Modeling Interaction of a Tropical Cyclone with Its Cold Wake

Monday, 18 April 2016: 1:45 PM
Miramar 1 & 2 (The Condado Hilton Plaza)
Sue Chen, NRL, Monterey, CA; and R. L. Elsberry and P. A. Harr

This study examines the tropical cyclone (TC) intensity response to its cold wake first with time invariant stationary cold wakes using an uncoupled version of the Coupled Ocean/Atmosphere Mesoscale Modeling System for Tropical Cyclones (COAMPS-TC) and then with simulated cold wakes from the two-way air-ocean coupled version. These simulations reveal a new dynamical pathway that governs the time scale of the TC intensity reduction due to interaction with its cold wake. In concert with the conventional thermodynamic pathway, both can modulate the TC structure and intensity change.

The physical processes governing the complex dynamical pathway induced by the ocean cold wake revealed the shape and location of the wake are relevant to the TC intensity change because they affect the time delay of the vortex spin-down. it is found a long-trailing wake or irregularly shaped wake within the eyewall region forces a dynamic response that tends to offset the negative effect of reduced enthalpy flux and increase the time delay of the vortex spin-down. In addition, a 1 – 2 m s-1 increase of low- to mid-level inflow referred to as the “wake jet” occurs above an atmospheric cold pool that is induced by the reverse sensible flux transfer over the trailing cold wake that is augmented by negative long wave fluxes at night-time. As the low-level boundary level boundary inflow crosses the ocean wake, air parcels can be deflected upward and turned toward the center of TC, which helps retain the moisture within and above the boundary layer. Significant wake cooling underneath the eye also tends to damp the vorticity gradient in the eyewall region, which forces the eyewall to transition from an unstable ring vortex to a shallower stable Rankine-like vortex.

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