Secondary ice production in summer clouds over the Antarctic coast: an underappreciated process in atmospheric models

Georgia Sotiropoulou (1, 2) , Étienne Vignon (3, 4) , Gillian Young (5) , Hugh Morrison (6, 7) , Sebastian J O'Shea (8) , Thomas Lachlan-Cope (9) , Alexis Berne (3) , Athanasios Nenes (1, 10)

1 EPFL - Ecole Polytechnique Fédérale de Lausanne
2 Stockholm University
3 Environmental Remote Sensing Laboratory [Lausanne]
4 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
5 University of Leeds
6 NCAR - National Center for Atmospheric Research [Boulder]
7 UNSW - University of New South Wales [Sydney]
8 University of Manchester [Manchester]
9 BAS - British Antarctic Survey
10 FORTH - Foundation for Research and Technology - Hellas

The correct representation of Antarctic clouds in atmospheric models is crucial for accurate projections of the future Antarctic climate. This is particularly true for summer clouds which play a critical role in the surface melting of the ice shelves in the vicinity of the Weddell Sea. The pristine atmosphere over the Antarctic coast is characterized by low concentrations of ice nucleating particles (INPs) which often result in the formation of supercooled liquid clouds. However, when ice formation occurs, the ice crystal number concentrations (ICNCs) are substantially higher than those predicted by existing primary ice nucleation parameterizations. The rime-splintering mechanism, thought to be the dominant secondary ice production (SIP) mechanism at temperatures between −8 and −3 ∘C, is also weak in the Weather and Research Forecasting model. Including a parameterization for SIP due to breakup (BR) from collisions between ice particles improves the ICNC representation in the modeled mixed-phase clouds, suggesting that BR could account for the enhanced ICNCs often found in Antarctic clouds. The model results indicate that a minimum concentration of about ∼ 0.1 L−1 of primary ice crystals is necessary and sufficient to initiate significant breakup to explain the observations, while our findings show little sensitivity to increasing INPs. The BR mechanism is currently not represented in most weather prediction and climate models; including this process can have a significant impact on the Antarctic radiation budget.

Domaines: Sciences de l'environnement

Georgia Sotiropoulou, Étienne Vignon, Gillian Young, Hugh Morrison, Sebastian J O'Shea, et al.. Secondary ice production in summer clouds over the Antarctic coast: an underappreciated process in atmospheric models. Atmospheric Chemistry and Physics, 2021, 21 (2), pp.755-771. ⟨10.5194/acp-21-755-2021⟩. ⟨hal-03154111⟩