East Asia Atmospheric River catalog: Annual Cycle, Transition Mechanism, and Precipitation

Abstract

An all‐season East Asia Atmospheric River (EA AR) catalog is constructed based on PanLu2.0. The annual cycle of EA AR exhibits eight stages, synchronizing with the seasonal‐to‐subseasonal variation of precipitation and their associated atmospheric steering. Particularly, extension of the western North Pacific subtropical high (WNPSH) to south China sea, due to the springtime east‐west thermal contrast, steers ARs over Southeast China (SEC), inducing spring precipitation. During the Asian summer monsoon season, the spatial variation of the AR main route echoes the northward displacement of WNPSH, coincides with the prevailing monsoonal wind onset and stepwise propagation of rain belt. The warm moisture‐laden air of the wintertime ARs confronts the dry and cold air over SEC, contributing to the winter precipitation. ARs offer substantial potential predictability of (heavy) precipitation days over the midlatitude from the late spring to early summer, and over SEC and south Japan from late winter to early spring.

Define East Asian Monsoon Annual Cycle via a Self‐Organizing Map‐Based Approach

“…Additionally, the latitudinal position of rain belts in the Mid‐summer is mainly confined in the south (20°N‐25°N) (Figure ), which is likely to result from the influence of tropical cyclones at this time (Cheng & Lu, 2020; Day et al., 2018; Pan & Lu, 2020). Rain belts then largely disappear in the Fall stage (Figure ) due to weaker moisture transports from the tropics.…”

“…As such, we employ a neural‐network‐based algorithm, the self‐organizing map (SOM), to classify the East Asian monsoon stages all year round. This method projects high‐dimensional data onto a low‐dimensional one and preserves the topological features (Kohonen, 2001), which has shown great potentials in classifying meteorological field patterns (Chiang et al., 2017; Dai et al., 2020; Johnson, 2013; Kong et al., 2017; Nishiyama et al., 2007; Pan & Lu, 2020). The results of the SOM‐based approach are then assessed with the monsoon onset dates documented in the literature.…”

Distinct Features of Atmospheric Rivers in the Early Versus Late East Asian Summer Monsoon and Their Impacts on Monsoon Rainfall

“…A series of studies have reported that AR frequently forms over the northwestern Pacific and causes heavy rainfall events in eastern China, Korea, and western Japan when making landfall. Unlike the U.S. west coast where AR is most frequent in winter, East Asian AR (hereafter, simply AR unless specified) is most pronounced in summer (Guan & Waliser, 2015; Kamae, Mei, & Xei et al., 2017; Kamae, Mei, Xie, Naoi, & Ueda, 2017; Mundhenk, Barnes, & Maloney, 2016; Pan & Lu, 2020). This contrasting seasonality is caused by the East Asian summer monsoon (EASM), which is characterized by the expansion of the western North Pacific subtropical high (WNPSH) and the associated monsoon rainfall (Chen et al., 2004; Wang & LinHo, 2002).…”

“…This sub‐seasonality implies that the nature of the EASM AR may vary from month to month and from region to region. Pan & Lu (2020) in fact showed that the subseasonal evolution of the EASM AR consists of four stages and that each stage is closely related with the subseasonal‐to‐seasonal variation of the atmospheric steering. Although such an objective classification is useful, only monthly evolution is considered below for a practical purpose.…”

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

“…Therefore, we refer to the participating algorithms in ARTMIP as AR “detection” algorithms (or ARDTs). Recently, various research groups have developed AR “tracking” algorithms for AR lifecycle tracking (Guan & Waliser, 2019; Rhoades, Jones, O'Brien, et al., 2020; Pan & Lu, 2019, 2020; Payne & Magnusdottir, 2014; Shearer et al., 2020; Xu et al., 2020b, 2020a; Zhou et al., 2018; Zhou & Kim, 2019). Comparison between AR tracking algorithms has been shown by previous studies.…”