Breakout Summary Report


ARM/ASR User and PI Meeting

Cloud-aerosol-precipitation-radiation interaction studies over the Southern Ocean and Antarctic
25 October 2022
4:15 PM - 6:15 PM
Roger Marchand

Breakout Description

The purpose of the breakout session was to review the understanding of cloud-aerosol-precipitation-radiation interactions that have been gained from analysis of data collected during recent field campaigns (and associated modeling activities) over the Southern Ocean and Antarctic (including AWARE, MARCUS, and MICRE) with an objective to identify questions that still remain to be answered and discuss development of strategies for future campaigns and measurements that need to be undertaken to address the remaining questions. A series of short 5-minute talks were given, in which the presenters were asked to focus on the breakout objective.

Main Discussion

Minghui Diao:
- Extending approach of Shupe et al. 2007 to look at cloud phase
- Qs that needs more focus:
o What processes drive the shift of cloud regimes from lower to higher latitudes?
o What is the reason that E3SM EAMv1 does not reproduce the cloud vertical structure?
- Suggest need for long-term data set (for statistical comparisons and unbiased sampling) in combinations with more shipborne (lower to higher latitudes) and/or aircraft observations taking a Lagrangian approach.

Ann Fridlind:
- Only one Antarctic case (from AWARE) in library of case studies used by GISS, and there needs to be development of cases for SO.
- Stressed need for multiple case studies for a specific regimes (transitions) and need for a Lagrangian approach.
- Importance of aerosols and INP (MICRE is deficient in this regard)
- Lots of fog in the MICRE data set/clouds in stable conditions deserves some attention.

Andrew Gettelman:
- Strong nudging
- Using MICRE data to examine a one-moment and a 2-moment microphysics scheme in the ECMWF-IFS SCM
o Radiation (surface and TOA) is remarkably good, but only when simulations are run with strong nudging. Without strong nudging there is a large drift in boundary-layer thermal structure.
o Too much LWP with two-moment microphysics. (Large LWP errors occur when LWP is appreciable and so has little effect on radiation).
o Not enough ice in the simulations, and difficult to get the model to generate more. (The only secondary ice process represented in the currently available Morrison scheme is Hallett-Mossop. Andrew is not convinced this is a problem with secondary ice.)
- We don’t know ice number well enough. (The amount/number of small ice particles in mixed-phase clouds is not easily determined with current aircraft, and such ice does not have much effect on the radiation).

Paul DeMott:
- As regard annual cycle of INP from MICRE
o INPs at upper end of MARCUS (likely island effects – see Raman et al., ACPD)
o Seasonal INP variation

Key Findings

Roj thoughts: This is more of a summary than a set of key findings.
- Discussion revolved more about measurement needs (things missing from existing campaigns) than the science drivers (though there are questions hiding behind such). Common themes were to obtain more sampling south of 60S (esp. in the transitions season when biological activity is starting up) and more characterization of winter conditions (which can be contrasted with summer).
- Different people want more information on the small or the large end of the aerosol size distribution for NPF and biological INP, respectively. Size-resolved INP, vertical profiles (including free troposphere) were also mentioned more than once.
- Small ice (or rather a lack measurements that accurately separate the distribution of small ice and small liquid particles) in mixed-phase clouds is a major issue (limiting model evaluation and studies of ice processes).
- The existing data sets don’t include much information on surface properties, emissions, fluxes.
- It is clear that more needs to be done to develop modeling test cases for the SO with existing data. Work by Atlas (2020) is a good start but there needs to be modeling with interactive aerosols and/or focus on secondary ice processes. There is interest in understanding the transition between overcast and open low clouds mesoscale structures, suggesting a need for measurements that support a Lagrangian analysis framework.







Future Plans


Action Items