Abstract:Using four-dimensional variational Doppler radar assimilation system (VDRAS) simulation and radar mosaic data, a weak squall line influenced by northeast cold vortex on 16 May 2012 was analyzed. The result showed that strong convergence line on the surface was an important factor causing convective occurrence under the weak hydrostatic instability, and was also an important reason for the quickly developing of the system at the early stage. Cold air was continuously transported to Yangtze-Huaihe River Valley under the control of northeast cold vortex. Because of precipitation dragging by convection within squall line, the dry and cold air was entrained into convection and continuously moved downward, causing strong cold pool as the result of evaporation. The main reason for weak squall line is that after the formation of cool pool, vertical wind shear is not perpendicular to the squall line with weak magnitude, causing imbalance between them. Besides, weak 〖JP2〗hydrostatic instability and low relative humidity are part of reasons for the weak squall line. The major difference between this case and other squall lines in eastern China is the strong convergence line and relative dry environment, which means less moisture content is delivered to middle level and less latent heating is released. Finally, upward motion is more dependent on balance between cool pool and vertical wind shear.