Influence of atmospheric rivers, cyclones and fronts on precipitation in the Arctic – a climatological perspective

The enhanced warming in the Arctic compared to the global mean – a phenomenon called Arctic Amplification - has different effects, including impacts on the hydrological cycle and thus the precipitation. In the Arctic, there are two major sources of moisture leading to increased precipitation formation: The enhanced local evaporation due to the missing insulation due to reduced sea-ice cover and the increased poleward moisture transport which is often associated with atmospheric rivers (ARs).

Previous studies have shown that ARs are a significant source for rain and snow in the Arctic. ARs are dynamically linked to the extratropical cyclones and fronts. Thus, AR-related precipitation can be not only concentrated within the AR itself, but also occur within the cyclone and frontal boundaries. Therefore, we developed a new method to distinguish precipitation within the AR shape and the precipitation related to cyclones and fronts based on ERA5 reanalysis. Thereby, we estimate how much precipitation occurs within AR, cyclone and frontal boundaries, separately and overlapping together. We applied this method for different case studies during two campaigns performed at and around Svalbard within the Collaborative Research Center “Arctic Amplification: Climate Relevant Atmospheric Surface Processes, and Feedback Mechanisms (AC)³”. Differences in the contributions of ARs, cyclones and fronts to the total precipitation could be identified comparing the both campaigns. During the early summer campaign (ACLOUD), precipitation (both rain and snow) was more confined within the AR shapes, especially in the area in which the AR is connected to fronts. In contrast, during the early spring campaign (AFLUX), precipitation (predominantly snow) was more restricted to the cyclone regions without connection to ARs and fronts. Generally, a higher precipitation intensity was found within ARs, especially when they are connected with cyclones and fronts.

In a climatological perspective, we apply this method to the ERA5 reanalysis data (1979 - 2020) to quantify the occurrence and influence of ARs and related cyclones and fronts. For this extended analysis, we consider the whole Arctic. This allows us to analyse the change of precipitation (in terms of type and frequency) related to the different weather systems during the last four decades. Furthermore, we can assess seasonal differences. In summary, we can investigate in which regions ARs, cyclones and fronts have a greater impact and if and how it also depends on different surface types (sea ice, open ocean, and land).

This work is supported by the DFG funded Transregioproject TR 172 “Arctic Amplification (AC)³“.