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

The most basic ingredients of a nocturnal mesoscale convective system (MCS) are relatively well documented. The interactions between convection, an often-present nocturnal stable layer, and the resulting mechanisms that govern propagation and maintenance are less clear. In particular, the specific roles of processes generated by the MCS itself, and those external to the MCS, have not been fully explained or quantified. For example, some past studies have suggested that long-lived back-building convection is dependent on a mesoscale lifting mechanism separate from the MCS, whereas others have questioned that result.

To further explore this question, a series of simulations were conducted with varied methods for initiating convection. Surprisingly, simulations in a homogeneous environment initialized by an environmental sounding from a case with regions of both forward and backward propagation, a strong low level stable layer, and a single 2 K 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.