Assessing the Impact of Surface Coupling and Observations on Arctic Cyclone Forecast Performance

Arctic cyclones (ACs) have a significant impact on Arctic climate, particularly during the summer months when they can contribute to the accelerated decline of Arctic sea ice. ACs are influenced by various processes from the tropopause to the surface. At the tropopause, subsynoptic-scale tropopause polar vortices (TPVs) often precede the intensification of ACs. Mid-tropospheric water vapor and radiative heating complicates the predictability of both ACs and TPVs. Near the surface, baroclinicity is crucial for the initiation and the intensification of the Arctic cyclones. Being a contributor to the baroclinity, sea ice distribution itself changes rapidly due to the surface winds and waves, and even cloud coverage brought byACs.

In this study, we use the Community Earth System Model 2 (CESM2) with increased resolution over the Arctic region and the Data Assimilation Research Testbed (DART) to perform a hierarchy of Observing System Simulation Experiments (OSSEs) designed to isolate important processes in AC and TPV development for a simulated intense, long-lived AC. The impact of modeling on the forecast performances is evaluated by comparing CESM2 simulations run with atmospheric-only and fully-coupled configurations. The impact of observation assimilation on the forecast performance is evaluated through two approaches: first, assimilating additional dropsonde observations along the TPV track that mimic intensive observation periods in field campaign, and second, incorporating sea ice observations using DART’s weakly-coupled assimilation option. Early results highlight the benefits of accurately representing the vertical distribution of water vapor and its influence on AC and TPV coupling and intensification.