Breakout Summary Report

ARM/ASR User and PI Meeting

2 - 6 May 2016

Session Title: MAGIC
Session Date: 4 May 2016
Session Time: 1:30 PM - 3:30 PM
Number of Attendees: 0
Summary Authors: Ernie Lewis

Breakout Description

There was a breakout session on MAGIC at which presentations were given describing results, with discussion following.

Main Discussion

A series of talks were given in which results from MAGIC were presented, each followed by discussion. Approximately 26 people attended.

Presentations:
- Ernie Lewis: MAGIC breakout session introduction
- Ed Luke: MBL cloud rain rate retrievals during MAGIC
- Greg McFarquhar: An overview of MARCUS
- David Painemal: Aerosol proxies and their co-variability with cloud microphysics during MAGIC
- Rob Wood (and Johannes Mohrmann): Using MAGIC data to constrain the marine boundary layer CCN budget in the Sc-Cu transition region
- Weidong Yang: Spectrally-invariant properties of clouds in transition zones during MAGIC

The next two presentations were not given orally due to time constraints, but the authors suggested that people go immediately to the poster sessions to see their posters:
- Chris Bretherton (and Jeremy McGibbon): Comparison of ship-following large-eddy simulations with cloud and boundary layer structure observed in MAGIC
- Maike Ahlgrimm: Ship-following single-column model preliminary results – a proof of concept


Ed Luke presented preliminary results on radar/lidar retrievals of precipitation rate. Discussions followed on how can evaporation rate be calculated and how common precipitation was during MAGIC (it was not very common). There was great interest in a data product on precipitation rate, and Ed said that he planned on producing one for the entire campaign.

Greg McFarquhar discussed the MARCUS program. Discussions were on the representativeness of the longitude of the transects, the importance of the direct effect, sea spray freezing, and the importance of supercooled water – most of which are not directly relevant to MAGIC.


David Painemal presented results on various aerosol-cloud indices, and noted that different proxies gave different indices. The index determined from relating CCN(0.4%) to number concentration from the UHSAS was near unity, whereas that relating CCN(0.4%) to the scattering at 450 nm was near 0.l7, which has implications for remote sensing. Discussions included whether correlating at the same RH levels would make more sense than correlating with height and whether the results could be applied to an ARM CCN VAP.

Rob Wood presented a budget of CCN during MAGIC, and showed that winter median CN concentrations were less than summer median values by up to two times as far as 145 degrees west, and that winter centroids of back trajectories were much farther west (i.e., more marine) in winter than in summer. He concluded that the winter rain rate exceeded the summer rate by ~70%, and that in the winter the main aerosol source is the free troposphere, and the main sink is precipitation. He stressed the value of another MAGIC deployment capturing the spring season. Discussions included the source of the free tropospheric aerosol (nucleation?), whether or not the free troposphere really was the source of the MBL aerosol, the effects of using different precipitation values on the results, the importance of wind speed (there seemed to be little wind-speed dependence of the results), and the difference between more frequent precipitation in summer (as demonstrated by Xiaoli Zhou et al.'s 2015 J. Climate paper) and more precipitation mass in winter.

Weidong Yang presented results on the spectral invariance properties of clouds in transition zones, comparing results from the SASZe, CIMEL, and SSFR, and applied these results to determine whether the mixing was inhomogeneous or homogeneous, concluding that in 17 cases, more than 70% were inhomogeneous.

Key Findings

There were several key findings.

Ed Luke's determinations of precipitation rate will be a valuable addition to the overall data set, and generated great interest.

David Painemal's results that different aerosol-cloud indices gave different values was notable. The index relating CCN (0.4%) and UHSAS number concentration was near unity (which demonstrated the importance of the UHSAS), but that relating CCN(0.4%) and scattering at 450 nm (measured by the nephelometer) was near 0.7, with implications for the ability to use remote sensing to obtain cloud-active number concentration. The HSRL backscatter was consistent with the nephelometer results, and this correlation demonstrates that surface measurements are representative of cloud base. He concluded that the MWR was the best instrument during MAGIC for cloud properties. HOWEVER, only the physical retrievals for the 2-channel MWR have been run; the statistical retrievals, and retrievals for the 3-channel MWR have not been run, and these have been noted as being of key importance.

Rob Wood's analyses of CCN budget and his results that CN concentrations were less in winter than in summer were noteworthy, as was the result that precipitation rate was greater in winter, despite the fact that precipitation occurred more often in summer. His conclusion that the main source of the aerosol was the free troposphere would be a major finding. His conclusion that the dominant aerosol sink was precipitation highlights the need for produces such as those that Ed Luke is developing.

Weidong Yang's analysis of the spectrally invariant cloud features demonstrated that both homogeneous and inhomogeneous mixing occurred during MAGIC, although inhomogeneous mixing dominated.

Discussions of Chris Bretherton's and Maike Ahlgrimm's results are not presented here.

Issues

An issue noted by many is the lack of available data in the archive that is required for analysis, including statistical retrievals from the 2-channel and 3-channel microwave radiometers (MWR) and retrievals from the radar wind profiler (RWP). Additionally, data from the ASSIST have not yet been processed. Request was also made for a Microbase or similar product for modeler-friendly cloud and water distribution.

Needs

Analyses of the MWR (both 2- and 3-channel versions), RWP, and ASSIST data by the mentors is a need that was stressed by several investigators. Additionally, a Microbase or similar product for modeler-friendly cloud and water distribution was requested. Several investigators stated that having the precipitation retrieval (that Ed Luke is working on) and Christine Chiu's product, both of these for the entire deployment, placed in the archive would be very useful.
The need for data for the full seasonal cycle (i.e., a full year) on the MAGIC transect to address some of the observed summer/winter differences in clouds, aerosols, and precipitation was stated. While this is obviously not possible with the current data set, it would be were another MAGIC deployment to take place.