Effective Buoyancy, Dynamic Pressure, and Deep Convective Triggering by Cold Pools

Abstract:

While it is well-known from simulations and observations that cold pools play a key role in the triggering of deep convection, the question remains as to whether this forcing is primarily dynamical or thermodynamical in nature. We address this question by decomposing vertical forces into the dynamic pressure force and effective buoyancy of Davies-Jones (2003), and then apply this to cloud-resolving simulations of deep convection. We find that dynamical forces dominate the triggering, give physical explanations for why this should be, and compare to a shallow convection scenario where the force balance may be different. The thermodynamical properties of cold pools also turn out to play a key role, however, in that the lofted air often comes from mature `warm pools’ whose gust fronts are anomalously warm and moist, as emphasized by Tompkins (2001).