Atmospheric Response to Antarctic Coastal Polynyas

Abstract

The lack of sea ice in Antarctic coastal polynyas enables strong ocean-to-atmosphere heat fluxes and intense sea-ice production. Although these features are primarily driven by intense offshore winds, their impact on local atmospheric conditions remains poorly understood. This study employs a high-resolution polar Weather Research and Forecasting model configuration over the Prydz Bay region, East Antarctica, home to two major coastal polynyas: Cape Darnley and Mackenzie Bay polynyas. Sensitivity experiments over three winters (2014–2016) comparing simulations with and without polynyas reveal a marked and spatially confined atmospheric response. Polynya openings induce substantial surface heat release (up to 700 W m⁻²), warming near-surface air by over 5 K and triggering convection and clouds. This results in a thickening of the atmospheric boundary layer and the development of stronger surface winds (up to 4 m s⁻¹) that converge toward a low-pressure anomaly. A particular emphasis is placed on the mechanisms controlling wind anomalies, using a dedicated wind tendency analysis. This diagnosis highlights that the processes involved depend on location and altitude within the polynya region and involve a balance between vertical mixing, horizontal advection, and pressure gradient forces—vertical mixing acting as the initiating factor. This study provides a novel modeling framework used to isolate the atmospheric response to coastal polynyas, overcoming limitations of previous studies and coarse-resolution models. It offers new insights into the role of polynyas in modulating regional climate and improving understanding of the processes driving their dynamics.