Initiation of an elevated mesoscale convective system with the influence of complex terrain during Meiyu season

A mesoscale convective system (MCS) was initiated on the lee side of the Wuling Mountain in central-east China in the late afternoon (1700 LT) on June 27, 2016, and led to an early morning precipitation peak. We investigated the convective initiation (CI) mechanism of this MCS using radars and automatic weather station observations, WRF model simulation, and analysis from the radar data assimilation system Variational Doppler Radar Analysis System. It was found that the convection initiation was elevated as indicated by an elevated convergence zone and updraft located above 1,625 m from the ground. A zero convective inhibition layer was located at 850 hPa, over a stable boundary layer (BL) resulting from the daytime rainfall in the plain region, and provided a favorable condition for the elevated CI. Our study suggested that the transition of mountain-plain thermal wind near sunset was the trigger for the convective initiation. An early afternoon mountain-plain thermal circulation was disrupted when the east-facing lee side slope was in the shadow of sunshine after 4 p.m. As a result, a local-scale northwest downslope wind accelerated and led to a downstream convergence above the stable BL, where the elevated convection was initiated near 1,625 m above ground level. By combining the model simulation, the analysis from data assimilation, and the observations, this study is the first to provide a detailed analysis of CI mechanism of elevated convection in a complex topography region during the Meiyu season in China.