Breakout Summary Report

ARM/ASR User and PI Meeting

Session Title: Aerosol Processes in Deep Convection: Discovery to Parameterization (AP, CAPI)
Session Date: 22 June 2021
Session Time: 11:00 AM - 1:00 PM
Number of Attendees: 100
Summary Authors: Manvendra Dubey, Jiwen Fan, Jim Smith, and Chris Cappa

Breakout Description

This session will showcase recent process findings in interactions of aerosols with moisture, radiation, and hydrometeors in updrafts, including convective invigoration, new particle, and secondary aerosol formation, latent heat release, and water-altering aerosol optics and microphysics. Examples of large-eddy simulations (e.g., the LASSO activity), WRF, and conceptual model simulations informed by observations will be discussed, with the goal to build informed convection parameterizations in climate models.

Main Discussion

The discussion centered around the aerosol process gaps that limit our ability to properly represent deep convection in climate models. It ranged from the mature analysis of shallow aerosol cumulous interactions by ARM’s LASSO long-term model-data integration using SGP observations, the research-grade discovery of convective invigoration made during the GoAmazon campaign, the upcoming analysis of the deep convective life cycle observed in CACTI with LASSO, and the recent ACPC modeling for the TRACER campaign. Long-standing high bias in upper tropospheric black carbon in global models relative to airborne observations was attributed to deep convective scavenging of aerosols. Proper treatments of cloud convection by scavenging have now been implemented in some global models to fix this bias.

New techniques to measure how water uptake alters light absorption by black and brown carbon that will be deployed during TRACER-CAT should provide constraints on how these humidity-dependent radiative effects are represented in global models. Novel connections between lightning enhancements and aerosol effects in deep convection were described for future research. Significant secondary organic aerosol formation in cold convective updrafts was measured in pyrocumulous outflow during FIREX-AQ and simulations indicate invigoration by latent heat release can loft smoke into the upper troposphere and lower stratosphere. Dynamical effects in deep convection like cold-pool production were discussed. New fine-scale cloud chamber studies of high supersaturation in the wake of hydrometeors were presented and used to inform secondary ice treatments in LES models.

Key Findings

Deep convection is an important gap in global models and ARM/ASR campaigns and science are providing new aerosol process information and should be prioritized for analysis using the LASSO and ACPC LES modeling frameworks. Such analysis should lead to robust aerosol deep convection parameterization in the high-resolution E3SM. The aerosol, moisture, and cloud couplings and feedbacks between the boundary layer and the upper troposphere and lower stratosphere mediated by deep convection need to be addressed in E3SM. New observations of megafires and pyrocumulonimbus from ground, air, and space provide new data sets across scales that can be used to achieve this.

Issues

Synergy between LASSO and ACPC should facilitate effective analysis of ARM field data to develop new and robust deep convective parameterizations.

Needs

Nurture cross-cutting collaborative science between laboratory experiments, field observations, LES simulations, and E3SM parameterization development.

Decisions

Create a cross cutting aerosol process and CAPI collaboration to examine aerosol-cloud, SOA, lightning, and sub-grid ice nucleation processes and develop methods to treat them in E3SM.

Future Plans

Develop a review article on the state of knowledge of aerosol process relevant to deep convection, identify gaps, and facilitate filling them by targeted white papers.

Action Items

Report out and update on our topic at next ASR/ARM team. Encourage and track publications by the large breakout group in deep convection aerosol processes and the feedbacks they trigger in global climate models by coupling the surface to the upper troposphere and the lower stratosphere.