A potential vorticity component-based study of the extratropical transitions of hurricanes Danielle and Earl (1998)

• Main Author: McTaggart-Cowan, R.
• Format: Thesis
• Language: English
• Published: McGill University 2003
• Subjects: Earth Sciences - Atmospheric Sciences; North Atlantic
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19557

This thesis documents a study of the simultaneous North Atlantic extratropical transition (ET) and intensification (ET/R) of ox-hurricanes Danielle and Earl (1998), with the goal of identifying the midlatitude and remnant tropical cyclone (TC) features germane to the ET/R process. Using potential vorticity (PV) based diagnostics and an extension of piecewise PV inversion techniques that accounts for atmospheric water, the initial conditions of the Mesoscale Compressible Community model are altered by the individual removal of possible forcing features. Results from ensuing sensitivity tests are compared to the control simulation and changes in the structure and/or the intensity of ET/R are diagnosed. It is found that the existence of a trough upstream of the remnant TC is a necessary forcing for redevelopment and that larger north-south trough amplitudes result in stronger vortex reintensification. Transitions occurring in the equatorward entrance region of a baroclinic jet are likely to undergo baroclinic mode redevelopment, whereas those taking place in the poleward exit region of the jet usually take on tropical mode characteristics. Baroclinic mode storms are insensitive to the structure of the TC remnant; tropical mode redevelopment, however, rely heavily on both the circulation and the moisture associated with the ex-tropical feature. Considered pragmatically, the results of this study amount to a list of the key ingredients necessary for the ET/R of the storms studied, which will be of use in the forecasting of similar events. A broader application of the findings in the context of current ET research yields insight into both the dynamics and thermodynamics of these extreme events.