Breakout Summary Report

The recently concluded Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) involved the deployment of the AMF1 from February 2023 to February 2024 at Scripps Pier and Mt. Soledad in La Jolla, California. The deployment’s objective was to record 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 provided 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 and ASR program missions 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. Those upwelling-driven clouds are susceptible to aerosol indirect effects and feedbacks, which challenge climate models, among other models, in accurately simulating them. 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 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. With record-breaking precipitation in southern California, ostensibly driven by intense atmospheric rivers in 2023, we have a wide range of potential case studies for analyzing cloud-aerosol-precipitation interactions.The goal of this session is to report new results and datasets based on EPCAPE observations that may be of interest for process understanding and modeling. We invite scientists interested in EPCAPE observations to give short presentations on their planned studies or present new results, highlighting any data or collaboration needs. In this session, planned and new studies will be described by contributed and invited talks. The session will be divided into three topic areas based on submitted abstracts, with time for discussion as part of each topic. The participants will be invited to discuss the implications of their work and potential collaborations.

The Main Discussion included one-slide presentations of new results, as summarized below:

• Lynn Russell presented a summary of the climatology of EPCAPE and discussed potential approaches to collaboration with regional and global models.

• Israel Silber provided a brief introduction to ARMTRAJ and its availability for EPCAPE.

• Jim Smith presented new results on the composition and hygroscopicity of ultrafine particles.

• Dan Lubin showed examples from the radiometers deployed to Mt. Soledad.

• Mark Miller presented results on cloud brightness related to turbulence.

• Markus Petters described results of CCN measurements in clouds.

• Lauren Robinson showed the comparison of SATCORPS to in situ drop distributions at Mt. Soledad.

• Seethala Chellappan explained her analysis of atmospheric regimes during EPCAPE.

• Joe Galewsky showed differences in isotopic water vapor measurements in coastal air masses.

• Mikael Witte presented opportunities for collaboration between EPCAPE and SCILLA.

• Matt Lebsock discussed results from 3 completed papers describing G-band radar results.

• Ryan Farley described the composition changes observed during in-cloud events at Soledad.

• There are lots of EPCAPE results available, and several key potentials for collaboration.

• Modeling should focus on relationships/correlations in addition to case studies, since these do not require forcing/nudging.

• Identification of ways in which models can be supported by EPCAPE observations requires additional information exchange between SFAs and EPCAPE team. [Lynn Russell]

• Sector-specific sampling of models is not routine and could provide good comparison simulations for ARM campaigns. [Susannah Burrows]

• Real atmospheric behavior may have different levels of fluctuations than are present in proxies like the pi chamber. [Rob Wood]

• Comparison of drop spectra between ground, aircraft, and satellite show some differences. [Mikael Witte, Lauren Robinson, Seethala Challappan]

• SOM node options can influence the results of the analysis, although similar results are foundfor different regimes/regions. [Mark Miller]

• Seethala Chellappan identified the need for additional data products for EPCAPE on precipitation rate from KaZR and cloud optical depth from the CIMEL sun photometer (SPHOTCOD).

• Proof-of-concept simulations to show aerosol relationships that are similar between models and observations.

• A repository for model output related to EPCAPE would be very useful.

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• Lynn will set up some cases on a google sheet to add relevant parameters for proof of concept and announce it on EPCAPE listserve.

• Lynn will follow up with modelers to identify useful relationships to be reproduced in models.

• Lynn has contacted Die Wang and Shaocheng Xie to request the additional data products for EPCAPE on precipitation rate from KaZR and cloud optical depth from the CIMEL sun photometer (SPHOTCOD); she will follow up at monthly EPCAPE meetings.

• Lynn will continue to organize and lead monthly EPCAPE meetings to provide opportunities to address measurement questions and collaboration opportunities.