Seasonal and Spatial Variations of the M2 Internal Tide in the Yellow Sea

The seasonality of internal tides is particularly conspicuous in shelf seas due to the dramatical variations in the marine environment. In this paper, the seasonal and spatial variabilities of M-2 internal tides in the Yellow Sea (YS) are investigated using a high-resolution numerical ocean model. The freshwater runoff of the Yangtze River is also considered. Because most nonlinear internal waves are of tidal origin, the simulated internal tides show good spatial consistency with the satellite-detected nonlinear internal waves. During summer, the M-2 internal tides are ubiquitous and originate from multiple generation sites (e.g., the west coast of the Korean Peninsula and the Yangtze River estuary). During other seasons, the spatial coverage of the internal tides becomes very limited. Multiple sources combined with seasonal onset and decay lead to complex seasonal interference patterns. The wavelengths vary both spatially and temporally, depending on the water depth and ocean stratification. Between spring and autumn, a seasonally reversed pattern of radiation of baroclinic energy flux is found in the southern YS, which may be induced by the seasonal variability of the YS Warm Current. Seasonal stratification controls the seasonality of the generation, propagation, and dissipation of internal tides and is maintained by the monsoon, seasonal circulation, and Yangtze River runoff. Our simulations suggest that, although internal tide dissipation is dispensable for the tidal energy budgets in the YS, internal tides seem to be the leading order contributor to the midcolumn diapycnal mixing, as they are more efficient mixers than barotropic tides. Plain Language Summary Due to limited in situ observations and lack of attention, the basic characteristics of internal tides (especially the seasonal) in the Yellow Sea (YS) are still poorly understood. In this study, we have investigated the seasonal behaviors of the M-2 internal tides in the YS by utilizing a numerical ocean model. The behaviors of the M-2 internal tides vary significantly by season, which are very active during summer but are very weak during winter. The seasonal stratification in the YS is thought to be responsible for the seasonal behaviors of internal tides. We also found that the mixing induced by internal tide is nonnegligible in the summer shelf sea.