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SUMMARY:Hurricane dynamics: on the role of Vortex Rossby Waves (VRWs) - Br
 unet\, G (Weather Science\, Met Office)
DTSTART:20131028T110000Z
DTEND:20131028T120000Z
UID:TALK48554@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Despite the fact that asymmetries in hurricanes\, such as spir
 al rainbands\, polygonal eyewalls and mesovortices\, have long been observ
 ed in radar imagery\, many aspects of their dynamics still remain unsolved
 \, particularly in the formation of the secondary eyewall. To fill this ga
 p\, a simple 2D barotropic model (Martinez et al.\, 2010) and the high-res
 olution PSU-NCAR non-hydrostatic mesoscale model (MM5) are used to study h
 urricane asymmetries (Chen et al.\, 2003\; Martinez et al.\, 2011).The Emp
 irical Normal Mode (ENM) diagnostics (Brunet\, 1994)\,  together with the 
 Eliassen-Palm (EP) flux calculations are used to isolate wave modes from t
 he model datasets to investigate their impact on the changes in the struct
 ure and intensity of the simulated hurricanes (Chen et al.\, 2003). \n\nTh
 e ENMs are obtained in a similar manner as Empirical Orthogonal Functions 
 (EOFs) but with the use using a quadratic form instead of Euclidean norm. 
 The quadratic forms are global invariants\, the pseudo-momentum and pseudo
 -energy wave activities\, of the linearized equations about a basic state 
 (Brunet and Vautard\, 1996). ENM theory bridges two important diagnostic t
 ools of geophysical fluid dynamics: principal component analysis and norma
 l mode theory.\n\nThe role of internal dynamics on concentric eyewall gene
 sis is further evaluated using the full physics MM5 simulation. The leadin
 g modes of the ENM diagnostics exhibit mainly characteristics of VRWs and 
 their contribution to the EP flux divergence induced two regions of maximu
 m tangential wind acceleration\; one inside the primary eyewall which acco
 unts for eyewall contraction and the other outside the primary eyewall whi
 ch explains the development of the secondary eyewall (Martinez et al.\, 20
 11).\n\nWe will point out the expected implication of these results in the
  context of numerical weather prediction at different space-time resolutio
 ns for intensifying and mature hurricanes of different strengths.\n
LOCATION:Seminar Room 1\, Newton Institute
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