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[Roger Edwards]

EJSSM Forum comments are welcome on this manuscript.

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Abstract

Airmass boundaries have been documented as a major influence on convective initiation and development, particularly in supercell thunderstorms. Therefore, this study seeks to determine the specific influence of an airmass boundary on supercell development through idealized numerical modeling. To do this, convective initiation is simulated in an environment that represents a case where supercells were observed forming along a preexisting airmass boundary. Three simulations are conducted, which illustrate convective initiation in the warm sector, cool sector, and along the airmass boundary. Deep convection occurs in all simulations; however, a steady-state supercell is only produced in the boundary simulation. Analysis of these results reveals that the airmass boundary supports supercell formation and development by increasing the strength of the updraft, creating and supporting a low-level mesocyclone, and enhancing the gust front. In this study, the airmass boundary is found to have a profound impact on the simulated storm, and is necessary for supercell development and longevity even with an ambient environment that supports supercells.

[Chuck Doswell]

Matt Bunkers brought up the Loftus et al. (2008) paper, but I believe the authors misunderstood that paper's relevance to their work.  Yes, in that paper, we were talking about non-supercells, but

1) supercells typically are also multicell storms, despite the traditional interpretation them as a single, quasi-steady cell,
2) multicell storms also typically are sustained for longer than the lifetime of a single cell (the time a "bubble" takes to go from near the surface to the top of storm

Hence, the presence of a boundary could produce vertical motion on its own that would help sustain a storm.  The thermal bubble method for storm initiation isn't very realistic.  It's sustained ascent that can result in a sustained convective storm (that includes more than one "cell") regardless of whether or not it's a supercell.

In the study by Loftus et al., it was found that there was a spectrum of sustained discrete nonsupercell storms, with some showing a predominantly "bubble-like" succession of individual cells, others showing a predominantly "plume-like" continuous updraft, and those in between.