Evaluating simulations of ship tracks in a high-resolution model

Abstract. Clouds, and in particular their interactions with aerosols, remain a major source of uncertainty in climate projections, due to the wide range of scales over which cloud processes act on. This uncertainty limits our capability to simulate potential solar radiation management strategies, such as marine cloud brightening (MCB). A good natural analogue for investigating MCB is analysis of ship tracks, as they mimic the intended effect and allow us to investigate time evolving aerosol perturbations. In this study, we model a real case of ship tracks, and evaluate model performance through comparisons with satellite observations. We evaluate our model simulations against three criteria, in order to ascertain whether this model is suitable for simulating MCB accurately. Our findings highlight a key deficiency in activation parameterisations when simulating high aerosol concentrations – such as those expected in MCB scenarios. While the model can replicate the mean cloud properties within ship tracks, it struggles to capture their temporal evolution. Specifically, in precipitating clouds, enhancements in droplet number concentration (N_d) and liquid water path (LWP) are overestimated and persist too long. This discrepancy between model and observations is linked to excessive model sensitivity to aerosol loading in precipitating conditions, leading to unrealistically easy suppression of drizzle, and ultimately resulting in simulated ship tracks which overestimate the cooling effect in these cases. We identify scenarios in which current formulations of parameterisations are not suitable for use in simulating high-concentration aerosol perturbations, such as MCB, and scenarios in which models are more capable.