Description and evaluation of a new contrail cirrus parameterization in the ARPEGE-Climat atmospheric model

The impact of aviation on climate change due to CO 2 emissions is well established and is far less uncertain than the one due to non-CO 2 effects. Among these effects, the formation and evolution of contrails into cirrus-type clouds remains highly uncertain. An overlooked source of uncertainty arises from the climate model sensitivity to the adjustable parameters used to represent the effects of subgrid-scale processes. The limited number of climate models that explicitly represents contrails makes it challenging to evaluate the model sensitivity of contrail radiative forcing to these parameters. In order to better characterize the contrail radiative forcing and its evolution, it is necessary to develop their representation within a wide range of existing climate models. In this study, we develop and evaluate a new parameterization of contrail cirrus for the ARPEGE-Climat atmospheric model. The model representation of the ice-supersaturated regions in which contrails persist, as well as the contrail microphysical properties, is consistent with in-situ and satellite observations. The ERA5 atmospheric reanalysis is then used to nudge ARPEGE-Climat with the novel parameterization. The nudged simulation results are used to estimate the global mean contrail radiative forcing for the year 2019. Our findings suggest that the global mean contrail coverage is 1.1%. This value is located within the range of 0.6–1.2% based on previous studies. Furthermore, the global annual mean contrail radiative forcing is estimated to be 45.6 30–66 mW·m –2 . This value falls within the lower range of current best estimates for 2018, 111 33–189 mW·m –2 .