26th Conference on Hurricanes and Tropical Meteorology


A proposed potential vorticity mechanism for sub-tropical cyclogenesis and tropical transition (Formerly Paper Number 2C.5)

Jenni L. Evans, Penn State Univ., University Park, PA; and M. P. Guishard

The development of Atlantic subtropical cyclones is examined in terms of the potential vorticity (PV) anomalies, associated with cold upper cut-off lows and lower troposphere circulations. It is proposed that mixed baroclinic/barotropic instability, and then PV superposition may provide a conceptual reasoning for the cyclogenesis (and subsequent tropical cyclogenesis) of warm season subtropical storms, such as Karen during 2001 and Michael in 2000. At the relevant stages in their life cycles, these storms may be defined as Type 2 (cyclogenesis source) subtropical cyclones, as described by Simpson (1952). Results from a two-layer model are presented, in support of this theory.

extended abstract  Extended Abstract (176K)

Poster Session 1, Posters
Wednesday, 5 May 2004, 1:30 PM-1:30 PM, Richelieu Room

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