Evaluation of high-resolution Polar WRF 3DVar forecasts over the Svalbard

The polar lows cause severe weather phenomena with strong near-surface winds above 15 m s^-1. The prediction of the polar lows is difficult because the polar lows are smaller than the synoptic scale lows and develop rapidly and strongly. To simulate the polar lows accurately in high-resolution, the regional model that could consider polar environmental characteristics is required. The Polar Weather Research and Forecasting (PWRF) model has been used to predict the polar atmosphere and to produce the Arctic System Reanalysis data. Nonetheless, the verification of the PWRF forecasts has mostly been carried out for specific observation campaign periods. Thus, more validations for other polar low cases are necessary to evaluate the performance of the PWRF in predicting the polar lows.

In this study, the performance of the high-resolution PWRF forecasts over the Svalbard is evaluated. The forecasts from the own analysis-forecast cycling with three-dimensional variational (3DVar) data assimilation system are compared with the cold start forecasts. Three cases are selected from January to February in 2011-12 when the gust speeds above 20 m s^-1 due to the polar lows are observed over the Svalbard.

For all experimental cases, the 10 m wind speeds and sea level pressures are realistically simulated. In terms of time series, the 10 m wind speed forecasts are more similar to the 1-h average wind speed observations than the gust speed observations at 10 m. Compared to the cold start forecasts, the forecasts in the 3DVar cycling system show smaller bias and RMSE for the 10 m wind speed and sea level pressure. More specific results will be presented in the meeting.