Spatial and temporal characteristics of atmospheric rivers in Scandinavia and their influence on the regional precipitation

Atmospheric rivers (ARs) play an important role in both the global and regional climate systems. While there is extensive research on ARs and their relationship to precipitation in North America and East Asia, the role of ARs in the regional climate of Scandinavia remains understudied.

In this study, we investigated the characteristics of ARs making landfall over Scandinavia, their influence on regional precipitation, and how they are affected by the North Atlantic Oscillation (NAO). To achieve this, we analysed the ARs between 1980 and 2019 detected by four different AR Detection and Tracking algorithms (ARDT), from the Atmospheric River Tracking Method Intercomparison Project (ARTMIP). Combined with ERA5 reanalysis precipitation data, we quantified the AR related precipitation over the region.

We found that ARs are present during up to 35% of the total annual precipitation in Scandinavia, with the average AR-associated rainfall rate exceeding the non-AR rates. Clustering the ARs that intersect Scandinavia revealed four main AR patterns. For the two most frequent patterns, located in southern Scandinavia, ARs account for up to 32% of the total annual precipitation. Furthermore, for all patterns, AR activity reaches a maximum during autumn and whilst the NAO is in a strong positive phase. The results from the four ARDTs show similar spatial patterns, but with a notable difference in the magnitude of AR influence on precipitation. Our findings indicate that ARs are an important factor in Scandinavian precipitation, and highlight the value of using multiple ARDTs to obtain more robust results.