Abstract
The Philippine Sea in the western Pacific is a region with high mesoscale eddy kinetic energy that is buffeted by intense typhoons. Such typhoons generate strong near-inertial waves (NIWs), making this region ideal for studying interactions between typhoon-driven NIWs and mesoscale eddies. To study such interactions, a field campaign was conducted in the Philippine Sea that targeted an anticyclonic eddy after the passage of Super Typhoon Mawar. The study was part of the US Office of Naval Research Departmental Research Initiative ARCTERX (Island Arc Turbulent Eddy Regional Exchange). During the campaign, ship and float-based velocity measurements revealed layers of intense vertical shear oscillating at slightly sub-inertial frequencies in the anticyclone. The shear layers were stronger toward the eddy center and coincided with patches of elevated turbulence. An idealized numerical simulation initialized with a symmetric eddy modeled after observations and forced by reanalysis winds was used to study the formation of NIWs by Typhoon Mawar and their interactions with the eddy. The model captured the structure and vertical propagation of the observed shear layers and demonstrated how the dynamics of the NIWs in the anticyclone are consistent with NIW trapping following the theory of ζ-refraction. The simulated shear layers were not as intense as those that were observed and could not explain the patches of enhanced turbulence. Processes not included in the model, more specifically the internal tides that are particularly strong in the Philippine Sea, likely contribute to the discrepancy. Energy exchange between the NIWs and the anticyclone diagnosed using the model output was weak, suggesting that typhoon-driven NIWs play a secondary role in the energetics of eddies in the Philippine Sea, or that the idealized nature of the model limited wave-mean flow energy exchange.