A Kilometer-Scale Coupled Atmosphere-Wave Forecasting System for the European Arctic

Accurately simulating the interactions between the components of a coupled Earth modeling system (atmosphere, sea ice, and wave) on a kilometer-scale resolution is a new challenge in operational numerical weather prediction. It is difficult due to the complexity of interactive mechanisms, the limited accuracy of model components, and scarcity of observations available for assessing relevant coupled processes. This study presents a newly developed convective-scale atmosphere-wave coupled forecasting system for the European Arctic. The HARMONIE-AROME configuration of the ALADIN-HIRLAM numerical weather prediction system is coupled to the spectral wave model WAVEWATCH III using the OASIS3 model coupling toolkit. We analyze the impact of representing the kilometer-scale atmosphere-wave interactions through coupled and uncoupled forecasts on a model domain with 2.5-km spatial resolution. To assess the coupled model's accuracy and uncertainties we compare 48-h model forecasts against satellite observational products such as Advanced Scatterometer 10-m wind speed, and altimeter-based significant wave height. The fully coupled atmosphere-wave model results closely match both satellite-based wind speed and significant wave height observations as well as surface pressure and wind speed measurements from selected coastal station observation sites. Furthermore, the coupled model contains smaller standard deviation of errors in both 10-m wind speed and significant wave height parameters when compared to the uncoupled model forecasts. Atmosphere and wave coupling reduces the short-term forecast error variability of 10-m wind speed and significant wave height with the greatest benefit occurring for high wind and wave conditions. SIGNIFICANCE STATEMENT Accurately simulating the Earth system (atmosphere, sea ice, and wave) on a kilometer-scale resolution is a new challenge in numerical weather prediction. It is difficult due to the complexity of interactions between the atmosphere, ocean surface, and sea ice. Other obstacles in the development of a coupled forecasting system include the limited accuracy of individual model components as well as the limited availability of observations that represent coupled processes. This study presents a newly developed high-resolution atmosphere-wave coupled forecasting system for the European Arctic. We show the impact of representing kilometer-scale atmosphere-wave interactions and assess the accuracy of the coupled forecast model by comparing model results against satellite-based observations of 10-m wind speed and significant wave height. Results show the fully coupled atmosphere-wave forecasting system closely matches satellite observations of 10-m wind speed and significant wave height as well as measurements of wind speed from coastal observation sites. The coupled atmosphere-wave system also reduces the variability of forecast errors for both 10-m wind speed and significant wave height for high wind speeds and large wave magnitudes.