Abstract:Mesoscale observations are used to study cases of severe convective weather that occurred near Tianmu Mountain in subtropical high synoptic situation in order to understand the impact of Tianmu Mountain on convective initiation (CI). The results show that, when Zhejiang Province is at the edge of subtropical high, the low level flow is southwesterly and the Froude number is low, the upstream flow passing over the mountains forms a convergence line at the lee side of Huang Mountain and Tianmu Mountain, which factors CI in conjunction of thermal conditions. The thermal effect of the mountain causes cumulus clouds above the mountain area. The distribution of the cumulus clouds is consistent with the orography. Meanwhile, a belt of cumulus clouds forms at the lee side as a result of the convergence line. The convergence line extends tens of kilometers, and the direction changes with the ambient wind direction. Convective cells are initiated at the western end of the convergence line near the mountain. This suggests that CI may occur when the thermal forced cumulus clouds move above the convergence line and continue to develop. In other words, thermal and dynamic effects of the mountain trigger the CI together.