Spatial and Temporal Variability of Ice Nucleating Particles over the Southern Ocean
Authors
Paul J. DeMott — Colorado State University
Thomas C Hill — Colorado State University
Kathryn Moore — Colorado State University
Ezra Ezra Levin Levin — Colorado State University
Jessie Creamean — Colorado State University
Sonia Kreidenweis — Colorado State University
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Andrew Gettelman — National Center for Atmospheric Research (NCAR)
Susannah M. Burrows — Pacific Northwest National Laboratory
Simon Alexander — Australian Antarctic Division
Alain Protat — Australian Bureau of Meterology
Martin Schnaiter — Karlsruhe Institute of Technology (KIT)
Emma Jarvinen — National Center for Atmospheric Research (NCAR)
Greg McFarquhar — University of Oklahoma
Roger Marchand — University of Washington
Category
ARM field campaigns – Results from recent ARM field campaigns
Description
Timeline of INP number concentrations per standard liter at three temperatures at Macquarie Island during MICRE, starting in March 2017 and ending in March 2018.
A contributing hypothesis for explaining climate model overestimates in shortwave radiation reaching the Southern Ocean (SO) surface is that clouds topping the marine boundary layer (MBL) more deeply supercool due to inadequate sea spray emissions of ice nucleating particles (INPs) (e.g., McCluskey et al., GRL, 2018; 45, 11,989–11,997; Vergara-Temprado et al., PNAS, 2018; 115, 2687-2692). Concurrent observations of INPs and cloud properties to test this hypothesis are limited. The Macquarie Island Cloud and Radiation Experiment (MICRE) provided an annual cycle of immersion freezing INP concentrations (‑5 to ‑28°C), and the Measurements of Aerosols Radiation and CloUds (MARCUS) campaign captured spatial variability of immersion freezing INPs during cruises from Tasmania to Antarctic stations. Supporting aerosol and cloud property data were collected during both campaigns, and from ship and aircraft platforms during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES), an NSF campaign.
INP number concentrations and active site densities were derived for particles rinsed from filters and measured with the CSU ice spectrometer, and in situ and remotely-sensed aerosol data. INP compositions were inferred as biological via their losses from thermal treatment at 95°C, and organic via their losses following carbon digestion with H2O2. Total aerosol chemistry, sequencing for aerosol DNA genomic analyses, and real-time bioaerosol measurements were also made.
Preliminary results are: 1) INP concentrations in the SO MBL are up to 50 times lower than reported by Bigg (JAS, 1973; 30, 1153–1157); 2) higher INP concentrations occur closest to Australia and Antarctica; 3) INP emissions maximize in Austral winter; 4) organic INPs dominate the SO MBL year-round; and 5) biological INPs that trend with bioaerosol abundance and genomic diversity dominate at modest supercooling. Analyses are being used to refine marine INP parameterizations and compare to in situ and remotely measured cloud properties, and will be implemented in modeling studies to address the primary hypothesis stated above. Low INP concentrations are consistent with widespread supercooled clouds that were observed, but cannot explain localized higher cloud ice concentrations, presumably from secondary ice formation. Preliminary modeling studies suggest vertical variations in INP types, as also observed, with mineral types aloft and marine INPs in the MBL.
