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1.
基于相干多普勒测风激光雷达于2018年8月在山东德州获取的为期一个月的风廓线观测数据,进行了低空急流的判定、识别与统计分析。参考BONNER对低空急流的判定标准,对1 500 m高度以下的每10 min平均风廓线数据进行低空急流识别与统计,急流发生频率仅为3.6%。参考张世丰对低空急流的判定标准,统计了350 m高度以下10 min平均风廓线的低空急流风速、高度、风向及风切变等结构特征。急流发生频率为24.9%,急流速度主要介于6～10 m·s-1之间,急流高度出现3个峰值,分别位于110 m、160 m和220 m左右,急流风向主要为偏东风和偏南风。结果表明,多普勒激光雷达可以获取高时空分辨率的风廓线数据,进而可以有效检测低空急流结构的存在及其特征。 相似文献
2.
We analyzed wind profiler data collected over Ulsan airport during the period from 2008 to 2009 to examine the characteristics of low level jets (LLJs). The Ulsan airport is located within the narrow valley with north-south axis. The frequency analysis results indicates that the nearly 19% of the total nocturnal periods have the presence of jets and LLJ occurrence rate is high in winter (32%) and low in summer (10%). The mode in the wind speed histogram is 4?C6 m s?1. A majority of jet occurs below 100 m (about 77.8 m) above ground. The predominant wind direction of jet is northerly. In order to examine the favorable conditions for LLJ formation of Ulsan airport, we investigated temperature difference between valley and plain at the surface and synoptic wind direction and speed at 850 hPa. Our results show that air temperature in the valley is lower than over the plain during the nighttime, indicating the existence of thermal forcing for along-valley wind. Under a significant temperature difference along the valley, westerly wind speed at 850 hPa is slightly weaker on LLJs event night than no event night, indicating weaker north-south large-scale pressure gradient on LLJ event night. The magnitude of northerly wind at 850 hPa is much stronger on event night than no event night, implying higher downward transfer of northerly wind on event night. Our findings suggest that jet formation over Ulsan airport is related to the strong northerly wind at 850 hPa in the presence of thermal forcing due to temperature contrast between valley and plain. 相似文献
3.
利用WRF模式对2016年6月30日—7月6日长江流域的一次大暴雨天气过程中的低空急流进行数值模拟,在成功模拟低空急流基础上,分析此次急流过程中可能的影响机制;同时对地形高度进行敏感性试验,分析地形因素对此次低空急流可能的影响。(1)此次低空急流发生时,东侧为西太平洋副热带高压,西侧则为西南涡。这种“东高西低”的高低压配置为低空急流的形成与发展提供了有利的背景场。(2)高空急流和低空急流的耦合作用是低空急流发展的一个重要背景条件。(3)垂直方向高空动量不断下传为低空系统的发展提供了动力支持,是低空急流发生的一个重要条件。(4)逆温和垂直风切变之间的正反馈机制是低空急流形成与加强的因素之一。(5)山体在急流生成及发展过程中对气流有摩擦和阻挡作用,这种阻挡作用随着山体地形高度的增加而有所加强,同时山脉的走向会改变原始的风向,使得急流前端超前或滞后。青藏高原有强背风波效应,它的绕流和挤压作用会使得低空气流表现为狭长的带状,使动量更加聚集从而风速增加形成低空急流。 相似文献
4.
THE RELATIONSHIP BETWEEN LARGE-SCALE LOW-LEVEL JET OVER EAST ASIA AND MONSOON AS WELL AS CROSS-EQUATORIAL CURRENTS IN SUMMER 
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下载免费PDF全文 Sun Shuqing 《Acta Meteorologica Sinica》1987,1(1):43-50
A review regarding the investigation of the background circulation of large-scale low-level jet (LLJ) over East Asia is given,which indicates the important effect of the monsoon westerlies on LLJ and the relationship between LLJ and cross-equatorial currents.The data of the Global Analyses provided by ECMWF are used to investigate the relationship between LLJ and monsoon as well as cross-equatorial currents.It indicates that a large amount of momentum of the monsoon westerlies is transferred downstream to the LLJ area,strengthening the jet speed.Most of LLJs over Asia are connected with the cross-equatorial currents in the Eastern Hemisphere.The cross-equatorial currents near 80°E are the main currents connected with the LLJ in May.However,once the Somalia jet is established,it becomes the main flow together with cross-equatorial currents near 105°E to influence the LLJ over East Asia. 相似文献
5.
Chunguang CUI Wen ZHOU Hao YANG Xiaokang WANG Yi DENG Xiaofang WANG Guirong XU Jingyu WANG 《大气科学进展》2023,40(4):711-724
Here, we analyze the characteristics and the formation mechanisms of low-level jets(LLJs) in the middle reaches of the Yangtze River during the 2010 mei-yu season using Wuhan station radiosonde data and the fifth generation of the European Centre for Medium-Range Weather Forecasts(ERA5) reanalysis dataset. Our results show that the vertical structure of LLJs is characterized by a predominance of boundary layer jets(BLJs) concentrated at heights of 900–1200 m.The BLJs occur most frequently at 230... 相似文献
6.
A sustained heavy rainfall event occurred over the Sichuan basin in southwest China during 10–18 August 2020, showing pronounced diurnal rainfall variations with nighttime peak and afternoon minimum values, except on the first day. Results show that the westward extension of the anomalously strong western Pacific subtropical high was conducive to the maintenance of a southerly low-level jet (LLJ) in and to the southeast of the basin, which favored continuous water vapor transport and abnormally high precipitable water in the basin. The diurnal cycle of rainfall over the basin was closely related to the periodic oscillation of the LLJ in both wind speed and direction that was caused by the combination of inertial oscillation and terrain thermal forcing. The nocturnally enhanced rainfall was produced by moist convection mostly initiated during the evening hours over the southwest part of the basin where high convective available potential energy with moister near-surface moist air was present. The convective initiation took place as cold air from either previous precipitating clouds from the western Sichuan Plateau or a larger-scale northerly flow met a warm and humid current from the south. It was the slantwise lifting of the warm, moist airflow above the cold air, often facilitated by southwest vortices and quasi-geostrophic ascent, that released the convective instability and produced heavy rainfall. 相似文献
7.
东亚大尺度低空急流的背景流场与东半球的越赤道气流 总被引：2，自引：1，他引：2
本文介绍了关于东亚大尺度低空急流背景流场的研究,指出其上游的季风西风带对它的重要作用,以及它与东非地区越赤道气流之间的关系。利用欧洲中期预报中心提供的资料,考查了1979,1982和1983年8个夏季月的东亚大尺度低空急流,进一步研究了它们的上游流场和背景气流,指出东亚地区的低空急流主要以亚洲季风为背景。大风动量一次一次地沿着季风气流向急流区传播,它还与越赤道气流关系密切;绝大多数大尺度低空急流是东半球几支越赤道气流东传后汇合的产物。5月,以80°E附近的越赤道气流为主;6月中旬后,索马里地区低空急流建立,东非越赤道气流成为主要的影响系统,并经常与105°E的越赤道气流共同作用影响我国或东亚地区的低空急流。 相似文献
8.
Dongqian Wang Yaocun Zhang Anning Huang 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(3):259-270
The major features of the south-westerly low-level jet (LLJ) in the lower troposphere over Southeast China and its climatic impacts are investigated by using FNL reanalysis data and observational precipitation data. Results show that LLJ mainly occurs in spring and summer and the occurrence frequency of LLJ over southeast China has significant diurnal cycle, most LLJ occur in the nighttime (0200 LST and 0800 LST). The high nocturnal occurrence frequency of LLJ is mainly resulting from increased nocturnal ageostrophic wind. Research on the climatic impacts of large-scale conditions depicts that, the occurrence of LLJ in April mainly results from the northward shifting of western pacific subtropical high (WPSH), and the occurrence of LLJ in July results from the strengthening of detouring flow around Tibetan Plateau. Analysis of the climatic effects of LLJ on precipitation distribution in 3 rainy seasons over Southeast China indicates that the rainfall events with strong intensity correspond to strong LLJs. The LLJ affects the precipitation over Southeast China by transporting water vapor and triggering upward motion. Rainfall regions well corresponds to the regions of the moisture convergence and strong upward motion triggered by LLJ. Negative wind divergence anomalies at 850 hPa and positive wind divergence anomalies at 200 hPa over the Yangtze-Huaihe River Valley strengthen the upward motion over this region, which are conductive to produce more precipitation over the Yangtze-Huaihe River Valley. 相似文献
9.
The low-level jet （LLJ） is closely related to severe rainfall events, air pollution, wind energy utilization, aviation safety, sandstorms, forest fire, and other weather and climate phenomena. Therefore, it has attracted considerable attention since its discovery. Scientists have carried out many studies on LLJs and made significant achievements during the past five or six decades. This article summarizes and assesses the current knowledge on this subject, and focuses in particular on three aspects： 1） LLJ classification, definition, distribution, and structure; 2） LLJ formation and evolutionary mechanisms; and 3） relationships between LLJ and rainfall, as well as other interdisciplinary fields. After comparing the status of LLJ research at home （China） and abroad, we then discuss the shortcomings of LLJ research in China. We suggest that this includes： coarse definitions of the LLJ, lack of observations and inadequate quality control, few thorough explorations of LLJ characteristics and formation mechanisms, and limited studies in interdisciplinary fields. The future prospects for several LLJ research avenues are also speculated. 相似文献
10.
Characteristics and Mechanisms of Low-Level Jets in the Yangtze River Delta of China 总被引：2，自引：1，他引：1
A dataset obtained using a wind-profile radar located at the Yangtze River Delta in China ( $31.14^{\circ }$ N, $121.81^{\circ }$ E) in 2009 was used to investigate the characteristics and evolution of low-level jets (LLJs) along the east China coast. The study investigated the daily and seasonal structures of LLJs as well as several possible causes. A total of 1,407 1-h LLJ periods were detected based on an adaptive definition that enabled determination of four LLJ categories. The majority (77 %) of LLJs were found to have speeds $<$ 14.0 m s $^{-1}$ (maximum of 34.6 m s $^{-1})$ and occur at an average altitude below 600 m (76 % of the observed LLJs). The dominant direction of the LLJs was from the south-south-west, which accounted for nearly 32 %, with the second most common wind direction ranging from $040^{\circ }$ to $100^{\circ }$ , albeit with a number of stronger LLJs from the west-south-west. A comparison of LLJs and South-west Jets revealed that the frequencies of occurrence in summer are totally different. Results also revealed that in spring and summer, most LLJs originate from the south-south-west, whereas in autumn and winter, north-east is the dominant direction of origin. The peak heights of LLJs tended to be higher in winter than in other seasons. The horizontal wind speed and peak height of the LLJs displayed pronounced diurnal cycles. The Hilbert–Huang transform technique was applied to demonstrate that the intrinsic mode functions with a cycle of nearly 23 h at levels below 800 m, and the instantaneous amplitudes of inertial events (0.0417–0.0476 h $^{-1}$ frequencies) have large values at 300–600 m. The variations in the occurrences of LLJs suggested connections between the formation mechanisms of LLJs and the South-west Jet stream, steady occupation of synoptic-scale pressure system, and land–sea temperature contrasts. 相似文献
11.
Two cases of low-level jet events and the interaction of the involved physical processes are investigated. The vertical distribution of the dominant atmospheric motions is studied, using data from a SODAR-RASS system and in situ instrumentation, at a coastal region of the Eastern Mediterranean (Messogia Plain in Attica—Greece). The first low-level jet (LLJ) case was observed during the cold period, after the passage of a cold front and could be characterized as purely synoptic. Coherent inertial motions were found to follow the frontal surface at both the wind components, with larger amplitudes at the alongfront wind component, a fact consistent with the deformation theory. The contribution of the diurnal cycle was found weak in both the components, due to the cloudiness and the small diurnal temperature range, while the synoptic scale dominated the northerly wind component. The second LLJ case represents two successive summertime large-scale jets. The absence of cloudiness and the increased solar radiation provided a favorable environment for the development of local flows which interacted with the synoptic wind field. This interaction led to a LLJ with an oscillating core and a variable depth. The diurnal cycle had a strong imprint on the wind component along the sea breeze direction (easterly), while the synoptic variations dominated the northerly wind component. Strong amplitudes of a coherent quasi 2-day variation were also found in both the cases. 相似文献
12.
低空急流的研究进展与展望 总被引：6，自引：0，他引：6
低空急流与强降水事件、空气污染、风能利用、航空安全、沙尘暴、森林火灾及其他诸多天气、气候现象存在着密切的联系,因此自发现之日起便受到人们的广泛关注。在过去的半个多世纪中,中外气象学家围绕着低空急流事件开展了大量的研究并取得了丰硕的研究成果。对这些成果进行了综合回顾,重点对低空急流的分类和定义、分布状况及结构特征,低空急流形成演变机制,低空急流与降水及其他领域的关系等三个方面的研究工作进行了总结。最后通过对比分析中外针对低空急流事件的研究历史和现状,指出了中国现有研究工作中所存在的诸如低空急流选取标准宽松、观测数据缺乏且质量控制不完善、低空急流自身特征与形成演变机制研究数量和深度有限、交叉领域研究工作匮乏等方面的问题,并对未来的研究方向进行了展望。 相似文献
13.
低空急流的单多普勒速度特征 总被引：8，自引：2，他引：8
对低空急流的单多普勒天气雷达径向速度图像进行数值模拟，并利用合肥多普勒天气雷达的观测资料，对2000年6月24—27日安徽省境内发生的暴雨过程进行了分析。结果表明：不论风向如何变化，低空急流的多普勒正负速度区关于显示中心成对称分布，从多普勒速度的零速度线分布可以得到实际风场的风向廓线。在多普勒速度图上，安徽淮北地区暴雨过程主要发生在正负速度中心的中心轴的左侧200km范围内。低空西南急流的维持，为暴雨的产生和维持提供了充足的水汽。 相似文献
14.
Nocturnal CO2 exchange over a tall forest canopy associated with intermittent low-level jet activity
A. Karipot M. Y. Leclerc G. Zhang T. Martin G. Starr D. Hollinger J. H. McCaughey G. R. Hendrey 《Theoretical and Applied Climatology》2006,85(3-4):243-248
Summary Nocturnal eddy-covariance carbon dioxide fluxes have uncertainties arising from non-stationary atmospheric processes. Low-level
jets (LLJ) are one of the prominent nocturnal boundary-layer phenomena observed over non-mountainous terrain, and are capable
of generating shear and turbulence close to the ground. The influence of intermittent LLJ activity on nocturnal carbon dioxide
exchange measurements is investigated using wind profile observations and eddy-covariance flux measurements over a tall forest
canopy. Results suggest that the buildup and venting of CO2 are closely associated with LLJ activity during the night. Of significance in quantifying nocturnal fluxes, this paper demonstrates
how low-level jet activity introduces sporadic coupling between the canopy and the atmosphere. 相似文献
15.
Yong CHEN Junling AN Yele SUN Xiquan WANG Yu QU Jingwei ZHANG Zifa WANG Jing DUAN 《大气科学进展》2018,35(12):1455-1468
Three-month wind profiles, 260 m PM1 concentrations [i.e., particulate matter (PM) with an aerodynamic diameter ≤ 1 μm], 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. 相似文献
16.
We investigate the mesoscale dynamics of the mistral through the wind profiler observations of the MAP (autumn 1999) and ESCOMPTE (summer 2001) field campaigns. We show that the mistral wind field can dramatically change on a time scale less than 3 hours. Transitions from a deep to a shallow mistral are often observed at any season when the lower layers are stable. The variability, mainly attributed in summer to the mistral/land–sea breeze interactions on a 10-km scale, is highlighted by observations from the wind profiler network set up during ESCOMPTE. The interpretations of the dynamical mistral structure are performed through comparisons with existing basic theories. The linear theory of R. B. Smith [Advances in Geophysics, Vol. 31, 1989, Academic Press, 1–41] and the shallow water theory [Schär, C. and Smith, R. B.: 1993a, J. Atmos. Sci. 50, 1373–1400] give some complementary explanations for the deep-to-shallow transition especially for the MAP mistral event. The wave breaking process induces a low-level jet (LLJ) downstream of the Alps that degenerates into a mountain wake, which in turn provokes the cessation of the mistral downstream of the Alps. Both theories indicate that the flow splits around the Alps and results in a persistent LLJ at the exit of the Rhône valley. The LLJ is strengthened by the channelling effect of the Rhône valley that is more efficient for north-easterly than northerly upstream winds despite the north–south valley axis. Summer moderate and weak mistral episodes are influenced by land–sea breezes and convection over land that induce a very complex interaction that cannot be accurately described by the previous theories. 相似文献
17.
对2018年8月28日北京首都航空公司CBJ5759航班在中国澳门国际机场发生重着陆事件分析结果,显示:(1)机场位于低空切变线南侧,低空西南急流与海陆地形辐合作用下形成的暖区局地对流引发分散性短时强降水和弱雷暴;对流北侧突然增强的偏南风使机场跑道附近顺风增加,引发低空风切变;(2)高分辨率数值模拟结果表明低空风切变发生时段内存在西南急流脉动,急流北侧的风场由西南风转为偏南风,促使海陆边界的热力和动力不稳定条件加强,有利于局地对流系统发展和其辐散出流增强,加速边界层内风场变化;(3)当飞机在下降过程中经过对流系统前侧激发的偏南风急流区时,水平风的垂直切变形成的顺风切变大于垂直风变化,增加的顺风使飞机空速减小,导致飞机升力减小并造成重着陆;(4)此次事件中天气系统的变化通过影响对流的发展间接促进低空风切变的发生,因此可在对沿海机场的低空风临近预报时通过加强对海上风场变化的监测来预估一定风险。 相似文献
18.
Thara V. Prabha Monique Y. Leclerc Anandakumar Karipot David Y. Hollinger Erich Mursch-Radlgruber 《Boundary-Layer Meteorology》2008,126(2):219-236
Observations of low-level jets (LLJs) at the Howland AmeriFlux site in the USA and the jet’s impact on nocturnal turbulent
exchange and scalar fluxes over a tall forest canopy are discussed. Low-frequency motions and turbulent bursts characterize
moderately strong LLJs, whereas low-frequency motions are suppressed during periods with strong LLJs and enhanced shear. An
analysis based on the shear-sheltering hypothesis seeks to elucidate the effect of LLJs on flux measurements. In the absence
of shear sheltering, large eddies penetrate the roughness sublayer causing enhanced mixing while during periods with shear
sheltering, mixing is reduced. In the absence of the latter, ‘upside-down’ eddies are primarily responsible for the enhanced
velocity variances, scalar and momentum fluxes. The integral length scales over the canopy are greater than the canopy height.
The variance spectra and cospectra from the wavelet analysis indicate that large eddies (spatial scale greater than the low-level
jet height) interact with active canopy-scale turbulence, contributing to counter-gradient scalar fluxes. 相似文献
19.
F. Replogle Jr. 《Boundary-Layer Meteorology》1983,27(4):327-343
A time-dependent integrated dynamical boundary-layer model is used to study various features of the nocturnal low-level jet (LLJ). The basic concept is that of Thorpe and Guymer (1977). It is extended by entrainment processes, advection and an equation for the upper height of the turbulent layer. Applications show the role of the energy terms and how the LLJ changes considerably under synoptic forcing processes of variable geostrophic wind. 相似文献
20.
The characteristics of low-level jets (LLJ) observed at the “Centro de Investigacion de la Baja Atmósfera” (CIBA) site in Spain are analysed, focussing on the turbulence generated in the upper part of the jet, a feature that is still to be thoroughly understood. During the Stable Boundary Layer Experiment in Spain (SABLES) 1998, captive balloon soundings were taken intensively, and their analyses have highlighted the main characteristics of the jet’s wind and temperature structure, leading to a composite profile. There are indications that the turbulence has a minimum at the level of the wind maximum, with elevated turbulence in a layer at a height between two and three times that of the LLJ maximum, but no direct measurements of turbulence were available at these heights. In September 2001, a 100-m tower at the same site was re-instrumented to give turbulence measurements up to 96.6 m above ground level. All occurrences of LLJ below this height between September 2002 and June 2003 have been selected and significant turbulence above the LLJ has been found. Simulations with a single-column turbulence kinetic energy model have been made in order to further investigate the generation of elevated turbulence. The results correlate well with the measurements, showing that in the layer above the LLJ, where there is significant shear and weakly stable stratification, conditions are conducive to the development of turbulence. 相似文献