Breakout Summary Report

 

ARM/ASR User and PI Meeting

EPCAPE
22 June 2021
11:00 AM - 1:00 PM
90
Lynn Russell, Allison Aiken, Susannah Burrows

Breakout Description

Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) is planned for deployment of AMF1 from February 2023 to January 2024 at Scripps Pier and Mt. Soledad in La Jolla, California. The session will focus on the science plan, additional collaborative contributions, and discussion of related science questions. The focus of this project 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 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 presented an overview of the EPCAPE science plan and introduced the science highlight topics that would be covered by the other speakers. She described the two planned locations for EPCAPE at the Scripps Pier and Mt. Soledad. She showed the frequency of cloud presence at Mt. Soledad, providing both a higher altitude for radar measurements and a site for in situ cloud droplet sampling.

Matt Christensen showed a comparison of AOD and CCN measurements at ENA to investigate ACI. Markus Petters described the scientific rationale behind the proposed addition to EPCAPE of a comparison of aerosol activation, composition, and oxidation. Mark Miller showed differences in cloud properties between continental and marine air masses. Allison Aiken described the importance of characterizing local sources with a second site, including quantifying scattering and absorbing aerosols for direct effects. Mikael Witte described the processes of on/offshore eddies providing east-west mixing of pollution, and the need for characterization of that as well as entrainment by aircraft measurements. The Lagrangian sampling plan for the proposed aircraft allows for characterization of east-west gradients as well as north-south processing. Susannah Burrows described the E3SM new aerosol treatment with multiple modes and composition, which illustrates the importance of accurate descriptions of the size distribution. She showed the need to compare the E3SM predictions to long-term measurements of aerosol and CCN. She expressed interest in joint modeling between large-eddy simulations and climate models. Linking model footprints to back trajectories could provide additional insight. The possibility of linking ACI to rain rate may provide a strong constraint for modeling. Dan Lubin reviewed the history of key measurements of cloud radiative properties in the San Diego area.

Key Findings

A substantial number of diverse science questions can be addressed with the EPCAPE data set; additional questions may be answered if additional measurements are supported.

Issues

There was a general discussion of science, measurement, and logistical issues related to EPCAPE. Fred Brechtel asked about adding the TBS and, if so, with which measurement packages? There was general agreement that the TBS could provide important supporting measurements, in particular during the spring intensive. Additional information is needed to assess what air-space restrictions might allow for a launch location.

Graham Feingold asked how changes in LWP would be attributed to aerosol rather than temperature changes. Dave Turner discussed accuracy of LWP measurements for this region. Paquita Zuidema suggested the possibility of additional ceilometers to provide measurements of spatial heterogeneity. Zuidema and Turner added ideas about a possible mini/meso-net of radiometers and ceilometers, if there is instrument and facility availability. Collis mentioned WSR ADAP and the possibility that Bragg returns might add to small-scale characterization of the heterogeneity of rain.

In general, modelers were interested in characterizing the spatial heterogeneity of the region with multiple ground-based instruments near the two EPCAPE sites. This interest seems to be motivated both by the complexity of the coastal interface as well as the interest in growing the ARM approach beyond the constraints of single-site studies, perhaps as a result of the demonstrated value of the network established at SGP. The scope of this is likely limited to robust, relatively inexpensive instruments that require little maintenance and access. However, given the potential impact of this approach for modeling studies, there will likely be substantial interest if such data can be collected.

Needs

Several participants raised questions about whether EPCAPE could be expanded to include additional measurements that would allow more complete estimates of some quantities, especially radiative fluxes.

One need is for additional upstream measurements in order to expand the Lagrangian history of the air masses. Witte will request Twin Otter deployment from ONR. AEROMMA may also provide chemical measurements in the region. There is interest for TBS deployment, which will be pursued when the appropriate call is issued. Other collaborators are investigating the possibility of research vessels.

Another need for modeling is for gridded measurements, which may be possible to add for small autonomous instruments that could be distributed on rooftops of University or local buildings. Turner, Zuidema, and Russell will schedule a discussion of what might be possible to request.

Another suggestion was to request or provide archiving of airport sonde data during the project. This may include the San Diego, Carlsbad, and Miramar airports.

Decisions

Not applicable.

Future Plans

EPCAPE will continue monthly planning meetings and other preparations for the field campaign.

Action Items

Russell will add interested participants to EPCAPE mailing list and will support proposals for additional measurements and analysis. Additional preparations for EPCAPE will proceed by interested investigators in collaboration with ARM staff, including a kick-off meeting, state and University planning and permissions, and additional measurement proposals to various agencies.