Breakout Summary Report

ARM/ASR User and PI Meeting

Breakout Description

This session featured seven talks followed by general discussion. An introductory talk was given by Adam Varble with an overview of the Convective Processes Working Group (CPWG) including the mission statement, research themes, summary of discussion at previous CPWG meetings, and recent relevant field campaigns (TRACER, SAIL, BNF). We highlighted the relevant ARM Translator Group contacts for any questions concerning ARM data sets and resources. We introduced Die Wang as the new CPWG co-chair as Adam is stepping down.

Main Discussion

The science talks were:

-Potential sources of low-frequency gravity waves observed within MCS stratiform regions (Hannah Vagasky, Clark Evans, and Becky Adams-Selin)

-Machine learning-based investigation of the variables affecting summertime lightning over the Southern Great Plains and southeastern South America (Siyu Shan, Dale Allen, Zhanqing Li,and Kenneth Pickering)

-Machine Learning Analysis of western U.S. fire impacts on hailstorms in the central U.S. (Jiwen Fan, remote)

-How does vertical wind shear influence hydrometeor characteristics in supercell thunderstorms? (Jake Mulholland, remote)

-Turbulence effects on droplet collision-coalescence: a key to understanding observed rain formation in cumulus clouds (Kamal Kant Chandrakar)

-On the quantification and mechanisms of cumulus entrainment, detrainment, and dilution (Dan Kirshbaum)

-Entrainment, detrainment, and dilution of dry and moist thermals (Hugh Morrison)

Discussion centered mainly on cloud entrainment and dilution. There was also discussion about the role of microphysics-dynamics interactions, use of LASSO-CACTI in CPWG-related research, and issues concerning model resolution and convergence moving to fine scales.

Key Findings

Key results from the talk and discussion were:

-Similar to previous years, discussion largely centered on the role of entrainment and dilution on deep convective properties. There was discussion on how entrainment can be difficult to diagnose, even in higher-resolution models. Direct observational constraint is also very difficult. There was focused discussion on observational needs for this. A better handle on high-resolution flow structure and vertical velocities would be a good first step. Expanded use of stereo camera and coincident remote-sensing and in situ observations to constrain and evaluate simulations of thermal dynamics could also help. In general, how to best design, target, and use observations with increasingly detailed, high-resolution modeling is a topic that requires more attention.

-There was limited discussion of dynamics-microphysics interactions. A few people mentioned the role of droplet number concentration and warm cloud microphysics in affecting convective dynamics. More extensive discussion of this topic took place in the context of aerosol invigoration of deep convection in the Tuesday breakout devoted to this. However, discussions generally lacked nuance and focus that are needed for progress and will be a goal for future meetings.

-There was discussion on how the results presented in the session, and the discussion of entrainment and mixing in particular, might be relevant to convection parameterizations. It was noted that there is no current scheme based on the dynamics of thermals, even though it is now accepted that most convective clouds have structures resembling a set of thermals. There was some question about what constitutes a thermal – whether this can be thought of simply as a rising parcel, or whether it should be thought of as having a distinctive ring vortex-like circulation with a finite size.

-The discussion on entrainment and mixing has implications for km-scale convection-permitting models. More investigation of this is needed in the deep convective “gray zone” given that many weather and climate models are now run at these resolutions, which present unique challenges to overcome relative to traditional climate models.

Issues

N/A

Needs

N/A

Decisions

We feel it would be useful to have a separate breakout session next year on convective microphysics, given that the CPWG sessions the past several years have focused mainly on convective dynamics. Morrison offered to lead and/or co-chair such a session and will solicit input from others who may be interested.

Future Plans

Given that this breakout tends to focus on convective dynamics, particularly entrainment and mixing, we feel a breakout session next year specifically focused on convective microphysics would be useful. This could include the topic of convective invigoration, but the idea would be to cover the topic more broadly, not just aerosol interactions.

We still feel that a targeted future workshop on entrainment and dilution in deep convective clouds might be useful, potentially leading to a review article. However, there are no definite plans for this, and the main barrier is to find someone with the time to lead such an effort.

Action Items

N/A