Lightning activity during convective cell mergers in a squall line and corresponding dynamical and thermodynamical characteristics

Classical bow echoes (CBEs) normally develop due to rear‐inflow jets, while merger‐formation bow echoes (MFBEs) evolve from the merger between linear systems and preline convection. MFBEs are rarely documented before, and the key processes remain unclear because of the small‐scale and fast‐evolving merging processes. Using radar observations during 2015–2019, this study examines the characteristics of these two types of bow echoes over South China. Eighteen MFBEs and 11 CBEs are identified, accounting for 62% and 38% of the total 29 bow echoes, respectively. MFBEs commonly occur over coastal regions in the afternoon, where southerly sea breezes provide favorable thermodynamic conditions. About half CBEs develop over mountainous areas in the morning, and northerly winds enhance the local baroclinity and kinematic convergence. A new Merger‐Classical index is proposed to distinguish the environments for the development of two types of bow echoes, disclosing the more favorable near‐surface thermal conditions for MFBEs. In addition, more severe weather occurs in metropolitan area near the Pearl River Delta region during MFBEs, in which the accumulated precipitation is about 2.5 times higher than that during CBEs. This study reveals the discrepancies between MFBEs and CBEs over South China, emphasizing the MFBEs account for more than half of the total bow echoes and cause more high‐impact weather in the metropolitan area. This study proposes a new perspective on the environment in which bow echo forms by merger process over South China, urging for more research to explore the underlying processes.

Section: Characteristics Of Convective Systemmentioning

confidence: 99%

A Climatological Study on the Two Types of Bow Echoes Over South China

Zhou,

Zhao,

et al. 2023

“…The WRF ‐ELEC source package for running E ‐WRF is made publicly available at https://sourceforge.net/projects/wrfelec/ (Fierro et al., 2013; Mansell et al., 2005, 2010). The BLNET lightning data, radar data, and the E‐ WRF outputs can all be found in the Zenodo repository (https://doi.org/10.5281/zenodo.6547800; Lu, Qie, Xiao, et al., 2021). The figures were processed by Origin (version 2018, https://www.originlab.com/) and NCL (version 6.6.2, https://www.ncl.ucar.edu/), and the scripts can also be found in the Zenodo repository (https://doi.org/10.5281/zenodo.6547800; Lu, Qie, Xiao, et al., 2021).…”

Section: Data Availability Statementmentioning

confidence: 99%

Effects of Convective Mergers on the Evolution of Microphysical and Electrical Activity in a Severe Squall Line Simulated by WRF Coupled With Explicit Electrification Scheme

Qie

Xian

et al. 2022

Self Cite

Severe convective thunderstorms, which occur frequently during the warm season, cause significant loss of life and property amounting to several billion RMB in China. Among the threats they carry, lightning activity can be lethal and destructive. Convective merger (CM) is a process in which two or more convective cells or storms merge into a larger storm, then share a common cloud material and dynamical circulation, which is critical for the development, maintenance, and reinforcement of some intense weather systems like thunderstorms, hailstorms, and so on (

“…(2004) examined 273 bow echoes in the United States during 1996–2002 and they found that about 50%–55% of bow echoes underwent mergers and proceeded the bow development quite rapidly after the merger. The quasi‐linear convective system (QLCS: A generic term including SLs and bow echoes) was found to intensify in both spatial range and intensity, and/or produced severer weather like stronger straight‐line winds, heavier rainfall, more frequent lightning, and even tornadoes after the merger (e.g., French & Parker, 2012; Fujita, 1978; Lu et al., 2021). French and Parker (2014) conducted a series of idealized numerical experiments to explore the exact role of the SL‐SC merger in the bow echo formation.…”

Section: Introductionmentioning

confidence: 99%

A Merger‐Formation Bow Echo Caused by Low‐Level Mesovortex in South China

Liu

Zhao

et al. 2023

This work studied a high winds‐producing bow echo that occurred over South China in the pre‐rainy season using radar observations and high‐resolution analyses from the Variational Doppler Radar Analysis System. The bow echo developed from a quasi‐linear convective system (QLCS) and acquired a well‐defined bow shape after merging with a pre‐line convective cell (CC). Interestingly, the rear‐inflow jet (RIJ), which has been well recognized to play a key role in the formation of a bow echo, was not found in this merger‐formation bow echo (MFBE). The reason is that the QLCS developed in the monsoon environment of high humidity and weak vertical wind shear, leading to a weak cold pool and line‐end vortices. A new pathway of bow echo formation was proposed which highlighted the importance of the low‐level mesovortex (MV) on the leading edge of the QLCS. Vertical vorticity budget analyses revealed that the MV originated from a weak vertical vorticity band ahead of the QLCS and grew rapidly during the merger, because of the enhanced low‐level convergence in between which led to vortexgenesis via vertical stretching of vertical vorticity. The up‐scale growth of the MV produced a RIJ‐like flow wrapping cyclonically from north of the QLCS which forced the system to bulge out and finally evolve into a bow echo. This MV contributed foremost to the near‐surface gales as well. These findings shed light on the diverse formation mechanisms of bow echoes and associated high winds in the moist monsoon environment of South China.