Enhanced Arctic moisture transport toward Siberia in autumn revealed by tagged moisture transport model experiment

Climate change significantly impacts the Arctic and circum-Arctic regions, causing amplified warming approximately twice the global average. This Arctic amplification weakens the latitudinal thermal gradient, potentially triggering abnormal mid-latitude weather. The hydrological cycle plays a crucial role in these interactions, regulating ice-albedo feedback and radiative energy transfer. A key unresolved issue is the effect of Arctic warming on continental snowfall, particularly its role in regulating the surface energy budget during seasonal transitions and its influence on subsequent weather patterns. Earlier studies demonstrated the 'memory effect' of snow cover, influencing later weather events like heatwaves and wildfires. The rapid reduction in Arctic sea ice and warming of the Arctic Ocean are expected to increase snow cover over northern Eurasia. While previous research indicated a link between Arctic moisture and snowfall over Europe and western Siberia, the extent of equatorward moisture transport from the Arctic Ocean and its decadal changes remained unclear. This study aimed to quantify the amount of water vapor evaporated from the Arctic Ocean and its transport to northern Eurasia, specifically Siberia, during recent decades of significant Arctic sea ice retreat, using a tagged moisture transport model driven by reanalysis data.

Numerous studies have explored the impact of Arctic warming on the hydrological cycle and its consequences for mid-latitude weather patterns. Research has shown a link between Arctic sea ice loss and increased snowfall over Eurasia, with studies highlighting the role of moisture transport from the Barents Sea in influencing snowfall over Europe and the Scandinavian Peninsula. Idealized modeling experiments and Lagrangian moisture transport models have predicted increased Siberian snow cover with an ice-free Arctic Ocean. However, questions remained about the quantitative aspects of equatorward moisture transport from the Arctic Ocean and its variability over time. This study builds upon these previous efforts by using a tagged moisture transport model to directly address these knowledge gaps.

The study employed a tagged moisture transport model driven by the JRA-55 reanalysis dataset for the period 1981–2019. The model tracked moisture evaporated from the Arctic Ocean (defined in Fig. 1) and its subsequent transport. Bias correction was applied to evapotranspiration and precipitation data from the reanalysis using independent reference datasets (Continuous Satellite-derived Global Record of Monthly Land Surface Evapotranspiration and GPCP v2.2 combined) to ensure accuracy. The analysis focused on the transport of Arctic moisture to Siberia, using longitude-time cross-sections (Fig. 2) to visualize its movement. Linear trends in Arctic moisture (Fig. 3 and 4) were calculated to assess changes over time. Daily maximum values of Arctic moisture (Fig. 5) were analyzed to identify extreme transport events. Synoptic patterns associated with high Arctic moisture transport events were examined (Fig. 6) to understand the underlying meteorological processes. Supplementary figures provide additional details on the spatial distribution of Arctic moisture, evaporation changes, and the proportion of Arctic moisture in total precipitable water.

The study revealed a significant increase in the transport of Arctic moisture to Siberia, particularly during autumn and early winter. Western Siberia showed enhanced Arctic moisture content in September, consistent with observed increases in snow cover. Eastern Siberia experienced a sharp increase in the annual maximum daily amount of Arctic moisture during October–December, associated with cyclonic activities along coastal regions. The increasing trend of Arctic moisture is more pronounced in western Siberia in September and eastern Siberia in October-December. Analysis of daily maximum Arctic moisture revealed a significant increasing trend in eastern Siberia during October–December, suggesting that extreme moisture transport events contribute substantially to the overall increase. The interannual variability in the maximum daily Arctic moisture content was substantial, with a clear upward trend observed after the late 2000s in western Siberia and after around 2005 in eastern Siberia. The increased Arctic moisture in recent decades appears to contribute to increased total precipitable water, potentially influencing radiation balance and warming in eastern Siberia. Case studies of high Arctic moisture transport events highlighted the roles of cyclonic/anticyclonic systems in strengthening equatorward winds, facilitating moisture transport from an ice-free ocean to Siberia. The study demonstrated that while an ice-free ocean is important, the moisture pathways can be case-dependent.

The findings demonstrate a clear link between Arctic sea ice retreat, increased Arctic Ocean evaporation, and enhanced moisture transport to Siberia, particularly during autumn and early winter. The results are consistent with observed increases in Siberian snow cover. The significant role of extreme moisture transport events in driving the overall increase in Arctic moisture emphasizes the need for further investigation into the meteorological mechanisms responsible. The observed increase in Arctic moisture may have implications for the radiative balance and further warming in Siberia. The simultaneous occurrence of poleward and equatorward moisture transport highlights the complex interactions within the Arctic climate system. The increase in Arctic moisture transport could have significant consequences for snowfall patterns and the broader hydrological cycle in Siberia. Further research should investigate the relationship between changes in evaporation, atmospheric moisture transport, and storm tracks in the Arctic.

This study provides strong evidence for increased autumn/early winter moisture transport from the Arctic Ocean to Siberia, linked to Arctic sea ice retreat and increased evaporation. The findings highlight the importance of considering Arctic moisture transport in understanding Siberian snowfall and regional climate change. Future research should focus on refining the understanding of the atmospheric dynamics driving this transport, including the interaction between Arctic cyclones, and its implications for extreme weather events. Investigating the role of terrestrial evapotranspiration in the circum-Arctic hydrological cycle is also warranted.

The study relies on reanalysis data, which has inherent uncertainties. The model's representation of complex atmospheric processes might be simplified. The focus on Siberia limits the generalizability of the findings to other regions. While bias correction was applied, residual biases in the reanalysis data could still affect the results. The analysis of synoptic patterns is based on a limited number of case studies. Further research using higher-resolution models and observational data is needed to validate and expand upon these findings.