Breakout Summary Report

ARM/ASR User and PI Meeting

Breakout Description

Lynn Russell, Virendra Ghate, David Painemal, and Shaocheng Xie introduced three case studies from EPCAPE by showing aerosol, satellite, sounding, radar, and other observations for April 27-28, May 16-17, and July 3-4. Each case includes persistent and continuous low-cloud (<1km) over Scripps Pier and at Mt. Soledad.

Main Discussion

 Xue Zheng presented two types of simulations for EPCAPE. The first was E3SM/RRM SCREAM and the second was WRF nested-domain. Her team is interested in the diurnal cycle of the boundary layer and clouds. Prior work looked at the VOCALS diurnal cycle, but expectation is that EPCAPE may provide a better comparison as well as a larger data set. She also noted the importance of evaluating SCREAM with aerosol as passive tracers to assess the role of local transport. A key opportunity is to use the cloud microphysical features to compare with the model.

 Po-Lun Ma expressed interest in using coarse (1 degree) and fine (3 km) resolution E3SM with specialized diagnostic tools to compare with observations. EPCAPE will provide an appropriate data set to evaluate northeastern Pacific ACI, which can be evaluated with their diagnostic tools. He noted the interest of Colleen Kaul in LES simulations, which currently do not include terrain.

 Jingyi Chen plans to use WRF-LES with Lagrangian forcing and WRF-Chem, making use of the observed aerosol size distributions. Her group will use lessons learned from ACTIVATE simulations for EPCAPE. She expects to use single-column modeling to test large-scale forcing. The objective is to provide guidance on cloud parameterization. WRF-LES will be used to assess the effect of aerosol on liquid water path. WRF-Chem will be used to assess how aerosols affect cloud fraction.

 The group discussion noted the need to pay attention to the topographic effects. The issue with the coarse-resolution model (GCM) is the poor simulation of coastal clouds, i.e., the lack of clouds at the grid cells of the coastline. Increasing spatial and vertical resolution are key for simulating clouds, suggesting a nesting approach to resolve the coastline. However, since coarse-resolution modeling is still important as CMIP6-like models are still used for aerosol cloud interactions, an important approach would be to compare offshore clouds (1 or 2 grid cells to the east) with the EPCAPE observations. This approach is justified due to the frequent homogeneity of the stratocumulus cloud deck offshore up until it reaches the pier.

Aerosol characterization of the free troposphere is challenging and yet critical for LES. MERRA-2 reanalysis, CALIPSO aerosol extinction profiles, and in situ observations could be used to derive aerosol properties above the boundary layer.

There are potential challenges of LES at the coast due to terrain and advection of the continental boundary layer. WRF-nested domain should be able to resolve those continental effects. In addition, satellite data from GOES-16 can provide useful information to determine the timing and extent of the impact of continental effects on the open ocean MBL.

Key Findings

There are already several possible low cloud case studies for the EPCAPE data set from April, May, and July. Low cloud events are continuing through August, yielding a data set rich with radar, lidar, and in situ measurements of aerosols and clouds.

Issues

Coastal cloud predictions are challenging at both the smallest (LES) and largest (GCM) scales for different reasons. Some existing models lack either the spatial resolution or terrain representation required.

Needs

Follow-up discussions of EPCAPE results are needed online and in person. A data and analysis workshop in summer 2024 may help to foster model intercomparisons. Modeling studies need to be better coordinated.

Decisions

Examples of EPCAPE case studies will continue to be shared with the modeling community in order to support simulations. Regionally focused modeling studies with topography may be ideal for EPCAPE coastal cloud studies, especially those with eddy-resolving grid scales. LES with idealized topography may be appropriate for comparisons to pier measurements as they are 300 m upwind of terrain features. GCMs may need to use grid cells to west of site for comparison to pier in order to work around the current limitations of simulating terrain effects. An hierarchical modeling approach from low- to high-resolution with different complexities may be necessary for EPCAPE case studies and inferring low-resolution model parameterization development from knowledge learned from high-resolution model simulations and process-level studies.

Future Plans

EPCAPE Science Team continues to meet monthly online to follow up on these and other issues. Modeling teams will continue to be invited to present their plans for simulations.

Action Items

Identify funding opportunities for analysis of EPCAPE results.