Breakout Summary Report

ARM/ASR User and PI Meeting

2 - 6 May 2016

Session Title: Cloud Phase Breakout Session
Session Date: 2 May 2016
Session Time: 1:00 PM - 3:00 PM
Number of Attendees: 0
Summary Authors: Gijs de Boer

Breakout Description

Agenda:
1:00-1:15:  Gijs de Boer: Welcome and update on ongoing group activities (case study overview)
1:15-1:30:  Andrew Gettelman:  Cloud phase and model biases — ongoing work
1:30-1:45:  Mariko Oue: Polarimetric analysis of Arctic clouds using Oliktok Ka/W-SACR2
1:45-2:00: Paul Lawson:  New observational tools for understanding cloud phase and mixed-phase clouds
2:00-2:15:  Jing Yang:  Aerosol, cloud type, life cycle-dependent liquid-ice mass partition
2:15-3:00:  Discussion on resources, ideas, plans, and future directions

Main Discussion

With the first case study wrapped up and submitted for publications, the group was polled on potential future activities. It was noted that we have a wide variety of new resources available, including the Oliktok Point facility, the ACME-V data set, AWARE data, Macquarie measurements, and output from global models, including forecast runs discussed by Andrew Gettelman in his presentation.

Several ideas were brought forward as potential group activities:
- The first was to provide additional detail on the spatial scales to which liquid and ice are truly intermixed. This would impact both the effectiveness of the Bergeron process as well as the rate at which riming occurs. While this was seen as an interesting question, it was not clear that existing ARM instrumentation and ongoing work within ASR could answer this question.
- A second set of questions that was raised had to do with ice nucleation. These included questions on where within the cloud ice nucleation happens, what the source of ice nuclei is at high latitudes, and questions surrounding the ability to capture long time series (i.e., annual cycle+) of measurements relevant for understanding ice nucleation. This set of questions is of course very interesting to the cloud phase group, as similar questions are often raised with regard to understanding mixed-phase clouds and their behavior. However, it was mentioned that these questions are perhaps more directly handled by the ice nucleation group, instead of the cloud phase group. Additionally, this led to the philosophical question of what the role of the cloud phase group really was, with two main paths presented – the first being detailed process-level studies providing information on things like ice nucleation, and the second being synthesis-type studies that work to bridge the fine-scale details that may come from PI projects and the models. While both were viewed to have merit, the group seemed to agree that the second path was perhaps a better fit.
- The third set of questions presented had to do with understanding the partitioning of phase in both a variety of observational data sets and models. This was motivated by the figure shown by Jing Yang (U. Wyoming), which demonstrated different relationships between temperature and liquid mass fraction in clouds. This topic was received favorably and includes multiple layers of understanding. First, there needs to be some effort to understand how different techniques measure phase differently (e.g., aircraft measurements vs. surface remote sensing). Secondly, there needs to be a study to provide similarly derived estimates across a variety of locations that experience mixed-phase cloud conditions to see where the differences lie. It was noted that this does not need to be limited to high-latitude locations. Thirdly, the idea was presented that maybe it would be interesting to see how derived liquid mass fraction from surface sensors compares to those from satellite sensors (e.g., CloudSat/CALIPSO). This would allow for more global evaluation of this relationship between T and liquid fraction. Finally, comparisons of the various relationships and model-derived relationships should be completed. Now that models are using information on aerosols in their ice nucleation schemes, we could expect to see differences between different locations in simulations. It was also noted that this question could benefit from extended in-cloud sampling as may be possible by tethered balloon, using instruments that detect cloud phase in situ.

Toward the end of the session, the group discussed two additional topics:
- Coordination between the phase/mixed-phase group and the ice nucleation group. This discussion was limited, but in the end it was stated that we should continue to make clear that information on ice nucleation is critically needed to understand mixed-phase clouds. This continues to be a key gap in our understanding that limits progress on understanding cloud lifetime.
- Group communications: It was acknowledged that once-per-year meetings are insufficient for fostering larger group activities. The decision was made to have a summary directly following the meeting and a follow-up phone call approximately one month from the end of the meeting. During this phone call, the idea is to set up avenues for collaboration, likely focused on the third point in the previous section. From there, the individual groups would carry forward with their efforts, communicating as necessary, and the larger group would follow up with quarterly phone calls. Additionally, the point was raised that there may be opportunities for additional in-person meetings if necessary, either at large community meetings (e.g., AGU) or in a smaller workshop setting. Also, the cloudphase@arm.gov listserve was updated with new interested parties.