The high moisture content and strong wind velocities associated with ARs usually bring about heavy precipitation, especially when they intercept mountain terrains ( Neiman et al. The two main sources of moisture in ARs are local moisture convergence along the cold front of an extratropical cyclone and the direct poleward transport of tropical moisture ( Bao et al. More than 90% of total water vapor flux at midlatitudes is found to be associated with ARs ( Zhu and Newell 1998 Neiman et al. Nontechnical terms such as “Pineapple Express,” “Hawaiian fire hose,” and “Maya Express” are commonly synonymous to this phenomenon in North America ( Dirmeyer and Kinter 2009 Lackmann and Gyakum 1999). The word “rivers” was used as an analogy of the filamentary water flux to that within the world’s largest rivers ( Gimeno et al. Although the term “atmospheric rivers” was first used by Zhu and Newell (1998), knowledge about these filamentary plumes of enhanced moisture in the lower troposphere has been known for a while ( Gimeno et al. However, TMEs are characterized by high horizontal export of tropical moisture content to higher latitudes ( Lu and Lall 2016), and WCB are defined as cyclonic-relative airflows as strongly ascending in the vicinity of extratropical cyclones and their fronts ( Eckhardt et al. In the hydrometeorological literature, other terms such as warm conveyor belt (WCB) and tropical moisture exports (TMEs) are also used to define similar mesoscale and synoptic-scale features with high water vapor content impacting the hydrological cycle in many parts of the world ( Gimeno et al. ARs are narrow channels of enhanced water vapor within the atmosphere that are responsible for most horizontal transport of moisture outside of the tropics ( Zhu and Newell 1998 Ralph et al. In midlatitudes a sizeable fraction of moisture is transported through atmospheric rivers (AR) ( Neiman et al. An enhanced presence of low- and midlevel moisture between 700 and 850 hPa and pronounced increases of wind velocities (more than 30 m s −1) with high values of the meridional component between 750 and 850 hPa were identified over the Southern Alps during the event. Analysis of the vertical profiles of moisture transport dynamics during the passage of a landfalling AR during 11–12 October 2016 revealed the key characteristics of a snow-generating AR in the Southern Alps. The contributions of ARs to the large snowfall events at Mueller Hut and Mt Larkins were 70% and 71%, respectively. Considering the frequency of large snowfall events, approximately 61% of such events at Mahanga were associated with narrow corridors of strong water vapor flux, known as atmospheric rivers (ARs). Our findings show that large snowfall events in the Southern Alps generally coincide with strong fields of integrated vapor transport (IVT) within a northwesterly airflow and concomitant deepening low pressure systems. ERA-Interim reanalysis data were used to characterize the hydrometeorological features of the selected events. The large snowfall events are defined as those events with daily snow depth increase by greater than the 90th percentile at each site. ![]() In this study, records from three recently developed automatic weather stations (Mahanga, Mueller Hut, and Mt Larkins) near the Main Divide of the Southern Alps were used to identify large snowfall events between 20. Synoptic-scale moisture transport during large snowfall events in the New Zealand Southern Alps is largely unknown due to a lack of long-term snow observations.
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