Breakout Summary Report

ARM/ASR User and PI Meeting

Session Title: Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE)
Session Date: 24 October 2022
Session Time: 4:00 PM - 6:00 PM
Number of Attendees: 100
Summary Authors: Lynn Russell, Dan Lubin, Israel Silber, Mark Miller, Abigail Williams

Breakout Description

The Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) is planned for deployment of AMF1 from February 2023 to February 2024 at Scripps Pier and Mt. Soledad in La Jolla, California. The goal of this session is to discuss updates to the implementation plan, with discussion of coordination among platforms and measurements. Issues related to measurements needed for modeling and quick-look assessments of cases during the study will be discussed. The focus of EPCAPE is to characterize the extent, radiative properties, aerosol interactions, and precipitation characteristics of stratocumulus clouds in the Eastern Pacific across all four seasons at a coastal location. The combined observations will provide an unprecedented set of constraints for questions of cloud and aerosol climatology, cloud-radiative fluxes, and aerosol-cloud interactions. The relevance of this campaign to the ARM mission is its strategic location in an accessible and economically important region of the world that lacks long-term observations of its frequent, persistent, and climatically important coastal stratocumulus cloud cover. The clouds lie in one of the largest regions of upwelling-driven stratocumulus layers that are likely most impacted by aerosol indirect effects, but climate models do not accurately simulate the processes that control their radiative effects. Furthermore, the coastal orography incites significant additional uncertainties related to cloud turbulence, air motion spectrum, and drop size distributions. Finally, the aerosol in the region ranges from a clean marine background to frequent intrusions from a large and regionally homogeneous, well-characterized, surface-based pollution sources (the Los Angeles-Long Beach urban port megacity), providing a large dynamic range of aerosol conditions for investigation.

Main Discussion

Lynn Russell introduced the session and the planned measurement talks that would be covered by the other speakers. She gave a brief description of the EPCAPE campaign. Dan Lubin introduced the history of research on California coastal clouds and surveyed previous studies of coastal marine Sc. John Liggio talked about CVI, CIMS (mass spectrometer) measurements at Mt Soledad to improve our understanding of cloud chemistry and organics, as well as a fog monitor to examine aerosol-droplet interactions in fog. Markus Petters described the full instrument suite that will be deployed at Soledad to measure size distributions and number concentrations. He also discussed aerosol science such as examining the influence of gas-phase species on CCN activation. Kate Benedict described the LANL deployment at EPCAPE to study aerosol (black and brown carbon, and cloud processing impact on aerosol characteristics, etc.). Mikael Witte talked about the Twin Otter campaign to untangle the complex mesoscale dynamics offshore, primarily occurring during the “June gloom” period. Shaocheng Xie described the ARM data products that are expected for EPCAPE (ARSCL, AERIoe, DLPROF, MPLCMASK, VARNAL, SACRGRID, etc.).
Israel Silber and Mark Miller led a discussion about plans for modeling the EPCAPE region. Israel Silber made the point that EPCAPE would support modeling studies at different scales. Mark Miller reflected on what we did not accomplish at Pt. Reyes, given that it was the first deployment for AMF. An important limitation compared to the pier deployment of EPCAPE was that the site was 0.5 mi inland. There are important questions about how the turbulence profile behaves and what the PBL parameterizations are. Rob Wood suggested LES studies on drizzle and drizzle formation. Mikael Witte described the need for detailed aerosol-cloud interactions, using observations, using both data analysis and modeling.
AEROMMA update is that there will be a limited amount of flight time around EPCAPE site.
Shaocheng Xie suggested large-scale models, such as SCM, can apply what is learned from high-resolution models to large-scale models. Christopher Williams asked which instruments and algorithms are deployed to look at dynamics and microphysics. He noted the need to have the right measurements to validate what we want to look at with models, and the important role of translating those measurements for models.
Mikael Witte noted that there is not yet anyone funded to do modeling ahead of EPCAPE but that his group may be able to run some high-resolution simulations over the Southern California Bight to see what sampling we want to do.
Israel Silber said that radar measurements will provide some information on drizzle and discussed the scanning strategies appropriate for model initialization/evaluation.
Christopher Williams and Shaocheng Xie mentioned the work on moving some analyses from PI products to VAPs based on needs.

Key Findings

There is a substantial number of diverse science questions that can be addressed with the EPCAPE data set; an important path forward would be a workshop to foster collaborations and to identify the quintessential and scientifically most interesting cases, both from the aerosol and cloud perspectives, that would benefit from modeling at different scales. Such modeling would, where possible, combine aerosol and cloud processes through collaboration to gather new insights and enable model evaluation and intercomparison. Key focus areas for the workshop will include improvement and expansion of community LES case studies for offshore clean and polluted marine stratocumulus, developing an approach for coastal LES/regional/global modeling case studies, and using trajectory analyses to identify aerosol sources and aging time scales.

Issues

Further scientific discussion is needed to identify the priorities for modeling going forward. While there are many possible areas of investigation for EPCAPE, targeting areas for model intercomparisons and broad collaboration would provide more powerful results.

Needs

The main need identified was for continued communication with the expanded science team, as well as a workshop to bring together modelers to identify the best science questions for the data set.

Decisions

N/A

Future Plans

EPCAPE will continue monthly planning meetings and other preparations for the field campaign. In addition, EPCAPE science team members will propose a workshop to address the issues identified here.

Action Items

Russell will add interested participants to EPCAPE mailing list and will support proposals for additional measurements and analysis. Russell will help to form a team to lead the workshop discussed and work with them to propose the workshop to DOE ASR.