The Role of Atmospheric Rivers in Extratropical and Polar Hydroclimate

Abstract

Atmospheric rivers (ARs) are narrow, long, transient, water vapor-rich corridors of the atmosphere that are responsible for over 90% of the poleward water vapor transport in and across midlatitudes. However, the role of ARs in modulating extratropical and polar hydroclimate features (e.g., water vapor content and precipitation) has not been fully studied, even though moistening of the polar atmosphere is both a key result and amplifier of Arctic warming and sea ice melt, and precipitation is key to the surface mass balance of polar sea ice and ice sheets. This study uses the Modern-Era Retrospective analysis for Research and Applications, Version 2 reanalysis to characterize the roles of AR water vapor transport on the column-integrated atmospheric water vapor budget in the extratropical and polar regions of both hemispheres. Meridional water vapor transport by ARs across a given latitude (examined for 40°, 50°, 60°, and 70°) is strongly related to variations in area-averaged (i.e., over the cap poleward of the given latitude) total water vapor storage and precipitation poleward of that latitude. For the climatological annual cycle, both AR transport (i.e., nonlocal sources) and total evaporation (i.e., local sources) are most correlated with total precipitation, although with slightly different phases. However, for monthly anomalies, the water budget at higher latitudes is largely dominated by the relationship between AR transport and precipitation. For pentad and daily anomalies, AR transport is related to both precipitation and water vapor storage variations. These results demonstrate the important role of episodic, extreme water vapor transports by ARs in modulating extratropical and polar hydroclimate. Plain Language SummaryThe term atmospheric river (AR) was coined by scientists Zhu and Newell in the early 1990s with the main result highlighting the importance of relatively infrequent, long conduits of strong moisture transport being responsible for most of the poleward transport of moisture across the midlatitudes and into the polar regions. While it is generally understood that this moisture is critical to the water and energy budgets of high latitudes, there have been no studies that have ever quantified the relationship between AR poleward moisture transports and the hydroclimate features of high latitudes. After a long hiatus in the consideration of the role of ARs on global climate since those of Zhu and Newell, this study quantifies the connections between water vapor transport by ARs across specific latitudes (e.g., 40°) and the hydroclimate poleward of this latitude. The findings show there are strong, time scale-dependent (e.g., daily and monthly) connections between ARs and high-latitude hydroclimate features. For example, the findings show a strong relationship between AR water vapor transport at a given latitude and the areaaveraged total precipitation of the region poleward. This and other results in this study indicate the importance of ARs in shaping our global weather and climate.

Observing and Modeling Ice Sheet Surface Mass Balance

“…In general, coastal regions receive most of their precipitation from nearby ocean areas, while high‐elevation snowfall is sourced from remote, lower‐latitude regions, especially on the AIS (Delaygue et al, ; Sodemann & Stohl, ). The largest precipitation events are caused by “atmospheric rivers,” long‐fetched channels of high atmospheric moisture that protrude from the tropics or midlatitudes all the way to high latitudes (Gorodetskaya, Tsukernik, et al, ; Mattingly et al, ; Nash et al, ). In middle‐ and high‐elevation areas of the AIS, atmospheric rivers generate 30–100% of the annual precipitation (Gorodetskaya et al, ; Schlosser et al, ), depending on their strength, location, and frequency.…”

Simulating and Evaluating Atmospheric River‐Induced Precipitation Extremes Along the U.S. Pacific Coast: Case Studies From 1980–2017

“…A majority of annual precipitation along the U.S. West Coast originates from a few intense atmospheric river (AR) events each year, contributing up to half of the annual precipitation in some regions (Dettinger et al, 2011;Gershunov et al, 2017). These events, which are characterized by narrow and filamentary corridors of enhanced water vapor flux (Ralph et al, 2004;Zhu & Newell, 1998), are typically associated with extratropical cyclones over ocean basins and are responsible for the vast majority of poleward moisture transport in the midlatitudes (Nash et al, 2018). The synoptic characteristics and impacts of landfalling ARs over the Western United States have been well documented over the past decade (Dettinger et al, 2011;Guan & Waliser, 2015;Jackson et al, 2016;Kim et al, 2018;Rutz et al, 2014).…”

Experimental Subseasonal‐to‐Seasonal (S2S) Forecasting of Atmospheric Rivers Over the Western United States

“…Atmospheric rivers (ARs) are elongated regions of intense horizontal water vapor transport, which are often associated with a baroclinic midlatitude cyclone (Neiman et al, ; Ralph et al, ; Ralph et al, ; Zhang et al, ; Zhu & Newell, ). Many studies have revealed the important link between ARs and annual precipitation over different regions around the globe (Dettinger et al, ; Lavers et al, ; Ralph & Dettinger ; Neiman et al, ; Lavers & Villarini, ; Lamjiri et al, ; and others), their association with global floods and water availability (Ralph et al, ; Leung & Qian, ; Ralph & Dettinger ; Paltan et al, ; Corringham, ), their relationship to snowpack over the western U.S. (Goldenson et al, ; Guan et al, ; Huning et al, , ), their importance to extratropical climate and hydrology (Gorodetskaya et al, ; Nash et al, ), and their projected changes in a warming climate (e.g., Espinoza et al, ; Guirguis et al, ). In addition, a new AR scale has recently been introduced which groups ARs into categories based on their intensity, duration, and beneficial or hazardous impacts on society (Ralph et al, ).…”