5.2
The impact of dry mid-level air on hurricane intensity in idealized simulations with no mean flow
Scott Braun, NASA/GSFC, Greenbelt, MD; and J. Sippel and D. S. Nolan
This study examines the potential negative influences of dry mid-level air on the development of tropical cyclones, specifically, its role in enhancing cold downdraft activity and suppressing storm development. The Weather Research and Forecasting (WRF) model is used to construct two sets of idealized simulations of hurricane development in environments with different configurations of dry air. The first set of simulations begins with dry air located north of the vortex center by distances ranging from 0 to 270 km, while the second set of simulations begins with dry air completely surrounding the vortex, but with moist envelopes in the vortex core ranging in size from 0 to 150 km in radius. No impact of the dry air is seen for dry layers located more than 270 km north of the initial vortex center (~3 times the initial radius of maximum wind). When the dry air is initially closer to the vortex center, it suppresses convective development where it entrains into the storm circulation, leading to increasingly asymmetric convection and slower storm development. The presence of dry air throughout the domain, including the vortex center, substantially slows storm development. However, the presence of a moist envelope around the vortex center, even with an initial radius less than the radius of maximum wind, eliminates the deleterious impact on storm maximum intensity. Instead, storm size is significantly reduced. The simulations suggest that dry air slows intensification only when it is located very close to the vortex core at early times. When it does slow storm development, it is primarily by inducing outward moving convective asymmetries that temporarily shift latent heating radially outward away from the high-vorticity inner core.
Session 5, Structure and evolution of tropical and extratropical cyclones I
Tuesday, 2 August 2011, 10:30 AM-12:15 PM, Marquis Salon 456
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