A 36-h nested-grid numerical simulation of the life cycle of a convectively generated, inertially stable, warm-core mesovortex is presented. The vortex evolved from a mesoscale convective complex that developed from a squall line over Oklahoma during 7–8 July 1982. A modified version of the Pennsylvania State University /National Center for Atmospheric Research mesoscale hydrostatic model with a fine-mesh grid resolution of 25 km is utilized for this study. The model simultaneously incorporates parameterized convection and a grid-resolved convective scheme containing the effects of hydrostatic water loading, condensation (evaporation), freezing (melting) and sublimation. Genesis, intensification and maintenance of a low- to midtropospheric closed meso-β scale cyclone as well as the associated surface pressure perturbations, the evolution of moist convection, and the distribution and magnitude of total rainfall are simulated by the model. Similarly, the observed amplification of a 700-mb meso-α scale short-wave trough, the development of a midlevel warm-core structure and an upper-level mesoanticyclone during the mature stage, the quasi-stationary nature of the vortex circulation, and the vertical distribution of horizontal wind and relative vorticity in the vicinity of the rotating mesoscale convective system (MCS) are all reasonably well simulated up to 36 h. During the mature stage of the rotating MCS, both the observed and simulated vertical structure are characterized by a low-level mesohigh in association with a cool pool and sinking motion, a midtropospheric warm-core structure, and an upper-level cold dome with an associated anticyclonic circulation. The horizontal momentum and equivalent potential temperature are uniformly distributed in the vortex layer with the vorticity maximum located between 600 and 700 mb. The model simulation shows that the upward motion and cyclonic vorticity associated with the front and vortex system are out of phase. The phase difference appears to be a propagation mechanism of the rotating MCS and the low-level front. Another important finding is that most of the vortex properties tilt downstream with height during the decay period. Such a vertical distribution helps explain why a well-defined and long-lived hydrostatic surface mesolow did not form in either the observations or the simulation. It also helps explain why other midlatitude rotating MCSs often exhibit weak surface pressure predictions. It is found that a propagating mesoscale vorticity disturbance, preexisting low-level frontal forcing and a convectively favorable environment ahead of the front help generate an organized area of upward motion wherein the vortex develops. However, it is the resolvable-scale latent heat release that appears to be directly responsible for producing the rotating MCS. The quasi-stationary nature of the rotating MCS is related to the fact that the vortex develops within a slow-moving, low-level horizontal deformation field. The vortex is well maintained because of the weak horizontal and vertical shear in the deformation zone and the generated 1arge inertial stability of the vortex. The results indicate that in some situations, numerical forecasts of the genesis, evolution and rainfall of rotating MCSs are possible up to 36 h using the currently available observations if a high-grid resolution model can be utilized.
No takes yet. Share an insight, caveat, or question.
Zhang et al. (1988) studied this question.