The next generation sea-ice model neXtSIM, version 2

Abstract. Sea ice is a key component of the climate system, and sea-ice models are required to realistically simulate climate, ocean, or atmosphere in general circulation models at high latitudes. In this paper, we present the latest version of the next-generation sea-ice model, neXtSIM, which has been developed with a particular focus on ice dynamics and motion. While many large-scale sea ice models can represent regional-to-global sea ice evolution, their representation of sea ice dynamics varies little across models, as they all use a very similar representation of the ice's internal stresses. While this works reasonably well for several quantities (e.g. sea ice volume), it fails to capture sea ice deformation features and the resulting localised changes in thickness and concentration, which likely play an essential role in ice–atmosphere–ocean interactions. The neXtSIM model has been at the core of efforts by its developers and users to explore new modelling approaches to address this shortcoming. Here, we document neXtSIM, now in version 2 of its development, to foster its use for the sea ice community and release a public version of the model. We describe the sea ice dynamics and the core of the model in detail, and discuss parameters specific to the brittle rheologies included in neXtSIM. We also document the model's specificity arising from its Lagrangian framework and its implications for coupling with other components of Earth system models. We hope that the insights provided in this study and the public release of the model will trigger innovative research in the sea ice modelling community.