Bumpy topographic and Kuroshio impacts on the transbasin evolution of large-amplitude internal solitary wave in the northern South China Sea

The bumpy bottom topography is a quite common feature in the northern South China Sea. The characteristic width and height of these bumps over continental slope/shelf regions can be very comparable to those of the large-amplitude mode-1 internal solitary waves (ISWs). However, there is still little knowledge about the specific impacts of the bumps on the evolution of transbasin ISW. Here, we show that the prominent bumps over both continental slope and shelf regions play significant roles in modulating the wave transformation and energy variation. The bump over continental slope is capable of triggering solitary-like mode-2 internal wave packet, and the bump over continental shelf can further result in three wave groups. Up to 80% of the ISW energy is lost over the continental slope region, while over the shelf region another 10% of ISW energy is lost. Both onshore- and offshore-propagating internal waves are found to be excited due to the influence of bumpy bottom topography, and are clarified by the local generation mechanism. Further, the Kuroshio effects on the spatiotemporal variability of the long extended internal solitary wavefront in the northern South China Sea are analyzed on the basis of the reconstructed daily ocean’s interior fields covering a 23-year period (1993-2015). We show that, for nearly half of the 23-year time period, the propagation of ISW front is significantly speeded or slowed by the Kuroshio intrusions. The Kuroshio looping path is the most efficient intruding state in speeding the ISW front. There are up to 60% and 77% of the looping time period when the northern and southern portion of the front are speeded, respectively. However, the Kuroshio leaking and leaping paths are comparatively less efficient in speeding the propagation of ISW front, especially at the southern portion, where the front are speeded at only 36% and 15% of the leaking and leaping time period, respectively. Also, we find that the propagation of the ISW front affected by Kuroshio intrusions exhibits an obvious north-south difference. Approximately, in a quarter of the 23-year time period, the northern portion of the ISW front is significantly speeded relative to the southern portion, or vice versa. These significant variations of ISW front can be illustrated according to the three typical Kuroshio intruding patterns.