Evaluation of a sub-kilometre NWP system in an Arctic fjord-valley system in winter
Teresa Valkonen, Patrick Stoll, Yurii Batrak, Morten Køltzow, Thea Schneider, Emmy E. Stigter, Ola Bakke Aashamar, Eivind Støylen, Marius O. Jonassen
Abstract
Terrain challenges the prediction of near-surface atmospheric conditions, even in kilometre-scale numerical\nweather prediction (NWP) models. In this study, the ALADIN-HIRLAM NWP system with 0.5 km\nhorizontal grid spacing and an increased number of vertical levels is compared to the 2.5-km model system\nsimilar to the currently operational NWP system at the Norwegian Meteorological Institute. The impact of\nthe increased resolution on the forecasts’ ability to represent boundary-layer processes is investigated for the\nperiod from 12 to 16 February 2018 in an Arctic fjord-valley system in the Svalbard archipelago. Model\nsimulations are compared to a wide range of observations conducted during a field campaign. The model\nconfiguration with sub-kilometre grid spacing improves both the spatial structure and overall verification\nscores for the near-surface temperature and wind forecasts compared to the 2.5-km experiment. The subkilometre experiment successfully captures the wind channelling through the valley and the temperature field\nassociated with it. In a situation of a cold-air pool development, the sub-kilometre experiment has a\nparticularly high near-surface temperature bias at low elevations. The use of measurement campaign data,\nhowever, reveals some encouraging results, e.g. the sub-kilometre system has a more realistic vertical profile\nof temperature and wind speed, and the surface temperature sensitivity to the net surface energy is closer to\nthe observations. This work demonstrates the potential of sub-kilometre NWP systems for forecasting\nweather in complex Arctic terrain, and also suggests that the increase in resolution needs to be accompanied\nwith further development of other parts of the model system.