Abstract:

Based on the NCEP FNL(National Center for Atmospheric Research Final Analysis) and GDAS(Global Data Assimilation System) 1°×1° reanalysis data, ground observation data from May 2 to 4 in 2016, the rainstorm process in Northeast China caused by the explosive development of the surface cyclone in spring was investigated.The large-scale circulation background, water vapor source and transport, dynamic mechanism, and thermal conditions were analyzed.The results show that the Huang-Huai cyclone locates near 40°N intensified northward and the central pressure drops 24 hPa from 14:00 on February 2 to 14:00 on February 3, exceeding the definition standard of the explosive cyclone.The 500 hPa upper trough is rapidly strengthened and developed into a closed vortex, and the low-level shear line is strengthened and developed into a low-level vortex.The obvious low-level jet forms in the east of the trough, which provides water vapor and heat for the rainstorm area and the rainstorm is typical warm shear precipitation in Northeast China.Isentropic potential vortexes transport downwards from the upper level of 320 K to the lower level of 305 K and gradually move to the southeast.The downward transmission of the upper level positive potential vortexes enhances the development of surface cyclones and the convergence of ascending movement, which is conducive to the increase of rainstorms.The specific humidity above 6 g·kg^-1 will be useful for rainstorm forecasts in late spring and early summer in Northeast China.Water vapor mainly comes from the Northwest Pacific Ocean, such as the East China Sea and the Yellow Sea.The rainstorm area is consistent with the negative area of water vapor flux divergence at 850 hPa, the vertical velocity at 700 hPa, and the absolute vorticity large value at 850 hPa.The strong rainfall area corresponds to the dense zone of equivalent potential temperature at 850 hPa and the warm frontogenic area.The precipitation is located in the energy front area and the side of the warm area.

Key words: Explosive cyclone, Rainstorm, Isentropic potential vortex