Conditions for convective deep inflow from buoyancy forcing and non-local effect

May 19, 2021 3:00pm to 4:00pm
270 Seminar


Speaker: Yi-Hung Kuo

Institution: UCLA, Atmospheric & Oceanic Sciences


The concept of convective updrafts plays a central role in deepconvective parameterizations. The traditional view interprets the entrainment of environment air into clouds via local, small-scale turbulent mixing. Computational and observational evidence, on the other hand, has pointed to an organized coherent updraft structure drawing mass uniformly from a deep layer (0-4 km). Furthermore, this "deep inflow" has been observed in the presence of organized and isolated convective events. This work aims to explain the seemingly universal deep-inflow feature by studying the vertical acceleration response to buoyancy under the anelastic framework. A buoyancy patch of horizontal extent D can incite acceleration above and below the patch. Leading contributions to this vertically non-local influence have vertical e-folding scale comparable with or greater than D/2 pi, and are insensitive to the internal turbulent nature of the patch. For convective events with D of a few kilometers that contribute strongly to precipitation production, this leads to the updraft mass flux profile increasing approximately linearly with height---providing a simple explanation for widespread occurrence of deep inflow over scales ranging from cumulonimbus to mesoscale. This non-local effect also implies a near-surface CIN layer or thin negatively buoyant layer within the patch can only exert limited influence on convective updrafts. This effect is included in cloud resolving models or super-parameterization but is omitted in common convective parameterizations.