Abstract:

This paper statistically analyzed spatial-temporal distribution features of triggered local convective weather under the control of the Western Pacific subtropical high (WPSH) in midsummer in the Yangtze Delta region from 2015 to 2019.The results show that the daily variation of the triggered local convection indicate a unimodal shape from noon to evening, and the high-frequency areas are located at the vicinity of large cities, the hilly areas, as well as the junction of water and land, but the convection rarely occurs over the rivers and lakes, canyons or basins.It is also found that high-frequency regions of the Southward type are mostly located in mountainous and coastal areas in the low-level westerly wind field, which is in favor to the surface heating.The high-frequency regions of the Northward type are located in inland, due to the low-level easterly wind weakening the surface heating and reducing the convection occurrence in the coastal area.The statistical analysis of the given convective parameters of two subtropical high types shows that the convective available potential energy (CAPE) value plays an obvious reference role in judging whether local convection is triggered.For coastal areas, the CAPE value of the Southward type is slightly higher than that of the Northward type, while it is opposite in inland areas.The lifting index (LI) and lifting condensation level (LCL) values of the Southward type are lower than that of the Northward type, reflecting intense stratification instability of the Southward type.

Key words: Infrared image, Convective available potential energy, Lifting index, Lifting condensation level