Multiscale analysis of typhoon-induced oceanic responses: A Case Study of Typhoon Kalmaegi in the South China Sea

A localized multiscale energetics framework is used to study the multiscale typhoon-induced upper oceanic responses, in the case of Typhoon Kalmaegi in the South China Sea. A diagnostic methodology of the time-varying energetics, on the basis of the multiscale window transform (MWT) —namely, localized multiscale energy and vorticity analysis (MS-EVA) decomposes HYCOM variable fields into a low-frequency background flow window, a mid-frequency flow window and a high-frequency process window. The background window represents mesoscale processes and Kuroshio currents well and the mid-frequency window captures near-inertial processes influenced by typhoon-induced wind stresses. The scale-scale kinetic energy transfers from the near-inertial window to the background window, mainly on the right-hand side of the typhoon track. Advection and pressure work redistribute energy contribute to the accumulation of kinetic energy in the mid-frequency flow window and enhances ocean mixing. Negative vorticity has a significant impact on the distribution and downward propagation of the near-inertial energy, leading to heterogeneity in the mixing of the upper ocean. We offer new insights into understanding the multiscale interactions between typhoons and the upper ocean.