[A-CG42] Science in the Arctic Region

[ACG42-07] Poleward Penetrating Atmospheric Rivers over Eastern Siberia during Summer

*Yoshiki Fukutomi¹, Tetsuya Hiyama¹ (1.Institute for Space-Earth Environmental Reasearch, Nagoya University)

Keywords:Atmospheric rivers, Eastern Siberia, Heavy precipitatiom, Intraseasonal-scale waves, Synopric-scale disturbances, Atmospheric hydrological caycle

Atmospheric rivers (ARs) have been recognized as one of the important causes of heavy precipitation in mid- and high-latitude regions over the recent decade. Several recent studies have shown that formation of ARs were observed also in higher-latitude land regions of northern Eurasia, suggesting that ARs play an important role in the hydrological cycle in the region. This study investigates intense ARs which produce heavy precipitation over eastern Siberia. The impacts and origin of moisture intrusions into eastern Siberia associated with the ARs are explored by using atmospheric reanalysis (JRA-55) and gauge-satellite observed precipitation (MSWEP) data. Daily AR events are detected based on the characteristics of vertically integrated water vapor transport (IVT) derived from the reanalysis data. A total of 86 AR events are detected over eastern Siberia during summers (June−August) of 1979−2022. Composite analysis is performed on IVT and various atmospheric fields to reveal the structure and evolution of large-scale circulation patterns associated with the AR formation. The composite IVT exhibits a southwest-northeast oriented band of poleward moisture flux across the mountainous terrain of southeastern Siberia. The spatial pattern of the AR is well-defined by the IVT values exceeding 150 kg m^-1 s^-1. The AR is responsible for moisture intrusion from Northeast Asia into eastern Siberia. The moisture intrusion significantly contributes to produce heavy precipitation in the convergent zone of the IVT. A core of the heavy precipitation zone is found to be embedded in the meridionally elongated AR band. Downstream development of an intraseasonal Rossby wave train propagating across northern Eurasia is the main mechanism for generating the ARs over eastern Siberia. A trough as a part of the wave train amplifies over central−eastern Siberia through wave energy dispersion. The amplified trough facilitates poleward moisture flux across the mountainous terrain. The heavy precipitation zone associated with the AR is produced by baroclinic development of the synoptic-scale waves within the intraseasonal wave train. The intraseasonal wave train provides favorable conditions for the development of the synoptic-scale waves which generate extratropical cyclones and precipitating fronts associated with the AR.