Characteristics of environmental parameters for multi-intensity short-duration heavy rainfalls over East China

Based on hourly rainfall observations and 6-hourly final analysis from National Centers for Environmental Prediction (NCEP) over East China between May and September from 2002 to 2009 and using the spatiotemporal matching technique, we acquired the short-duration heavy rainfall samples of 20-49.9 mm·h^-1 (Type A), 50-79.9 mm·h^-1 (Type B), and those exceeding 80 mm·h^-1 (Type C), and then analyzed by type the spatiotemporal distribution characteristics of the physical quantities such as water vapor, thermodynamic variables, uplift triggering and vertical wind shear, which are used to characterize the environmental conditions of their occurrence and development. Results show that total precipitable water (TPW) characterized by water vapor conditions has certain significance for three types of short-duration heavy rainfalls. TPW values essential to Type A, Type B and Type C short-duration heavy rainfalls are 27 mm, 32 mm and 42 mm, respectively. The higher the short-duration heavy rainfall is, the more water vapor content it needs. About 50% of all the short-duration heavy rainfalls happen in the wet environment of TPW greater than 60 mm. The physical quantities characterizing thermodynamic, energetic, dynamic and vertical wind shear are not significant for judging the environmental conditions of three types of short-duration heavy rainfall, which shows the amount of water vapor in the ambient atmosphere may be a necessary factor in determining the level of short-duration heavy rainfall. The high probability density range of Type B and Type C short-duration heavy rainfalls is approximately between 55 mm and 70 mm in TPW, and 5 m·s^-1 and 15 m·s^-1 in 0-6 km vertical wind shear. Additionally, Type C short-duration heavy rainfalls have two significant high probability density regions in the probability density scatter diagrams of the TPW vs. the best convective available potential energy (BCAPE), and the 0-6 km vertical wind shear vs. BCAPE, which may be related to the two mechanisms of CAPE affecting the generation of high-level short-duration heavy rainfalls.