A comparative analysis of two thunderstorms that occurred in the Nanjing area was conducted by using NCEP,sounding,lightning location and Doppler radar data,in Nanjing and Changzhou,with the aim being to study the differences among the key factors causing thunderstorms in spring and summer.One of the thunderstorms took place on 22 February 2012,and the other was on 10 August 2011.The results of the analysis of the atmospheric energy structure show that the wind-potential temperature plots can reveal the dynamic,thermodynamic and water vapor characteristics before the occurrence of thunderstorms.Specifically,the tropopause height increases,providing sufficient space for the development of the thunderstorm.The "ultra-low" temperature phenomenon of the tropopause is a sign of thermal instability,while the clockwise rotation of the wind direction along with an increase in the height provides favorable dynamic conditions for the thunderstorm.Meanwhile,large quantities of water vapor are transported by the moisture gradient in the vertical direction.Comparison of the physical diagnosis reveals that the dynamical lifting effect of the spring thunderstorm is stronger than that in summer,with the latter mainly caused by heat convection;the dynamical suction effect in the upper troposphere is not predominant.Comparison of the characteristics of Cloud-to-Ground(CG) lightning evolution indicates that the CG lightning frequency of the spring thunderstorm is low,but the percentage of positive CG lightning is high.The situation for the summer storm is just the opposite,showing multiple peaks.The percentage of negative CG lightning is high.In the mature stage,the radar echo top height has a negative correlation with the CG flash rate,and it reaches its peak before the occurrence of CG flashes.Comparison of the radar data shows that the echo of the spring thunderstorm appears similar to a stratocumulus cloud precipitation echo.There is obvious wind shear,strong warm advection,and convergence activities in the storm.The echo of the summer thunderstorm shows it to be a convective precipitation process.There is wind shear and convergence activities in the summer thunderstorm,and a clear vortex tube can also be found.It shows the features of a local thunderstorm.Analysis of the matching of relationships between the radar echo intensity and the CG distribution reveals that,tor both the weak spring thunderstorm and the strong summer strong thunderstorm,the locations of CG flashes correspond well to the convergence zone and radar reflectivity.Most of the CG lightning of the spring thunderstorm happens around the regions where the echo intensity is above 40 dBz,or in the regions where the echo intensity is approximately 30 dBz.The CG lightning of the summer thunderstorm mainly occurs in the regions where the echo intensity is above 40 dBz.In developing stage of the strong thunderstorm cloud,CG flashes are mainly distributed on the side of the stretching direction of the storm,and they can be the guidance of the radar echo.Most of the CG flashes happen in the vertical wind shear area.