Physical Characteristics and Spatial Variability of Ice Nucleating Particles over the Southern Ocean

Observations of ice nucleating particles (INPs) were made in the Southern Ocean Marine Boundary Layer (MBL) during the Clouds, Aerosols, Precipitation Radiation and atmospherIc Composition Over the southeRN ocean II (CAPRICORN II) study on the R/V Investigator during January - March 2018. Measurements of INPs active in the immersion freezing mode were made in real time with a Continuous Flow Diffusion Chamber (CFDC) at temperatures below -25°, and via offline analyses of aerosol filter and seawater samples using the Colorado State University Ice Spectrometers (IS) from -10 to -28°. An identical CFDC and aerosol filters were on-board the NSF/NCAR G-V aircraft during the concurrent Southern Ocean Cloud Radiation Aerosol Transport Experimental Study (SOCRATES), which collected INP measurements in the MBL, below and above cloud, and in the free troposphere in the same region as CAPRICORN II. Chemical treatments performed on the aerosol filters were used to infer the fraction of biological, organic, and mineral INPs, which varies with latitude in the MBL. Data from four G-V overflights of the R/V Investigator are used to investigate the vertical structure of INPs in this region, as well as their source. Additional size and compositional information about the atmospheric INPs were determined using electron microscopy analyses of INPs collected from the CFDCs. Indirect inference of the size of INPs in the MBL using an aerosol concentrator suggests the majority of INPs are smaller than 500 nm, unlike many continental INPs.