Arctic Storm Activities in Ensemble Simulations by the HIRHAM-NAOSIM Regional Coupled Climate Model

Arctic storm activities have shown intensification during recent decades, along with which a number of intense storms have contributed to or caused extreme climate events, such as the record low of sea ice cover in summer 2012 and the unprecedentedly abrupt warming event in winter 2015/16. In this study, we examined Arctic storm activities in ensemble simulations from 1979-2014 by using the HIRHAM-NAOSIM regional coupled climate model. Specifically, we employed a storm identification and tracking algorithm and used 6 hourly model output of sea level pressure data to derive location, intensity, and duration of each storm, based on which we constructed Arctic regional climatology and variability of storm activities and compared the results with the same statistics derived from the ERA-Interim reanalysis. The climatological seasonal cycle from all ensemble simulations demonstrates a stronger intensity in winter and a weaker intensity in summer, consistent with what is revealed by previous study using global reanalysis. The simulated storm activities also show large interannual variability though differences exist among different ensembles. To understand the across-ensemble spread, we examined impacts of underlying sea ice and ocean properties, which were perturbed initially for the ensemble simulations. At the same time, physical mechanisms responsible for the interannual variability are also investigated.