Meetings > PI / Science Team Meeting

Breakout Summary Report

 

ARM/ASR User and PI Meeting

10 - 13 June 2019

Shortwave-Absorbing Aerosols and Their Interactions with Clouds (e.g., LASIC)
12 June 2019
1:30 PM - 3:30 PM
40
Paquita Zuidema

Breakout Description

Biomass-burning aerosols represent complex mixtures of black carbon and organic aerosols that also contain brown carbon. The aerosol chemical compositions and black carbon properties will change with age, affecting the aerosol’s optical and cloud-nucleating properties in time-dependent ways. These affect the direct aerosol radiative effect, which also depends on the underlying albedo, either of the earth’s surface or clouds. Clouds, if present, in turn adjust to the presence of smoke. Clouds can adjust both semi-directly to the absorbed sunlight, or indirectly through changes to their microphysics when clouds and aerosols mix. The dominant processes will vary with the aerosol-cloud vertical structure, which can vary seasonally, while the dominant cloud adjustments will also evolve as the clouds advect.



Modeling efforts are necessary to help articulate the significant processes, with model-observational closure/validation studies promoting confidence in model-based analyses. The characterization of truly aged biomass-burning aerosol, its relationship to the prevalent marine cloud, and the processes by which the clouds interact with the smoke, motivated the LASIC (Layered Atlantic Smoke Interactions with Clouds) campaign held in the remote southeast Atlantic on Ascension Island, spanning June 1, 2016 - October 31,
2017. This session is intended to highlight work based on LASIC, but is not limited to just LASIC, as the motivating issues occur globally. Lab studies are also encouraged. We invite all attendees with relevant material. This session will be coordinated with a session focusing more on properties of brown carbon led by Yan Feng and Art Sedlacek.



Agenda:



Presentations



  • Cloud Processing of Biomass Burning Plumes Drives Black Carbon to Center Stage (1:32-1:46, Art Sedlacek & Ernie Lewis)

  • CALIOP and HSRL-2 Measurements of Aerosol Layers over the SE Atlantic (1:46-1:59, Rich Ferrare & Sharon Burton)

  • Assessment of LASIC Micro-Pulse Lidar and Retrievals (1:59-2:12, Paytsar Muradyan & Paquita Zuidema)

  • LES Intercomparison of Lagrangian Shallow Cloud Evolution Under Smoky Conditions (2:12-2:25, Robert Wood)

  • Realistic Lagrangian LES (2:25-2:38, Takanobu Yamaguchi or Graham Feingold)

  • Low Cloud Reduction Within the Smoky Marine Boundary Layer and the Diurnal Cycle (2:25-2:38, Jianhao Zhang and Paquita Zuidema

  • Aerosol Radiative Effects over Ascension Island using LASIC Observations and MERRA-2 (2:38-2:51, Allison Collow/Mark Miller)

  • Modeling Aerosol-Cloud-Radiation Interactions in the Southeast Atlantic: Understanding Impacts and Uncertainties (3:02-3:15, Pablo Saide)


    • Discussion/other topics (3:15-3:30)


    • Other continuing inter-comparisons: instrumental and modeling-observational. Do something LASIC focused (Yan Feng)

    • Joint LASIC/CLARIFY/ORACLES/AEROCLO-Sa workshop May 18-22 2020 Miami

    • ACP/AMT Special Issue, LASIC overview paper plans

Main Discussion

The session was split ~evenly into discussions of the biomass-burning aerosol aging and characterization, and into their interactions with the shallow clouds. Art Sedlacek’s presentation on how the aerosol evolves to a thinly coated, black carbon mass core possessing a low single-scattering albedo over time garnered a lot of discussion. The Lagrangian large-eddy simulations of smoke/cloud systems upstream of Ascension also received a lot of discussion. These represent the cutting-edge in LES research, as they incorporate prognostic aerosol that allow for a much deeper investigation of aerosol-cloud interactions than is possible with, e.g., fixed cloud droplet number concentrations. Another discussion item was the LASIC micropulse lidar, for which two independent sets of extinction retrievals have been developed. Lastly, permeating the whole session, were references to knowledge gained from the aircraft campaigns deployed during the time of LASIC, notable the UK CLARIFY experiment deployed from Ascension and the NASA ORACLES field campaign. Another discussion item was that of a model-observational intercomparison study of the seasonal and diurnal cycle observed at Ascension (this would take advantage of the time scale sampling that is a unique contribution of the AMF1 deployment).

Key Findings


  • A view is developing on how biomass-burning aerosol ages during long-range transport. The aerosol that is sampled at Ascension is typically highly aged, as it has needed to be entrained into the boundary layer prior. Cloud processing removes the larger particles, as these are activated first, and the smaller, more sunlight-absorbing aerosols remain. Some questions remain re. the aerosol composition of the non-black-carbon components that still need to be worked out

  • The presence of the sunlight-absorbing aerosol within the boundary layer has a noticeable impact on the low-cloud response. Low-cloud cover is less (the boundary-layer semi-direct effect) but the diurnal cycle is complex and holds some surprises. This includes a pronounced moisture stratification during the night that helps maintain decoupling within the boundary layer. The sub-cloud layer does cool and become well mixed throughout the night, and the initial radiative warming at first helps drive vertical motion, before a thermal stratification sets in. This documentation, now under review (https://www.atmos-chem-phys-discuss.net/acp-2019-448/), makes extensive use of the 8x daily/radiosondes of the LASIC IOP.


Issues

I can’t really say there are issues as such, but one thing I do think is imperative to come out of the LASIC campaign is a quantitative assessment of the aerosol vertical structure as deduced from the micropulse lidar. I (Zuidema) think the best way to do this is through a peer-reviewed publication, ideally led by the instrument mentor Paytsar Muradyan, as this will help establish her as well. I will work with Paytsar to accomplish this.

Needs

N/A

Decisions

See future plans.

Future Plans


  • A LASIC campaign overview BAMS-type paper will be developed in the coming year.

  • A joint LASIC/CLARIFY/ORACLES/AEROCLO-Sa workshop will be held in Miami, May 18-22, 2020, building on one held in Paris in April 2019 prior to the EGU meeting. CLARIFY/ORACLES/AEROCLO-Sa are aircraft deployments held in the southeast Atlantic during time frames that overlap with LASIC. Bringing scientists together from the various campaigns in April 2019 began collaborations that we expect to be scientifically fruitful. We will use the lasic@arm.gov email list to disseminate information to interested DOE ASR researchers.

  • A joint ACP/AMT Special Issue has been launched: https://www.atmos-chem-phys.net/special_issue978.html. "New observations and related modelling studies of the aerosol–cloud–climate system in the Southeast Atlantic and southern Africa regions."

  • A model-observational comparison focused on Ascension Island, led by Yan Feng of Argonne National Lab. This would build on a similar ORACLES-led intercomparison that is currently underway. We expect the execution of this project to be reasonably efficient, by making use of the same protocols, and beginning with the participation of the same models, as in the ORACLES-led study.

  • A publication on the micropulse lidar retrieval data set led by Paytsar Muradyan (instrument mentor) and Paquita Zuidema.

  • A relevant proposal for an AGU session has been accepted: Cloud-aerosol-radiation-climate interactions in the southeast Atlantic. Session ID: 82392


Action Items

See future plans.