Are Multiseasonal Forecasts of Atmospheric Rivers Possible?

Abstract

Atmospheric rivers (ARs)-corridors of intense moisture flux with transport intensity of over 180,000 tons of moisture per second-are uniquely characterized by plume-like features with a length over 1,000 km and a width about one-third of its length (Newell et al., 1992;Ralph et al., 2018;Zhu & Newell, 1998). AR intensity and duration span a wide range and sometimes can lead to different socio-economic impacts. Previous work has categorized ARs into five categories according to certain intensity and duration criteria (Ralph et al., 2019). The flood damage caused by ARs grows exponentially from one category to the next (Corringham et al., 2019). Due to the shallow scale-height of specific humidity (2.2 km), the strongest transport is confined in the bottom 3 km of the troposphere (Ralph et al., 2004). The bottom-heavy moisture transport causes AR activity to be strongly influenced by the topography over the land. Although the term AR derives from the nature of its geometry, its transport is not continuous (Dacre et al., 2015). In fact, the duration and Abstract Atmospheric rivers (ARs) exert significant socioeconomic impacts in western North America, where 30% of the annual precipitation is determined by ARs that occur in less than 15% of wintertime. ARs are thus beneficial to water supply but can produce extreme precipitation hazards when making landfall. While most prevailing research has focused on the subseasonal (5 weeks) prediction of ARs, only limited efforts have been made for AR forecasts on multiseasonal timescales (3 months) that are crucial for water resource management and disaster preparedness. Through the analysis of reanalysis data and retrospective predictions from a new seasonal-to-decadal forecast system, this research shows the existing potential of multiseasonal AR frequency forecasts with predictive skills 9 months in advance. Additional analysis explores the dominant predictability sources and challenges for multiseasonal AR prediction.Plain Language Summary Atmospheric rivers (ARs), narrow corridors of intense moisture transport and heavy precipitation, are an important water resource but also a cause of flooding-related disasters for western North America. Consequently, predictions of AR frequency several seasons in advance potentially would be of great value, but such operational forecasts are currently lacking due to the challenges in simulating such intense, small-scale weather phenomena and their predictability sources on seasonal timescales. In this study, we examine the forecast skill of AR frequency on seasonalto-multiseasonal timescales (3 months) in a new generation seasonal-to-decadal prediction system developed at the Geophysical Fluid Dynamics Laboratory. We find that AR frequency can be skillfully forecast at least 9 months in advance over certain regions of the west coast of North America, such as California and Alaska, while the forecasts are only reliable for the first season in other regions. This regional variability can be further explained by the large-scale climate ...

When Will Humanity Notice Its Influence on Atmospheric Rivers?

“…Previous research has examined ARs in SPEAR and AM4 showing its capability of reproducing the observed climatology, including frequency, numbers and geometry (Zhao, 2020). In addition, SPEAR also shows the capability of forecasting multiseasonal AR activity and capturing interannual variability in the present climate (Tseng et al., 2021), which gives us additional confidence for projecting future AR activity.…”

“…In addition, SPEAR also shows the capability of forecasting multiseasonal AR activity and capturing interannual variability in the present climate (Tseng et al, 2021), which gives us additional confidence for projecting future AR activity.…”

An anomalous warm-season trans-Pacific atmospheric river linked to the 2021 western North America heatwave

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On the seasonal prediction and predictability of winter surface Temperature Swing Index over North America

“…The focus of this study is on the December-January-February (DJF) season from SRF initialized on 1 st December. SPEAR's SRF has shown significant seasonal forecast skill in predicting a wide range of essential indicators of climate variability, including but not limited to the SST, SAT over land, mid-latitude baroclinic waves, Antarctic/Arctic sea ice, Kuroshio extension, North American summertime heat extremes, and atmospheric rivers over Western North America (Lu et al, 2020;Bushuk et al, 2021Bushuk et al, , 2022Tseng et al, 2021;Zhang et al, 2021;Jia et al, 2022;Joh et al, 2022).…”