A Theory for Long-Lived Mesoscale Convective Systems

It is proposed that certain long-lived mesoscale convective systems maintain themselves through an interaction between quasi-balanced vertical motions and the diabatic effects of moist convection. Latent heat release, evaporation and melting of precipitation, and thermal radiation are all shown to contribute to the creation of a positive potential vorticity anomaly in the lower troposphere. This anomaly can interact with a sheared environment so as to induce further lifting of low-level air and subsequent release of conditional instability.