William Gustafson, principal investigator for the Large-Eddy Simulation (LES) ARM Symbiotic Simulation and Observation (LASSO) workflow, sent in this update.
As I begin writing this next entry in the series on deciding where to apply LASSO next, I am in the Chicago airport waiting to fly home from ARM’s 2018 Developers’ Meeting, which was held at Argonne National Laboratory this year. At the meeting, I heard from folks that are very excited about the previous blog entry on expanding LASSO to simulate maritime clouds at the Eastern North Atlantic atmospheric observatory. Likewise, I know many of you are excited about the next possibility, which is expanding LASSO to simulate mixed-phase clouds in the Arctic.
Two possibilities currently being considered include doing this for the upcoming MOSAiC field campaign, where an ice breaker will be embedded into the Arctic sea ice for a year, or for the North Slope of Alaska (NSA) atmospheric observatory at Utqiaġvik, Alaska. Scientifically, there are many reasons for gaining better understanding of the Arctic, but I will not lay them out here. You can find a great summary of them on Multidisciplinary drifting Observatory for the Study of Arctic Climate’s (MOSAiC’s) website.
ARM has been making measurements on the North Slope since 1996, and there have been many modeling studies associated with these observations, such as the large-eddy simulation intercomparison associated with the Indirect and Semi-Direct Aerosol Campaign (ISDAC) field campaign. One takeaway from this intercomparison is that proper representation of cloud microphysics is extremely important for properly simulating arctic clouds, and there are still many unknowns in terms of how to do it correctly.
As such, LASSO simulations for arctic mixed-phase clouds will be significantly more complicated than the current warm-phase cloud simulations at the Southern Great Plains (SGP) atmospheric observatory. Background aerosol assumptions will play a larger role, layering of the clouds, and the increased uncertainty that comes with the mixed-phase regime all will impact how LASSO would be implemented. However, providing LASSO data bundles for this regime also is an opportunity to bring further clarity on how to improve atmospheric models for the Arctic.
In fact, Gijs de Boer, Atmospheric System Research (ASR) science team lead for Oliktok Point at NSA, sees the challenges as a strong motivation for pursuing the arctic option—this will provide much more data that researchers can use to improve process understanding and microphysics parameterizations.
Discussion at the 2018 Joint ARM/ASR Principal Investigators Meeting highlighted several science drivers for pursuing the Arctic. These include:
- Transition of the cloud state between liquid and ice phases
- Simulation of phase partitioning and its relation to cloud lifetime
- Understanding cloud and aerosol layering and their connection to atmospheric thermodynamic state
- Sensitivity of lower clouds to radiative forcing due to outgoing longwave radiation and radiation from higher clouds.
Model Configuration Changes
Successfully simulating the Arctic would require many changes to the LASSO model configuration compared to that used at SGP. For example, the more stable boundary layer, thinner clouds and distinct layering of the clouds, and the atmospheric state in the troposphere would require using an increased model resolution. We would likely also need to provide a more realistic aerosol profile to input into the microphysics, and this profile would need to change day to day to accommodate the greater impact of aerosol perturbations in this relatively pristine environment.
Decisions would also be needed for how to handle the coastal interface at Utqiaġvik. Surface fluxes over the ocean will be very different than over land, which could dictate using a nested modeling approach instead of period lateral boundaries. Or we could target conditions when the land-based observations are more representative and consistent with a periodic model domain.
MOSAiC has been suggested as a simpler environment to use for beginning to work through the multiple configuration choices necessary for running an arctic LASSO case. MOSAiC will be in a more homogeneous environment than NSA. The observations planned for MOSAiC include detailed sea ice and snow properties that will be of use in understanding surface fluxes and how to properly handle the LES lower boundary.
Join the Discussion
How would you use Arctic LASSO simulations? What types of research would they benefit? What observations would you want included in the data bundle? What new observations would ARM need to add to complement and/or evaluate the LES? We created a forum for users to share their thoughts and discuss their ideas to help ARM management and the LASSO team make the right decision for expanding LASSO.
We invite you to participate in the forum discussion on Github, where we have begun an entry on the arctic expansion option. Community input is critical for motivating the next phase!
Ovchinnikov M, AS Ackerman, A Avramov, AN Cheng, JW Fan, AM Fridlind, S Ghan, J Harrington, C Hoose, A Korolev, GM McFarquhar, H Morrison, M Paukert, J Savre, B J. Shipway, MD Shupe, A Solomon, and K Sulia. 2014. “Intercomparison of large-eddy simulations of Arctic mixed-phase clouds: Importance of ice size distribution assumptions.” Journal of Advances in Modeling Earth Systems, 6, 223–248, 10.1002/2013ms000282.