Lead Impacts on the Moist Static Energy Budget of the Low-Level Arctic Atmosphere in Large-Eddy Simulations based on MOSAiC Data

Elongated cracks in the Arctic sea-ice cover, so-called leads, expose the cold atmosphere to the relatively warm ocean, and are thus critical to the Arctic energy budget. Here, high-resolution large-eddy simulations (LES) are used to examine the impact of Arctic sea-ice leads on the wintertime lower atmosphere. Fourteen simulated cases representing various realistic atmospheric states are studied based on MOSAiC campaign data, expanding on previous LES studies of leads, which often utilize 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 the 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 near-surface long wave net radiation. The response of clear-sky cases, however, critically depends on initial relative humidity. Moist clear-sky cases can transition to a cloudy state when condensed plumes form, becoming radiatively active and acting as efficient “radiator fins”. Here, energy is efficiently removed from the atmosphere, a surprising behavior argued to have implications for sea-ice melt. In contrast, dry clear-sky cases produce little condensation, and radiative effects remain minimal.