A set of decadal simulations has been completed and evaluated for gains using the Regional Arctic System Model (RASM) to dynamically downscale data from a global Earth system model (ESM) and two atmospheric reanalyses. RASM is a fully coupled atmosphere - land - ocean - sea ice regional Earth system model. Nudging to the forcing data is applied to approximately the top half of the atmosphere. RASM simulations were also completed with a modification to the atmospheric physics for evaluating changes to the modeling system. The results show that for the top half of the atmosphere, the RASM simulations follow closely to that of the forcing data, regardless of the forcing data. The results for the lower half of the atmosphere, as well as the surface, show a clustering of atmospheric state and surface fluxes based on the modeling system. At all levels of the atmosphere the imprint of the weather from the forcing data is present as indicated in the pattern of the monthly and annual means. Biases, in comparison to reanalyses, are evident in the ESM forced simulations for the top half of the atmosphere but are not present in the lower atmosphere. This suggests that bias correction is not needed for fully-coupled dynamical downscaling simulations. While the RASM simulations tended to go to the same mean state for the lower atmosphere, there is a different evolution of the weather across the ensemble of simulations. These differences in the weather result in variances in the sea ice and oceanic states.

Off the coast of Victoria Land, Antarctic an area of open water - the Terra Nova Bay Polynya (TNBP)- persists throughout the austral winter. The primary force driving the development of this almost ice-free stretch of water are extreme katabatic winds flowing down the slopes of Transantarctic Mountains. The surface-atmosphere coupling and ABL transformation during the katabatic flow between 18-25 September 2012 in Terra Nova Bay are studied, using observations from Aerosonde unmanned aircraft system (UAS) observations, numerical modeling results and Antarctic Weather Station (AWS) measurements. Our analysis demonstrates that the intensity and persistence of katabatic winds is governed by sea level pressure (SLP) changes in the region. Whereas the duration and intensity of the flow, determines the polynya extent. When cold, dry air brought with the winds interacts with relatively warm surface of the polynya the convection starts to develop and overcomes the previously stable atmosphere. In general, the intensity of the flow, surface conditions in the bay and regional SLP fluctuations are all interconnected and together modify local atmospheric and surface conditions. The importance of valid forecast of katabatic events for Antarctic aircraft operations is unambiguous. The Antarctic Mesoscale Prediction System (AMPS) performs this task well, but due to exaggerated sea ice concentrations (SIC) incorrectly represents vertical ABL properties and air mass modification over the TNBP. Altogether, this research provides a unique description of TNBP development and its interactions with the atmosphere and katabatic winds, thus enhancing our understanding of the complex processes taking place in this region.