Dual-Doppler radar observation analysis of a quasi-linear convective system in South China in 2008

A quasi-linear convection system (QLCS) in the stratiform region on 6 July 2008 has been investigated using dual-Doppler radar data collected from Guangzhou and Shenzhen. Three dimensional wind field, kinematic and thermodynamic structure are analysed and the maintenance mechanism of QLCS is discussed. The results are as follows. (1) The QLCS was formed in stratiform cloud precipitation region and has a moderate vertical wind shear with a weak unstable synoptic environment. The surface existed obvious meso-β-scale shear line during the QLCS development and the QLCS formed along the shear line.During the system passaged, water vapor was close to saturation without cold pool. (2) When the QLCS was in mature phase, the areas of vertical ascending motion and positive vorticity had banded structure, convections developed almost vertically, most of the strong radar (>4 dBz) echo developed to a height of about 5 km, and there was no tilting to the front of the system. The kinematic structures of the QLCS at the mature stage showed that their inside convective updrafts were smaller and the maximum value (6 m·s^-1) appeared at middle and high levels. Deep convergence formed by the relative influxes in the front low level (2 km or less) and the deep rear inflow (8 km) existed in the convection. (3) Inside the QLCS convections, there was a perturbation high with pressure decreasing from low to high levels. Very small perturbation potential temperature indicated that the buoyancy effect was weak. The vertical momentum budget calculation indicated that the vertical pressure gradient force produced by the perturbation pressure formed by convergence was the main mechanism for the convection maintenance.