P1.16 Warm-seclusion Extratropical Cyclone Development: Sensitivity to the Nature of the Incipient Vortex

The development of intense warm-core seclusion (Shapiro and Keyser 1990) extratropical storms can occur from several different precursor disturbances. These include tropical cyclones that have undergone extratropical transition, maritime extratropical cyclones with both coldcore baroclinic and shallow diabatically generated warm core backgrounds (Moore and Montgomery 2004), and polar lows. With the most intense, bomb-like deepening (Sanders and Gyakum 1980) or rapid intensification is triggered by a tropopause fold or frontal fracture (Browning et al. 1997), in which statically stable, high potential vorticity spills into the middle troposphere slightly upstream of the surface low. With the inclusion of copious amounts of latent heating provided by warm western boundary ocean currents, the growth rate of baroclinic instabilities may be significantly enhanced by latent heat processes (Emanuel et al. 1987). Another facet of the problem involves the impact of distant mobile upper-level troughs (Molinari and Vollaro 1989) interacting with tropical cyclones as well as low-level cyclonic extratropical circulations. Four separate storm systems that culminate in a mature warm seclusion are numerically modeled using the PSU/NCAR MM5 model and analyzed to better understand the brief time period in which the tropopause fold is triggered and the overall thermal structure of the system begins to warm as the pressure drops rapidly. A central question to address concerns whether the mechanism for triggering rapid cyclogenesis and the subsequent warm seclusion development is dependent upon the origin of the incipient cyclonic vortex.