典型槽型转脊型黑风天气过程成因分析

2010年4月24-27日甘肃省河西走廓、西北东部及华北出现了大风沙尘暴天气过程,河西走廓出现黑风天气,损失十分严重。针对这次罕见的槽型转脊型黑风天气过程,应用2002-2011年3-5月逐日08时和20时高空流场资料、高空图资料和地面每隔3 h天气图资料,对其天气形势演变、高空垂直风场及水平相对螺旋度场进行了深入对比分析。结果表明:4月24日20时700～500 hPa有较强冷空气入侵,700 hPa大气层结存在剧烈的高低空不稳定,≤-1 000 m2·s-2强螺旋度负值中心是黑风爆发的动力因素,25-27日08时700 hPa≥15 m·s-1低空急流区的存在是这次大风天气得以持久维持的关键原因。

The Turning Causes of Trough to Ridge in a Typical Black Sandstorm Process Occurred in North-west China

On April 24-27, 2010, a strong sandstorm and gale process occurred in Hexi Corridor, Gansu, developed to black sandstorm and affected most areas in north-west China, brought about serious economic loss. In order to have a thorough understand over the causes of that disastrous weather process, we analyzed and compared the weather circulation changes, the high vertical wind fields, and the horizontal relative helicities of this black sandstorm process. The daily surface to upper wind grid data at 08:00 and 20:00 and the upper weather maps and three-hourly surface weather maps were used to calculate the horizontal helicities from near ground surface up to 500 hPa from March to May during 2002-2011. The results showed that the strong cold air at 700-500 hPa, the violent unstable atmospheric layer at 700 hPa, and the helicity’s negative value less than -1 000 m2·s-2 at 20:00 on April 24 were dynastic factors leading to the outbreak of the black sandstorm. The existence of low-level jet bigger or equal 15 m·s-1 at 700 hPa at 08:00 on April 25-27 was a critical factor for the windstorm to form and last.