HR: 09:40h
AN: A11G-08    [Abstracts]
TI: Tropical-Cyclone Intensification and Predictability in Three Dimensions
AU: * Montgomery, M
EM: mtmontgo@nps.edu
AF: Michael Montgomery, Hurricane Research Division NOAA/AOML Rickenbacker Causeway, Miami, FL 33149, United States
AU: Montgomery, M
EM: mtmontgo@nps.edu
AF: Michael T. Montgomery, U.S. Naval Postgraduate School 589 Dyer Road, Monterey, CA 93943, United States
AB: We present numerical model experiments to investigate the dynamics of tropical-cyclone amplification and its predictability in three dimensions. For the prototype amplification problem beginning with a weak tropical storm strength vortex, the emergent flow becomes highly asymmetric and dominated by deep convective vortex structures, even though the problem as posed is essentially axisymmetric. The asymmetries that develop are highly sensitive to the surface moisture distribution. When a small random moisture perturbation is added in the boundary layer at the initial time, the pattern of evolution of the flow asymmetries is dramatically changed and a non-negligible spread in the local and azimuthally-averaged intensity results. We conclude that: 1) the flow on the convective scales is not deterministic and only those asymmetric features that survive in an ensemble average of many realizations can be regarded as robust; 2) there is an intrinsic uncertainty in the prediction of maximum intensity using either maximum wind or minimum surface pressure metrics. There are clear implications for the possibility of deterministic forecasts of the mesoscale structure of tropical cyclones, which may have a large impact on the intensity and on rapid intensity changes. Other aspects of vortex structure are addressed also including the analogous problem on a beta-plane, a prototype problem for tropical-cyclone motion. The results provide deeper insight into the dynamics of the intensification process and suggest limitations of deterministic prediction for the mesoscale structure. Larger-scale characteristics are found to be less variable than their mesoscale counterparts.
DE: 3329 Mesoscale meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting