SEMINAR: MPO Seminar: Dr. Robert Hart, TODAY, at 3:00 p.m., S/A103, Slab Seminar room

[Sandrine Apelbaum <sapelbaum@rsmas.miami.edu>]

MPO Seminar

Dr. Robert Hart

Florida State University

"Three Tropical Cyclone Problems:  Genesis, Eye size and eyewall tilt, and Footprint"

Room: Slab seminar room, S/A 103

Date: Thursday, November 3, at 3:00 p.m. 

Abstract:

This talk will summarize the ongoing research of several graduate students here at FSU.   The first part will demonstrate how NASA GRIP and PREDICT data are being used to quantify the evolution of three dimensional structure of pre- and post-genesis disturbances.         Fields of dropsondes are tessellated with triangles, and then all the triangles that converge at a similar vertex are used as a polygon on which vorticity is calculated using Stokes theorem for circulation.   A similar process is used to calculate divergence.    This process lets us reliably calculate kinematics from irregularly spaced data, without the degradation resulting from regridding to a Cartesian grid.   Horizontal and vertical profiles of these kinematic (as well as thermodynamic) fields, and other fields such as potential vorticity and vertical velocity, are examined.     Interpretation of these evolutions will be presented, in particular for their evidence for or against existing genesis theories.    A brief summary of a new approach on performing vorticity budgets utilizing a spectral gap in vorticity power (rather than the conventional symmetric-asymmetric separation) will be presented.

Classic Sawyer-Eliassen theories explain why it is an eyewall must tilt:   if you have a gradient wind vortex that is close to thermal wind balance within a horizontal temperature gradient, the eyewall must tilt outward with height.    The greater the horizontal temperature gradient, the greater the eyewall tilt.   Loss of momentum to the sea through friction only increases the tilt.  Yet, there remain unanswered questions:   how does the variability of this tilt influence intensity change and its prediction?   How does the development of concentric eyewalls influence the inner-eyewall’s tilt?  If a storm passes over a warm anomaly of ocean heat content, does the sudden introduction of buoyancy into a system (that was previously neutral to buoyancy) lead to a sudden uprighting of the eyewall in light of the additional upward force on parcels?    Recent work by Stern and Nolan (2008) documented and quantified the variation of the vertical structure of radius-of-maximum winds (RMW) and found little relationship with intensity or intensity change.   In contrast, we present an edge-detection technique applied to APR-2 and recon radar to quantify the structure of the eye and eyewall and its tilt.    An analysis of this tilt and its reasonably strong relationship to intensity and intensity change are presented and discussed.   The results are compared to those of Stern and Nolan (2008).

                                  Finally, our naiveté regarding the inherent role of tropical cyclones in climate is illustrated by the fact that we do not have a compelling argument regarding the aggregate occurrence and their dynamic and thermodynamic footprint on their environment.  Through composites of tropical cyclone structure using newer reanalyses (MERRA, CFSR, ERAI), the presentation is concluded by examining the magnitude of this footprint in space and time.       Composites of the components of moist static (and kinetic) energy are presented and used to potentially provide insight into the reasoning for surprisingly uniform spacing between coexisting TCs in each basin.

Sandrine Apelbaum

Meteorology and Physical Oceanography 
Rosenstiel School of Marine and Atmospheric Science
University of Miami
4600 Rickenbacker Causeway
Miami, FL 33149-1098
Tel     (305) 421-4057
Fax     (305) 421-4696

sapelbaum@rsmas.miami.edu