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1.
An automated procedure employing principal-component analysis and a two-stage cluster analysis was developed to classify the synoptic meteorological conditions prevailing over Urumqi, one of the most heavily polluted cities in the world. Six clusters representing different circulation patterns and air-mass characteristics were classified using surface- and upper-meteorological variables during the heating period from 2001 to 2008, and the relationships between synoptic clusters and air quality were evaluated. The heaviest air-pollution episodes occurred when Urumqi was in either an extremely cold, strong anticyclone or at the front of a migrating cyclone, both with light winds, wet surface air, and relatively dry upper air. Moderate pollution was seen when Urumqi was in the pre-cold/cold frontal passages with lower temperatures and light winds or moderate anticyclone with relatively warmer, drier air. When Urumqi was at the front of a migrating anticyclone or in a weak anticyclone with moderate winds and most warm, dry air, or in the cold/post-cold frontal passages with relatively strongly northerly airflows and precipitation, relatively good air quality could be seen. These results suggest that air pollution in Urumqi is very closely related to the synoptic meteorological conditions, which provides an important basis for not only the prediction and control of urban air-quality problems here but also for the analysis of the differential impacts of weather and pollution on human morbidity.  相似文献   

2.
Summary  The development and movement of sea breezes under the influence of a thermally induced synoptic coastal trough and coastal terrain are simulated. These simulations are analyzed in the context of an extensive observational data set. The synoptic trough acts to determine the presence and intensity of the sea breeze through the advection of warm air in the surface layer whereas local topography acts to enhance the breeze and turn the low-level flow. Interaction between the sea breeze circulation and the trough assists trough movement across the coastline. Received June 16, 1999/Revised November 3, 1999  相似文献   

3.
The structure and evolution of the sea breeze in the north-west part of the Mediterranean (Catalonia, north-east Spain) is studied both experimentally and, predominantly, using numerical models to increase understanding of sea-breeze structure and three-dimensional (3D) pollution distributions in coastal environments. Sea-breeze components are modelled and analyzed using the fifth-generation Pennsylvania State University–National Centre for Atmospheric Research Mesoscale Model (MM5). The results show that the growth and structure of the sea-breeze circulation is modulated by the synoptic flow and especially by the complex topography of the area. 3D pollution transport in a sea breeze is modelled by coupling the MM5 to the Community Multiscale Air Quality (CMAQ) model, with results indicating that topography and synoptic flow are the main factors modulating horizontal and vertical pollutant transport in sea-breeze episodes. In this way, horizontal dispersion is limited by the complex topography of the area, whilst the sea-breeze flow is intensified by anabatic upslope winds that contribute to vertical pollutant transport. The numerical model results also indicate that the sea-breeze circulation with a weak return flow at upper levels grows due to a synoptic onshore wind component. However, such a sea-breeze circulation is capable of transporting pollutants towards the coast.  相似文献   

4.
A high-resolution mesoscale numerical model (MM5) has been used to study the coastal atmospheric circulation of the central west coast of India, and Goa in particular. The model is employed with three nested domains. The innermost domain of 3 km mesh covers Goa and the surrounding region. Simulations have been carried out for three different seasons—northeast (NE) monsoon, transition period and southwest (SW) monsoon with appropriate physics options to understand the coastal wind system. The simulated wind speed and direction match well with the observations. The model winds show the presence of a sea breeze during the NE monsoon season and transition period, and its absence during the SW monsoon season. In the winter period, the synoptic flow is northeasterly (offshore) and it weakens the sea breeze (onshore flow) resulting in less diurnal variation, while during the transition period, the synoptic flow is onshore and it intensifies the sea breeze. During the northeast monsoon at an altitude of above 750 m, the wind direction reverses, and this is the upper return current, indicating the vertical extent of the sea breeze. A well-developed land sea breeze circulation occurs during the transition period, with vertical extension of 300 and 1,100 m, respectively.  相似文献   

5.
Summary This work presents a numerical study of non-reactive pollutant dispersion in sea breeze conditions. Sea breeze circulation is investigated using a 3-D mesoscale meteorological model. Simulation was conducted for the area of Tarragona (Spain) which has an important petrochemical industry in the coastal region and complex terrain. Results from the meteorological model were used as input to a Lagrangian particle model in order to analyze the pollutant dispersion of an elevated plume emitting near the shoreline. The simulation was performed for 24 h and an analysis of the meteorological and concentration fields was untertaken for this time period. The results are compared with measured surface data. Good correlation exists between observed and simulated conditions indicating that the coupling of the meteorological and particle models provides a good tool for analyzing air pollution in complex situations.With 13 Figures  相似文献   

6.
Synoptic patterns identified by an automated procedure employing principal- component analysis and a two-stage cluster analysis, and backward trajectory analysis clustered by the HYSPLIT4.9 model were used to examine air quality patterns over¨ Uru¨mqi, China, one of the most heavily polluted cities in the world. Six synoptic patterns representing different atmospheric circulation patterns and air-mass characteristics were classified during the winter heating periods from 2001 to 2008, and seven trajectory clusters representing different paths of air masses arriving at ürümqi were calculated during the winter heating periods from 2005 to 2008. Then air quality was evaluated using these two approaches, and significant variations were found across both synoptic patterns and trajectory clusters. The heaviest air-pollution episodes occurred when ürümqi was either in an extremely cold, strong anticyclone or at the front of a migrating cyclone. Both conditions were characterized by with light winds, cold, wet surface air, and relatively dry upper air. ürümqi was predominately influenced by air masses from the southwest and from local areas. Air pollution index (API) levels were highest for air masses originating from the southwest with a longer path or for the local area, because of transport from semi-desert/desert regions by strong winds and because of local heavy pollution emissions, respectively. The interactions between these two analytical approaches showed that poor diffusion conditions, together with local circulation, enhanced air pollution, besides, regional air-mass transport caused by strong winds contributed to serious air quality under relatively good diffusion conditions.  相似文献   

7.
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8.
Summary The wind regime of the Lake Tekapo Basin is examined with reference to the interaction of multi-scale local, regional and synoptic circulations. Analysis of the historical wind direction record from Mt John identifies airflow from three principal directions to most frequently affect the study area. Both seasonal and diurnal trends in the frequency of each directional category are identified, which reflect the influence of local thermal forcings and seasonal changes in synoptic circulation on the Lake Tekapo windfield. Meteorological observations from a network of automatic weather stations and anemographs within the study area identified Lake Tekapo to generate its own circulation system, a lake/land breeze. This combines with the larger scale valley wind, which during ideal conditions continues after sunset in the upper reaches of the lake catchment. During light to moderate foehn northwesterly conditions, the combined lake breeze/valley wind system remains decoupled from the prevailing synoptic airstream. Towards evening when local thermal circulations weakened, a channelised foehn airstream often becomes dominant over the entire field area. Observations made during this investigation have a number of applied implications with respect to air pollution dispersion modelling and forecasting within alpine lake basins.With 7 Figures  相似文献   

9.
海陆风环流在天津2009年9月26日局地暴雨过程中的作用   总被引：8，自引：4，他引：4  
利用常规天气资料、地面加密自动站资料、天津中尺度模式产品资料以及卫星云图和多普勒雷达等资料,对2009年9月26日出现在天津地区的局地暴雨过程进行天气学、动力学诊断分析和中尺度分析.结果表明,本次暴雨的天气尺度主要的影响系统是500 hPa高空槽,中尺度系统是由海陆风环流形成的地面中尺度辐合线.降水前天津市具有较好的热力不稳定条件,较好的能量储备,有利的动力条件,一定量级的水汽辐合,边界层的东风将渤海的水汽输送至天津市,是本次过程的主要水汽来源.天气尺度的积云对流与海风锋的碰撞触发不稳定能量的释放,引发第一阶段的强降水,边界层东风急流再度加强所产生的抬升效应引发第二阶段的降水.中尺度切变线通过提供带状辐合上升运动起着胚胎和组织积云对流的作用,使得降水回波和对流云团沿中尺度切变线发展、加强和移动,产生了明显的列车效应,导致了这场历史罕见的秋季局部暴雨过程,也充分凸显出海陆风环流对本次暴雨的重要作用.  相似文献   

10.
Sea-breeze dynamics in the Marseille area, in the south of France, is investigated in the framework of the ESCOMPTE experiment conducted during summer 2001 in order to evaluate the role of thermal circulations on pollutant transport and ventilation. Under particular attention in this paper is the sea-breeze channelling by the broad Rhône valley and the narrow Durance valley, both oriented nearly-north–south, i.e., perpendicular to the coastline, and its possible impact on the sea-breeze penetration, intensity and depth, which are key information for air pollution issues. One situation of slight synoptic pressure gradient leading to a northerly flow in the Rhône valley (25 June 2001) and one situation of a weak onshore prevailing synoptic wind (26 June 2001) are compared. The impact of the Rhône and Durance valleys on the sea-breeze dynamics on these two typical days is generalized to the whole ESCOMPTE observing period.The present study shows by combining simple scaling analysis with wind data from meteorological surface stations and Doppler lidars that (i) the Durance valley always affects the sea breeze by accelerating the flow. A consequence is that the Durance valley contributes to weaken the temperature gradient along the valley and thus the sea-breeze circulation. In some cases, the acceleration of the channelled flow in the Durance valley suppresses the sea-breeze flow by temperature gradient inhibition; (ii) the Rhône valley does not generally affect the sea breeze significantly. However, if the sea breeze is combined with an onshore flow, it leads to further penetration inland and intensification of the low-level southerly flow. In this situation, lateral constriction may accelerate the sea breeze. Simple scaling analysis suggests that Saint Paul (44.35°N, about 100 km from the coastline) is the lower limit where sea breeze can be affected by the Rhône valley. These conclusions have implications in air quality topics as channelled sea breeze may advect far inland pollutants which may be incorporated into long-range transport, particularly in the Durance valley.  相似文献   

11.
A linked three-dimensional PBL and dispersion model in coastal regions   总被引：2，自引：0，他引：2  
In this paper a 3-D mesoscale PBL dynamic prognostic model for a coastal region with complex terrain was developed to simulate the 3-D flow field under a local sea-land breeze circulation. The output from the PBL model was used as an input to an Eulerian numerical model which can be used to simulate finely the temporal and spatial distributions of an air pollutant (SO2) during a sea-land breeze developing in a coastal region. With respect to its use as a diagnostic model, only a few data would be required to simulate the background winds controlled by a larger scale synoptic system, and then provide initial winds for the PBL model.Having linked the three models and defined the coefficients of turbulent diffusion in a simple form, an integrated 3-D numerical air quality model suitable for the coastal environment was designed. The period of May 29, 1986 was selected for simulating and analysing the distribution of air pollutants over the coastal area of Bohai-sea in Northern China. The results indicated that the calculated concentrations corresponded with the observed ones on the whole. Thus this linked model has been shown to be feasible and useful in practice.  相似文献   

12.
造成北京PM10重污染的二类典型天气形势   总被引：11，自引：5，他引：6  
利用北京空气质量监测资料和NCEP再分析资料,分析了北京发生PM10重污染的天气形势。研究表明:1)虽然北京地区PM10重污染(API指数3级以上)每年只有10 d左右,但与之关联的轻微或轻度空气污染(API指数3级)天数,却可能占全年3级污染总天数的40%-50%。因此,分析研究造成北京PM10重污染的天气形势,对于空气污染的预警预报以及污染源的控制和管理,都具有十分重要意义。2)通过海平面气压场的主观分析,确定了二类北京PM10重污染的典型天气形势,即高压南下东移阻滞型和与北上台风(或热带低压)相关联的弱高压控制型,并指出了后者在2008年奥运会期间,对开展北京空气污染预报和污染控制的指导作用。  相似文献   

13.
The characteristics of the sea breeze in the Attica region of Greece, in which Athens is located, have been studied for occasions of weak synoptic-scale pressure gradient. The analysis is based on synoptic observations from six meteorological stations, three on the coast and three inland. The three inland stations and one of the coastal stations lie almost in a straight line at different distances from the coast. For each meteorological station, the basic characteristics of the sea breeze were determined, i.e.,
  1. The mean number of sea-breeze days for each calendar month.
  2. The monthly mean wind speed for each synoptic hour.
  3. The times of onset and cessation of the sea breeze.
  4. The monthly vector mean wind, and its constancy ‘Constancy’ is defined as 100{itV{inr}/V{ins}}, where {itV{inr}} is the magnitude of the vector mean wind, and {itV{ins}} is the scalar mean wind speed. See Brooks and Carruthers (1953). (In this paper, the factor 100 is not used.) for each synoptic hour.
  5. For days on which there was a sea breeze at Helliniko (the coastal reference station), the percentage number of days on which there was also a sea breeze at the given station.
An attempt was also made to determine further characteristics, such as the inland penetration of the sea breeze, its depth, the spatial and temporal variation of wind speed and direction, and the existence of the return flow. Finally, the properties of the land breeze are briefly outlined.  相似文献   

14.
Summary  According to past experience, the nearly stagnant conditions caused by the presumed equilibrium between the Saronikos Gulf sea breeze and an opposing synoptic flow is identified as the principal mechanism leading to high pollution episodes in Athens during the summer. However, previous experimental work has not examined in detail the interaction of the sea breeze flow with the opposing background flow. In this context, recent experimental work covering the basic key-locations of the Athens Basin focused on the inland propagation of the southerly sea breeze from the coast to the northern part of the basin mainly under moderate northerly background wind. During this campaign, a network of four meteorological stations established along the Athens Basin and a high range acoustic sounder at the centre of Athens operated over a two months time period in the summer of 1993. In addition, tethered balloon flights in the centre of Athens and on a sea vessel about 15 km offshore were employed during an experimental day with moderate opposing background wind. The results from this experimental campaign include the documentation of the sea breeze delay and its intensity as a function of a sea breeze index and features of the vertical structure of the sea breeze over land as well as over sea. Received March 20, 1998 Revised October 12, 1998  相似文献   

15.
The daytime boundary-layer heating process and the air-land heat budget were investigated over the coastal sea-breeze region by means of observations over the Sendai plain in Japan during the summer. In this area, the onset of the sea breeze begins at the coast around 0900 LST, intruding about 35 km inland by late afternoon. The cold sea breeze creates a temperature difference of over 10°C between the coastal and inland areas in the afternoon. On the other hand, warm air advection due to the combination of the counter-sea breeze and land-to-sea synoptic wind occurs in the layer above the cold sea breeze in the coastal region. Owing to this local warm air advection, there is no significant difference in the daytime heating rate over the entire atmospheric boundary layer between the coastal and inland areas. The sensible heat flux from the land surface gradually decreases as distance from the coastline increases, being mainly attributed to the cold sea breeze. The daytime mean cold air advection due to the sea breeze is estimated asQ adv local =–29 W m–2 averaged over the sea breeze region (035 km from the coastline). This value is 17% of the surface sensible heat fluxH over the same region. The results of a two-dimensional numerical model show that the value ofQ adv local /H is strongly affected by the upper-level synoptic wind direction. The absolute value ofQ adv local /H becomes smaller when the synoptic wind has the opposite direction of the sea breeze. This condition occurred during the observations used in the present study.  相似文献   

16.
To examine the correlation between the sizes of sea breeze fronts and pollutants under the influence of synoptic fields, a numerical simulation was conducted in the southeast coastal area of the Korean Peninsula, where relatively high concentrations of pollutants occur because of the presence of various kinds of industrial developments. Sea breeze and sea breeze front days during the period 2005-09 were identified using wind profiler data and, according to the results, the number of days were 72 and 53, respectively. When synoptic forcing was weak, sea breeze fronts moved fast both in horizontal fields and in terms of wind velocity, while in the case of strong synoptic forcing, sea breeze fronts remained at the coast or moved slowly due to strong opposing flows. In this case, the sea breeze front development function and horizontal potential temperature difference were larger than with weak synoptic forcing. The ozone concentration that moves together with sea breeze fronts was also formed along the frontal surfaces. Ozone advection and diffusion in the case of strong synoptic forcing was suppressed at the frontal surface and the concentration gradient was large. The vertical distribution of ozone was very low due to the Thermal Internal Boundary Layer (TIBL) being low.  相似文献   

17.
The atmospheric boundary layer (ABL) is characterized by the turbulence eddies that transport heat, momentum, gaseous constituents and particulate matter from Earth’s surface to the atmosphere and vice versa. Thus, the determination of its height has a great importance in a wide range of applications like air quality forecasting and management. This study aims at estimating the height of the ABL in a suburban environment and at investigating its temporal variation and its relationship with meteorological variables, like temperature and wind. For this purpose, radiosonde data from the suburban area of Thessaloniki, Greece, are analyzed. The data analysis reveals that ABL height is usually below 200 m in the morning hours during all seasons of the year and that is also low when near-surface temperature and wind speed are low too. Additionally, noon ABL height exhibits a strong seasonal variation, reaching higher values during summer than during winter.Very high values of ABL height, of the order of ~3,000 m, are occasionally observed in Thessaloniki during summer. Moreover, sea breeze development during summer is related to a slight reduction of the ABL height.  相似文献   

18.
This paper presents a method for grouping weather types that occur over an area, which combines meteorological parameters, reflecting air mass characteristics at the surface, with synoptic conditions prevailing over an area. Five quantitative meteorological parameters are used in the procedure: temperature, precipitation, relative humidity, wind velocity and sunshine duration. In addition, two qualitative variables related to the prevailing circulation type and whether it is cyclonic or anticyclonic are also included. The study period is 43 years (1958–2000) and is restricted to the cold and wet sub-period of the year, December–March. Weather types are defined using a relatively new method of cluster analysis, two-step cluster analysis, which allows the simultaneous use of both quantitative and qualitative variables. The aim of the present study is to distinguish primary weather patterns so that the investigation into the relationship between weather patterns and circulation types will be more effective. For Athens, six weather types are created, whereas for Thessaloniki five are produced. For both stations, only two weather types are related to anticyclonic situations. The majority of the identified weather types correspond to a distinctive and well-defined synoptic situation. Each weather type differs from the others, not only in terms of the circulation conditions referring to it, but also with reference to meteorological variables such as temperature and precipitation. The results of the evaluation of the aforementioned procedure are considered to be highly satisfactory.  相似文献   

19.
The sea-land breeze circulation （SLBC） occurs regularly at coastal locations and influences the local weather and climate significantly. In this study, based on the observed surface wind in 9 conventional meteorological stations of Hainan Island, the frequency of sea-land breeze （SLB） is studied to depict the diurnal and seasonal variations. The statistics indicated that there is a monthly average of 12.2 SLB days and an occurrence frequency of about 40%, with the maximum frequency （49%） in summer and the minimum frequency （29%） in autumn. SLB frequencies （41%） are comparable in winter and spring. A higher frequency of SLB is present in the southern and central mountains due to the enhancement effect of the mountain-valley breeze. Due to the synoptic wind the number of SLB days in the northern hilly area is less than in other areas. Moreover, the WRF model, adopted to simulate the SLBC over the island for all seasons, performs reasonably well reproducing the phenomenon, evolution and mechanism of SLBC. Chiefly affected by the difference of temperature between sea and land, the SLBC varies in coverage and intensity with the seasons and reaches the greatest intensity in summer. The typical depth is about 2.5 km for sea breeze circulation and about 1.5 km for land breeze circulation. A strong convergence zone with severe ascending motion appears on the line parallel to the major axis of the island, penetrating 60 to 100 km inland. This type of weak sea breeze convergence zone in winter is north-south oriented. The features of SLBC in spring are similar both to that in summer with southerly wind and to that in winter with easterly wind. The coverage and intensity of SLBC in autumn is the weakest and confined to the southwest edge of the central mountainous area. The land breeze is inherently very weak and easily affected by the topography and weather. The coverage and intensity of the land breeze convergence line is significantly less than those of the sea breeze. The orographic forcing of the cen  相似文献   

20.
Meteorological measurements were carried out at North Chennai semi rural area during pre-monsoon period as a part of an air quality study program. Analysis of the data showed the effects of coastal terrain namely the land-sea breeze circulation, temperature cooling during the sea breeze, difference in onset times at these sites etc. Sea breeze onset was observed with a sharp turning of the wind from westerly to south easterly associated with rise in wind speed. Advection speed of the front was about 2.0 m s− 1. A simple mesoscale meteorological model (MAM-I) developed at Kalpakkam for coastal atmospheric dispersion estimation was used to simulate the observed characteristics. All the major features observed could be simulated by the model while significant difference was noticed in sea breeze frontal movement. MAM results were also inter-compared with MM5. There were no significant differences in the estimate of mean parameters by both the models. It is concluded that the simple model, which takes less run time in a desktop PC, is adequate enough for practical application of providing wind field for plume dispersion models at coastal sites.  相似文献   

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