Atmospheric response to Antarctic coastal polynyas

Antarctic coastal polynyas are ice-free areas forming in sea ice-covered regions, primarily driven by strong katabatic winds that push sea ice offshore. These polynyas enable ocean-to-atmosphere heat exchange, driving intense sea ice production and dense water formation. Despite their role in generating Antarctic Bottom Water (AABW), which constitutes 30-40% of global ocean volume, their atmospheric dynamics remain poorly understood. This study investigates the atmospheric impacts of Antarctic coastal polynyas using high-resolution (3 km) WRF simulations, focusing on the Prydz Bay region, including the Cape Darnley (CDP) and Mackenzie Bay polynyas (MBP). A sensitivity experiment without polynya, highlights the significant atmospheric changes when polynyas are open: a major heat release toward the atmosphere (up to 1000 W·m⁻²) increases the air temperature (over 5.5°C), creates a low-pressure anomaly (-70 Pa), an acceleration of the surface winds (over 5 m·s⁻¹) and an intense atmospheric convection leading to a thicker boundary layer (+400 m) and more clouds. Two recirculation anomaly cells develop upstream and downstream of the polynya. An analysis of meridional wind trends reveals that the dynamical response of the atmosphere to the polynya opening is controlled by a balance between the pressure gradient forces, the advection and the vertical diffusion, reinforced by the strong vertical turbulent mixing above the polynya. These results underline the substantial influence of polynyas on local atmospheric dynamics, and suggest potential feedback mechanisms that could influence polynya dynamics and consequently the AABW formation.