A Dual Regime of Mesoscale Convective Systems in the East Asian Monsoon Annual Cycle

Abstract

Eastern China is perennially hit by mesoscale convective systems (MCSs), yet it remains an open question as to whether and how their general properties change throughout the annual cycle. By leveraging high‐resolution satellite observations and a hybrid tracking algorithm, we present a 20‐year (2001–2020) climatology of MCSs over eastern China during eight subseasonal‐to‐seasonal (S2S) monsoon stages. MCSs contribute up to 50% of the stage‐total precipitation and over 60% of the rainband‐zone precipitation during the Pre‐Meiyu and Meiyu episodes, and their contributions remain non‐trivial during the transition seasons. We discover two contrasting regimes of MCSs that alternate immediately upon the Pre‐Meiyu and the Fall onsets. The wintertime regime features fast‐propagating shallow systems initiated at night in a strongly sheared and dry environment. The summertime regime, instead, features an outbreak of MCSs in the south, where the systems often initiate in the afternoon and propagate 2–3 times slower than the cold‐season ones. Based on multivariate clustering analysis, the nighttime MCSs that dictate the winter stages often initiate over a deep nocturnal boundary layer with moist rear inflows upgliding above it. In contrast, the afternoon‐initiated MCSs under the summertime regime feature a pronounced convective available potential energy (CAPE) "tongue" and upslope flows in their southeast quadrant. The southwesterly moist ascending flows are likely to shallow the convective inhibition at the tip of the CAPE tongue and facilitate the intense updrafts of the MCSs. Findings here may offer insights into S2S weather prediction and facilitate agricultural and water management throughout the year.

Intensification of Mesoscale Convective Systems in the East Asian Rainband Over the Past Two Decades

“…In the early‐summer season, East Asia is largely influenced by the East Asian summer monsoon system (Ding & Chan, 2005; Xie & Sampe, 2010) which forms a Meiyu (China)‐Baiu (Japan)‐Changma (Korean) rainband along ∼30°N (Figure 1a). In this period, successive MCSs form, propagate eastward along this rainband and often generate persistent extreme precipitation and floods in active years (Cheng et al., 2022; Guan et al., 2020). For example, in 2020, large regions of East Asia experienced an exceptionally wet rainy season (Figure S1b in Supporting Information ) and intense MCS precipitation (Figure 1b), which led to severe impacts and consequential economic losses (Clark et al., 2021).…”

“…In the early-summer season, East Asia is largely influenced by the East Asian summer monsoon system (Ding & Chan, 2005;Xie & Sampe, 2010) which forms a Meiyu (China)-Baiu (Japan)-Changma (Korean) rainband along ∼30°N (Figure 1a). In this period, successive MCSs form, propagate eastward along this rainband and often generate persistent extreme precipitation and floods in active years (Cheng et al, 2022;Guan et al, 2020).…”

The Impact of Urbanization on Mesoscale Convective Systems in the Yangtze River Delta Region of China: Insights Gained From Observations and Modeling

“…MCS is also one of the major convective systems affecting the summertime rainfall episodes across China (D. D. Chen et al., 2019; J. H. Chen et al., 2019, 2020). They seem to have a preferential occurrence in the middle and lower reaches of the Yangtze River Delta (YRD, Cheng et al., 2022). Nevertheless, it remains unclear how the MCS responds to local urban influences in the lower reaches of YRD region.…”

“…H. Chen et al, , 2020. They seem to have a preferential occurrence in the middle and lower reaches of the Yangtze River Delta (YRD, Cheng et al, 2022). Nevertheless, it remains unclear how the MCS responds to local urban influences in the lower reaches of YRD region.…”

Trends in Warm Season Mesoscale Convective Systems Over Asia in 2001–2020

“…Lower‐tropospheric moisture, as one of the important ingredients in deep moist convective processes, exerts crucial influences on the initiation and maintenance of MCSs (Houze, 2004; Klein et al., 2021), which can be modulated by large‐scale circulations (Laing & Fritsch, 2000; Schumacher & Rasmussen, 2020). For example, the long‐range transport of moisture driven by monsoonal circulations from the tropics contributes greatly to the initiation of MCSs (Cheng et al., 2019, 2022; P. Li et al., 2020). Moreover, the abundant moisture in the quasi‐stationary Meiyu front promotes MCSs to develop in the frontal zone (S. J. Chen et al., 2000; G. Chen et al., 2017; Cui et al., 2020; Guan et al., 2020; Luo & Chen, 2015).…”