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
In order to understand the activity characteristics of low-level jets in the Nanjing area,statistical analysis and comparative study are carried out on their monthly and diurnal variations,characteristics of their cor...In order to understand the activity characteristics of low-level jets in the Nanjing area,statistical analysis and comparative study are carried out on their monthly and diurnal variations,characteristics of their cores and accompanying weather conditions using wind profile data in 2005-2008 collected by two wind profilers.The results show that low-level jets have significant monthly and diurnal variations.They occur more frequently in spring and summer than in autumn and winter and are more active in early morning and at night,with the maximum wind speed usually occurring at midnight.The central part of the low-level jet occurs mainly at the height of less than 1400 meters,and the enhancement of central speed is beneficial to the appearance of precipitation.Meanwhile,when the low-level jet appears in summer,it helps cause heavy rain.The statistical results of the boundary wind profiler are well consistent with those of the tropospheric wind profiler.Two kinds of wind profilers also have the capability of continuously detecting the development of low-level jets.展开更多
Based on the previous research on the model of rainstorm weather with low-level jet in Xiangtan,using the classification result of radar echo characteristics,the wind profile data provided by new generation of weather...Based on the previous research on the model of rainstorm weather with low-level jet in Xiangtan,using the classification result of radar echo characteristics,the wind profile data provided by new generation of weather radar in Changsha and hourly rainfall data,a thorough study of the heavy rainfall from 2 to 5 July 2016 in Xiangtan was conducted. It was concluded that heavy precipitation had the characteristics of the WPSH pattern of rainstorm with low-level jet at early stage,and then it converted to cold shear jet pattern in latter stage. When low-level southwest jet began to have momentum download,that is to say,there was more than 12 m/s of southwest jet below 1 km,and it rapidly strengthened and expanded downward,it was conducive to the occurrence of short-term rainstorm. The low-level jet would not immediately cause a strong precipitation when it reached the station,with a certain lag. A positive correlation existed between the increase of low-level jet index and precipitation intensity,and low-level jet index could predict the occurrence of heavy rainfall and rain intensity.展开更多
Using a mesoscale model,a numerical study on a heavy rainfall case occurring in the Changjiang-Huaihe River Basin is made in this paper.The influence of the intensity of northeasterly wind in front of the Qinghai-Xiza...Using a mesoscale model,a numerical study on a heavy rainfall case occurring in the Changjiang-Huaihe River Basin is made in this paper.The influence of the intensity of northeasterly wind in front of the Qinghai-Xizang high at upper level on the low level wind field and development of mesoscale systems as well as heavy rainfall is investigated.The model well reproduced the heavy rainfall process and the weather systems associated.And it indicates that the strong northeasterly flow around the high at upper troposphere will bring about not only the strengthening of low level southeasterly wind,but also the appearance of shear-line and mesoscale vortex at low level.The coupling of northerly wind at upper level and southerly wind at lower level constructs a vertical indirect circulation which is most favourable for the development of convective motions.Its ascending branch in the shear-line area is very strong and shows a pronounced mesoscale characteristic.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
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.
基金Open Research Foundation for Radar Meteorology and Severe Weather in Nanjing(BJG201203)Research Fund for Fundamental Theories in Institute of Meteorology and oceanography,PLA University of Science and Technology+1 种基金National Natural Science Foundation of China(41005018)Young Scientists Foundation(41105023)
文摘In order to understand the activity characteristics of low-level jets in the Nanjing area,statistical analysis and comparative study are carried out on their monthly and diurnal variations,characteristics of their cores and accompanying weather conditions using wind profile data in 2005-2008 collected by two wind profilers.The results show that low-level jets have significant monthly and diurnal variations.They occur more frequently in spring and summer than in autumn and winter and are more active in early morning and at night,with the maximum wind speed usually occurring at midnight.The central part of the low-level jet occurs mainly at the height of less than 1400 meters,and the enhancement of central speed is beneficial to the appearance of precipitation.Meanwhile,when the low-level jet appears in summer,it helps cause heavy rain.The statistical results of the boundary wind profiler are well consistent with those of the tropospheric wind profiler.Two kinds of wind profilers also have the capability of continuously detecting the development of low-level jets.
基金Supported by Forecasters' Special Project of Hunan Meteorological Bureau in 2016(XQKJ16C003)
文摘Based on the previous research on the model of rainstorm weather with low-level jet in Xiangtan,using the classification result of radar echo characteristics,the wind profile data provided by new generation of weather radar in Changsha and hourly rainfall data,a thorough study of the heavy rainfall from 2 to 5 July 2016 in Xiangtan was conducted. It was concluded that heavy precipitation had the characteristics of the WPSH pattern of rainstorm with low-level jet at early stage,and then it converted to cold shear jet pattern in latter stage. When low-level southwest jet began to have momentum download,that is to say,there was more than 12 m/s of southwest jet below 1 km,and it rapidly strengthened and expanded downward,it was conducive to the occurrence of short-term rainstorm. The low-level jet would not immediately cause a strong precipitation when it reached the station,with a certain lag. A positive correlation existed between the increase of low-level jet index and precipitation intensity,and low-level jet index could predict the occurrence of heavy rainfall and rain intensity.
基金This work was supported by the National Natural Science Foundation of China under the auspices of Project Contract No.49335061.
文摘Using a mesoscale model,a numerical study on a heavy rainfall case occurring in the Changjiang-Huaihe River Basin is made in this paper.The influence of the intensity of northeasterly wind in front of the Qinghai-Xizang high at upper level on the low level wind field and development of mesoscale systems as well as heavy rainfall is investigated.The model well reproduced the heavy rainfall process and the weather systems associated.And it indicates that the strong northeasterly flow around the high at upper troposphere will bring about not only the strengthening of low level southeasterly wind,but also the appearance of shear-line and mesoscale vortex at low level.The coupling of northerly wind at upper level and southerly wind at lower level constructs a vertical indirect circulation which is most favourable for the development of convective motions.Its ascending branch in the shear-line area is very strong and shows a pronounced mesoscale characteristic.
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。
