Understanding and modelling sources of ice nucleating particles in Earth System Models

Description

Sea-spray aerosol is enriched in marine organic matter originating from phytoplanktonic material. Although the complex biology and chemistry controlling the emitted aerosol is not yet fully understood, the inclusion of organic matter into sea spray may alter the magnitude of sea spray emissions, and enable sea spray to act as a source of ice nucleating particles (INPs). This presentation will describe OCEANFILMS (Burrows et al., 2014), an approach to modelling the relationship between ocean biogeochemistry and emitted sea spray aerosol chemistry for Earth System Models. OCEANFILMS has recently been implemented in version 1 of the Energy Exascale Earth System Model (E3SM), developed by the U.S. Department of Energy (Burrows et al., ACPD, in revision). The conceptual approach of OCEANFILMS will be described and resulting impacts on simulated aerosols and clouds will be highlighted. Additionally, this presentation will describe an approach to simulating sea spray contributions to atmospheric INPs appropriate for regional and global atmospheric models, and its direct evaluation with time-matched observations (McCluskey et al., submitted). In this study, the OCEANFILMS parameterization was implemented into version 1 of the Community Earth System Model (CESM1), and a recently-developed active site density parameterization for marine INP (McCluskey et al., 2018) was applied to calculate the INP concentrations from simulated sea spray aerosol. Simulated dust INP were parameterized as well (DeMott et al., 2015). Nudging of atmospheric winds was used to match observed meteorology during two recent field campaigns – a coastal campaign at Mace Head, Ireland, and a shipboard campaign in the Southern Ocean. The resulting INP concentrations were compared with observed INP concentrations. For these case studies, model-observation agreement was improved by the inclusion of sea spray aerosol as an additional source of INP and sea spray aerosol was a dominant contributor to the INP population at cloud-relevant altitudes. This study demonstrates the need to account for INPs associated with sea spray aerosol and their subsequent influence on cloud phase transitions.