14A.1 A framework for studying the inner core of tropical cyclones using large eddy simulation

Thursday, 3 April 2014: 1:30 PM
Garden Ballroom (Town and Country Resort )
George H. Bryan, NCAR, Boulder, CO; and D. P. Stern and R. Rotunno

In this presentation we describe a framework for studying the inner core of tropical cyclones (encompassing the eye, eyewall, and principal rainband) using large eddy simulation (LES). We first spin-up a realistic mature TC using the axisymmetric version of the numerical model CM1. These results, plus perturbations, are then used as initial conditions for the 3D version of CM1, which is configured with an inner mesh suitable for LES (here, horizontal grid spacing Δ ≤ 62.5 m).

This talk will focus on two primary challenges with this approach: 1) the difficulty in transitioning to and maintaining resolved turbulence in the neutral shear flow within the LES mesh, and 2) the uncertainty associated with parameterized surface processes. We will describe solutions for these two challenges and, as a simple but informative method of verification, we will present azimuthally averaged output and compare against recent observation-based studies of TCs. We show that two features in particular --- the depth of the inflow layer, and the height of maximum winds --- are not reproduced well by our LES unless the two challenges discussed above are addressed adequately.

A companion presentation by D. Stern will focus on the turbulent structures within the eye/eyewall interface of the simulated TC, and another companion presentation by R. Rotunno will examine the effects of the simulated turbulence on the mesoscale dynamics of the TC.

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