A054-07
Observation-Enabled Assessment of Simulated Southern Ocean Aerosol and INP Populations in the Community Atmosphere Model Version 6
Tuesday, 8 December 2020: 19:24
Virtual
Christina S McCluskey1, Andrew Gettelman2, Charles Bardeen1, Paul J DeMott3, Cynthia H Twohy4, Darin W Toohey5, Bryan Jeremy Rainwater6, Lynn M Russell7, John M Reeves8, Jorgen B Jensen8, Sonia M Kreidenweis9, Thomas Christopher James Hill3, Kathryn Moore9, Ezra JT Levin9, Ruhi Humphries10, Melita D Keywood11, Simon Alexander12, Laura Riihimaki13, Greg M McFarquhar14, Xi Zhao15 and Xiaohong Liu16, (1)National Center for Atmospheric Research, Boulder, CO, United States, (2)NCAR, Boulder, CO, United States, (3)Colorado State University, Fort Collins, CO, United States, (4)NorthWest Research Associates Boulder, Boulder, CO, United States, (5)Univ Colorado, Boulder, CO, United States, (6)University of Colorado at Boulder, Boulder, CO, United States, (7)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (8)NCAR, Broomfield, CO, United States, (9)Colorado State University, Atmospheric Science, Fort Collins, CO, United States, (10)CSIRO Marine and Atmospheric Research, Aspendale, Australia, (11)Climate Science Centre, CSIRO Oceans & Atmosphere, Aspendale, Australia, (12)Australian Antarctic Division, Kingston, TAS, Australia, (13)Pacific Northwest National Lab, Richland, WA, United States, (14)Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, Norman, OK, United States, (15)Texas A&M University College Station, Texas, United States, (16)University of Wyoming, Department of Atmospheric Science, Laramie, WY, United States
Abstract:
In many Earth System Models, including the Community Atmosphere Model version 6 (CAM6), biases in Southern Ocean (SO) low-level, mixed-phase cloud occurrence and phase are sensitive to the representation of primary ice nucleation. While many processes subsequent to primary ice nucleation also require attention, this study focuses on assessing simulated SO aerosol quantities and their consequential impacts on predicting SO ice nucleating particles (INPs), which are responsible for primary ice nucleation.
Observations from the DOE-ARM MARCUS ship-based campaign, the ground-based MICRE study, and the NSF SOCRATES flights confirm marine sources dominate the SO aerosol, with some influence of dust aerosol detected above clouds. Low INP concentrations measured both in the SO marine boundary layer and aloft suggest that this pristine aerosol sustains low-level supercooled liquid clouds over the SO.
Instrument simulators, designed based on instrumentation specifications, were “deployed” in CAM6 simulations over the SO study periods with dynamics specified from reanalysis data. Simulated marine and dust aerosol vertical profiles roughly matched observations, with maximum sea salt number concentrations (Nss) in the marine boundary layer and maximum dust number concentrations (Ndst) above 4 km. Below 3 km, Nss were a factor of 100 higher than Ndst, though simulated Ndst range over 3 orders of magnitude likely due to variability in simulated dust scavenging. Because the ice nucleation ability of dust aerosol is three orders of magnitude greater than that of marine aerosol for a given aerosol surface area, we find that errors even for low Ndst impacted predicted INP populations. In fact, INPs estimated from CAM6 simulated aerosol quantities resulted in dust-dominated INP populations at all altitudes, inconsistent with SO observations.
Following the SO aerosol and INP assessment, observationally-guided modifications to specific processes, including dust aerosol scavenging, estimated impacts of marine organic aerosol, and INP parameterizations, will be investigated to reduce INP prediction biases. The improvements achieved from this study will ultimately facilitate observation-enabled evaluation and development for cloud processes subsequent to primary ice nucleation.
