18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Thursday, 2 August 2001: 10:30 AM
The role of latent heat release in the formation of a warm occluded thermal structure in an intense continental cyclone
Derek J. Posselt, Univ.of Wisconsin, Madison, WI; and J. E. Martin
Poster PDF (1.2 MB)
The role of latent heat release (LHR) in the development of the warm occluded structure of an intense continental cyclone is examined. The cyclone of interest developed in association with a vigorous upper-level jet/front system, and eventually attained a sea-level pressure minimum of 964 hPa. A significant portion of the precipitation shield associated with this storm was located in its occluded quadrant, to the north and west of the cyclone center. It is suggested that the associated LHR eroded the tropopause level potential vorticity (PV) in this region through diabatic redistribution. In so doing, LHR promoted the formation of a treble clef shaped tropopause PV anomaly, shown in prior work to be the unambiguous signature of an underlying warm occluded thermal structure.

This hypothesis is investigated through use of the Fifth Generation Penn State/NCAR Mesoscale Modeling System (MM5). Companion simulations are performed, one including and one excluding the effects of latent heat release, and the corresponding evolutions of the post-mature phase circulations and thermal structures are compared. The circulation associated with the diabatically generated PV is quantified using piecewise PV inversion, and its role in altering the tropopause PV distribution is assessed. A similar analysis is performed on a maritime cyclone of equal intensity that was associated with a fairly stationary, cutoff upper-level disturbance. A comparison of the development of the occluded structures of both storms is offered.

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