Updraft and Downdraft Statistics of Simulated Tropical and Midlatitude Cumulus Convection

This paper presents a detailed analysis of updraft and downdraft statistics of simulated tropical oceanic and midlatitude continental cumulus convection, with an emphasis on the individual terms in the vertical momentum budget. Strong convective cores with absolute vertical velocities over 1 m s−1 and total condensate mixing ratios over 0.1 g kg−1 are sampled from several long-term simulations, driven by the observed large-scale advective forcings over the eastern Atlantic and Oklahoma regions. The median updraft and downdraft velocities are weakly dependent upon height, but the 90th percentile of the updraft velocity varies strongly with height, with a maximum in the middle troposphere. The median updraft thermal buoyancies are only about 0.5 K higher than those of downdrafts. As in aircraft measurements, positive thermal buoyancies exist for more than half of downdraft cores, and negative thermal buoyancies exist for a significant number of updrafts. The existence of the nonhydrostatic pressure gradients can explain such a surprising result first obtained from aircraft measurements. On the other hand, the largest differences between tropical and midlatitude convection occur in the strongest 10% of the drafts, not in the median drafts. For updrafts, the difference is related to the larger thermal buoyancy and relatively smaller condensate mixing ratio in midlatitudes, in addition to the larger dynamic triggering in the subcloud layer. The larger dynamic effects of the nonhydrostatic pressure gradient forces are responsible for the larger downdraft velocities in midlatitudes, in addition to the drier environments.