Climatological characteristics of atmospheric rivers over Northern Eurasia during summer

Abstract An atmospheric river (AR) is a synoptic precipitation system characterized by a sharp, narrow band structure that facilitates strong moisture transport. ARs are typically associated with the development of extratropical cyclones, fronts, and cloud bands, which generate heavy precipitation and flooding in mid-latitude continental coastal regions. ARs are hypothesized to trigger high-impact weather events in high-latitude continental inland regions. This study examined the structure and characteristics of ARs over northern Eurasia during summer (June–August) over a 43-year period (1979–2021), with a focus on continental ARs and their hydrometeorological impacts in Siberia. ARs were identified through hierarchical clustering analysis of vertically integrated water vapor transport data, focusing on events with intensities that exceeded a predefined threshold. The analysis classified AR patterns into five distinct types over northern Eurasia. Relationships among AR types, extratropical cyclones, frontal activity, and cloudiness were analyzed using composite analysis based on Japanese 55-year Reanalysis atmospheric data, gridded Multi-Source Weighted-Ensemble Precipitation data, and satellite-based International Satellite Cloud Climatology Project data. These results facilitated further characterization of ARs as either inland or Arctic coastal types. Inland ARs tended to extend eastward and northeastward into warm frontal zones; extratropical cyclone development occurred along their western and northwestern edges. Intense precipitation bands were aligned with these warm frontal zones. In contrast, coastal ARs exhibited a more zonal orientation, in which their axes were nearly parallel to warm frontal zones associated with extratropical cyclone activity over Arctic coastal regions. A well-developed, enhanced precipitation band was coincident with a warm frontal zone, which displayed an axis north of the AR axis. Deep convective and nimbostratus cloud activity within this band indicated that these cloud types likely constitute the primary source of precipitation over northern Eurasia.