Role of atmospheric rivers in shaping long term Arctic moisture variability
Zhibiao Wang, Qinghua Ding, Renguang Wu, Thomas J. Ballinger, Bin Guan, Deniz Bozkurt, Deanna Nash, Ian Baxter, Dániel Topál, Zhe Li, Gang Huang, Wen Chen, Shangfeng Chen, Xi Cao & Zhang Chen
Nature Communications volume 15, Article number: 5505 (2024) Cite this article
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Abstract
Atmospheric rivers (ARs) reaching high-latitudes in summer contribute to the majority of climatological poleward water vapor transport into the Arctic. This transport has exhibited long term changes over the past decades, which cannot be entirely explained by anthropogenic forcing according to ensemble model responses. Here, through observational analyses and model experiments in which winds are adjusted to match observations, we demonstrate that low-frequency, large-scale circulation changes in the Arctic play a decisive role in regulating AR activity and thus inducing the recent upsurge of this activity in the region. It is estimated that the trend in summertime AR activity may contribute to 36% of the increasing trend of atmospheric summer moisture over the entire Arctic since 1979 and account for over half of the humidity trends in certain areas experiencing significant recent warming, such as western Greenland, northern Europe, and eastern Siberia. This indicates that AR activity, mostly driven by strong synoptic weather systems often regarded as stochastic, may serve as a vital mechanism in regulating long term moisture variability in the Arctic.
Introduction
Arctic surface air temperatures have shown a warming trend at a rate more than twice that of the global average in recent decades, attributed to various Arctic Amplification (AA) processes driven by both anthropogenic and natural climate forcing1,2,3,4,5,6,7,8,9. As constrained by the Clausius–Clapeyron (CC) relationship, Arctic atmospheric warming also leads to atmospheric moistening, resulting in higher specific humidity, greater cloud cover and cloud water content, and more precipitation across the Arctic10,11,12,13. This moisture increase has substantially altered the Arctic hydrological and cryospheric variability over the past few decades14,15, owing to various moisture-related positive feedbacks connected to changing radiative properties of the atmosphere, clouds, and surface conditions.
This increase in moisture is prominent throughout the year, with the most significant rise occurring during the summer months (June–July–August, abbreviated as JJA)16,17, which has been attributed to multiple sources triggered by global warming, including increased evaporation from local ocean and surrounding continents18, enhanced sublimation of ice and snow within the Arctic19,20, and intensified moisture transport from lower latitudes15,16,21,22,23,24,25,26,27. Climate models forced by historical anthropogenic emissions can replicate a warmer and more humid Arctic in summer, featuring a rather uniform rise in atmospheric temperature and specific humidity across most of the Arctic. Future climate projections suggest that this wetting trend will intensify under continued global warming scenarios, and bring about a number of cascading effects in the Arctic, such as a precipitation regime shift from snow to rain that will substantially change local ecosystems in the coming decades28,29,30,31. While these modeling studies highlight the dominance of the CC relationship in shaping Arctic temperature and specific humidity, it is evident that over recent decades summertime changes in these parameters are influenced by large-scale circulation variability, manifested as a long-term trend toward the local barotropic high-pressure anomaly situated over Greenland over the past four decades. This summertime circulation trend pattern is thought to have origins, in part, from internal climate variability and contribute to warming in the mid-to-lower troposphere of the Arctic, as well as the melting of sea ice and the Greenland ice sheet (GrIS) through adiabatic warming processes32,33,34,35,36,37. Thus, both anthropogenic forcing and internal variability should be factored in when considering the underlying mechanisms behind recent moisture trends in the Arctic.
https://www.nature.com/articles/s41467-024-49857-y
