Evaluating Droplet Size Distribution Evolution in Aerosol-constrained Simulations of Tropical Cumulus Congestus against Airborne Polarimetry Observations

Abstract

The evolution of cumulus congestus within tropical oceanic and maritime environments is modulated by the interaction of convective dynamics, liquid- and ice-phase microphysical processes, aerosol loading, and entrainment of ambient environmental air. Characterizing this evolution requires robust observational constraints of aerosol properties and cloud macrophysics and microphysics. The NASA Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) field campaign in 2019 targeted growing cumulus congestus clouds using airborne in situ and remote sensing platforms. In situ aircraft microphysical measurements and retrievals from the Research Scanning Polarimeter (RSP) both show that cloud droplet number concentrations decrease and effective radius increases with increasing cloud top height, with droplet size distributions (DSDs) that broaden with height. These observed components are responsive to an active collision-coalescence process that produce millimeter-sized drops, onsetting warm-rain formation. Here, we present an analysis of CAMP2Ex RSP data showing the evolution of droplet number concentrations and DSDs with height and its variation with RSP-retrieved aerosol number concentrations. For one case study (RF14, 9/25/2019), we perform large eddy simulations (LES) at 100-m horizontal grid spacing using bin and bulk microphysics schemes. Detailed multi-modal, vertically resolved aerosol measurements from the Fast Integrated Mobility Spectrometer (FIMS) are used as input. The relative ability of the bulk and bin schemes to produce the observed DSD evolution, from activation to warm-rain production, is evaluated. Sensitivity experiments are performed to assess the roles of height-varying aerosol concentrations, rain-forming collision-coalescence, and entrainment in realizing observed droplet number concentration and effective radius profiles. Additionally, we share the prospect of detailed aerosol properties, droplet number concentrations, and DSDs, similar to as acquired by RSP, becoming available from polarimeters on NASA’s PACE satellite mission, launched in early 2024.

Authors 10

1. Bastiaan van Diedenhoven corresponding Aachen SRON Netherlands Institute for Space Research Earth Science Division

   Space Research Organisation Netherlands

   Affiliation as printed

   SRON Netherlands Institute for Space Research, Earth Science Division, Leiden, Netherlands (b.van.diedenhoven@sron.nl)

2. McKenna Wallace Stanford corresponding

   Goddard Institute for Space Studies · Columbia University

   Affiliation as printed

   Center for Climate Systems Research (CCSR), Columbia University, New York, New York, USA

   NASA Goddard Institute for Space Studies (GISS), New York, New York, USA

3. Ann M. Fridlind corresponding

   Goddard Institute for Space Studies

   Affiliation as printed

   NASA Goddard Institute for Space Studies (GISS), New York, New York, USA

4. Andrew S. Ackerman corresponding

   Goddard Institute for Space Studies

   Affiliation as printed

   NASA Goddard Institute for Space Studies (GISS), New York, New York, USA

5. Jian Wang corresponding

   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. Otto Hasekamp corresponding Aachen SRON Netherlands Institute for Space Research Earth Science Division

   Space Research Organisation Netherlands

   Affiliation as printed

   SRON Netherlands Institute for Space Research, Earth Science Division, Leiden, Netherlands (b.van.diedenhoven@sron.nl)

7. Snorre Stamnes corresponding

   Langley Research Center

   Affiliation as printed

   NASA Langley Research Center, Hampton, Virginia, USA

8. Brian Cairns

   Goddard Institute for Space Studies

   Affiliation as printed

   NASA Goddard Institute for Space Studies (GISS), New York, New York, USA

9. Andrzej P. Wasilewski

   Goddard Institute for Space Studies

   Affiliation as printed

   NASA Goddard Institute for Space Studies (GISS), New York, New York, USA

10. Mikhail D. Alexandrov

    Goddard Institute for Space Studies · Columbia University

    Affiliation as printed

    Department of Applied Physics and Mathematics, Columbia University, New York, New York, USA

    NASA Goddard Institute for Space Studies (GISS), New York, New York, USA