水平螺旋度在沙尘暴预报中的应用

An application of the horizontal helicity to forecasting sandstorm.

中文关键词:  水平螺旋度, 沙尘暴, 预报应用

英文关键词:Horizontal helicity, Sandstorm, Forecast and application

中文摘要:

      为了更准确地预报中国北方沙尘暴的强度和范围，应用2002—2010年3—6月逐日08和20时高空流场资料、高空图资料和地面每3 h的天气图资料，计算近地面至500 hPa的水平螺旋度。结果表明，螺旋度负值中心值越大，辐合上升运动越强，风速越大，对应沙尘暴的强度就越强。螺旋度负值中心常常在河西走廊附近最强，沙尘暴发生在螺旋度负值中心附近或下游。在沙尘关键区（40°—48°N，84°—120°E）当出现螺旋度≤-600 m2/s2的负值中心时，6 h内该区或其下游将产生能见度低于500 m的强沙尘暴, 螺旋度负值中心与下游沙尘暴发生区有良好的对应关系。通过对中国北方区域性强沙尘暴典型个例、甘肃省河西走廊东部沙尘天气的对比分析，螺旋度有较强的日变化，白天强于夜间，对冬春季中国北方干旱区的冷锋型沙尘暴天气有较强的预报能力。

英文摘要:

      To more accurately forecast the strength and scope of a sandstorm over northern China, the daily 08:00 and 20:00 BT wind grid data at the upper levels and upper weather maps, as well as every 3 hour surface weather maps are used to calculate the horizontal helicities from near surface up to 500 hPa from March to June during 2002-2010. The main results show that the bigger the helicity’s negative value is, the stronger the convergent rising movement and the wind velocity are, and thus the stronger the forming sandstorm is. The helicity’s negative center is often the strongest near the Hexi Corridor of Gansu Province with the sandstorm often happening over the downstream region or near the Helicity’s negative center within 24 hours. Over the sand dust key region (40°-48°N，84°-120°E), when the helicity center value ≤-600 m2/s2, the strong sandstorm whose visibility is less than 500 m within 6 hours will happen in the center or its downstream region with the negative value center fitted well with the sandstorm’s occurring areas downstream. By contrasted and analyzed among the northern China typical large scale strong sandstorm cases and between the sandstorm and non sandstorm weathers in east of the Hexi Corridor of Gansu Province, it is found that the horizontal helicity has strong daily variation which is stronger in daytime than in night, and shows a strong ability of forecasting cold front sandstorm from winter to spring over the arid regions of northern China