西北干旱区机场低空风切变基本特征分析

Analysis of basic characteristics of low-level wind shear in the arid regions of northwest China

为提升对西北干旱区低空风切变特征的认识,对该区域民航飞行安全提供可靠的气象服务保障,以新疆为例,利用机场语音方式航空器报告、机场例行观测实况报文、维萨拉(Vaisala)气象自动观测系统数据、飞机机载探测资料、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析资料(ERA5)对新疆区域17个机场接收的低空风切变报告进行统计,并对喀什机场一次典型低空风切变事件进行分析。结果表明:新疆地区低空风切变四季均有出现,夏季出现频率最高,低空风切变在90~300 m高度范围内频发,主要集中发生在中午至傍晚时段,中等强度的低空风切变出现频次最多,小机型飞机更易遭遇低空风切变。低空风切变发生时机场常受500 hPa西风气流型、低涡型、低槽型天气系统影响,且多伴有低空急流、地面大风及对流云等情况,特殊的地形环境也是影响新疆部分机场低空风切变频发的原因之一。对喀什机场一次典型低空风切变个例分析后发现,在低槽型天气系统影响下,飞机进近和复飞过程中遭遇了强风切变,包括强水平风向、风速的切变和强垂直风切变,在中小尺度系统影响下飞机在下降过程中极有可能遭遇下击暴流,从而引发强低空风切变。

In order to improve the understanding of the characteristics of low-level wind shear in the arid regions of northwest China and to provide reliable meteorological service guarantee for the flight safety of civil aviation in this region,the low-level wind shear reports received at 17 airports in Xinjiang region located in the arid regions of northwest China were statistically analyzed by using airport speech aircraft report,airport routine observation live message,Vaisala meteorological automatic observation system data,aircraft airborne detection data,and European Centre for Medium-Range Weather Forecasts(ECMWF)fifth-generation atmospheric reanalysis data(ERA-5),and a typical low-level wind shear event at Kashgar Airport was analyzed.The results show that low-level wind shear occurs in all seasons in Xinjiang,with the highest frequency in summer.Low-level wind shear occurs frequently in the height range of 90-300 m,mainly in the period from noon to evening.Medium-intensity low-level wind shear occurs most frequently,and small aircraft are more likely to encounter low-level wind shear.When the low-level wind shear occurs,the airport is often under the influence of westerly airflow type,low vortex type and low trough type in the 500 hPa situation field,and is often accompanied by low-level jet,ground gale and convective cloud.The special terrain environment is also one of the reasons that affect the frequent occurrence of low-level wind shear in some airports in Xinjiang.After analyzing a typical low-level wind shear case at Kashgar Airport,it was found that under the background of low-trough weather situation,the aircraft encountered strong wind shear during approach and re-flight,including strong horizontal wind direction,wind speed shear and strong vertical wind shear.Under the influence of small and medium-sized systems,the aircraft is very likely to encounter downburst during the descent process,which leads to strong low-altitude wind shear.