2010
Abstract The Luzon Strait is the main impact pathway of the Kuroshio on the circulation in South China Sea (SCS). Based on the analysis of the 1997–2007 altimeter data and 2005–2006 output data from a high resolution global HYCOM model, the total Luzon Strait Transport (LST) has remarkable subseasonal oscillations with a typical period of 90 to 120 days, and an average value of 1.9 Sv into SCS. Further spectrum analysis shows that the temporal variability of the LST at different depth is remarkable different. In the upper layer (0–300 m), westward inflow has significant seasonal and subseasonal variability. In the bottom layer (below 1 200 m), eastward outflow exhibits remarkable seasonal variability, while subseasonal variability is also clear. In the intermediate layer, the westward inflow is slightly bigger than the eastward outflow, and both of them have obvious seasonal and subseasonal variability. Because the seasonal variation of westward inflow and eastward outflow is opposite, the total transport of intermediate layer exhibits significant 50–150 days variation, without obvious seasonal signals. The westward Rossby waves with a period of 90 to 120 days in the Western Pacific have very clear correlationship with the Luzon Strait Transport, this indicates that the interaction between these westward Rossby waves and Kuroshio might be the possible mechanism of the subseasonal variation of the LST. Key words: Luzon Strait Transport, subseasonal variability, Rossby waves
1 Introduction The Luzon Strait is the main pass way between the South China Sea (SCS) and the Western Pacific Ocean, with a width of more than 350 km and a depth of more than 2 500 m. When the northward Kuroshio flows to the Luzon Strait, it may have complicated water exchange with the SCS, which has a prominent impact on the circulation of the northeastern SCS. The water exchange via Luzon Strait compensates 47% heat receipts and 90% freshwater receipts gotten by SCS from the atmosphere (Qu et al., 2006). As discussed by previous studies, changes of SST in SCS can result in dramatic changes in weather patterns across the Indo-Pacific basin (Ashok et al., 2001; Neale and Slingo, 2003; McBride et al., 2003), which implies that the Luzon Strait Transport (LST) is expected to play an important role in regulating the SST patterns and vertical stratification in SCS and its adjoining tropical Indian-Pacific oceans. It is also suggested that the LST transfers the ENSO signal from the Western Pacific Ocean into SCS (Qu et al., 2004). Furthermore, the existence of LST significantly (by as much
as 47%) reduces the Indonesian Through Flow (ITF) heat transport (Tozuka et al., 2007). As one of the primary links in the global water exch
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