Local Wind System Research Articles

Further development of the urban bioclimate model UBIKLIM, taking local wind systems into account

The urban bioclimate model UBIKLIM is an application model providing an assessment on the influence of urban climate on human beings. On a calm summer's day with fair weather conditions it calculates the meteorological parameters air temperature, humidity, wind velocity and short and long wave radiation based on a digital height model and appropriate land use information. These meteorological parameters determine the heat exchange conditions of human beings and thus can be analyzed with the help of the Klima-Michel model into physiologically significant terms. The result is a bioclimate map on a scale that is appropriate for climate-related planning in an urban environment. In urban areas lying in a distinct relief, a superimposed wind regime, such as a down valley wind, can modify the bioclimate considerably. Up to now it was not possible for UBIKLIM to take this situation into account. In this point UBIKLIM has been developed further, but its easily applicable character has been preserved. This has been realized, firstly by combining an orographically induced wind field with the one calculated in UBIKLIM as a function of land use esp. of urban structure, and secondly by introducing an algorithm by working out conveyance processes in the direction of the superposed wind field. UBIKLIM fills the gap between meso and micro scale models. Results of the further developed model are shown in the example of the city of Freiburg im Breisgau which is influenced by the distinct relief at the southern edge of the Black Poorest.

Topographic Distortion of a Cold Front over the Snake River Plain and Central Idaho Mountains

The topographic distortion of a cold front over the Snake River Plain (SRP) and central Idaho Mountains on 3 December 1998 is described using high-density surface observations from MesoWest, a collection of meteorological networks over the western United States. Although relatively unperturbed upstream of central Idaho, the cold front became distorted as it was deflected and accelerated up the low-elevation SRP, where a pronounced frontal bulge developed. The speed of the cold front over the SRP was comparable to the magnitude of the postfrontal winds that, due to terrain channeling, were oriented normal to the front. Meanwhile, the front advanced more slowly over the central Idaho mountains and southwest Montana, becoming increasingly diffuse over the former. Eventually, cold air surrounded the central Idaho Mountains and the two portions of the cold front merged over eastern Idaho. The cold front intensified as it moved from the eastern to central SRP, with rapid changes in temperature and pressure observed at locations in the southern half of the SRP. Intensification of the cross-frontal temperature gradient in this region appeared to be the result of confluence between southerly prefrontal winds, which experienced downslope warming to the lee of the Jarbidge–Caribou Highlands, and terrain-channeled postfrontal winds. Although the rapid changes in temperature and pressure suggested that the front developed the local structure of a gravity current, the frontal motion over the SRP was not consistent with gravity current theory and instead appeared to be the result of advection of the front by the terrain-induced flow field. The case study illustrates the value of high-density and multielevation MesoWest observations for advancing knowledge of frontal evolution over the western United States and improving operational surface analyses. Such observations aid in the identification of large-scale airmass and circulation changes that can be masked by boundary layer processes, valley inversions, and local and mesoscale terrain-induced wind systems.

Climatic patterns in a tropical rainforest in Brunei

Meteorological parameters were monitored on an hourly basis over ten months during 1991–2, from altitudes of 45 and 913 metres in an undisturbed tropical rainforest in Brunei, near the north‐west coast of Borneo. In general, the observed characteristics of the climate accorded with the regional meteorological systems and with published results from other studies in northern Borneo, although a greater degree of temporal variability was apparent. The seasonal variability was probably enhanced by the El Niño Southern Oscillation event of early 1992. Rainfall events were typically highly variable in nature, although storm intensity profiles were broadly similar. High magnitude and high intensity events are common among the large total number of events. More rain, of generally higher intensity, fell on the mountain. The total daily solar energy receipt was similar at both altitudes owing to greater cloud cover on the mountain. Temperatures varied significantly with season at both altitudes and the mean lapse rate was 4.5°C/km. Relative humidity at 913 metres tended to be significantly higher during the day and significantly lower at night than at 45 metres. Wind directions were dominantly controlled by local mountain and valley wind systems. Wind speeds were significantly higher during the dry seasons and at the higher altitude. Previous studies have shown that small but significant variations in meteorological parameters can have distinct ecological responses, and rainfall characteristics are important controls on geomorphological processes.

Simulation of the air quality during a field study for the city of Graz

The research project DATE Graz (Dispersion of Atmospheric Trace Elements taking the city of Graz as an example) aimed at the investigation of mesoscale γ pollution dispersion of a city in complex terrain. The winter episode investigated here was characterised by an anticyclonic fair weather situation. Local wind systems developed together with strong temperature inversions. During such an episode air quality is dominated by emissions from within the city. The city of Graz is situated in the southeast of the Alps in the transition area of mountainous to flat land. The city itself is located in the valley of the river Mur, which forms a basin surrounded by small mountains. In order to understand the emitter–receptor relationship a mesoscale dispersion model was applied for the simulation of air quality during the winter episode. Input for the simulation was the emission inventory and extensive meteorological measurement data. Results of the simulation reflect the distinct patterns of daily variations of air quality level measured. The influence of meteorology, emission patterns and chemical reactions are evident and can be qualitatively and partly quantitatively simulated by the model. A validation attempt was made using air quality data from the monitoring network. The introduction shows the importance of anticyclonic fair weather conditions on pollution dispersion in mountainous regions. Section 2 describes the meteorological situation and the instrumentation during the winter measurement campaign. Section 3 deals with the simulation model, initial and boundary conditions and the emission inventory for the city. In Section 4 the simulation results are compared to measurements. Finally conclusions are drawn.

Vertical Interactions in a Nocturnal Multi-Scale Wind System Influenced by Atmospheric Stability in a Coastal Area

The winter wind regime of Goteborg, located on the West coast of Sweden, is composed of three different wind systems besides the ambient wind; a nocturnal low level jet (NLLJ), a winter land breeze (WLB) and an urban heat island circulation (UHIC). An inversion divides the air column into two layers, one between 10 – 50 m and one between 50 – 100 m. The UHIC is located in the lower layer, the WLB in the top layer and the NLLJ above the top layer. The intensity of the interacting processes depends on the stability of each layer as calculated from the bulk Richardson number (BRilow and BRihigh) using continuous data collected during four years (1991 – 94) from two sites (one within and one outside the urban area) and sampled at three levels. In the evening the WLB develops from the ground level and increases in height until after midnight. At about the same time an UHIC develops in the urban area, below the WLB and causing an uplift of the latter. However, at both sites the WLB does not exceed the 100 m level. At this time BRi in both layers are below one resulting in continuous coupling between the WLB, the UHIC layers and the regional wind. Consequently, the exchange of momentum is still effective between all layers and this is highlighted by a change in the wind direction and a regulation of wind-speed to more constant levels. When BRihigh≥1, the layers become frictionally decoupled, as indicated by a return in the wind direction in the top level to the regional wind, and an acceleration of the top wind. The top level then becomes incorporated in to a nocturnal low-level jet (NLLJ) system. The normally acknowledged development of the NLLJ, with a start around sunset, is in this case delayed for several hours at the top level. The reason for this is that there are meso-scale/local wind systems present in layers beneath the jet causing an interaction between the layers. In the morning, when the layers are again coupled the top layer wind is once more influenced by the WLB and therefore changes direction and speed. The local and meso-scale wind systems thus delay the current nocturnal wind development.

An urban climate analysis of Graz and its significance for urban planning in the tributary valleys east of Graz (Austria)

In Graz, the capital of the Austrian province of Styria, located southeast of the main ridge of the Alps, an extensive urban climate analysis was successfully completed in 1995. In the following paper the most important features of the Graz city climate like the different local wind systems, the heat islands as well as the fog and inversion conditions shall be described and illustrated with the help of maps and diagrams. Furthermore, the description of the spreading conditions of air pollutants in selected inversion weather situations will shall play an important role. The results of the study, above all the map of city climatopes are based on the latter a map of planning tips serve as an important basis for urban planning and have already been used for the setting up of a land-use and development plan. Finally the paper will focus its interest on the exceptional quality of the tributary valleys east of Graz, where as a consequence of their highly significance for fresh air supply, a zoning into areas of restricted and banned construction has been carried out. This inclusion of climatological results in urban planning is unique within Austria and is now also being practised in other cities of the province of Styria.

Rapid urban growth, land-use changes and air pollution in Santiago, Chile

This paper is a contribution to the understanding of the topoclimatic and environmental geography of the basin where Santiago — one of the most polluted Latin American city – is located. In the first part, land-use change is analysed looking at the climatic transformation caused by the rapid transit from natural semiarid surface to urban areas. In the second part, seasonal weather and daily cycles of slope winds and the available ventilation are described trying to relate those patterns with the spatial distribution of air pollution. A combination of meteorological, geographical and cultural factors explain extreme air pollution events: meteorologically, Santiago is under permanent subsidence inversion layers. Geographically, the city is located in a closed basin surrounded by mountains. Culturally, the urban area has the highest population concentration (40% of the national total), industries (near 70% of the total) and vehicles, which are the main sources of smog. The urban and suburban transport system is based on a large number of buses (diesel) and private cars, both experiencing a rapid growth from the past few years. The city and specially the transport system generates high emissions of pollutant, but the natural semiarid deforested soils and slopes are also important sources. The local wind system can explain the differential spatial distribution on the concentration of air pollutants in the city and its periphery. In winter (rain season) concentrations of particulate matter are higher at the centre and the SW part of the city. The andean piedmont area (E part of the city) shows minimum values, suggesting major ventilation effects of slope and valley winds. Ozone exceeds air quality standards in summer (dry season) at all sites in the centre and periphery. However, the O 3-concentrations are higher on preferred residential areas located at the piedmont area (E part of the city), suggesting air pollution transport effects. Currently, there is no consideration of these local climatic features in the process of urban planning.

Metphomod - a Numerical Mesoscale Model for Simulation of Regional Photosmog in Complex Terrain: Model Description and Application During Pollumet 1993 (Switzerland)

A prognostic three-dimensional Eulerian model for the simulation of summer smog was implemented which fully couples meteorological processes and gas phase chemistry. The model includes modules for atmospheric dynamics, atmospheric turbulence, transport, gas-phase chemistry, short- and long-wave radiation transfer, and surface interactions, including emission and deposition of trace gases. The model was tested in a numerical study of 29–30 July 1993 on the Swiss Plateau and compared to the data of the POLLUMET measurement campaign. Model results were found to be in good agreement with measurements. The model revealed a complex interaction of long range transport, dispersion of plumes from urban areas, and local influences of the complex Swiss topography on local wind systems, and local ozone concentration maxima during that episode.

Development and interaction of thermally driven flows over Attiki peninsula under northerly background wind—a case study

A simulation of the thermally driven flow field prevailing over Attiki peninsula in Greece was made, by using the DEMOKRITOS Transport Code System applicable to terrains of high complexity. Two particular days included in the MEDCAPHOT experimental campaign over Attiki, i.e. 14 and 15 September 1994, dominated by mesoscale flow systems and characterised by high pollution levels, were simulated. The model reproduced reasonably the main features of the local wind systems, as well as their interaction, exhibiting a satisfactory agreement with the observations.

High resolution simulation of a flow past the Pyrenees

A hydrostatic model is applied to a case study from the Pyrenean field experiment PYREX. The results from this simulation are compared with measurements, with the aim to evaluate the model behaviour in the case of a flow past a steep orography. The initial and boundary data, which were used for the simulation, were produced with the T213 reassimilation system at Reading by the European Center for Medium-Range Weather Forecasts (ECMWF). The comparison of the results with observations show that the local wind systems are captured reasonably well by the model. In particular the evolution of two counter rotating eddies in the lee of the Pyrenean mountain range are simulated correctly in space and time. Also the calculated orographic drag and vertical wave momentum flux agreed well with the measurements.

Weather forecasting for aviation and marine operations in the Antarctic Peninsula region

AbstractAn account is given of one Austral summer's experience of forecasting for flying activities and marine operations around the Antarctic Peninsula. Data available included surface and upper‐air observations, analyses and forecasts from the UK Meteorological Office global, 19‐level model and AVHRR satellite imagery. The numerical analyses and forecasts provided good guidance and correctly represented most of the synoptic‐scale features. A number of mesoscale disturbances affected the central Peninsula area and the AVHRR imagery was very valuable in allowing the development and track of these systems to be followed. The major problems were the absence of observations to the west of the Peninsula, the lack of radiosonde ascents from the Peninsula itself and the complexity of local wind systems as a result of the topography. Forecasting frontal activity over the ocean areas was also very difficult because of the unavailability of precipitation forecasts in the GRIB data.

An assessment of boundary-layer air mass characteristics associated with topographically-induced local wind systems

Measured and derived meteorological parameters are used to examine the changes in air mass associated with local winds of differing origin. Research conducted explores the usefulness of wet bulb potential temperature, equivalent potential temperature, virtual potential temperature and relative humidity as indicators of air mass change during sea breeze, foehn wind and nocturnal drainage flow events. The complex interactions between these different topographically-induced wind systems in South Canterbury, New Zealand, provide an environment in which marked changes in air mass characteristics are common. Results demonstrate that under a considerable range of boundary-layer conditions, measured wet bulb potential temperature when used in conjunction with windspeed and direction enables quick and accurate determination of air mass origin. Relative humidity was also found to respond closely to changes in local air mass type, but its dependence on air temperature makes it a less reliable indicator.

Air quality modeling for the city of Graz

Graz, a historical grown city in the south-east of Austria, sometimes faces problems with air pollution, mainly during wintertime. The old part of the city is the largest residentially used historical downtown in Central Europe. Due to its geographical position at the southeastern edge of the Alps, Graz often has weather situations with calm winds and strong inversions between October and March. The local wind system is marked by wind shears: near the surface, cold air flows in from the south, while in higher altitudes warm air from the north flows over the basin of Graz. During these winterperiods with mighty inversions air quality values exceed the threshold limits. The reason is that the old structure of the downtown area with narrow streets and a lot of old domestic heating systems in many of the old buildings causes relatively high pollution levels. In the winter of 1988/89, the NO2 threshold values for smog-alarm (0.8 mg/m3, 3-h mean value) were exceeded several times at three air quality monitoring stations in the city of Graz. Therefore, a research project was initiated with the aim to find out the reasons for the bad air quality. The project comprised the setting up of an emission inventory as well as meteorological measurement campaigns and numerical simulations concerning the pollution dispersion in the area of Graz. The following report will try to show the interaction of the emission inventory on one hand and the determinations of flow conditions and pollutant dispersion on the other hand in order to analyze the air quality in the city. The emission inventory contains the emissions of air pollutants in a high temporal and spatial resolution. Before determining the surface flow fields, the meteorological conditions leading to the high pollution values were analyzed. After that, the boundary conditions were defined with the help of tethered balloon measurements. With these boundary conditions, quasi-steady-state flow fields were simulated. The dispersion of pollutants was calculated in a transient form using the stored flow fields. Conversion of pollutants was determined with the help of a parameterized version of the Eschenroeder-Martinez reaction mechanism. The period of winter 1990/91 with the highest pollution concentration was simulated to validate this model. The results show that the simulated and measured values of CO, NO and NO2 correspond well with each other in the centre of the city, while the correspondence is not as good in the outskirts of the city were lower pollution levels are observed. It turned out that the suggested methodology is well suited for analyzing winter situations with high pollution levels.

Combination of Local Wind Systems under Light Gradient Wind Conditions and Its Contribution to the Long-Range Transport of Air Pollutants

The meteorological structure and transport mechanism of long-range transport of air pollutants from the coastal region to the mountainous inland region were investigated using joint field observation data. The observations were conducted during 26–30 July 1983 over a wide area from the coastal region around Tokyo Bay to the mountainous region located in central Japan. Air, polluted around the Tokyo Bay area during the early morning remained there until noon, being transformed by photochemical reactions. It was then transported inland, at first by the extended sea breeze and thereafter by the large-scale wind system, toward the thermal low generated in the mountainous central region. At about 1600 Japan Standard Time (JST), polluted air penetrated into the mountainous region, and after sunset it drained down along the valley in the form of a gravity current. The path of the polluted air was in good agreement with the air trajectory started Tokyo at an altitude of 100 m, calculated from pilot-balloon data. Its transport speed reached a maximum value (7.5 m s−1) at about 1500 JST, when the thermal low was most fully developed. Daytime temperatures over the mountainous central region (Saku) were higher than those over the Kanto Plain (Takasaki), and the thermal effects of the mountainous central region (average height; 1200 m) extended to more than 3000 m in height. The vertical temperature profiles at these locations showed a linear variation in the daytime. At the 700 m level, the temperature difference between these locations attained 3.6°C when the thermal low was most fully developed. The pressure difference between the mountainous central region (Matsumoto) and the Kanto Plain (Kumagaya) was calculated using the vertical temperature profiles observed at 1500 JST. The pressure difference between these locations decreased with altitude and became almost zero at an altitude of 1900 m, indicating the vertical extent of the thermal low. From these results it became obvious that the creation of the thermal low and the wind blowing toward the thermal low was due to the difference in temperature between the air above the plain and that on the plateau.

Mechanism of spring high oxidant episode— A meteorological analysis in and around the Hokuriku district, Japan

In order to clarify the mechanism of spring surface level high oxidant episodes, both upper and surface level ozone observations were carried out from April to June 1983. The results were analyzed using aerological data and AMeDAS (Automated Meteorological Data Acquisition System) data. During the observation period, there were 11 days with high oxidant episodes which were defined as when the recorded ozone concentration exceeded 100 ppb at any of five stations. Meteorological conditions under which the surface episodes occurred were examined for three cases when upper level ozone distributions were observed, and the mechanism of the episode were investigated. In this paper, the analysis for one case is explained in detail. For this case: (i) the peak time of oxidant (ozone) concentration at each surface station was controlled by the transition pattern of photochemical oxidant under the local wind system and (ii) the stratospheric air with high concentrations of ozone intruded into the troposphere through the tropopause gap (tropopause folding) behind the cyclone and continued to descend gradually. In the lower troposphere, it descended further due to the influence of topography, and contributed to high surface oxidant episodes. The descent of stratospheric ozone was related to the position of both cyclones and anticyclones. The other two cases had similar upper meteorological conditions but different surface wind systems such as land and sea breeze.

Inland penetration of the sea breeze over the suburban area of Tokyo

Observational results of the structure of the sea breeze over the urban and suburban areas of Tokyo for four summer days are presented. On two of these days, the inland penetration of the sea breeze front could be clearly traced. In one case, the sea breeze was first observed along the shores of Tokyo Bay around 0900 JST, and propagated in three hours through the Tokyo City area, the width of which is about 20 km. It then advanced inland at a rate of 16 km h−1. Prior to the arrival of the sea breeze at the suburban site, the mixing height had remained at about 600 m for four hours. With the arrival of the sea breeze front, accompanied by an abrupt change in wind speed and direction, the mixing height increased sharply to 1700 m. It is suggested that this behavior and the structure of the front are intensified due to the urban effect, or the difference in the thermal characteristics between the urban and rural areas. On the days without a sea breeze front, the land breeze system during the early morning was less intense, allowing the sea breeze to develop simultaneously with the inland valley wind and easily form a large-scale local wind system during the morning hours. In both cases, the vertical motion accompanying the local wind system works as a feedback mechanism to control the local winds by modifying the thermal and pressure fields.

Tropical Forest Bird Counts and the Effect of Sound Attenuation

Tropical Forest Bird Counts and the Effect of Sound Attenuation

Valley winds and slope winds ? Observations and elementary thoughts

This paper presents a state-of-the-art account of valley wind research, with a bias towards a typical large Alpine valley and towards weak-gradient synoptic conditions. At the center of our attention is the quasiperiodic thermal forcing mechanism which drives the local wind system, in particular the role of slope winds and of topographic relief. Slope winds are at the small-scale end of a whole spectrum of thermally direct circulations which act to transmit the sensible heat input along the slopes to the valley atmosphere via compensating vertical motions. We surmise that the dynamics of slope winds, which react instantly to changes of the insolation or radiation balance, is characterized by local, instantaneous equilibria, rather than by conventional entrainment and boundary layer concepts. As described by Steinacker, the area-height distribution of a valley segment is a fundamental geometric factor which affords a quantitative measure of the slope area available for heat exchange, and of the air volume which must be heated or cooled. Using this concept, one can easily explain why the daily range of the valley mean temperature is, on average, more than twice as large as that of the atmosphere over the adjacent plain. This horizontal temperature contrast between plain and valley, reversing sign twice daily, builds up a corresponding pressure contrast hydrostatically, thereby causing up- and downvalley winds.

Spatial patterns of atmospheric pollen transport in a montane region

Annual pollen deposition (pollen cm −2 yr −1) was sampled for 6 yr in the southern Sierra Nevada, the Owens Valley, and the Inyo Mountains of central California. Spatial pollen distributions were examined for anemophilous plants which are limited to growth sites (1) at high elevations on one or both mountain ranges, (2) on lower mountain slopes, and (3) on the Owens Valley floor, Pollen deposition values for high- and low-elevation plants changed by a factor of 5 to 10 between adjacent sample sites which straddle boundaries of the plant communities in which the source plants grow. Pollen deposition values were high and variable within communities in which the species grew. Pollen deposition beyond source populations was low and uniform despite great differences in distance of sites from pollen sources. The step function that seems to characterize pollen distribution patterns implies that pollen from distant populations may be of little value in interpreting vegetation stability and change reflected by fossil pollen stratigraphy. The physical isolation of pollen embedded in the local mountain-valley wind system from that in the prevailing westerlies may explain part of the spatial distribution of the pollen.

An Examination of the Role of Local Wind Systems in the Concentration and Dispersion of Smoke Pollution in Christchurch, New Zealand

An Examination of the Role of Local Wind Systems in the Concentration and Dispersion of Smoke Pollution in Christchurch, New Zealand