Analysis of Backbuilding of a Simulated MCS in an Environment with a Low-Level Stable Layer

Past studies have indicated the importance of gradual lifting of an inflow layer over a cold pool produced on the leading edge of convection in the maintenance of convection located behind and offset from the leading line. However, analysis of soundings collected during the Plains Elevated Convection at Night (PECAN) field campaign indicates substantial variability in the stability of the nocturnal boundary layer and some cases with observed off-boundary back-building had little indication of a surface cold pool. Further, simulated MCSs with strong low level stable layers that produce this off-boundary back-building suggest that in some cases, it may be supported by a variety of wave structures. In the maintenance of back-building convection in environments with a low level stable layer, the specific roles of processes generated by the MCS itself, and those external to the MCS, have not been fully explained or quantified.

To further explore this question, a series of simulations were conducted with varied methods for initiating convection. Surprisingly, simulations using a homogeneous base state determined by an environmental sounding from a case observed during the Plains Elevated Convection at Night (PECAN) field campaign that had regions of both forward and backward propagation and a strong low level stable layer, and initialized with a single warm bubble produced an MCS that had regions of both forward and backward propagation. Additionally, unlike the findings of Peters and Schumacher (2015), the back-building in this simulation appears to be supported primarily by processes within back-building convection itself, rather than by a cold pool produced by the leading line. The results of these simulations suggest that external forcing is not a requirement of backbuilding convection.