Extreme daily precipitation in Belgrade and their links with the prevailing directions of the air trajectories

The main goal of this study was to present the statistical analysis of the daily precipitation exceeding 20 mm in Belgrade and their links with the prevailing directions of the air trajectories at 500, 1,500 and 5,000 m. For the extreme precipitation analysis, the generalised extreme value (GEV) distribution and generalised Pareto distribution (GPD) were used. The estimated return levels for 100- and 10-year return periods using GEV and GPD were obtained. Four-day backward trajectory simulations were conducted for days with precipitation exceeding 20 mm to investigate the regional transport of the air moisture towards Belgrade using the hybrid single-particle Lagrangian integrated trajectory model. The air trajectories were classified into 13 trajectory categories by the origin and direction of their approach to Belgrade. Three of the most frequent categories of air flow from south-west, south-east and north-west contributed to more than a half of the observed precipitation. Almost 74.5 % of precipitation totals in Belgrade fell during the warmer part of the year. These were directly connected with the intensive convection of colder and humid, usually maritime, air masses.     

Determination of O3-, CO- and PM10-transport in the metropolitan area of São Paulo, Brazil through synoptic-scale analysis of back trajectories

Summary This study is aimed to qualitatively analyze the impact of remote sources on air pollution in the Metropolitan Area of S?o Paulo (MASP). Air-mass back trajectories from June to August of 1999 were calculated using a three-dimensional kinematic trajectory model and grouped into trajectory clusters. Correlations of individual trajectory clusters with O₃, CO and PM₁₀ concentrations were determined. In this model, trajectories were obtained using the means of the three wind velocity components (U, V and W). The three-dimensional wind field was derived from the Regional Atmospheric Modeling System, and downscaling was employed. Coarse and fine nested grids (64-km and 16-km horizontal resolution, respectively) were used. Every 12 h (at 00 and 12 UTC), a back-trajectory ensemble, using the 64-km grid, was calculated for five defined endpoints at intervals of 0.5° N, S, E and W of the MASP (λ = 23° 33′S, ϕ = 46° 45′W), that last endpoint being centered in the MASP. To analyze cluster trajectories, the five trajectory ensembles from each day were allocated into one of four clusters (northeast, southeast, southwest or northwest quadrant) based on the origin of the trajectory over 4 days. Days on which all five trajectories originated from the same quadrant were classified as “core” days. Core day concentrations of CO, O₃ and PM₁₀ during the study period were evaluated. The results show that, during the study period, air-mass back trajectories in the MASP originated from all four quadrants: northeast (32%), southeast (12%), southwest (19%) and northwest (37%). Our analysis of back-trajectory clusters in the MASP suggests a transport to ambient air of O₃ precursors and O₃ from the northeast region, which is associated with agricultural activities involving biomass burning.     

合肥市PM10 输送轨迹分类研究

应用聚类分析的方法,对2001—2005年合肥市逐日72 h后向轨迹按季节分类,结合PM10日均浓度观测资料,分析了不同输送轨迹与该地区PM10浓度之间的关系。结果表明:不同方向后向轨迹所对应的PM10平均浓度有明显不同;最高PM10平均浓度对应的后向轨迹在春、秋和冬季都是来自西北方向,它们与季节平均的相对距平分别为44%,20%和31%;夏季为东北方向,与季节平均的相对距平为20%;其次为本地轨迹,各季的相对距平分别为5%,16%,18%和17%。根据分析得出合肥地区6组易于出现高浓度PM10的后向轨迹及对应的天气形势,并简要分析了其特征。气溶胶的远程输送主要发生在自由大气层,区域输送主要发生在边界层内。合肥地区大气污染事件超过50%与远程输送有关。移动快的气团不一定对应低浓度的PM10。     

ISENTROPIC TRAJECTORY ANALYSES OF POLLUTANT TRANSPORT IN NORTHEAST ASIA-INFLUENCE ON CHINA FROM NEIGHBORING COUNTRIES*

The transport of air pollutants from several big cities in the north of China and the neighboring countries is researched by using the isentropic trajectory model. The trajectories are calculated twice daily for the cities in January, April. July and October for the period of 1992-1994. The statistical method has been used to deal with trajectory dots at intervals of 30 min forthe for ward and backward trajectories during 0-24 h and 24-48 h. The probability distribution diagrams of trajectory show clearly the ensemble properties of isentropic trajectories for each city and the dominant transport directions of pollutants. They possess notable seasonal variations. The forward trajectory areas of the Ulaan Baatar in Mongolia can spread over North China. and those of the Chita in Russia can influence Northeast China except in summer. In July the forward trajectory of Pyongyang and Seoul can extend northward to the boundaries of China.     

ISENTROPIC TRAJECTORY ANALYSES OF POLLUTANT TRANSPORT IN NORTHEAST ASIA-INFLUENCE ON CHINA FROM NEIGHBORING COUNTRIES

The transport of air pollutants from several big cities in the north of China and theneighboring countries is researched by using the isentropic trajectory model. The trajectories arecalculated twice daily for the cities in January, April. July and October for the period of 1992-1994. The statistical method has been used to deal with trajectory dots at intervals of 30 min forthe forward and backward trajectories during 0-24 h and 24-48 h. The probability distributiondiagrams of trajectory show clearly the ensemble properties of isentropic trajectories for each cityand the dominant transport directions of pollutants. They possess notable seasonal variations. Theforward trajectory areas of the Ulaan Baatar in Mongolia can spread over North China. and thoseof the Chita in Russia can influence Northeast China except in summer. In July the forwardtrajectory of Pyongyang and Seoul can extend northward to the boundaries of China.     

东北亚地区污染物输送的等熵轨迹分析——周边国家对中国的影响

利用等熵轨迹模式研究了中国北方和邻国几个大城市排放的污染物的输送趋势。计算了１９９２－１９９４年期间１，４，７和１０月的每天两次轨迹，并以这些城市为目标，对其前向或后向轨迹线上每３０ｍｉｎ的轨迹点作统计，画出等熵轨迹概率分布图。这些图形表明，等熵轨迹的概率分布能很好地反映污染物的中、远程输送且有明显的季节变化。就前向轨迹区而言，在除夏季外的其它季节里，蒙古乌兰巴托的轨迹区能覆盖到中国华北，俄罗斯的赤塔也能影响到中国东北的大兴安岭地区。而平壤和汉城的前向轨迹区在夏季可向北伸展到中国     

Climatic change in mixed-layer trajectories over large regions

Summary Using a modified version of the NOAA ARL/ATAD model, a series of over 300,000 mixed-layer back trajectories were calculated in eighteen hour time steps through the period 1948–1985 for seventeen trajectory endpoints in and around the state of Virginia. Results of these trajectory runs were aggregated both seasonally and annually to a spatial grid system covering approximately the eastern two-thirds of the United States. From this were generated plots of trajectory frequencies, residence times and transport times. A principal components analysis was performed on the spatial distribution of the gridded trajectory frequency data. The first principal component is dominated by mixed-layer-flow from the Ohio Valley and the Upper Midwest. A time-series plot of this component indicates a dramatic increase in this northwesterly flow over the study period, especially in the 1950s and early 1960s. A possible link between this observed phenomenon and anthropogenic climate alteration is discussed.With 7 Figures     

The relationship between synoptic scale airflow direction and daily rainfall: a methodology applied to Devon and Cornwall, South West England

Summary Trans-scale relationships are established between fluctuations in the direction of the geostrophic flow over the British Isles and spatial variations in rainfall over Devon and Cornwall, South West England. The rationale for using such an approach is to provide the basis for assessing changes to the region’s rainfall climatology that may result from possible future enhanced greenhouse effect forced alterations to large-scale wind flow patterns. A new method, the concentration factor (CF), that relates rainfall totals to the frequency of the flow, is applied to investigate spatial variations in rainfall totals at twelve stations in the two counties under eight wind direction groups (N, NE, E, SE, S, SW, W, NW). S and SW flow types are found to produce the highest daily rainfall totals at all locations, with the three easterly groups (NE, E, SE) yielding higher daily precipitation intensities than the maritime NW group. Inter-annual and seasonal variations in daily wind direction – rainfall (WD/R) relationships are then assessed at two contrasting sites in Cornwall (St. Mawgan, Culdrose) using 40 years of data (1957–96). In general, there is a trend over this period toward maritime airflows (S, SW, W, NW) producing higher daily rainfall totals, with the continental groups (N, NE, E, SE) yielding lower totals relative to their frequency of occurrence. The trend toward maritime airflows producing higher rainfall totals is in line with recent trends in the North Atlantic Oscillation (NAO). Notable seasonal variations in WD/R relationships over Cornwall are interpreted in terms of the location’s exposure to the prevailing wind, sea temperature variations and the orography of the South West Peninsula. Received October 23, 2000/Revised February 2, 2001     

西藏昌都强降水的环流分型及其水汽轨迹分析

利用西藏自治区昌都市及周边18个气象观测站1989~2018年降水资料和NCEP/NCAR再分析资料,首先进行强降水个例筛选,在大气环流分型的基础上,应用后向轨迹模型分析了暴雨和大雨在不同环流形势下的水汽输送轨迹。结果表明：昌都产生强降水的大气环流形势分为高原低涡、高原槽及高原切变线3种类型,其中以高原切变线型为主,而降水强度最大的是高原槽型。不同环流形势下暴雨发生时三个等压面的水汽轨迹方向基本一致,均以偏南气流为主,水汽来源相对集中,容易在短时间内造成强降水;而大雨发生时三个等压面的水汽轨迹多以偏南气流为主,与暴雨相比,水汽来源较为分散且水汽条件较差。夏季昌都的水汽来源主要以印度洋、孟加拉湾、阿拉伯海、南海为主,最远可以追溯到大西洋。     

Comparison of statistical clustering techniques for the classification of modelled atmospheric trajectories

In this study, we used and compared three different statistical clustering methods: an hierarchical, a non-hierarchical (K-means) and an artificial neural network technique (self-organizing maps (SOM)). These classification methods were applied to a 4-year dataset of 5 days kinematic back trajectories of air masses arriving in Athens, Greece at 12.00 UTC, in three different heights, above the ground. The atmospheric back trajectories were simulated with the HYSPLIT Vesion 4.7 model of National Oceanic and Atmospheric Administration (NOAA). The meteorological data used for the computation of trajectories were obtained from NOAA reanalysis database. A comparison of the three statistical clustering methods through statistical indices was attempted. It was found that all three statistical methods seem to depend to the arrival height of the trajectories, but the degree of dependence differs substantially. Hierarchical clustering showed the highest level of dependence for fast-moving trajectories to the arrival height, followed by SOM. K-means was found to be the least depended clustering technique on the arrival height. The air quality management applications of these results in relation to PM₁₀ concentrations recorded in Athens, Greece, were also discussed. Differences of PM₁₀ concentrations, during certain clusters, were found statistically different (at 95% confidence level) indicating that these clusters appear to be associated with long-range transportation of particulates. This study can improve the interpretation of modelled atmospheric trajectories, leading to a more reliable analysis of synoptic weather circulation patterns and their impacts on urban air quality.     

Climatology of Regional Flow Patterns around Basel

Summary Recently a method has been developed to classify local-scale flow patterns from the wind measurements at a dense network of stations. It was found that in the area around Basel twelve characteristic near-surface flow patterns occur. However, as the dense network of stations was running for one year only during the MISTRAL field experiment, no reliable climatology of the flow patterns can be inferred from these data. Mainly the annual cycle is not well determined from a single year of observations. As there exist several routinely operated meteorological stations with longer data records in and near the area discussed, a method was searched to identify the local flow patterns from the wind observations at these few permanent stations. A linear discriminant analysis turned out to be the best method. Based on wind data from 11 stations which were simultaneously in operation during 1990–1995, a six-year climatology of the flow patterns could be obtained and compared to synoptic weather types. Although there are relations to existing synoptic classes there is no unique correspondence between them and the flow patterns. Received February 24, 1997 Revised June 9, 1997     

中国沿海城市的气块后向轨迹分析

该文讨论了大连、青岛、上海、福州、厦门和广州６个沿海城市的气块长距离后向输送轨迹。输送层假设在１５００ｍ上。计算了１９８５年１、４、７、１０月份的轨迹。轨迹分析得出：①气块后向轨迹与天气形势和季节有关，且南北方有差异；②北方沿海城市的７２小时气块后向轨迹输送距离要比南方沿海城市远些。     

Statistical Characterization of the Flow Structure in the Rhine Valley

The flow structure at the intersection between the Rhine and the Seez valleys nearthe Swiss city of Bad Ragaz has been documented by means of wind and pressuremeasurements collected from 9 September to 10 November 1999 during the MesoscaleAlpine Programme (MAP) experiment. To understand better the dynamics of theageostrophic winds that develop in this part of the Rhine valley, some key questionsare answered in this paper including the following: (i) How does air blow at theintersection of the Rhine and Seez valleys? and (ii) what are the dynamical processes(mechanical or thermal) driving the flow circulations in the valleys? Statistical analysis of the wind and pressure patterns at synoptic scale and at the scaleof the valley shows that five main flow patterns, SE/S, NW/W, NW/N, NW/S, SE/N(wind direction in the Seez valley/wind direction in the Rhine valley) prevail. The SE/S regime is the flow splitting situation. It is mainly driven by a strong pressure gradient across the Alps leading to foehn, even though some nocturnal cases are generated bylocal thermal gradients. The NW/W and NW/N regimes are mechanically forced bythe synoptic pressure gradient (as the flow splitting case). The difference between thetwo regimes is due to the synoptic flow direction [westerly (northerly) synoptic flowfor the NW/W (NW/N) regime], showing that the Rhine valley (particularly from BadRagaz to Lake Constance) is less efficient in channelling the flow than the Seez valley.The NW/S (occurring mainly during nighttime) and SE/N (occurring mainly duringdaytime) regimes are mainly katabatic flows. However, the SE/N regime is also partlyforced at the synoptic scale during the foehn case that occurred between 18 October and 20 October 1999, with a complex layered vertical structure. This analysis also shows that, contrary to what was observed in a broad section of theupper Rhine valley near Mannheim, very few countercurrents were observed near BadRagaz where the valley width is much smaller.     

中国沿海城市的气块后向轨迹分析

该文讨论了大连、青岛、上海、福州、厦门和广州６个沿海城市的气块长距离后向输送轨迹。输送层假设在１５００ｍ上，计算了１９８５年１、４、７、１０月份的轨迹，轨迹分析得出：（１）气块后向轨迹与天气形势和季节有关，且南北方有差异；（２）北方沿海城市的７２小时气块后向轨迹输送距离要比南方沿海城市远些。     

中国区域主要颗粒物及污染气体的排放源清单

长三角4个省会（直辖市）城市（上海、南京、合肥、杭州）中,合肥与南京的PM_2.5浓度演变有较高的一致性。应用聚类分析的方法对2013-2015年合肥非降水日（日降水量低于10 mm）100 m高度（代表近地层）和1000 m高度（代表边界层中上部）的72 h后向轨迹进行分类,结合合肥2013-2015年PM_2.5日均浓度资料,探讨近地层和边界层中上部输送轨迹与长三角西部PM_2.5浓度的关系。近地层和边界层中上部分别得到7组和6组不同的后向轨迹;不同输送轨迹对应的PM_2.5浓度、重污染（重度以上污染,PM_2.5日均浓度大于150 μg/m³）天数、能见度、地面风速、相对湿度等都有显著不同,尤其是在近地层。100 m高度,平均长度最短、来向偏东的轨迹组对应的PM_2.5浓度均值最高（约是组内均值最低值的2倍）、重污染天数最多,且占比最高（30%）,重污染日对应的气流在过去72 h下降高度均值仅28 m,明显低于其他PM_2.5污染等级日;来向偏西北、长度较短的轨迹组,PM_2.5浓度均值和重污染天数为第2高,这一类轨迹占比14%,气流到达本地前存在明显的下沉运动,反映了远距离输送加剧本地PM_2.5重污染的特征。这两类轨迹常对应PM_2.5日均浓度的上升。PM_2.5平均浓度最低的2个轨迹组分别是来自东北和西南的较长轨迹组,所占比例分别为6.4%和10.3%,这2类轨迹往往对应着PM_2.5日均浓度下降。1000 m高度的结果与100 m高度结果类似,但PM_2.5平均浓度的组间差异不及100 m高度,与2001-2005年PM₁₀浓度与输送轨迹的关系不同。对3 a中84个重污染日两个高度的后向轨迹进行聚类,近地层和边界层中上部各得到7类和6类PM_2.5重污染日的天气形势。近地层92%的重污染日对应的海平面气压形势场上,从华北到华东属于均压区,气压梯度小,轨迹来向以偏东到偏北方向为主,垂直方向延伸高度在950 hPa以下。1000 m高度,77%的重污染日属于相对较短的轨迹组,对应的850 hPa高度场特征为从中国西北（新疆）到东南受高压控制,长三角或位于高压底部,或位于两高压之间的均压区。这对PM_2.5浓度预报有较好的指示意义。     

On the effect of large-scale atmospheric transport on chemistry and amount of atmospheric precipitation in the center of European Russia

The dependence of precipitation amount, acidity, and ionic composition on the atmospheric circulation is studied based on the computation of the back trajectories over the period of 1982–1993. Quantitative estimates of basic parameters of trajectories are derived, and their significant difference in the summer and wintertime is considered. The trajectory frequency for the cases with precipitation in the center of European Russia is computed at the regular grid points depending on the diurnal precipitation amount, acidity, and sulfate/chloride ratio. It is shown that in case of abundant precipitation both in summer and winter the highest frequency of trajectories is observed in the same regions. In the case of low precipitation, seasonal differences are observed. It is revealed that precipitation with pH > 5 is mostly connected with the air inflow from Scandinavia and the north of European Russia, while during the trajectory passage over Central and Southern Europe pH < 5 prevails in precipitation. The chlorine ions prevail most often when trajectories pass over central regions of the Mediterranean and of Middle Asia and (although somewhat less) over Scandinavia and northern Russian seas.     

Impact of Air Transport on Seasonal Variations and Trends of Surface Ozone at Kislovodsk High Mountain Station

The impact of air transport on the surface ozone variations is analyzed at Kislovodsk High Mountain Station for the period 1989–1996 on the basis of 2D back trajectories. It was shown that the contribution of photochemical and dynamical processes is different for the different seasons. In summer months the surface ozone concentration is governed by photochemical ozone production in semi polluted air from the regions of Northern Caspian, Southern Ural and Volga region. Time of the seasonal ozone maximum appearance is defined by joint influence of the processes of photochemical production and destruction in the eastern sectors and advection from Ukraine and Central Europe. The value of the seasonal minimum is determined by the processes of ozone destruction in the air coming from northeastern direction in the stable frontal zone. Distribution of sectors of the air transport changes from year to year and it can partly explain strong negative trend of the surface ozone concentration at the site.     

TRAJECTORY ANALYSES OF THE DUSTSTORMS OVER EAST ASIA*

The transports of dust are calculated using 3-dimensional(3-D) trajectory method for three cases of duststorms in the terrain-following coordinate system,and the synoptic processes are also discussed for each case.The case of 17-20 April 1980,a severe duststorm was associated with the rapid development of a cyclone over the Mongolia Plateau.The dust moved from west to east across several deserts,formed a typical dust path in spring.The other two were weaker and the dust was triggered by the strong wind behind the cold front from northwest or north.Because the vertical velocity is considered in 3-D trajectory analysis,trajectories calculated should better reveal the transport rule of the dust particles and the results seem to be more consistent with the synoptic processes.The trajectory analysis on the 2-D isobaric surfaces is simpler but can be used only in the conditions with weak vertical wind shear and weak vertical velocity.The difference of trajectories at lower levels between two methods may be caused by the different treatment of orography.     

GPCC's new land surface precipitation climatology based on quality-controlled in situ data and its role in quantifying the global water cycle

In 1989, the need for reliable gridded land surface precipitation data sets, in view of the large uncertainties in the assessment of the global energy and water cycle, has led to the establishment of the Global Precipitation Climatology Centre (GPCC) at Deutscher Wetterdienst on invitation of the WMO. The GPCC has calculated a precipitation climatology for the global land areas for the target period 1951–2000 by objective analysis of climatological normals of about 67,200 rain gauge stations from its data base. GPCC's new precipitation climatology is compared to several other station-based precipitation climatologies as well as to precipitation climatologies derived from the GPCP V2.2 data set and from ECMWF's model reanalyses ERA-40 and ERA-Interim. Finally, how GPCC's best estimate for terrestrial mean precipitation derived from the precipitation climatology of 786 mm per year (equivalent to a water transport of 117,000 km³) is fitting into the global water cycle context is discussed.     

澳大利亚气象研究中心的轨迹计算及其应用

从天气分析和预报提供的后向轨迹信息可以加强预报指导。澳大利亚气象研究中心（ＢＭＲＣ）开发了一个计算三维后向和前向轨迹的软件，使用的资料是澳大利亚气象局有限区域３６小时３个风速分量的业务预报。它们有三种可用的输出形式；后向轨迹、前向轨迹及３６小时气块垂直位移等值线场。这个软件已用于分析诊断研究。