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A vorticity-divergence view of internal wave generation by tropical cyclones: insights from Super Typhoon Mangkhut
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  • Noel G. Brizuela,
  • T. M. Shaun Johnston,
  • Matthew H Alford,
  • Olivier Asselin,
  • Daniel L. Rudnick,
  • Jim Moum,
  • Elizabeth J Thompson,
  • Shuguang Wang,
  • Chia-Ying Lee
Noel G. Brizuela
University of California, San Diego, University of California, San Diego

Corresponding Author:nogutier@ucsd.edu

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T. M. Shaun Johnston
Scripps Institution of Oceanography, Scripps Institution of Oceanography
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Matthew H Alford
Scripps Institution of Oceanography, Scripps Institution of Oceanography
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Olivier Asselin
Scripps Institution of Oceanography, UC San Diego, Scripps Institution of Oceanography, UC San Diego
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Daniel L. Rudnick
Scripps Institution of Oceanography, Scripps Institution of Oceanography
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Jim Moum
Oregon State University, Oregon State University
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Elizabeth J Thompson
NOAA Earth System Research Lab, NOAA Earth System Research Lab
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Shuguang Wang
Nanjing University, Nanjing University
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Chia-Ying Lee
Lamont Doherty Earth Observatory, Lamont Doherty Earth Observatory
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Abstract

Tropical cyclones (TCs) are powered by heat fluxes across the air-sea interface, which are in turn influenced by subsurface physical processes that can modulate storm intensity. Here, we use data from 6 profiling floats to recreate 3D fields of temperature (T), salinity (S), and velocity (u,v,w) around Super Typhoon Mangkhut (western North Pacific, September 2018). Vertical profiles of T and S show the gradual mixing of rainfall and thermocline waters into the mixed layer with diffusivities as high as κ~10^-1 m^2 s^-1, causing an asymmetric cold wake of sea surface temperature (SST). A linear model is used to explain observational estimates of vorticity (ζ), divergence (Γ), and their relation to w. Coupling between ζ and Γ gives rise to near-inertial waves (NIWs) in the TC wake. Observations agree with both output from a 3D coupled model and a linear theoretical statement of inertial pumping. Lastly, we discuss the role of turbulence in rain layer destruction and estimate that κ>10^-3 m^2 s^-1 above ~110 m depth up to 600 km behind the TC. These analyses provide an observational summary of the ocean response to TCs, demonstrate the advantages of ζ and Γ for the study of internal wave fields, and provide conceptual clarity on the mechanisms that lead to NIW generation behind TCs.