Exceptional Surface Wind Gusts in a Tropical Cyclone Large Eddy Simulation

Tuesday, 19 April 2016: 1:30 PM
Ponce de Leon A (The Condado Hilton Plaza)
Richard Rotunno, NCAR, Boulder, CO; and G. H. Bryan and D. P. Stern

Surface wind gusts exceeding 110 m/s are a feature of eddies that occur in our high-resolution large eddy simulation of an idealized tropical cyclone. Current observational work suggests that such wind gusts are within the realm of the possible. In the present study we have identified a coherent structure among the simulated large eddies that is associated with the high-speed surface wind gusts. The structure appears tornado-like in that it has a strong local pressure drop in association with high values of vertical vorticity. The associated circulation is, however, very shallow, essentially below the level of maximum azimuthal mean wind (~500m). These tornado-like eddies have maximum amplitude in the simulated azimuthal-mean eye-wall boundary layer. A ​​kinetic-energy budget in this region reveals the importance of the shear-production term associated with the vertical shear of the azimuthal wind and the amplification of those eddies by the so-called 'rapid-distortion' effect associated with the action of the radial variation of the azimuthal mean radial velocity in the TC corner flow.
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