Dynamics Governing the Maintenance and Evolution of a Simulated Mesoscale Convective System with a Training Convective Line

This research investigates the dynamics of a simulation of a Training Line – Adjoining Stratiform (TL/AS) Mesoscale Convective System (MCS) that was conducted with composite atmospheric fields as initial and lateral boundary conditions. Moisture, convective instability (which was maximized above ground level), and lift were continuously supplied to the location of the MCS by the large-scale environment, which maintained the minimum requirements for deep moist convection over a fixed region.

An initial southeastward moving convective line propagated along the southeastern outflow boundary (OFB), where wind shear conditions were favorable for robust kinematic lifting. A new convective line then developed to the west of the initial non-stationary convection (rearward off-boundary development, ROD). The linear morphology of ROD was facilitated by low-level convergence generated by low-level pressure perturbations along, and left in the wake of the leading convective line. Southwesterly low-level flow was thermodynamically stabilized as it lifted over the southwestern OFB due to a pattern of adiabatic cooling below latent heating. This flow traveled 80-100 km northeastward beyond the surface OFB to the point where large-scale lifting sufficiently re-destabilized the flow for deep convection. These factors explain both the temporal offset of ROD from the initial non-stationary convection, and the geographic offset of ROD from the surface OFB.

Eventually the western flank of the cold pool (and the associated thermodynamic stabilization affect) weekend and allowed new convection to develop near the OFB. This new convection locally intensified the cold pool, which drove the convection southward and away from the region of heavy rainfall. The MCS weakened as large-scale low-level lifting diminished.