Breakout Summary Report
ARM/ASR User and PI Meeting
COMBLE and high-latitude clouds over open water
25 June 2020
2:00 PM - 4:00 PM
130
Bart Geerts and Mikhail Ovchinnikov
25 June 2020
2:00 PM - 4:00 PM
130
Bart Geerts and Mikhail Ovchinnikov
Breakout Description
This session will present preliminary findings from the recently completed COMBLE campaign;as well as other studies of boundary layer clouds during cold-air outbreaks over open water. While the
emphasis is on Boreal open waters (COMBLE), we will also cover Southern Ocean observational and
modelling work (MARCUS).
Preliminary agenda:
• Aerosol-Cloud-Precipitation Interactions in Mixed-Phase Clouds over the Southern Ocean (Greg
McFarquhar)
• Overview of Data Collected in COMBLE (Nathan Wales)
• Case Study of a CAO in COMBLE (Yonggang Wang)
• Cloud Properties during Marine Cold Air Outbreaks in COMBLE: a Preliminary Survey (Bart Geerts)
• Large Eddy Simulation of CAO Clouds in the Fram Strait, validated against Airborne and Satellite
Measurements (Roel Neggers)
• Preliminary Plans for VAPs and Model Forcing Datasets in COMBLE (Shaocheng Xie)
• Discussion: approaches for LES/CRM model setups, initializations, and coordinated evaluation in
COMBLE (moderator: Mikhail Ovchinnikov)
• Discussion: data product needs (moderator: Mike Jensen)
Presentations will be ~10 min long, followed by Q&A.
Participants: We can make room for 1-2 additional brief presentations. Please contact Bart Geerts
(geerts@uwyo.edu) if you are interested in presenting.
Main Discussion
The COMBLE session was attended well. In addition to the 14 panelists/co-hosts, 169 people had registered and 116 of them tuned in, at least, for some parts of the webinar. During the session, there were about 100 participants on average. This is a very good attendance, considering that we were competing with the breakout on the new major ARM site in the SE US (AMF3).We started off with 3 polling questions yielding the following results:
1. One of the three research topics called for in the latest DOE ASR funding opportunity is “High-latitude atmospheric processes”. Did you (co )submit a proposal under this topic?
Yes: 12 (24%)
Intended to but did not
get around to it: 0 (0%)
No: 39 (76%)
2. What ARM datasets are you using, or do you intend to use, to study high-latitude atmospheric processes?
MARCUS: 4 (7%)
MOSAIC: 3 (5%)
COMBLE: 10 (18%)
Data collected in northern Alaska
(NSA and/or Oliktok Point): 5 (9%)
Multiple ARM sources: 33 (60%)
3. Is your research focus …
observational: 32 (50%)
modelling: 11 (17%)
rather balanced
between the two: 21 (33%)
Summarizing the poll results, three quarters of respondees did not participate as (co-)PI in proposals submitted to the latest ASR call for proposals on “High-latitude atmospheric processes”, indicating either that many attendees are not at the level of (co-)PI, and/or that many are keen to pursue this topic in response to furure FOAs. The majority of researchers (plan to) rely on data from multiple ARM sources at high latitudes. A fifth of those who named a main source of data for their current or future high-latitude research identified COMBLE, more than any other named field programs or permanent site. Given that the COMBLE campaign wrapped-up less than a month prior to the session, the significant interest in working with COMBLE data is a very encouraging sign. Half of the participants identify themselves as primarily observationalists, a third as those persuing a balanced approach, with the rest focusing more on modeling.
Next, we had a series of 10 min presentations. There was a rather lively Q&A exchange on the side of these talks, some of which were addressed live, others through typed responses. We were pressed for time, and in hindsight we probably had 1-2 talks too many, but the talks covered the full diversity of observational and modelling studies over the Southern Ocean and around the Arctic. Here are some key take-away points:
1. Aerosol-cloud-precipitation interactions in mixed-phase clouds over the Southern Ocean (Greg McFarquhar). This was an extensive summary of the fundamental questions motivating recent field campaigns over the Southern Ocean, including MARCUS and SOCRATES (NSF-funded). Greg summarized the findings from several recent papers, and mentioned a BAMS article in review on this work. Interestingly, much of the focus is turning towards the post-frontal shallow-cloud sector, where the largest model biases are found. This region is exactly the focus of COMBLE.
2. Overview of data collected in COMBLE (Nathan Wales). Generally good news. Data collection was better than anticipated, starting a month earlier than requested, continuing with a small crew when the pandemic broke out, and excellent instrument performance in harsh conditions, including the radars. Missing from the AMF1 site for most of the campaign duration were the MPL and two aerosol analyzers. Some credit for COMBLE’s success was given to Met Norway.
3. Cloud properties during marine cold air outbreaks (CAO) in COMBLE: a preliminary survey (Bart Geerts). A first attempt at a classification of the CAO cloud regime, and an early characterization of the environmental and cloud characteristics during CAOs. Two emerging “golden” cases centered on 13 March and 29 March 2020 were noted.
4. Case study of a CAO in COMBLE (Yonggang Wang). A very early case study of one of these “golden” cases. This presentation led to the quest for INTERPSONDE data not jut from the AMF1 site, but also from the Bear Island site.
5. Large Eddy Simulation of CAO Clouds in the Fram Strait, validated against airborne and satellite measurements (Roel Neggers). A report on the first detailed observational and LES study of a CAO over the Fram Strait, documented with in situ aircraft and dropsonde data. This study addresses the question why GCMs generally have a BL that is too deep and too warm near the sea ice margin. It also demonstrated the need to tweak initial conditions in order to improve LES performance.
6. An observational and modelling case study of post-frontal boundary-layer convection over the Southern Ocean in MARCUS (Zachary Lebo). A case study addressing the question of cloud phase partitioning in shallow convective clouds in the 0 to -20C temperature range. The P3 scheme was used, without cloud-active aerosol.
7. Status and calibration of the radar data in COMBLE (Alexis Hunzinger). The KAZR and scanning Ka/W-band radars performed very well during the 6m-long COMBLE campaign. The calibration process was detailed, with COMBLE data calibrating much better than CACTI. This is promising for composite studies covering data from all 6 months. Ideas for radar-based VAPs were presented and community input was sought.
8. Preliminary plans for VAPs and model forcing datasets in COMBLE (Damao Zhang). Damao mentioned the various lead translators, the core VAPs, and possible additional VAPs if requested by the community. This was discussed further at the end of the session (see below).
Finally, two open forums were held. The first one, moderated by Mikhail Ovchinnikov, discussed SCM/LES/CRM setup and evaluation as the basis to address biases in climate models. Model intercomparison(s) are envisioned based on COMBLE golden cases. Organizing such coordinated modeling efforts will require follow-up communication from the COMBLE team and will benefit from collaborative involvement of researchers, who participated in a recent multi-model study of a CAO case from the CONSTRAIN campaign (de Roode et al. 2019, http://dx.doi.org/10.1029/2018MS001443).
The second discussion, moderated by Mike Jensen, went back to the presentations by Alexis and Damao on current data plans, and raised the question of specialized data product needs. This discussion involved some oral exchanges (rather than just typed Q&A), including on an expansion of existing products, such as a refined PBL height.
In conclusion, this was a productive session that invariably led to many new ideas for research, and many behind-the-scenes follow-up exchanges. We certainly would be interested in another COMBLE-focused online session later this summer, to allow others to present, and to allow more in-depth discussions. We have the list of registered participants and can use that as the basis for organization.