Five-year climatology of local convections in the dabie mountains

Abstract

Local Convection in Dabie Mountains (LCDM) occurs more frequently over the Dabie Mountains and brings severe weather to adjacent areas. In order to understand the characteristics of LCDM, their spatial distribution, the monthly and diurnal variations, and possible mechanisms are investigated. Based on radar composite reflectivity data over the 5-y period of 2014-2018 during warm seasons (April-September), a total of 195 cases of LCDM are identified. The LCDM exhibits maximum frequency on the windward slopes of the Dabie Mountains with a secondary maximum on lee slopes. It is demonstrated that LCDM peaks in July and August, while their diurnal variation exhibits a major peak in the afternoon during 12:00-16:00 local solar time (LST). Most LCDM does not leave the Dabie Mountains (NoOut-Type), accounting for 89.7% overall, and has an average 3.5 h lifespan. In contrast, the lifespans of Out-Types (i.e., LCDMs that move away from the Dabie Mountains) are longer (5.8 h on average), while most Out-Type LCDMs develop on southern slopes (South-Type) and a few are also reinforced on northern slopes (North-Type). The South-Type mainly produces short-duration heavy precipitation, while the North-Type predominately generates thunderstorms high winds. It is suggested that LCDM is thermally induced, and that both the South-Type and North-Type are controlled by southerly wind perturbation. Lifting by upslope wind and heat sources over windward slopes has led to South-Type development, while ascent induced by wave-like perturbations on lee slopes has led to North-Type. These mechanisms should be further investigated in future work by using field experiments and numerical simulations.