Long-term variability in immersion-mode marine ice-nucleating particles from climate model simulations and observations

• Published in: Atmospheric chemistry and physics 2023-05, Vol.23 (10), p.5735-5762
• Main Authors: Raman, Aishwarya, Hill, Thomas, DeMott, Paul J, Singh, Balwinder, Zhang, Kai, Ma, Po-Lun, Wu, Mingxuan, Wang, Hailong, Alexander, Simon P, Burrows, Susannah M
• Format: Article
• Language: English
• Subjects: Aerosol composition; Aerosol concentrations; Aerosol measurements; Aerosols; Air sampling; Analysis; Antarctic expeditions; Approximation; Atmosphere; Atmospheric boundary layer; Atmospheric models; Atmospheric particulates; Bias; Biological activity; Climate; Climate models; Climate prediction; Clouds; Diagnostic systems; Dust; ENVIRONMENTAL SCIENCES; Expeditions; Experiments; Freezing; Global climate; Global climate models; Ice; Ice nucleation; Immersion; Latitude; Life cycle; Life cycles; Measurement; Modelling; Nucleation; Oceans; Ozone; Parameterization; Precipitation; Radiation; Radiation measurement; Radiation-cloud interactions; Sea spray; Simulation; Simulation methods; Southern Hemisphere; Spray; Submerging; Temperature; Time dependence; Work platforms
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-23-5735-2023

Ice-nucleating particles (INPs) in the Southern Ocean (SO) atmosphere have significant impacts on cloud radiative and microphysical properties. Yet, INP prediction skill in climate models remains poorly understood, in part because of the lack of long-term measurements. Here we show, for the first time, how model-simulated INP concentrations compare with year-round INP measurements during the Macquarie Island Cloud Radiation Experiment (MICRE) campaign from 2017–2018. We simulate immersion-mode INP concentrations using the Energy Exascale Earth System Model version 1 (E3SMv1) by combining simulated aerosols with recently developed deterministic INP parameterizations and the native classical nucleation theory (CNT) for mineral dust in E3SMv1. Because MICRE did not collect aerosol measurements of super-micron particles, which are more effective ice nucleators, we evaluate the model's aerosol fields at other high-latitude sites using long-term in situ observations of dust and sea spray aerosol. We find that the model underestimates dust and overestimates sea spray aerosol concentrations by 1 to 2 orders of magnitude for most of the high-latitude sites in the Southern Hemisphere. We next compare predicted INP concentrations with concentrations of INPs collected on filter samples (typically for 2 or 3 d) and processed offline using the Colorado State University ice spectrometer (IS) in immersion freezing mode. We find that when deterministic parameterizations for both dust and sea spray INPs are used, simulated INPs are within a factor of 10 of observed INPs more than 60 % of the time during summer. Our results also indicate that the E3SM's current treatment of mineral dust immersion freezing in the SO is impacted by compensating biases – an underprediction of dust amount was compensated by an overprediction of its effectiveness as INPs. We also perform idealized droplet freezing experiments to quantify the implications of the time-dependent behavior assumed by the E3SM's CNT-parameterization and compare with the ice spectrometer observations. We find that the E3SM CNT 10 s diagnostic used in this study is a reasonable approximation of the exact formulation of CNT, when applied to ice spectrometer measurements in low-INP conditions similar to Macquarie Island. However, the linearized 10 s diagnostic underestimates the exact formula by an order of magnitude or more in places with high-INP conditions like the Sahara. Overall, our findings suggest that it is import