宁夏雾的时空分布特征及预报方法研究

利用1961～2009年宁夏24个气象站大雾天气观测资料，在对雾的时空分布特征分析的基础上，结合同期NCEP／NCAR逐日再分析资料，对宁夏雾的环流背景和主要影响系统特征进行了分析，总结归纳出宁夏雾的预报指标，建立了宁夏雾的预报模型及预报业务系统。结果表明：1961—2009年，宁夏雾的发生频数呈逐渐增加趋势，南部固原市和中部干旱带发生频数逐渐减少，北部引黄灌区明显增加；固原市发生频数明显多于中北部地区；一年中，秋冬季是雾的多发季节，春末夏初是雾的少发季节。雾出现时，500～700hPa基本为较稳定的西西北气流，850hPa为偏南气流，地面为均压区；500～700hPa相对湿度较小，850hPa到地面湿度较大，850hPa相对湿度在70％～80％．地面湿度接近饱和，850hPaT—Td≤3℃；地面水平运动微弱，高空风垂直切变较小。大雾出现时，500～850hPa垂直速度场均为下沉气流，且多数大雾前日出现降水，近地面层有逆温存在。

Temporal and Spatial Distribution Characteristic and Forecast Methods Research of Fog in Ningxia

According to the foggy weather observation data of 24 stations during 1961-2006 in Ningxia,and the temporal and spatial distribution characteristics,and the daily NCEP/NCAR reanalysis data,the fogs were analyzed on the part of the circulation background and influence system. Forecast index of the fog was concluded,forecast model and forecasting operation system were established. The results showed that during 50 years,the change of fog days was gradually increase in Ningxia. Frequencies of fog were gradually decrease in the southern part and the central arid region of Ningxia,it is obviously increase in the yellow fiver irrigation area. The fog seasonal variation is the most in winter and autumn,is the least in late spring and early summer. During fog existing,the synoptic situation showed that west-north-west air current is more stable at 500-700 hPa,the air current is the southerly at 850 hPa,the surface system is mean pressure field; relative humidity is lesser at 500-700 hPa and is large at 850 hPa to the surface ,it is 70%-80% at 850 hPa and air is at or near the saturation point at surface and T-Td is less than or equal to 3 ℃ at 850 hPa.. Simultaneously,horizontal motion is feeble at surface,the vertical shearing upper wind is lesser. When dense fog appears,vertical speed field is all descending flow at 500-850 hPa,there is rainfall before majority fog beginning,and an inversion layer is in the ground layer.