Breakout Summary Report

ARM/ASR User and PI Meeting

Session Title: Warm Boundary Layer Processes (WBLP) Working Group Breakout
Session Date: 26 June 2020
Session Time: 2:00 PM - 4:00 PM
Number of Attendees: 200
Summary Authors: Yunyan Zhang and Rob Wood

Breakout Description

The Warm Boundary Layer Processes working group focuses on understanding and model
representation of processes controlling the structural and radiative properties of clouds, aerosols, and
their interactions with the underlying surface in the lowest few kilometers of the atmosphere. Research
areas include: 1) characterization of boundary layer and cloud dynamics; 2) cloud and aerosol microphysics
and their interactions; 3) factors influencing cloud formation; and 4) radiative processes that together
influence the vertical transfers of energy, moisture, and atmospheric components.
Participants: Please contact Robert Wood (robwood2@uw.edu) and Yunyan Zhang (zhang25@llnl.gov) if
you have suggestions for discussion items.

Main Discussion

The overarching theme for this breakout session was focused on warm boundary-layer processes, which include boundary-layer turbulence, clouds and precipitation, their interaction with the underlying surface, the associated radiative and microphysical processes, and the interaction with aerosols. We are interested in improving our understanding of these processes using ARM observations and improving the representation of these processes in models.
This year’s WBLP breakout consisted of three major parts: 1) thirteen contributed short talks (5 minutes each), 2) five short updates/summaries from projects and breakouts of interest to WBLP working group members, and 3) a group discussion on the Cloud and Precipitation Measurements Science Group (CPMSG) metrics and the decadal plan closely related to the WBLP working group topical areas.
The session was recorded and can be viewed at https://www.dropbox.com/s/g4t2n5d5yiqxdsv/Warm-Bound_gallery.mp4?dl=0

Key Findings

The thirteen short talks cover various topics in the WBLP working group.
• Youtong Zheng proposed a new paradigm to understand the importance of horizontal temperature advection during the decoupling of stratocumulus-topped boundary layer (STBL).
• Daniel Kirshbaum showed two bulk entrainment rate retrievals for continental shallow cumulus clouds and sensitivities to environmental factors.
• Steve Krueger talked about a new retrieval method for the cloud-top entrainment rate of STBL, its validation against LES and its first application using ARM data.
• Franziska Glassmeier presented a weak LWP adjustment in ship tracks due to short lifetime which might be the reason for the overestimate of anthropogenic aerosol’s cooling effect using ship-track data.
• Jim Hudson showed inhomogeneous mixing effects on stratus clouds and drizzle microphysics using POST field campaign data.
• Maria Cadeddu presented a new retrieval algorithm which considers drizzle scattering effect and effectively seperates cloud LWP, in-cloud drizzle LWP, and sub-cloud drizzle LWP.
• Xue Zheng used LES and MAGIC field campaign data to diagnose the biased behavior of drizzle processes in E3SMv1 that the sub-cloud precipitation fraction is unrealistically small and drizzle evaporates too close to the surface.
• Using shortwave spectrometer data, Alexander Marshak found that optical depth decreases towards cloud edges in all cases but inhomogeneous mixing is much more pronounced over ocean than over land.
• Jake Gristey used LES with 3D radiative transfer to train random forest and artificial neural network algorithms and directly mapped between shallow cumulus cloud properties and surface irradiance which will be widely applicable for 3-D radiation parameterizations.
• Zhien Wang and Hailey Shin showed a framework on the synergy between observation analysis and modeling, especially the role of large-scale forcing on the development of non-precipitation clouds based on LASSO simulations.
• Using COGS and satellite data, Jingjing Tian showed the difference in cloud fraction and cloud sizes between different land covers including forest, grassland and city areas around the SGP site.
• Philipp Griewank showed size decompositions of Lidar-observed and LES-modeled shallow cumulus clouds and the on-going evaluation of the multi-plume parameterization ED(MF)n.
• Using Doppler lidar data at SGP, Neil Lareau studied the variation of updraft intensity and width with height and found that intensity is sensitive to both cross wind and buoyancy however width is primarily sensitive to the buoyancy forcing, and also advertised his filed campaign proposal on vertical exchange and convective initiation over complex terrains for community feedbacks.

The session included five short working group updates.
• Shaocheng Xie gave an ARM infrastructure update on the WBLP-related development of core VAPs, new VAPs and cloud type data, highlighted the new LASSO high-frequency (10 minutes) observational data and the ongoing One-Page VAP description effort to address data issues and uncertainty concerns.
• Chongai Kuang briefed the southeast US AMF3 deployment and timelines and presented site selection challenges related to the WBLP concerns, such as the role of larger-scale versus meso-scale perturbations in the onset of shallow convection and encouraged community feedbacks.
• Dan Feldman gave a brief overview of SAIL field campaign, pointed out the WBLP-related topical areas, e.g. surface energy balances in complex terrain, summertime monsoonal precipitation and, encouraged community feedbacks on spatiotemporal heterogeneity and possible science interests in working with SAIL data.
• Paquita Zuidema gave a nice summary on the breakout of shortwave-absorbing aerosols especially on the talks related to aerosol-cloud interactions and major results from breakout discussions.
• Bill Gustafson gave a brief update on LASSO observation, forcing data and near-future activities on CACTI and ENA.

The working group meeting concluded with discussion on the CPMSG WBLP-related metrics and decadal plan led by Christine Chiu. Due to time limitations, we were only able to solicit on the feedback on the CPMSG goal and the major metric elements. There was a general agreement among the WBLP working group on the current adopted approach and elements of the metrics. There was insufficient time to solicit inputs for each major element such as details on specific WBLP-related problems and roadblocks. Instead, we collected volunteer name lists and will reach out for small-group discussions on each major roadblock. Jim Mather briefly talked about the ARM decadal plan and encouraged feedback on its structure and details.

Issues

If applicable

Needs

If applicable

Decisions

If applicable

Future Plans

If applicable

Action Items

• Work with the CPMSG team through small-group discussions and feedback on boundary layer turbulence and shallow convection measurement needs and roadblocks and timelines, and on the ARM decadal plan.
• A few WBLP-related potential breakout sessions were mentioned during the meeting and there is a desire that ARM/ASR can provide logistical support so that interested groups can meet virtually in fall. Perhaps leadership can reach out to those breakout session submitters whose requests could not be accommodated due to timing limitations to assess their desire to hold a virtual breakout in fall.
• Several AMS and AGU sessions pertinent to WBLP are open to abstracts now.