Evaluating atmospheric rivers and their influence on precipitation in the Arctic - comparing observational with reanalysis data

The Arctic as a whole has been experiencing significant warming and moistening with several potential factors at play. In general, the warming amplifies the Arctic hydrological cycle. There are two processes which could affect the water vapour content in the Arctic. These are the enhanced local evaporation due to reduced sea-ice concentration and extent and the modified poleward moisture transport from lower latitudes due to changing circulation patterns. An important contribution to the total poleward moisture transport comes from Atmospheric rivers (ARs). ARs have rare occurrence but are associated with anomalously high moisture transport compared to tropical cyclones. ARs are typically associated with not only moisture but also with significant heat advection. They can bring precipitation as rain and/or snow. Moreover, additional feedbacks can occur: the warming effect of the ARs on the surface, coupled with rain lowering surface albedo, can cause thinning and melting of Arctic sea ice and snow. This, in turn, could increase the relative role of the local evaporation compared to the moisture transported from lower latitudes.

In this study, we investigate the relationship between the poleward moisture transport by ARs and the precipitation in the Arctic. The focus is on AR events during the ACLOUD (May/June 2017) and AFLUX (March/April 2018) campaign within the Collaborative Research Center “Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms (AC)³”. For these campaigns, existing AR catalogues with the input of ERA5 reanalyses are used to detect AR events. Six ARs are detected: two coming from Siberia and four from the Atlantic.

These AR events are analysed in terms of the macro- and microphysical precipitation properties, including frequency, intensity, and type of precipitation (rain or snow).  For this purpose, we use ERA5 reanalyses data for the water vapour transport, precipitation amount and type, rain and snow profiles (convective, large-scale, total), as well as vertical profile of hydrometeors. Reanalysis products are evaluated using a set of observational data (satellite data and ground-based remote sensing measurements). This new multi-parameter, multi-dataset set will allow to investigate the occurrence of ARs and its influence on precipitation in the Arctic for the last decades.

 

“We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) –Projektnummer 268020496 –TRR 172, within the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3.“