A Study on Local‐Scale Thermal and Dynamical Mechanisms in the Initiation of a Squall Line Under Weak Forcing. Issue 5 (2nd March 2022)

• Record Type: Journal Article
• Authors: Xiao, Xian; Sun, Juanzhen; Ji, Lei; Zhang, Lina; Ying, Zhuming; Chen, Zhixiong; Chen, Mingxuan; Xu, Changyi
• Is Part Of: Journal of geophysical research. Volume 127:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-03-02
• Subjects: Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD035561
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: A convective system was initiated under weak forcing on the plains near Beijing on the afternoon of 26 June 2009 and developed into a squall line that resulted in heavy precipitation. Prediction of the convective initiation (CI) of the system was challenging due to the lack of precursors detectable by conventional observation networks. In this study, we investigated the CI mechanism using high‐resolution analyses obtained from the Variational Doppler Radar Analysis System via the assimilation of radar and dense surface observations. It was found that the CI was resulted from the interactions of a local cold air mass and the outflows from a weakened storm propagating from the nearby mountains. The cold air mass built up an unstable condition and veered air flow to form a local convergence zone in which moisture was accumulated. New convection was triggered as a result of strengthened convergence when the outflows from the dissipating storm approached the existing convergence zone. To confirm the critical role played by the local cold air mass, sensitivity experiments were conducted using WRF‐FDDA data assimilation and forecast system. The results suggested that the local cold air mass along with the southerly environmental wind and storm outflows exerted a dominant influence on the CI. Key Points: A squall line was initiated on the plains near Beijing under weak forcing, and developed into that resulted in heavy precipitation High‐resolution reanalysis and nudging systems show the local‐scale thermal and dynamical features associated with the convective initiation (CI) Interactions of a local cold air mass and the outflows from a weakened storm to trigger CI under weak forcing