Accurate atmosphere-ocean-sea ice model simulations of the Antarctic region are becoming increasingly necessary, particularly since 2016 when Southern Hemisphere sea ice reached its lowest extent since the start of the satellite era. This project will advance atmosphere-ocean-sea ice modeling in the Southern Ocean by enhancing the representation of atmospheric cloud physics and heat exchange between the ocean and sea ice in state-of-the-science models. Model development will incorporate recent observations of high latitude clouds and aerosols, leading to improvements that are critical for weather forecasting on subseasonal to seasonal timescales. These advancements will be subsequently incorporated into a high-resolution, fully coupled regional model of the atmosphere, ocean, and sea ice for the Southern Ocean, to be used to simulate the strong year-to-year variability of sea ice conditions observed in recent decades. It is crucial to enhance our understanding of this variability because it influences global weather patterns, helps reveal the underlying mechanisms driving both gradual and abrupt sea ice changes, ultimately improving the accuracy of both local and global numerical models. This project will advance the simulation of polar environments in two key ways. First, it addresses biases caused by parameterization of cloud microphysics (specifically supercooled liquid water clouds) and ocean-sea ice heat exchange in numerical models of the Southern Ocean. Reducing the