Extended Abstract

An Idealized Numerical Study on the Effects of Meiyu Front uponthe Initiation and Development of MCSs Producing RainstormsZHAO YuchunInstitute of Heavy Rain, Wuhan, CMAzhaoych@cma.gov.cnAimed at the fact th at the me soscale convective systems (MCSs) usuallydevelop on the Meiyu front, lasting a long time and producing rainstorms alongthe valleys of Yangtze river, a series of three-dimensional idealized numericalexperiments are carried out to investigat e the ef fect of moisture dif ferencebetween the two sides of Me iyu front, the impacts of basic flow, wind vertic alshear upon the MCSs’ development along the Meiyu front, and the convectionorganization by the Meiyu front.The mass imbalanc e resultin g from the Meiyu front can generatesmall-amplitude gravity waves, which may organize upward motions in t helow-level and trigger convection when coupled with diabatic heating, leading toa convective rain-band forming along the Meiyu front. The scale of theconvective systems i s usually 20~60km. The convection rain band movessouthward after its formation.The Meiyu front plays a role in the convection organization. The convectiveperturbations near the Meiyu front may develop into MCSs with a scale of100~200km. When convective perturbati on ef fected by low-level northerlywinds organized by Meiyu front, a convergence band forms in its low level andits flow structure tilts in the vertical direc tion, which is beneficial to themaintenance and development of MCSs.The basic flow’ s advection impacts t he Meiyu front’ s movement, which canoffset the southward movement of Me iyu frontal convection rain-band. Themoisture and energy transportati on by it is very important in the initiation anddevelopment of MCSs. The wind vertical shear resulting from wind directionvariations is beneficial to convection initiation and MCSs’ organization alo ngthe Meiyu front and impacts the moving di rection of convective systems, whilethat from wind velocity variations seems to be not favorable for the convectioninitiation on the Meiyu front and the long-time maintenance of MCSs.-73-