Synthetical Analysis on Sandstorm and Hail Weather Caused by "4.28" Qinghai-Xizang Plateau Cyclone
“4.28”青藏高原气旋产生沙尘暴、 冰雹天气系统结构分析

The various weather phenomena due to Qinghai-Xizang Plateau cyclone can cause complex mechanism of sandstorm and hail weather process. Plateau cyclone caused the sandstrom in Minqin country and thunder shower hail in Xihe county in south Gansu from 20:00 on 27 to 00:00 on 29 April 2007, lasted 32 hours that continued long time and hitted large area. The Qinghai-Xizang Plateau cyclone forming process are analyised： Namely the cold front formation complets the cyclone the fluctuation; in the north shear wave and south trough linking and connection process, the short wave trough of accompanying the positive vorticity advection move round the main upper trogh, the cyclone convergence center is formed, and temperature contrast on both sides of trough area oppear cold and warm transportation belts, front surface passing point is the maximun wind speed area, which is the generation stage of the cyclone. After the cyclone generating, the lower is damp, eddying and moving up, the high-level momentum along frontal area downlading in cyclone forehead, which causes the sandstorm. The cold air in trough formed condensation nucleus when the front surface occluded, it caused the severe convection weather to form hail in South Gansu.