Abstract
Near-inertial waves (NIWs) are a kind of internal wave, which are usually generated by synoptic wind forcing and play an important role in the oceanic energy budget. However, the lack of in situ observations limits our understanding of NIWs to some extent. Through a comparison with in situ observations, in this study, we first showed that the hybrid coordinate ocean model reanalysis results could reasonably reproduce the typhoon-induced NIWs, and we then adopted these data to investigate the NIWs induced by typhoon Megi in 2010 in the South China Sea (SCS). The results indicate that Megi-induced near-inertial kinetic energy was mainly concentrated in the SCS Basin. In the vertical direction, Megi-induced NIWs could propagate to 1000 m depth. The damping and modal content of Megi-induced NIWs were site-dependent: In the region near Megi’s track, NIWs were dominated by the first three baroclinic modes and damped quickly; whereas in two zones to the west of the Luzon Island and Luzon Strait, the e-folding time of Megi-induced NIWs could be longer than 20 days and higher modes (mode-4 to mode-7) were enhanced several days after the passage of Megi. Possible mechanisms of these phenomena were also explored in this study.
Highlights
Near-inertial waves (NIWs) are a kind of internal wave, which are ubiquitous in the global ocean
It is clearly shown that Megi-induced NIWs at point A were dominated by mode-2 which accounted for 45% of the total near-inertial kinetic energy density (NIKE)
Through a comparison with in situ 2010 in the South China Sea (SCS) were investigated in this study
Summary
Near-inertial waves (NIWs) are a kind of internal wave, which are ubiquitous in the global ocean. In the internal wave spectrum, NIWs appear as a predominant peak near the local inertial frequency, and act as a dominant mode of high-frequency variability in the ocean [1]. NIWs play an important role in the oceanic energy budget [2,3], as they can cause intense shear [4,5] and contribute to the elevation of turbulent mixing [6,7]. There are various mechanisms that can cause NIWs, among which, the most important is synoptic wind forcing. Nonlinear wave–wave interaction, including parametric subharmonic instability [17,18,19] and resonant triad interaction [20,21,22], lee waves [23], frontal jets [24] and mesoscale eddies [25], can induce NIWs under some conditions
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