LAUSR

Interactions between clouds and aerosols represent a large source of uncertainty in future climate projections. It is unclear, for example, how the lifecycle of mid-latitude storm systems — which includes the albedo and total lifetime of its clouds — are influenced by the presence of anthropogenic aerosols, confounding estimates of climate sensitivity. Using high-resolution global convection-permitting model simulations and satellite observations, Daniel McCoy from the University of Leeds, Paul Field from the UK Met Office and colleagues investigate how mid-latitude storm cloud properties are affected by increased aerosol concentrations. In comparing pristine versus polluted storms, it is shown that aerosols increase the liquid water content, cloud cover and consequently the albedo of polluted systems, enhancing outgoing short-wave radiation by upwards of 4 W m−2 within the storm. Such changes were also observed in a natural case study — the 2014–2015 Holuhraun volcanic eruption in Iceland — confirming the existence of an indirect aerosolinduced effect on mid-latitude storms. This improved understanding of aerosol–cloud interactions within extratropical cyclones will help constrain estimates of anthropogenic radiative forcing, and thereby improve climate projections. GS