Constraining the Uncertainty Associated With Sea Salt Aerosol Parameterizations in Global Models Using Nudged UKESM1‐AMIP Simulations

Journal of Geophysical Research Atmospheres, vol. 130

Abstract

Abstract Sea salt is the largest source of natural aerosol in the atmosphere by mass. Formed when ocean waves break and bubbles burst, sea salt aerosols (SSA) influence Earth's climate via direct and indirect processes. Models participating in the sixth Coupled Model Intercomparison project (CMIP6) demonstrate a negative effective radiative forcing (ERF) when SSA emissions are doubled. However, the magnitude of the ERF ranges widely from −0.35 0.04 W to −2.28 0.07 W , with the largest difference over the Southern Ocean. Differences in the response to doubled SSA emissions arise from model uncertainty (e.g., individual model physics, aerosol size distribution) and parameterization uncertainty (e.g., how SSA is produced in the model). Here, we perform single‐model experiments with UKESM1‐AMIP incorporating all of the SSA parameterizations used by the current generation of CMIP6 Earth system models (ESMs). Using a fixed SSA size distribution, our experiments show that the parameterization uncertainty causes large inter‐model diversity in SSA emissions in the models, particularly over the tropics and the Southern Ocean. The choice of parameterization influences the ambient aerosol size distribution, cloud condensation nuclei and cloud droplet number concentrations, and therefore direct and indirect radiative forcing. We recommend that modeling groups evaluate their SSA parameterizations and update them where necessary in preparation for future model intercomparison activities.

Authors 8

1. Abhijith U. Venugopal corresponding

   University of Canterbury

   Affiliation as printed

   School of Physical and Chemical Sciences University of Canterbury Christchurch New Zealand

2. Yusuf Bhatti Aachen Now at SRON Netherlands Institute for Space Research Leiden The Netherlands

   University of Canterbury · Space Research Organisation Netherlands

   Affiliation as printed

   Now at SRON Netherlands Institute for Space Research Leiden The Netherlands

   School of Physical and Chemical Sciences University of Canterbury Christchurch New Zealand

3. Olaf Morgenstern

   Deutscher Wetterdienst · University of Canterbury · National Institute of Water and Atmospheric Research

   Affiliation as printed

   National Institute of Water and Atmospheric Research Wellington New Zealand

   Now at German Meteorological Service Offenbach am Main Germany

   School of Physical and Chemical Sciences University of Canterbury Christchurch New Zealand

4. Jonny Williams

   National Institute of Water and Atmospheric Research · University of Reading

   Affiliation as printed

   National Institute of Water and Atmospheric Research Wellington New Zealand

   Now at Department of Meteorology Reading University Reading UK

5. Nick Edkins

   University of Canterbury · National Institute of Water and Atmospheric Research

   Affiliation as printed

   National Institute of Water and Atmospheric Research Wellington New Zealand

   School of Physical and Chemical Sciences University of Canterbury Christchurch New Zealand

6. Catherine J. Hardacre

   University of Canterbury

   Affiliation as printed

   School of Physical and Chemical Sciences University of Canterbury Christchurch New Zealand

7. Anthony Crawford Jones

   Met Office

   Affiliation as printed

   Met Office Exeter UK

8. Laura E. Revell corresponding

   University of Canterbury

   Affiliation as printed

   School of Physical and Chemical Sciences University of Canterbury Christchurch New Zealand