PNNL

Abstract

The OCEANFILMS parameterization for organic sea spray aerosol emissions has been implemented into a global Earth system model, the Energy Exascale Earth System Model (E3SM). OCEANFILMS is a physically-based model that links sea spray chemistry with ocean biogeochemistry using a Langmuir partitioning approach. Here we describe the implementation within E3SM and investigate the impacts of the parameterization on the model’s aerosols, clouds and climate. Four sensitivity cases are tested, in which organic emissions either strictly add to or strictly replace sea salt emissions (in mass and number), and are either fully internally or fully externally mixed with sea salt. The simulation with internally-mixed, added organics agrees best with observed seasonal cycles of organic matter in marine aerosol. In this configuration, marine organic aerosols contribute an additional source of cloud condensation nuclei, adding up to 30 cm3 to Southern Ocean boundary-layer CCN concentrations (S = 0:1%). The addition of this new aerosol source strengthens shortwave radiative cooling by clouds by -0.36 W/m2 in the global annual mean, and contributes more than -3.5 W/m2 to summertime zonal mean cloud forcing in the Southern Ocean, with maximum zonal mean impacts of about -4 W/m2 around 50S–60S. This is consistent with a previous top-down, satellite-based empirical estimate of the radiative forcing by marine organic aerosol over the Southern Ocean.