10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Influence of Heterogeneous Ice Nucleation of Sea Spray Aerosol on Southern Ocean Clouds
CHRISTINA MCCLUSKEY, Paul DeMott, Thomas Hill, Kathryn Moore, Sonia Kreidenweis, Ruhi Humphries, Alain Protat, Greg McFarquhar, Susannah Burrows, Andrew Gettelman, National Center for Atmospheric Research
Abstract Number: 1450 Working Group: Unraveling the Many Facets of Ice Nucleating Particles and Their Interactions with Clouds
Abstract Clouds occurring over the Southern Ocean (SO) are often comprised of supercooled liquid and are abundant, with an annual average cloud fraction greater than 0.8. Global climate models fail to simulate SO cloud phase and lifetime, leading to large Southern Hemisphere energy biases in climate model simulations. It is hypothesized that these shortfalls are due to poor numerical representations of ice phase transitions and ice microphysics. In a series of observational and modeling studies, we have characterized ice nucleating particle (INP) populations over the SO and investigated their role in primary ice nucleation and subsequent cloud glaciation in a global climate model.
Two methods were used to determine immersion freezing INP number concentrations (nINPs); 1) the ice spectrometer, an offline immersion freezing technique and 2) the continuous flow diffusion chamber, an online INP measurement. These two methods were deployed onboard the Australian Marine National Facility RV Investigator as part of the Clouds, Aerosols, Precipitation, Radiation and atmospherIc Composition Over the southeRN ocean (CAPRICORN) voyage from March to April in 2016. These data represent the first survey of INPs over the SO region in over four decades. Extraordinarily low nINPs were observed in this unique region, with no more than 1 INP active at -30 °C per liter of air. Using the atmospheric component (community atmospheric model, CAM5) of the DOE Community Earth System Model with implementation of a physically-based parameterization for sea spray organic aerosol, simulations using nudged meteorology were conducted for the CAPRICORN study period. Modeled aerosol mass, number and composition were used as input for various parameterizations proposed for predicting nINPs. Estimates of nINPs were in agreement with field observations and results demonstrated that a recent empirical marine INP parameterization may be used to predict observed concentrations of nINPs from the CAPRICORN project.
These new observational constraints and a marine INP parameterization allow for modeling studies to investigate the influence of INPs and primary ice nucleation on cloud phase in SO clouds. As such, the NCAR community atmospheric model (CAM5) will be used in a series of sensitivity simulations designed to explore different representations of INPs and subsequent primary ice nucleation. Simulated cloud occurrence and phase will be directly compared to ship and aircraft based observations, including comprehensive measurements of aerosol and cloud properties, made during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) from January to February 2018.