Case studies of variability in the depth of convective mass transport

Deep convective updrafts are the most efficient transporters of mass from the boundary layer to the upper troposphere and lower stratosphere. Vertical mass transport is parameterized in large-scale models and constrained by the environmental thermodynamic profile, with the parcel theory level of neutral buoyancy (LNB) acting as an upper bound on mass transport. It is generally accepted that due to entrainment the level of maximum detrainment (LMD), i.e. the altitude at which the most mass is detrained from the core updraft, will be significantly lower than the idealized LNB. Four case studies of strong summer-time convection, including both squall lines and supercells, are presented. In these cases, the observed level of maximum detrainment is calculated from dual-Doppler derived velocities, and a range of LNB values are calculated from environmental and model soundings representative of the background state. These cases show that the relationship between the LNB and the LMD is highly variable, and in two cases the LMD reaches and/or surpasses the LNB. These cases also demonstrate that the LMD can vary significantly over the lifetime of the storm, in one supercell case increasing by 3 km in 15 minutes. Testing of non-dual Doppler radar retrievals for constraining modeled transport, and initial results from model comparison of resolved and parameterized convection will be discussed.