Warm-phase Microphysical Evolution in Large Eddy Simulations of Tropical Cumulus Congestus: Constraining Drop Size Distribution Evolution using Polarimetery Retrievals and a Thermal-Based Framework

Abstract

Abstract. Improving parameterizations of convective microphysics in Earth system models (ESMs) requires well-constrained cases suitable for scaling between cloud-resolving models and ESMs. We propose a benchmark large eddy simulation (LES) cumulus congestus case study from the NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex) and demonstrate its observational constraints using novel polarimetric retrievals and in situ cloud microphysics measurements. Simulations using bulk and bin microphysics with observed aerosol input are compared to cloud-top retrievals of cloud droplet effective radius (Reff) and number concentration (Nd) from the airborne Research Scanning Polarimeter (RSP). The bulk scheme reasonably reproduces characteristic profiles of cloud-top Nd that decrease with altitude, while the bin simulation realizes greater discrepancies due to weaker precipitation formation. The Nd profile is strongly sensitive to the collision-coalescence process and the vertically resolved aerosol distribution, but appears well-constrained, whereas a persistent low-bias in Reff is evident in both schemes. Comparison of simulated and in situ droplet size distributions (DSDs) show that low-biased Reff originates from a cloud droplet mode that is too narrow relative to observations. Finally, a thermal-tracking framework demonstrates that the dilution of Nd throughout a thermal's lifetime is heavily determined by collision-coalescence and the height-varying aerosol distribution, and that in the absence of these, the impact of entrainment on diluting Nd is largely offset by continuous aerosol activation. Implications for developing warm-phase convective microphysics schemes for ESMs, evaluation of cumulus congestus using single column model versions of ESMs, and translating results to global, space-based polarimetry platforms are discussed.

Authors 8

1. McKenna Wallace Stanford corresponding

   Goddard Institute for Space Studies · Pacific Northwest National Laboratory · Columbia University

   Affiliation as printed

   Center for Climate Systems Research, Columbia University, New York, NY, USA

   NASA Goddard Institute for Space Studies, New York, NY, USA

   current affiliation: Atmospheric, Climate, and Earth Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA

2. Ann M. Fridlind

   Goddard Institute for Space Studies

   Affiliation as printed

   NASA Goddard Institute for Space Studies, New York, NY, USA

3. Andrew S. Ackerman

   Goddard Institute for Space Studies

   Affiliation as printed

   NASA Goddard Institute for Space Studies, New York, NY, USA

4. Bastiaan van Diedenhoven Aachen SRON Netherlands Institute for Space Research

   Space Research Organisation Netherlands

   Affiliation as printed

   SRON Netherlands Institute for Space Research, Utrecht, the Netherlands

5. Jian Wang

   Washington University in St. Louis

   Affiliation as printed

   Center for Aerosol Science and Engineering, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, Saint Louis, MO, USA

6. Toshihisa Matsui

   Goddard Space Flight Center · Earth System Science Interdisciplinary Center · University of Maryland, College Park

   Affiliation as printed

   Earth System Science Interdisciplinary Center – ESSIC, University of Maryland, College Park, MD, USA

   Mesoscale Atmospheric Processes Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA

7. Daniel Hernández‐Deckers

   Universidad Nacional de Colombia

   Affiliation as printed

   Grupo de Investigación en Ciencias Atmosféricas, Departamento de Geociencias, Universidad Nacional de Colombia, Bogotá, Colombia

8. R. Paul Lawson

   Stratton Park Engineering Company (United States)

   Affiliation as printed

   Stratton Park Engineering Company, Inc., Boulder, CO, USA