A long-lived and loosely organized squall line moved rapidly across U¨ru¨mqi, the capital city of Xinjiang Uygur Autonomous Region of China on 26 June 2005, generating hail and strong winds. The squall line was observed by a dual Doppler radar system in a field experiment conducted in 2004 and 2005 by the Chinese Academy of Meteorological Sciences and the local meteorological bureau in northwestern China. The 3D wind fields within the squall line were retrieved through dual Doppler analyses and a variational Doppler radar analysis system (VDRAS). The formation and structure of the squall line as well as the genesis and evolution of embedded convective cells were investigated. During its life period, the squall line consisted of six storm cells extending about 100 km in length, and produced hail of about 25 mm in diameter and strong surface winds up to 11 m s-1. Radar observations revealed a broad region of stratiform rain in a meso-β cyclone, with the squall line located to the west of this. Two meso-γ scale vortices were found within the squall line. Compared to typical squall lines in moist regions, such as Guangdong Province and Shanghai, which tend to be around 300-400 km in length, have echo tops of 17-19 km, and produce maximum surface winds of about 25 m s-1 and temperature variations of about 8-C this squall line system had weaker maximum reflectivity (55 dBZ), a lower echo top (13 km) and smaller extension (about 100 km), relatively little stratiform rainfall preceding the convective line, and a similar moving speed and temperature variation at the surface.
A heavy rainfall system was observed over the Yangtze River during Meiyu season by using dual-Doppler radar systems in the field experiment conducted by the project of National Fundamental Research Planning “Research on formation mechanism and the prediction theory of hazardous weather over China”. The three-dimensional mesoscale kinematic structure and process of a heavy rain on 22 and 23 July, 2002 are investigated by using the radial velocity and dual-Doppler radar technique. The results show that a southwest-northeast oriented rain band with the length of about 1000 km involves numbers of meso-β or meso-γ-scale convective cells with the size of 20―50 km. The heavy rain band in the middle reaches of the Yangtze River ex-ists in a low-level wind shear. The interaction between southwest low-level jet on the southern side of wind shear and east wind on the northern side formed the updraft. The wind disturbance, wind shear and convergence generate the convective action. The new cell developed in right rear flank of rain band and moved to the southwest wind area, where the vapor is abundant. This kind of echo can last a long time and developed well. The strong convective echoes are often ac-companied by the meso-γ-scale vortex and convergence.
LIU Liping1, RUAN Zheng1 & QIN Danyu2 1. Chinese Academy of Meteorological Sciences, Beijing 100081, China
This paper investigated several approaches to remapping and combining multiple-radar reflectivity fields onto a unified 3D Cartesian grid with high spatial and temporal resolutions,and analyzed systematic ob- servation differences among multiple radars.The remapping approaches were evaluated by inspecting the spatial consistency of the reflectivity fields on vertical and horizontal cross sections on the equidistant line of radars,and the intensity change of 1-h accumulated precipitation before and after interpolation.The com- bining approaches were evaluated by continuity examination.The results show that for remapping schemes, the vertical interpolation with nearest neighbor on the range-azimuth plane is the most reasonable scheme that provides consecutive refiectivity fields and retains the high-resolution structure comparable to that of the raw data;for multiple-radar data mosaics,the distance-exponential-weighted mean scheme provides spatially consistent reflectivity mosaics.The mosaics can mitigate various problems caused by the radar beam geometry such as the cone of silence.
In this paper,NCEP reanalysis data,intensive observation data collected from field experiment,model simulation data,and topographic trial data are fully analyzed to study a severe heavy rainfall event during 5 6 June 2008 in South China.Unlike most warm region rainfall cases,this one is associated with an obvious vortex system,which draws in water vapor and energy from the southwest monsoon surges ahead of a low trough above the Bengal Bay (BLT,Bengal Low Trough).At the lower troposphere,three currents,especially the southwest current and the east current,converge into the southeast of the vortex.Thus,the distributions of strong vorticity,water vapor,and ascending motion cause frequently occurrence and growth of convection there.The possible reasons for this rainfall event are summarized as a conceptual model.
