Synoptic conditions and frontal dynamics during Cold Air Outbreaks in the Norwegian and Barents Sea

Abstract

Cold Air Outbreaks (CAOs) in the Norwegian and Barents Sea are investigated using ERA Interim. The focus is on the synoptic conditions, heat fluxes, potential temperature tendencies and the frontogenesis at the onset of the CAOs. Four regions are investigated using the time series of the mean CAO index inside each region. Composite analysis is the core of this work. CAOs in each region are detected and separated with respect to the mean wind direction at 900 hPa at the time step where the CAOs are on their most intense stage. Composites for the different types of CAOs in the different regions are calculated. The separation shows that most CAOs are associated with northerlies when the mean CAO index is maximum. The composite analysis is supplemented by two case studies, one of a CAO in the Fram Strait, December 22-27, 2015 and another one in the Barents Sea, January 11-20, 2015. The results from the case and composite studies are compared, and they resemble each other. One of the main conclusions from this work is that there is typically a large scale cyclone advecting cold air off the ice edge. In addition, there is often some baroclinic growth at the onset of and during CAOs. It is confirmed that CAOs are associated with sensible and latent heat uxes, and hence diabatic heating, which is already well established from the literature. The different contributions to frontogenesis along the CAO front are investigated through both the case and the composite studies, using the frontogenesis function. It is found that CAOs in the Fram Strait associated with northerlies are associated with stronger circulation than CAOs in the Barents Sea associated with easterlies.