A Theoretical and Observational Study of Midlatitude Mesoscale Convective Vortices (MCVs) in Vertical Shear

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Because of their longevity and ability to organize convection, mesoscale convective vortices (MCVs) have been the focus of studies seeking to improve the prediction of widespread, heavy precipitation events during the warm season. Although progress has been made in the past decade toward identifying conditions favorable for MCV generation, and in linking the strengthening of MCVs to convective regeneration in their vicinity, dynamical processes governing the MCV lifecycle are still not well understood. To better predict potential flooding events in association with MCVs requires a basic understanding of how MCVs form, and what permits them to maintain their coherence in adverse environmental flows. The Principal Investigator (PI) will address both questions under the aegis of the Bow Echo and MCV Experiment (BAMEX).Observations suggest that the formation and longevity of MCVs depend critically on how the MCV interacts with ambient vertical shear. To further understand this interaction the PI will conduct a combined theoretical, numerical, and observational study that builds on the PI and Co-PI's previous NSF research. The theoretical study will commence by examining the quasi-geostrophic `free' alignment of an idealized MCV. This sets the stage for a key theoretical analysis to determine the critical shear necessary to irreversibly shear apart a given MCV. Knowledge of the critical shear is believed central to distinguishing those MCVs that regenerate convection from those that do not. The impact of new convection triggered by the vortex's resistance to ambient shear will be studied systematically with the goal of determining the feedback of convection on the intensity of the MCV.Observational tests of the theoretical work will be carried out using airborne Doppler radar and dropsonde data from the BAMEX investigation of MCVs. In particular, the evolution of vorticity associated with the MCV and nearby convection will be documented using diagnostic tools previously developed to study the dynamics of the hurricane core and the genesis of tropical cyclones. Presently, no observational data set is yet available detailing the radial vorticity structure of an MCV, the evolution of MCV tilt and intensity, and the development of vorticity in association with regenerated convection, all of which are essential elements of the BAMEX research objectives.Successful completion of this research can potentially provide forecasters with the knowledge needed to extend the prediction time for some times of warm season convective storms.