Lead Impacts on the Moist Static Energy Budget of the Low‐Level Arctic Atmosphere in Large‐Eddy Simulations Based on <i>MOSAiC</i> Data

Abstract High‐resolution large‐eddy simulations (LES) are used to examine the impact of Arctic sea‐ice leads on the wintertime lower atmosphere. Leads expose the cold atmosphere to the relatively warm ocean, and are thus critical to the Arctic energy budget. Fourteen cases representing various realistic atmospheric states are studied based on campaign data from the Multidisciplinary drifting Observatory for the Study of Arctic Climate ( MOSAiC ), expanding on previous LES studies of leads, which often represented single idealized conditions. Control runs are contrasted against perturbed runs containing a 1.2 km wide idealized lead, which evolves through a prescribed open–refrozen–closed life cycle. Impacts on the moist static energy budget of the lower atmosphere are then investigated, also in the context of the well‐known bimodal state in the surface energy budget in the Arctic. During lead‐open phase all simulations show large increases in the turbulent heat fluxes, with a slight reversed effect after lead closure. These fluxes are well predictable from bulk theory applied to a given control atmospheric state. The atmospheric response depends strongly on the initial atmospheric conditions. Cloudy cases remain in a cloudy state, featuring a small increase in longwave net radiation. The response of clear‐sky cases, however, critically depends on initial relative humidity. Under moist, clear‐sky conditions, rising lead plumes condense into clouds that act as efficient “radiator fins.” These radiatively active plumes efficiently remove energy, potentially removing more heat from the atmosphere than the lead initially introduced. In contrast, dry clear‐sky cases produce little condensation, and radiative effects remain minimal.