Forty-year climatology and variability of atmospheric rivers in the Arctic using MERRA-2 reanalysis from 1980 to 2020

A significant increase in the atmospheric moisture content over the Arctic region has been recently documented, that might be caused by the enhanced poleward moisture flux which is expected to continuously increase in the future. This change can be attributed to different causes, in which increasing moisture transport intensity is included. In this study we focus on events with anomalous moisture transport confined to long, narrow and transient corridors, known as atmospheric rivers (ARs), which are expected to have a strong influence on Arctic mass and energy budget.

This study is based on MERRA-2 reanalysis (Modern-Era Retrospective analysis for Research and Applications, Version 2) extending from an historical period until present (1980-2020). ARs are identified using the tracking algorithms by Gorodetskaya et al. (2020) and Guan et al. (2018). We explored the frequency of ARs focusing on annual, seasonal and monthly values. Spatial patterns were analysed for the Arctic latitudes, covering both Atlantic and Pacific moisture transport pathways, and showing the importance of the Siberian moisture pathway during summer. Furthermore, we include a more detailed analysis performed at different sites north of the Arctic circle. Specific attention is given to the ARs characteristics during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from September 2019 to October 2020, as compared to the forty-year climatology and variability of the ARs in the Arctic.

Preliminary results show a higher frequency of ARs over the Norwegian and Barents Sea (Atlantic pathway), mainly during autumn and winter, although during May and June there is a high frequency of ARs over Western Siberia and Barents Sea. In contrast, the Canadian Artic has a lower frequency of ARs regardless the season, which is explained by a steep decrease of ARs frequency in the Gulf of Alaska and Bering Sea that block their progression to further north latitudes.

 

References:

Gorodetskaya, I. V., Silva, T., Schmithüsen, H., and Hirasawa, N., 2020: Atmospheric River Signatures in Radiosonde Profiles and Reanalyses at the Dronning Maud Land Coast, East Antarctica. Adv. Atmos. Sci., https://doi.org/10.1007/s00376-020-9221-8.

Guan, B., Waliser, D. E. and Ralph, F. M., 2018: An Intercomparison between Reanalysis and Dropsonde Observations of the Total Water Vapor Transport in Individual Atmospheric Rivers. J. Hydrometeorol., 19, 321–337, https://doi.org/10.1175/JHM-D-17-0114.1.

 

Acknowledgments:

This work is supported by FCT PhD Grant SFRH/BD/129154/2017 and developed in collaboration with Transregional Collaborative Research Centre (AC)³, AWI and U. Cologne.