Three-month wind profiles, 260 m PM_1 concentrations [i.e., particulate matter(PM) with an aerodynamic diameter ≤1μm], and carrier-to-noise ratio data at two Beijing sites 55 km apart(urban and suburban) were collec...Three-month wind profiles, 260 m PM_1 concentrations [i.e., particulate matter(PM) with an aerodynamic diameter ≤1μm], and carrier-to-noise ratio data at two Beijing sites 55 km apart(urban and suburban) were collected to analyze the characteristics of low-level nocturnal wind and PM in autumn and winter. Three mountain-plain wind events with wind shear were selected for analysis. The measurements indicated that the maximum wind speeds of the northerly weak low-level jet(LLJ) below 320 m at the suburban site were weaker than those at the urban site, and the LLJ heights and depths at the suburban site were lower than those at the urban site. The nocturnal 140 m mean vertical velocities and the variations in vertical velocity at the urban site were larger than those at the suburban site. A nocturnal breeze with a weak LLJ of ～3 m s^(-1) noticeably offset nocturnal PM transport due to southerly flow and convergence within the northern urban area of Beijing. Characteristics of the nocturnal LLJ, such as start-up time, structure, intensity, and duration, were important factors in determining the decrease in the nocturnal horizontal range and site-based low-level variations in PM.展开更多
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...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。展开更多
低空风切变严重威胁飞机起降安全,而激光测风雷达在晴空风切变监测方面具有显著优势,但其监测性能受到风场特点和监测算法的影响。由于无法对局地空间风场进行时空同步精细化探测,且风场具有阵性,导致风切变监测会出现虚警率、漏报等现...低空风切变严重威胁飞机起降安全,而激光测风雷达在晴空风切变监测方面具有显著优势,但其监测性能受到风场特点和监测算法的影响。由于无法对局地空间风场进行时空同步精细化探测,且风场具有阵性,导致风切变监测会出现虚警率、漏报等现象,只能通过数值模拟仿真的方式,对不同风场的监测性能进行分析评估。本文首先仿真构建了四种具有代表性的风场类型,然后模拟激光测风雷达平面-位置显示(Plane Position Indication,PPI)扫描方式获取不同仿真风场下的径向风速数据,最后利用八邻域系统算法对径向风速数据进行风切变监测,验证不同类型风场下激光测风雷达PPI扫描方式监测风切变算法的有效性。结果表明,激光测风雷达PPI扫描结果能够真实地反映风场情况;八邻域系统算法能够有效识别风切变;在进行风切变检测时,应尽可能地考虑到多个方位上的切变值,避免漏报。展开更多
基金supported by the National Key R&D Program of China (Grant No.2017YFC0209801)the National Natural Science Foundation of China (Grant Nos.41505091,91544221,41675137,41575124 and 41505116)
文摘Three-month wind profiles, 260 m PM_1 concentrations [i.e., particulate matter(PM) with an aerodynamic diameter ≤1μm], and carrier-to-noise ratio data at two Beijing sites 55 km apart(urban and suburban) were collected to analyze the characteristics of low-level nocturnal wind and PM in autumn and winter. Three mountain-plain wind events with wind shear were selected for analysis. The measurements indicated that the maximum wind speeds of the northerly weak low-level jet(LLJ) below 320 m at the suburban site were weaker than those at the urban site, and the LLJ heights and depths at the suburban site were lower than those at the urban site. The nocturnal 140 m mean vertical velocities and the variations in vertical velocity at the urban site were larger than those at the suburban site. A nocturnal breeze with a weak LLJ of ～3 m s^(-1) noticeably offset nocturnal PM transport due to southerly flow and convergence within the northern urban area of Beijing. Characteristics of the nocturnal LLJ, such as start-up time, structure, intensity, and duration, were important factors in determining the decrease in the nocturnal horizontal range and site-based low-level variations in PM.
文摘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。
文摘低空风切变严重威胁飞机起降安全,而激光测风雷达在晴空风切变监测方面具有显著优势,但其监测性能受到风场特点和监测算法的影响。由于无法对局地空间风场进行时空同步精细化探测,且风场具有阵性,导致风切变监测会出现虚警率、漏报等现象,只能通过数值模拟仿真的方式,对不同风场的监测性能进行分析评估。本文首先仿真构建了四种具有代表性的风场类型,然后模拟激光测风雷达平面-位置显示(Plane Position Indication,PPI)扫描方式获取不同仿真风场下的径向风速数据,最后利用八邻域系统算法对径向风速数据进行风切变监测,验证不同类型风场下激光测风雷达PPI扫描方式监测风切变算法的有效性。结果表明,激光测风雷达PPI扫描结果能够真实地反映风场情况;八邻域系统算法能够有效识别风切变;在进行风切变检测时,应尽可能地考虑到多个方位上的切变值,避免漏报。
