Breakout Summary Report

ARM/ASR User and PI Meeting

13 - 17 March 2017

Session Title: The Layered Atlantic Smoke Interactions with Clouds (LASIC) Campaign: First Results and Discussion
Session Date: 15 March 2017
Session Time: 10:30 AM - 12:30 PM
Number of Attendees: 50
Summary Authors: Paquita Zuidema and Allison Aiken

Breakout Description

The intent of this session was to bring together members of the ARM/ASR community interested in and/or working on the LASIC data sets, increase communication within the community, and acquaint everyone with LASIC status. The AMF1 deployment began in June of 2016, and will continue through October 31, 2017. Thus the breakout session took place approximately half-way through the campaign. The agenda follows:
10:30-10:45 Introduction and overview [Paquita Zuidema]
10:45-10:50 MAOS status and trace gas measurements
[Stephen Springston]
10:50-11:00 Surface aerosol measurements: preliminary results
[Alison Aiken]
11:00-11:10 Refractory Black Carbon (rBC) Aerosol Loadings, and Particle Microphysical and Optical Properties [Art Sedlacek]
11:10-11:20 Aerosol Vertical Structure: MPL status and preliminary results
Rodrigo Delgadillo
11:20-11:25 Radar Status [Bradley Isom]
11:25-11:35 3D Cloud Reconstruction [Christine Chiu]
11:35-11:50 Complementary Aircraft Campaigns: UK CLARIFY in August-September 2017 [Paquita Zuidema and Steve Abel]
11:50-12:05 Simulated aerosol radiative forcing by overlying and entrained smoke aerosol: Importance of background conditions and longwave impacts". Xiaoli Zhou, Andrew Ackerman, Ann Fridlind, Robert Wood, and Pavlos Kollias presented by Xiaoli Zhou
12:05-12:30 Discussion

Ultimately, discussion was interspersed during the presentations and the presentations went on until 12:30.

Main Discussion

see breakout description

Key Findings

1) Biomass-burning aerosol (BBA) is almost always present at the surface at Ascension, clearly seen in the SP2 black carbon mass concentration (rBC), the PSAP absorption coefficients, and the CCN counts (and other data sets not shown). Maximum rBC to date took place on August 13 (>1700 ng/m3), with clear synoptic variability throughout the campaign. The loadings are remarkable numbers given the distance from continental Africa. It is also interesting that rBC seems to be present even in November and December, after the nominal ‘biomass-burning season’ has passed. [Paquita Zuidema]
2) The MAOS is optimally sited for high-quality aerosol data collection, being removed from near-coastal sea salt, directly in the path of winds off of the ocean, and with little local (e.g., generator) influence. [Stephen Springston]
3) Non-refractory aerosol mass is dominated by highly oxidized organic aerosol, lacking the primary BBA markers. the OA/rBC ratio decreases with time, suggesting a change in fuel type or burning process. [Allison Aiken]
4) SP2-derived black carbon mass concentration and the PSAP absorption coefficients are highly correlated at all but the highest absorption values, indicating black carbon is by far the dominant absorber. A further investigation into why the absorption angstrom exponents deduced from the PSAP data are lower (~1) than values measured in primarily US wildfires (e.g., BBOP) is required. Low AAE values would indicate little brown carbon. An SP2 lagtime analysis, which provides insight into the surface coating of black carbon, suggests little removal of the coating by evaporation. This refines a current hypothesis that the coating becomes bleached, and thereby more optically transparent. [Art Sedlacek]
5) Preliminary analysis of the lidar data suggests significant aerosol occurs just above (and microphysically interacting with) the low cloud tops [Rodrigo Delgadillo]
6) Zhou et al.’s LES study found a stratocumulus-to-cumulus transition that was hastened in the presence of absorbing aerosols and enhanced moisture aloft, contrary to Yamaguchi et al. (2015).
For informational dissemination only:
- Christine Chiu will be implementing the ENCORE three-dimensional cloud reconstruction developed within Fielding et al. (2013) at Ascension.
- A UK research group, led by Jim Haywood, will bring the UK FAAM BAe-146 plane to Ascension for three weeks in August-September 2017, as part of their CLARIFY project. CLARIFY has goals similar to those of LASIC. The aircraft in situ vertical profiles will be important for connecting the surface-based data sets to the vertical column.

Issues

1) The characterization of the aerosol vertical structure, in particular the amount in the free-troposphere, remains a challenge. Less aerosol was measured at the surface in September than in August, when, climatologically, September is the month with the maximum aerosol loading. Whether this also reflects lower free-tropospheric aerosol loadings is not yet clearly indicated, but satellite estimates of the (clear-sky) aerosol optical depth and cloud droplet number concentration do suggest that the emissions from the African continental fires may have remained more confined to near the continent in September, rather than spreading westward.
2) It is unclear how well the Virkkula and Bond/Ogren corrections to the PSAP data apply. Art Sedlacek hypothesizes that scattering by largish sea salt particles may encourage an over-correction of the PSAP data.
3) Neither of the W-band radars, zenith nor scanning, are currently operational. The WACR did work during the first BBA season. Peter Argee (spelling?) will be going to Ascension to try to bring the W-band radars up. If he is not successful, the W-band radars will likely remain unavailable for the rest of the campaign.

Needs

1) Pin down the PSAP-determined single-scattering-albedo with help from a CAPS instrument.
2) Changes to the radar scanning strategy were discussed afterwards by Christine Chiu, Brad Isom, and Paquita Zuidema. An agreement was reached to focus the scanning on cross-wind RHIs, which Christine’s research group has found to be most conducive for 3D cloud reconstruction.
3) Zhou et al. and related work motivates establishing a process model set-up in the southeast Atlantic with more appropriate constraints (both Zhou et al. and Yamaguchi et al. modeling studies are a mish-mash of northeast Pacific and southeast Atlantic boundary conditions).

Decisions

1) A change to the radar scanning strategy.
2) A need to bring another instrument that measures absorption directly (CAPS) to Ascension.
3) Interest in a topical meeting after LASIC ends on ‘absorbing aerosols and low clouds’.

Future Plans

see Needs

Action Items

1) Submit an IOP/IPR to facilitate a one-month CAPS loan by Aerodyne to LASIC [PZ, AS, Andrew Freedman, Tim Onasch].
2) Refine the CWRHI scanning pattern for the KASACR [PZ and CC].
3) Communicate desire for topical meeting [done].