Abstract:Based on the multipletype observational data,this paper preliminarily analyses the mesoscale convective systems(MCSs) and weather background producing an extremely heavy rain along the Meiyu front in Hubei and Anhui provinces during 29—30 June 2009,and investigates the multiscale structure features of the Meiyu frontal rainstorm system.Then the mesoscale numerical model WRF with large domain and 9 km horizontal resolution is used to carry out a 3domainnested fine simulation for the heavy rain process.Morlet wavelet transformation is carried out to do spatial bandpassing filter for the model outputs,and the meso〖WTBX〗α,β〖WTB1〗 and 〖WTBX〗γ〖WTB1〗scale systems are separated out,in such a way that the three dimensional spatial dynamic and thermodynamic characteristics of the mesoscale systems with different scales are studied.The results are as follows.The extremely Meiyu frontal heavy rain is directly resulted from several MCSs with different scales,which are of different features on satellite cloud images and radar echoes.On meso〖WTBX〗α,β〖WTB1〗 and 〖WTBX〗γ〖WTB1〗scales,the Meiyu frontal heavy rain system has obvious different dynamic and thermodynamic structure features in horizontal and vertical directions.The meso〖WTBX〗α〖WTB1〗 and 〖WTBX〗β〖WTB1〗scale systems have obvious vertical circulation,while meso〖WTBX〗γ〖WTB1〗scale system has some features of inertial gravity waves and usually develops in meso〖WTBX〗α〖WTB1〗 and 〖WTBX〗β〖WTB1〗scale system.Lastly,a physic conceptual model is advanced for the typical Meiyu frontal rainstorm system.