The Challenge of Identifying Controls on Cloud Properties and Precipitation Onset for Cumulus Congestus Sampled During MC3E. Issue 6 (23rd March 2018)

• Record Type: Journal Article
• Authors: Mechem, David B.; Giangrande, Scott E.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 6(2018)
• Page Start: 3126
• Page End: 3144
• Publication Date: 2018-03-23
• Subjects: MC3E -- LES -- congestus -- radar -- forcing -- nudging; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/2017JD027457
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Controls on precipitation onset and the transition from shallow cumulus to congestus are explored using a suite of 16 large‐eddy simulations based on the 25 May 2011 event from the Midlatitude Continental Convective Clouds Experiment (MC3E). The thermodynamic variables in the model are relaxed at various timescales to observationally constrained temperature and moisture profiles in order to better reproduce the observed behavior of precipitation onset and total precipitation. Three of the simulations stand out as best matching the precipitation observations and also perform well for independent comparisons of cloud fraction, precipitation area fraction, and evolution of cloud top occurrence. All three simulations exhibit a destabilization over time, which leads to a transition to deeper clouds, but the evolution of traditional stability metrics by themselves is not able to explain differences in the simulations. Conditionally sampled cloud properties (in particular, mean cloud buoyancy), however, do elicit differences among the simulations. The inability of environmental profiles alone to discern subtle differences among the simulations and the usefulness of conditionally sampled model quantities argue for hybrid observational/modeling approaches. These combined approaches enable a more complete physical understanding of cloud systems by combining observational sampling of time‐varying three‐dimensional meteorological quantities and cloud properties, along with detailed representation of cloud microphysical and dynamical processes from numerical models. Key Points: The transition from shallow cumulus to congestus is governed by destabilization of the thermodynamic profiles The evolution of traditional stability measures by themselves is not able to explain differences in the simulations Conditionally sampled cloud properties (in particular, mean cloud buoyancy) are able to show the differences among the simulations