Coupling and propagating of mesoscale sea level variability between the western Pacific and the South China Sea

Abstract

The coupling and propagating features of mesoscale sea level variability between the western Pacific (WP) and the South China Sea (SCS) were studied based on time series analyses of satellite altimeter measured, along-track sea surface height anomalies (SSHA) along 21°N and the slope of the northern SCS. The analyses show that mesoscale sea level fluctuations in the WP have rather limited coherent effects on the SCS, and no statistically significant propagation of mesoscale variability through the Luzon Strait was observed except in the 45-day band. Evidence suggests that the 45-day fluctuation is very much likely a character of the Kuroshio originating from its low-latitude beginning.It is also suggested that the westward propagating Rossby waves will deform when they encounter the dynamical barrier of the Kuroshio. The Kuroshio will then acts on the SCS in its own way. The SCS is a relatively isolated system in the sense of coupling and propagating of oceanic mesoscale waves.

Pathways of mesoscale variability in the South China Sea

“…But the propagation velocities diminish to nearly zero at 122°E and 121°E in observations and simulations, respectively. It suggests that the directly westward propagation from the Pacific to the NSCS is not significant (Li et al, 2007).…”

“…So a 21-175 days band-pass filter is used to remove the low-frequent variability and suppress synoptic disturbances with periods shorter than 20 days. An additional harmonic filter is then applied to remove the possible tidal aliasing near 60-day (Li et al, 2007). This frequency band is similar to the MV definition in Wang et al (2000) except that they have to remove all signals shorter than 60 days due to strong tidal aliasing in previous altimetry products.…”

“…Although strong 3-6 months MV exists both in the NSCS and the western Pacific (Hu et al, 2001), Kuroshio appears to act as a barrier to the westward propagations of MV from the Pacific and only 45-day MV could enter the SCS via the Luzon Strait (Li et al, 2007). The investigation by Wu and Chiang (2007) also shows that the westward propagating eddies in the NSCS originate near the Luzon Strait rather than coming from the western Pacific.…”

Sea surface height oscillation with quasi-four-month period along the continental slope in the northern South China Sea

“…The Hovmöller diagrams of SSHAs are not shown because they can be referred to the work of Li et al (2007), who showed a similar space-time SSHA structure in the NSCS. Unlike that work, however, the SSHA values in the Hovmöller diagram analyzed here are cross-shore means of the high-pass filtered SSHAs in the selected area (the rectangular box in Fig.1), where the SSHO 4 resides.…”

“…These eddies increase the intraseasonal variation of sea surface height (SSH) (Zhuang et al, 2010). Documented periods of SSH intra-annual variation in the NSCS range from 1.5 to 8 months (Wang et al, 2000;Hu et al, 2001;Li et al, 2007). However, the dominant period of SSH intraseasonal variation along the continental slope has not been determined.…”