Atmospheric River Lifecycle Responses to the Madden‐Julian Oscillation

Abstract

We investigate how the Madden‐Julian Oscillation (MJO), the dominant mode of tropical subseasonal variability, modulates the lifecycle of cool‐season North Pacific atmospheric rivers (ARs). When the enhanced (suppressed) convection center is located over the Indian Ocean (western Pacific), more AR events originate over eastern Asia and with fewer over the subtropical northern Pacific. When the enhanced (suppressed) convection is over the western Pacific (Indian Ocean), the opposite changes occur, with more AR events originate over the subtropical northern Pacific and fewer over eastern Asia. Dynamical processes involving anomalous MJO wind and seasonal mean moisture are found to be the dominant factors impacting these variations in AR origins. The MJO‐related anomalous geopotential height patterns are also shown to modulate the propagation of the AR events. These MJO–AR lifecycle relationships are further supported by model simulations.

Uncertainties in Atmospheric River Lifecycles by Detection Algorithms: Climatology and Variability

“…We focus on the winter season (November to March) because it is the most active season for ARs and the MJO (Mundhenk et al, 2016;Stan et al, 2017). To investigate the MJO's influence on AR lifecycles, we calculate the lifecycle frequency of AR events following Zhou et al (2021). The lifecycle frequency is determined for each AR event, as the grid point-by-grid point sum of AR object binary masks within that event.…”

“…Thus the lifecycle frequency summarizes the extent of an area impacted by an AR event. Zhou et al (2021) show the MJO's impact on lifecycle frequency detected by one ARDT (Guan_Waliser). Here, we extend the analysis by including eight additional ARDTs.…”

“…Previous studies have discussed how ARs may be impacted by the MJO, including landfall activity, hydrological impacts, and subseasonal prediction (Baggett et al., 2017; Guan & Waliser, 2015; Guan et al., 2012, 2013; Mundhenk et al., 2016, 2018; Payne & Magnusdottir, 2014; Ralph et al., 2011; Zhou et al., 2021). Here, we examine the linkage between ARs and the MJO from the lifecycle perspective and evaluate the robustness of such linkages.…”

“…To investigate the MJO's influence on AR lifecycles, we calculate the lifecycle frequency of AR events following Zhou et al. (2021). The lifecycle frequency is determined for each AR event, as the grid point‐by‐grid point sum of AR object binary masks within that event.…”

“…ARs are essential to the global hydrological cycle and are often linked to societally impactful weather and climate extremes (Newell et al., 1992; Zhu & Newell, 1994). Due to their crucial role in water resource availability (Dettinger, 2013; Dettinger et al., 2011; Gorodetskaya et al., 2014) and their potential to produce heavy precipitation and flooding (Lavers et al., 2011, 2014; Neiman et al., 2008, 2013; Ralph et al., 2006; Waliser & Guan, 2017), numerous studies have investigated aspects of AR activity over the past two decades, including landfall activity (Hu et al., 2017; Rutz et al., 2014), connections to modes of climate variability (Gershunov et al., 2017; Guan & Waliser, 2015; Kim et al., 2017; Mundhenk et al., 2016; Payne & Magnusdottir, 2014; Zhou et al., 2021), subseasonal‐to‐seasonal prediction (DeFlorio, Waliser, Guan, Lavers, et al., 2018; DeFlorio, Waliser, Guan, Ralph, & Vitart, 2018; Lavers et al., 2014; Zhou & Kim, 2017;), and future projections (Gershunov et al., 2019; Lavers et al., 2013; Payne & Magnusdottir, 2015; Radić et al., 2015; Rhoades, Jones, Srivastava, et al., 2020; Shields & Kiehl, 2016b).…”