Abstract: Based on conventional meteorological observation and the NCEP (National Centers for Environmental Prediction) 6 hourly 1°×1° reanalysis data,the characteristics and causes of an elevated thunderstorm weather process happening in Zhengzhou area in early spring of 2015 were analyzed.The results showed that the ground cold pad,850 hPa and 700 hPa strong warm jet and trough at 500 hPa provide favorable dynamic,thermal and moisture conditions for the occurrence of an elevated thunderstorm.A large vertical wind shear between 700 hPa and 850 hPa and the large temperature difference between 700 hPa and 500 hPa show that there is a strong convective instability above the inversion layer,which is helpful for the occurrence of this elevated thunderstorm.A negative moisture vapor flux divergence and strong humidity advection at the low level provide an abundant water vapor for the elevated thunderstorm.Before the occurrence of thunderstorm,Δθ_se between 700 hPa and 500 hPa is above 0℃,and the atmosphere above 700 hPa is in a convective instability condition.The negative MPV1 (Moist Potential Vorticity) at the low level indicates that there is a moist symmetric instability condition in this layer,and the strong thunderstorm falls just in the convective instability zone and the negative area of MPV1.All these results indicate that this elevated thunderstorm is the result of joint interaction between convective instability and moist symmetrical instability.The warm air mass on the ground cold pad is gradually strengthened.It further exacerbates the atmospheric stratification stability above the inversion layer.By comparing with historical cases,it is found that the two elevated thunderstorm weather processes over Zhengzhou have some common features.The pumping action in front of 500 hPa troughs,low-level shear line,the convergence ascending motion at the left side of the low-level jet and the uplift of the ground cold pad should be the focus to forecast the elevated thunderstorms.

Key words: Elevated thunderstorm, Cold pad, Low-level jet, Convective instability, Moist symmetric instability