The Effect of Latent Heat Release on the Evolution of a Warm Occluded Thermal Structure

Abstract

The effect of latent heat release on the development of the occluded thermal structure in a major winter storm is examined through comparison of full physics (FP) and no-latent-heat-release (NLHR) simulations of the event performed using the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5). Though both simulations possess a well-developed occluded thermal ridge near the surface, the 3D structure of their respective occluded quadrants is quite different. In particular, the FP simulation depicts the canonical, troposphere-deep warm occluded thermal structure, whereas the NLHR simulation produces only a shallow, poorly developed one. Consistent with these differences in tropospheric thermal structure, the FP cyclone displays a robust treble clef potential vorticity (PV) distribution in the upper troposphere in its postmature phase, while a considerably less robust version characterizes the NLHR simulation. The PV minimum of the treble clef overlies a poleward sloping column of warm, weakly stratified air that extends through the depth of the troposphere and is a signature of the trowal, the essential structural feature of warm occluded cyclones. Consequently, examination of the role played by latent heat release in production of the occluded thermal structure in this case is made through consideration of its influence on the evolution of the upper-tropospheric PV morphology. It is found that direct dilution of upper-tropospheric PV by midtropospheric latent heat release initiates formation of a local, upper-tropospheric PV minimum, or low PV tongue, to the northwest of the surface cyclone center. The production of this PV minimum initiates a cutting off of the upper-tropospheric PV anomaly associated with the surface development. The upper-tropospheric circulation associated with this cutoff anomaly, in turn, forces the advection of low (1 PVU) values of PV into the developing PV trough. This combination of kinematic and diabatic processes acts to produce both the tropopause PV treble clef as well as the underlying warm occluded thermal structure in the FP simulation. In contrast, though an adiabatic kinematic tendency for production of a treble clef PV morphology operates in the NLHR simulation, the resulting PV and thermal structures are weaker and slower to evolve than those produced in the FP simulation. Thus, it is suggested that latent heat release plays an indispensable role in the production of the characteristic occluded thermal structures observed in nature.

Tropical plumes and extreme precipitation in subtropical and tropical West Africa

“…14 indicates the diabatic PV tendency in the 200-150 hPa layer using the method described in Cammas et al (1994) and Posselt and Martin (2004). The explosive cyclogenesis is accompanied by strong frontogenesis, cloudband formation and strong latent-heat release (not shown).…”

CLOUDSAT: Adding a New Dimension to a Classical View of Extratropical Cyclones

“…These models allowed for the examination of the role of various physical processes in cyclone development, in particular, latent heat release and cloud effects on radiation. Multiple studies noted that latent heat release not only contributed to the intensity of low pressure systems and the rapidity of cyclogenesis (Smagorinski 1956;Krishnamurti 1968;Tracton 1973;Chang et al 1982;Reed et al 1988;Kuo et al 1991;Davis 1992;Whittaker and Davis 1994;Stoelinga 1996), but also acted to change the spatial patterns of surface pressure and precipitation, as well as the structure and evolution of fronts (Baldwin et al 1984;Dudhia 1993;Posselt and Martin 2004;Reeves and Lackmann 2004). It was also found that changes in the cloud effect on radiative fluxes could have a significant effect on the development of baroclinic waves.…”

Influence of microphysical processes on the potential vorticity development in a warm conveyor belt: a case‐study with the limited‐area model COSMO

“…Furthermore they showed that the negative PV anomaly developing above the maximum heating strongly modified the upper-level PV pattern and the evolution of the downstream flow. Posselt and Martin (2004) showed that the existence of an occluded thermal structure was strongly dependent on diabatic heating. These results, among others, show the potential of diabatic heating processes to influence the dynamics in complex ways.…”