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

Abstract

Atmospheric river (AR) and its impact on monsoon rainfall in East Asia are investigated by considering their month‐to‐month variations during the East Asian summer monsoon (EASM). The AR in the EASM, defined as an anomalously enhanced plume‐like water vapor transport, frequently forms over eastern China, Korea and western Japan. However, its characteristics vary from the early (June‐July) to the late (August‐September) period of the EASM. In the early EASM, AR is typically characterized by a quasi‐stationary monsoon southwesterly along the northern boundary of the western North Pacific subtropical high (WNPSH), which is further intensified by a migrating extratropical cyclone in the north. In contrast, the late‐EASM AR, which is less frequent than the early EASM AR, is primarily organized by a migrating extratropical cyclone. The quasi‐stationary monsoon southwesterly is less influential as the northern boundary of the WNPSH shifts northward, being decoupled from the subtropical ocean. Both the early‐ and late‐EASM ARs contribute substantially to monsoon rainfall, especially to heavy rainfall events. In the early EASM, 35%–70% of total rainfall amount and 60%–80% of heavy rainfall events in eastern China, Korea and western Japan are associated with AR. Although weakened, AR‐related rainfall is still significant in the late EASM in Korea and western Japan. These results indicate that AR is a key ingredient of EASM precipitation and its subseasonal variations should be taken into account to better understand and predict AR‐related extreme precipitation in East Asia.

A Multi‐Inventory Ensemble Analysis of the Effects of Atmospheric Rivers on Precipitation and Streamflow in the Namgang‐Dam Basin in Korea

“…Above this range, the AR storms are generally more frequent than the non‐AR storms; AR storms notably outnumber non‐AR storms in the range over 390 mm storm −1 . Because most of the storms in the heaviest P range are the AR storms, the AR storms can induce higher flood potential than the non‐AR storms as pointed out in earlier studies (Hirota et al., 2016; Kamae, Mei, & Xie, 2017; Kamae, Mei, Xie, Naoi, & Ueda, 2017; Kim et al., 2021; Manda et al., 2014; Park et al., 2021a).…”

“…These three AR inventories have been used in a number of AR studies, from the global water-vapor transports to AR-related regional hydrology (Guan & Waliser, 2015;Espinoza et al, 2018;Kamae, Mei, Xie, Naoi, & Ueda, 2017;Kim et al, 2018;Park et al, 2021a;. Details of the AR detection method and its evaluation are referred to Guan and Waliser (2015), Kamae, Mei, Xie, Naoi, and Udea (2017), and Park et al (2021a). Note that intercomparison and/or evaluation of these AR inventories and associated detection methods are not a subject of this study.…”

“…The three AR inventories are constructed by applying detection schemes based on IVT at 6‐h intervals using the European Center for Medium‐Range Weather Forecasts global reanalysis ERA5 (Hersbach et al., 2020) for PS, the ERA‐interim reanalysis (Dee et al., 2011) for GW and the JRA‐55 reanalysis (Kobayashi et al., 2015) for KM. These three AR inventories have been used in a number of AR studies, from the global water‐vapor transports to AR‐related regional hydrology (Guan & Waliser, 2015; Espinoza et al., 2018; Kamae, Mei, Xie, Naoi, & Ueda, 2017; Kamae, Mei, & Xie, 2017; Kim et al., 2018; Park et al., 2021a; Waliser & Guan, 2017). Details of the AR detection method and its evaluation are referred to Guan and Waliser (2015), Kamae, Mei, Xie, Naoi, and Udea (2017), and Park et al.…”

“…Because ARs occur mostly in the warm conveyor belt of extratropical cyclones (ETCs) (Guo et al., 2020; Zhang et al., 2019), ARs are expected to affect not only WNA and WEU but also other regions during the seasons of strong ETC activities. Progresses in objective identification of ARs using gridded atmospheric data have facilitated analyzing ARs and their hydrological impacts in regions around the world other than WNA and WEU (Blamey et al., 2018; Bozkurt et al., 2021; Esfandiari & Lashkari, 2020; Gorodetskaya et al., 2014; Kamae, Mei, & Xie, et al., 2017; Kamae, Mei, Xie, Naoi, & Ueda, 2017; Kim et al., 2021; Mahoney et al., 2016; Moore et al., 2012; Massoud et al., 2020; Mundhenk et al., 2016; Park et al., 2021a; Ramos et al., 2015, 2018; Sharma & Déry, 2020b; Stohl et al., 2008; Viale et al., 2018; Ye et al., 2020). For East Asia (EA), previous studies (Kamae, Mei, Xie, Naoi, & Ueda, 2017; Kim et al., 2021; Park et al., 2021a) related the seasonal cycle of the AR frequency to the seasonal variations of the large‐scale circulation and related ETC activities around Korea and EA as ETC activities over EA substantially increase in spring and early summer, the period of the northward march of the EA monsoon rainfall, then rapidly decrease from July to August (Kang et al., 2018; Kang & Son, 2021).…”

Atmospheric river, a term encompassing different meteorological patterns

“…“Monsoonal ARs” have been studied recently over India and it has been found that this particular “monsoonal ARs” are not connected with extratropical stormtrack activity (Laskhmi & Satyanarayana, 2020; or Lakshmi et al, 2019). However, regarding East Asia Summer Monsoon it was shown that, during the early stage of the monsoon, the ARs coincided with the strong south‐westerly flow along the northern boundary of the regional subtropical high level pressure, while during the late monsoonal stage these ARs were more associated with extratropical cyclones (Park et al, 2021). On the other hand, “Continental ARs” often appear in global detection schemes.…”