Past, present, and future arctic radiative states simulated by Polar-WRF

Abstract. Two recurring radiative states (“transmissive” and “opaque”) strongly modulate the Arctic surface energy balance through their control on downwelling longwave radiation (DLR). Because these states are primarily governed by cloud processes, many coarse-resolution models fail to capture their behavior. This study evaluates how well the Polar-optimized Weather Research and Forecasting model (PWRF) simulates present-day DLR distributions associated with these states and examines projected changes into the future. While most physics parameterizations mirror those of the widely used Arctic System Reanalysis (ASR), we test several advanced microphysics schemes and assess the impact of model resolution. Both the P3 and Morrison two-moment schemes (candidates for the next ASR version) overproduce the opaque mode, whereas the Goddard scheme used in ASR overproduces the transmissive mode. The opaque bias in P3 and Morrison arises mainly from excessive low-level, optically thick clouds over sea ice. Among all schemes, P3 best preserves the distinctiveness of the two radiative modes. Using this scheme, PWRF forced with end-of-century CESM1 output projects a shift toward more frequent opaque conditions, consistent with long-term observations at the North Slope of Alaska. While PWRF shows promise as a tool for dynamically downscaling climate model output, persistent cloud-related biases, especially over ice, warrant caution in future projections. Continued improvements in cloud representation are essential to obtain more quantitative insight into Arctic radiative regime changes.