Proceedings of SPIE - The International Society for Optical Engineering, 2008
A comparative study of wintertime NO and NO 2 concentrations and the investigation of the influen... more A comparative study of wintertime NO and NO 2 concentrations and the investigation of the influences of meteorological conditions upon air quality in a valley near a motorway were performed in the Inn valley near Innsbruck, Austria. A DOAS with emitter/receiver unit and three retroreflectors was used for this study. One retroreflector was installed at a mast on the other side of the motorway (120 m path length) so that the path was about 10 m above motorway level. Another retroreflector was set up for a path parallel to the motorway and the third retroreflector was used to measure at a path perpendicular and away from the motorway. The path across the motorway was directly above the air quality monitoring station Vomp of Land Tyrol which is only three meters away from the motorway.
Proceedings of SPIE - The International Society for Optical Engineering, 2009
Beijing air quality suffers from frequently occurring inversion layers. These inversion layers ca... more Beijing air quality suffers from frequently occurring inversion layers. These inversion layers can last for several days and below these layers, pollution is accumulated. In the absence of inversions an urban boundary layer still exists delimiting the urban atmosphere from the free atmosphere. The height of this layer can potentially influence the urban atmospheric pollution. In both cases, particle concentration might change with height. A measurement campaign was performed to study those meteorological conditions, which are one of the causes for intensive air pollution in the region of Beijing during spring 2009. The mixing layer height (MLH) was studied by a ceilometer continuously. It was used to analyse the actual development of the height of inversion and boundary layers and the distribution of particles. Additionally, meteorological data from a radiosonde station are available. The measurements to study the vertical distribution of atmospheric layers in combination with particulate concentrations for specific times will be presented. The results of that campaign will be discussed.
Measurements and model developments with the objective to improve the quality and resolution of e... more Measurements and model developments with the objective to improve the quality and resolution of estimations of anthropogenic emissions are described. Measurement results on a chassis dynamometer were used to determine VOC profiles for exhaust gas emissions of passenger cars for different vehicle and fuel types and different driving modes. Further measurements resulted in emission factors and VOC profiles for lignite burning in residential stoves. Using remote sensing techniques benzene emission factors of gas stations and the efficiency of gasoline vapour recovery systems were measured.
Urban air quality and meteorological measurements were carried out in the region of Brescia (Ital... more Urban air quality and meteorological measurements were carried out in the region of Brescia (Italy) simultaneously to the acquisition of satellite data during winter and summer smog conditions in 1999. The main objectives of the campaigns were: delivery of data for the validation of air pollution interpretations based on satellite imagery, and determination of the aerosol optical thickness in spectral ranges similar to those used by satellites. During the winter campaign the ground-based network was complemented by local stations and by SODAR, DOAS, and FTIR remote sensing measurements. Size distributions of aerosol particles up to 4,000 m a.s.l. were measured by means of an ultra-light aircraft, which was also equipped with meteorological sensors and an ozone sensor. During the summer campaign an interference filter actinometer, an integrating nephelometer and an ozone LIDAR were operated additionally. The satellite images acquired and processed were taken from SPOT. Optical thickness retrieved from interference filter actinometer measurements were compared with the retrievals from the satellite imagery in the same spectral intervals. It is concluded that remaining aerosols in the reference image yield an off-set in the satellite retrieval data and that information about the vertical structure of the boundary layer is very important.
Remote Sensing of Clouds and the Atmosphere XIII, 2008
The impact of air traffic on the atmosphere was subject to several works in the last years. But l... more The impact of air traffic on the atmosphere was subject to several works in the last years. But little scientific work has been done concerning airport air quality. Airports themselves often measure concentrations of the main pollutants and use dispersion models to asses the air quality situation. Emission inventories of airport are not well known generally because a lot of different emission sources exist. A database is required to characterise real-world emission source strengths as well as air quality and meteorological data at airports that will serve as an input and as validation data for modelling work. Dedicated studies were performed to follow these objectives.
Mean seasonal profiles of wind speed, standard deviation of the vertical velocity and turbulence ... more Mean seasonal profiles of wind speed, standard deviation of the vertical velocity and turbulence intensity from SODAR measurements in three cities of different size, Moscow, Hanover and Linz, are compared to analytical approximations for the Prandtl and Ekman layer. Typical urban features in the profiles and differences to measurements at rural sites are discussed. Typical urban features are a greater slope in the wind profiles, enhanced turbulence intensities, and a vertical increase in magnitude of the turbulence. The analytical approach proposed by ETLING for the description of the vertical wind profile in the whole boundary layer is amended in the Prandtl-layer part by a correction function for atmospheric stability. The amended profile description turns out to render the best results for the approximation of urban wind profiles within the lowest 500 m above ground.
The objective of the studies presented in this paper is to present an analysis of spatial distrib... more The objective of the studies presented in this paper is to present an analysis of spatial distribution and temporal variation of particulate matter in Munich and Augsburg, Germany, and to identify and discuss the factors determining the aerosol pollution in both areas. Surface-based in-situ and remote sensing measurements of particle mass and particle size distribution have been performed in, around, and above the two cities. Two measurement campaigns were conducted in Munich, one in late spring and one in winter 2003. Another campaign has been on-going in Augsburg since 2004. Spatial and temporal variations are analyzed from this data (PM 10 , PM 2.5 and PM 1 ). There are higher particle mass concentrations at the urban site than at the surrounding rural sites, especially in winter. No significant difference in the major ionic composition of the particles between the urban and the rural site was detected. This is considered to be related to the spatial distribution of secondary inorganic aerosol that is more homogeneous than aerosol resulting from other sources like traffic or urban releases in general. During the measurement campaigns mixing layer heights were determined continuously by remote sensing (SODAR, ceilometer, RASS). Significant dependence of particle size distribution and particle mass concentration on mixing layer height was found. This finding paves the way to new applications of satellite remote sensing products.
Air quality is mainly determined by traffic, industrial and urban emissions as well as by specifi... more Air quality is mainly determined by traffic, industrial and urban emissions as well as by specific meteorological and topographic conditions. Focussing on nitrogen oxides and particulate matter, the temporal and spatial differences in air pollution in a deep Alpine valley with a major motorway were studied by a measurement campaign between November 2005 and February 2006 near Schwaz, Austria. The variation of air pollutant concentrations near the motorway was determined on the basis of path-averaged (DOAS) and in situ measurements. The layering of the valley atmosphere and the mixing-layer height were observed continuously by SODAR and ceilometer measurements. The winter-time weather conditions were characterized by exceptionally low temperature and high amount of snow in the valley. This resulted in the development of very stable cold pools with low wind speeds and accordingly high air pollution burden. During several periods the air pollutants accumulated from day to day and frequent exceedances of NO 2 and PM 10 thresholds were detected. Furthermore it could be concluded that the emission situation was not unusually high during these periods, at least concerning road traffic as the dominant source for nitrogen oxides. Analysis confirms that the typical weather phenomena associated with stable high-pressure regimes are the main factor for the observed pollution burden. During foehn and cold front passages, which interrupted these high pressure periods, concentration levels generally decrease at the valley ground and increase at the slope. Analysis reveals that this is a consequence of vertical mixing due to the influence of mountain specific wind systems, like thermally driven and quasi-periodic valley or slope winds. NO 2 concentration levels are a matter of concern regarding annual mean values as well as -previously not recorded -exceedances of the half-hourly threshold in severe winter conditions. Compared to previous investigations an increased NO 2 /NO x ratio was observed during the measurement campaign which is related to enhanced NO 2 emissions from road traffic in consequence to fleet composition and emission changes.
Ceilometer backscatter information is evaluated by comparison with parallel measurements. Data ar... more Ceilometer backscatter information is evaluated by comparison with parallel measurements. Data are presented from two years of combined ceilometer and RASS measurements at the same site and from comparison with a nearby (60 km) radiosonde for largerscale humidity information. This evaluation is designed to make MLH monitoring from ceilometer data more reliable. Finally, the detection of volcanic ash clouds with ceilometers is addressed.
An attempt is made to correlate the mixing heights, derived from ceilometer and Sodar measurement... more An attempt is made to correlate the mixing heights, derived from ceilometer and Sodar measurements, to those simulated by different atmospheric boundary-layer parameterization schemes. The comparison is performed at two sites (one suburban and one rural) close to Munich, Germany for two spring and two winter days. It is found that, under convective conditions, the mixing height determined, by both Sodar and ceilometer, corresponds to the middle or the top of the entrainment zone, respectively, as calculated from the eddy-viscosity profiles. Under stable conditions, the measured mixing height is related to the height where eddy viscosities attain their minimum values (Sodar) or to the height of residual mechanical turbulence (ceilometer). During a foehn case with weak turbulence, the measured mixing height from both Sodar and ceilometer is better inferred by considering the eddy-viscosity profiles during daytime and the height of the low-level jet during nighttime.
An observational dataset from a wintertime field campaign in the Inn Valley, Austria, is analysed... more An observational dataset from a wintertime field campaign in the Inn Valley, Austria, is analysed in order to study mechanisms of air pollution transport in an Alpine valley. The results illustrate three types of mechanisms: transport by a density current, backand-forth transport by valley winds, and transport by slope winds. The first type is associated with an air mass difference along the valley. Cooler air located in the lower part of the valley behaves like a density current and produces the advection of pollutants by upvalley winds. In the second type, strong horizontal gradients in pollution concentrations exist close to ground. Multiple wind reversals result in a back-and-forth transport of pollutants by weak valley winds. In the third type, upslope winds during daytime decrease low-level pollution concentrations and cause the formation of elevated pollution layers.
The typical features of a summer smog episode in the highly complex terrain of the Province of Bo... more The typical features of a summer smog episode in the highly complex terrain of the Province of Bolzano (Northern Italy) were investigated by numerical modelling with two non-hydrostatic models, ground-based monitoring stations, and vertical profiling with two sodars and an ultra-light aircraft. High ozone concentrations are most likely to appear in situations where the local circulation in the valleys is decoupled from the synoptic flow above during anticyclonic weather regimes. Both models (MM5 and TVM) produced similar results and were able to simulate the local winds in the valleys. A comparison of the measured data to the model simulation results made an evaluation of the performance of the two models in such complex terrain possible. Both models proved to be suitable for the simulation of the meteorological conditions during such summer smog episodes in complex terrain. r
The occurrence of nocturnal secondary ozone maxima was investigated by ground-level meteorologica... more The occurrence of nocturnal secondary ozone maxima was investigated by ground-level meteorological and air quality measurements in an urban park in Essen, Germany, during 29 individual summer measurement campaigns between May 1995 and September 1997. In addition, during an intensive measurement campaign in May 1997, SODAR measurements of wind and turbulence were made. The spatial and temporal distribution of nocturnal ozone maxima within the measurement network of the Environmental Protection O$ce of North Rhine}Westphalia was also analysed. Two case studies of nocturnal secondary ozone maxima are discussed in more detail. They represent two di!erent types of this phenomenon, associated with a nocturnal low-level jet (LLJ) and the passage of a front, respectively. In both cases, the nocturnal increase in ozone concentration was accompanied by a signi"cant increase in the standard deviation of the vertical wind speed across the lower stable boundary layer, indicating enhanced vertical mixing. During the LLJ case, ozone maxima were observed at 33% of the stations of the Environmental Protection O$ce network at approximately the same time. In the case of the front, the time of the ozone concentration rise could be allocated to the time of the passage of the front, moving from northwest to southeast across the study area. For the "rst time, the measurements presented here document turbulent mixing induced by shear forces in the whole layer between the core of the LLJ and the ground surface during secondary nocturnal ozone maxima.
A comparison of the determination of boundary-layer structures by a SODAR, by a RASS, and by a ce... more A comparison of the determination of boundary-layer structures by a SODAR, by a RASS, and by a ceilometer is presented. One important structure is the mixing-layer height (MLH). The comparison is focused on 3 days with an evolution of a convective boundary layer over a larger city in Germany. The three instruments give information that partly agree and partly complement each other. By this, a picture of the diurnal evolution of the vertical structure of this urban boundary layer is presented. The ceilometer gives information on the aerosol content of the air and the RASS provides a direct measurement of the vertical temperature distribution in the boundary layer. The RASS and the ceilometer add information on the moisture structure of the boundary layer that is not detected by the SODAR. On the other hand this comparison validates known techniques by which the MLH is derived from SODAR data. Especially the temperature information from the RASS agrees well with lifted inversions derived from the analysis of the SODAR data. The ceilometer, being the smallest instrument, has a potential to be used in future MLH studies. r
The spatial structure and the progression speed of the first ash layer from the Icelandic Eyjafja... more The spatial structure and the progression speed of the first ash layer from the Icelandic Eyjafjallajökull volcano which reached Germany on 16/17 April is investigated from remote sensing data and numerical simulations. The ceilometer network of the German Meteorological Service was able to follow the progression of the ash layer over the whole of Germany. This first ash layer turned out to be a rather shallow layer of only several hundreds of metres thickness which was oriented slantwise in the middle troposphere and which was brought downward by large-scale sinking motion over Southern Germany and the Alps. Special Raman lidar measurements, trajectory analyses and in-situ observations from mountain observatories helped to confirm the volcanic origin of the detected aerosol layer. Ultralight aircraft measurements permitted the detection of the arrival of a second major flush of volcanic material in Southern Germany. Numerical simulations with the Eulerian meso-scale model MCCM were able to reproduce the temporal and spatial structure of the ash layer. Comparisons of the model results with the ceilometer network data on 17 April and with the ultralight aircraft data on 19 April were satisfying. This is the first example of a model validation study from this ceilometer network data.
Proceedings of SPIE - The International Society for Optical Engineering, 2008
A comparative study of wintertime NO and NO 2 concentrations and the investigation of the influen... more A comparative study of wintertime NO and NO 2 concentrations and the investigation of the influences of meteorological conditions upon air quality in a valley near a motorway were performed in the Inn valley near Innsbruck, Austria. A DOAS with emitter/receiver unit and three retroreflectors was used for this study. One retroreflector was installed at a mast on the other side of the motorway (120 m path length) so that the path was about 10 m above motorway level. Another retroreflector was set up for a path parallel to the motorway and the third retroreflector was used to measure at a path perpendicular and away from the motorway. The path across the motorway was directly above the air quality monitoring station Vomp of Land Tyrol which is only three meters away from the motorway.
Proceedings of SPIE - The International Society for Optical Engineering, 2009
Beijing air quality suffers from frequently occurring inversion layers. These inversion layers ca... more Beijing air quality suffers from frequently occurring inversion layers. These inversion layers can last for several days and below these layers, pollution is accumulated. In the absence of inversions an urban boundary layer still exists delimiting the urban atmosphere from the free atmosphere. The height of this layer can potentially influence the urban atmospheric pollution. In both cases, particle concentration might change with height. A measurement campaign was performed to study those meteorological conditions, which are one of the causes for intensive air pollution in the region of Beijing during spring 2009. The mixing layer height (MLH) was studied by a ceilometer continuously. It was used to analyse the actual development of the height of inversion and boundary layers and the distribution of particles. Additionally, meteorological data from a radiosonde station are available. The measurements to study the vertical distribution of atmospheric layers in combination with particulate concentrations for specific times will be presented. The results of that campaign will be discussed.
Measurements and model developments with the objective to improve the quality and resolution of e... more Measurements and model developments with the objective to improve the quality and resolution of estimations of anthropogenic emissions are described. Measurement results on a chassis dynamometer were used to determine VOC profiles for exhaust gas emissions of passenger cars for different vehicle and fuel types and different driving modes. Further measurements resulted in emission factors and VOC profiles for lignite burning in residential stoves. Using remote sensing techniques benzene emission factors of gas stations and the efficiency of gasoline vapour recovery systems were measured.
Urban air quality and meteorological measurements were carried out in the region of Brescia (Ital... more Urban air quality and meteorological measurements were carried out in the region of Brescia (Italy) simultaneously to the acquisition of satellite data during winter and summer smog conditions in 1999. The main objectives of the campaigns were: delivery of data for the validation of air pollution interpretations based on satellite imagery, and determination of the aerosol optical thickness in spectral ranges similar to those used by satellites. During the winter campaign the ground-based network was complemented by local stations and by SODAR, DOAS, and FTIR remote sensing measurements. Size distributions of aerosol particles up to 4,000 m a.s.l. were measured by means of an ultra-light aircraft, which was also equipped with meteorological sensors and an ozone sensor. During the summer campaign an interference filter actinometer, an integrating nephelometer and an ozone LIDAR were operated additionally. The satellite images acquired and processed were taken from SPOT. Optical thickness retrieved from interference filter actinometer measurements were compared with the retrievals from the satellite imagery in the same spectral intervals. It is concluded that remaining aerosols in the reference image yield an off-set in the satellite retrieval data and that information about the vertical structure of the boundary layer is very important.
Remote Sensing of Clouds and the Atmosphere XIII, 2008
The impact of air traffic on the atmosphere was subject to several works in the last years. But l... more The impact of air traffic on the atmosphere was subject to several works in the last years. But little scientific work has been done concerning airport air quality. Airports themselves often measure concentrations of the main pollutants and use dispersion models to asses the air quality situation. Emission inventories of airport are not well known generally because a lot of different emission sources exist. A database is required to characterise real-world emission source strengths as well as air quality and meteorological data at airports that will serve as an input and as validation data for modelling work. Dedicated studies were performed to follow these objectives.
Mean seasonal profiles of wind speed, standard deviation of the vertical velocity and turbulence ... more Mean seasonal profiles of wind speed, standard deviation of the vertical velocity and turbulence intensity from SODAR measurements in three cities of different size, Moscow, Hanover and Linz, are compared to analytical approximations for the Prandtl and Ekman layer. Typical urban features in the profiles and differences to measurements at rural sites are discussed. Typical urban features are a greater slope in the wind profiles, enhanced turbulence intensities, and a vertical increase in magnitude of the turbulence. The analytical approach proposed by ETLING for the description of the vertical wind profile in the whole boundary layer is amended in the Prandtl-layer part by a correction function for atmospheric stability. The amended profile description turns out to render the best results for the approximation of urban wind profiles within the lowest 500 m above ground.
The objective of the studies presented in this paper is to present an analysis of spatial distrib... more The objective of the studies presented in this paper is to present an analysis of spatial distribution and temporal variation of particulate matter in Munich and Augsburg, Germany, and to identify and discuss the factors determining the aerosol pollution in both areas. Surface-based in-situ and remote sensing measurements of particle mass and particle size distribution have been performed in, around, and above the two cities. Two measurement campaigns were conducted in Munich, one in late spring and one in winter 2003. Another campaign has been on-going in Augsburg since 2004. Spatial and temporal variations are analyzed from this data (PM 10 , PM 2.5 and PM 1 ). There are higher particle mass concentrations at the urban site than at the surrounding rural sites, especially in winter. No significant difference in the major ionic composition of the particles between the urban and the rural site was detected. This is considered to be related to the spatial distribution of secondary inorganic aerosol that is more homogeneous than aerosol resulting from other sources like traffic or urban releases in general. During the measurement campaigns mixing layer heights were determined continuously by remote sensing (SODAR, ceilometer, RASS). Significant dependence of particle size distribution and particle mass concentration on mixing layer height was found. This finding paves the way to new applications of satellite remote sensing products.
Air quality is mainly determined by traffic, industrial and urban emissions as well as by specifi... more Air quality is mainly determined by traffic, industrial and urban emissions as well as by specific meteorological and topographic conditions. Focussing on nitrogen oxides and particulate matter, the temporal and spatial differences in air pollution in a deep Alpine valley with a major motorway were studied by a measurement campaign between November 2005 and February 2006 near Schwaz, Austria. The variation of air pollutant concentrations near the motorway was determined on the basis of path-averaged (DOAS) and in situ measurements. The layering of the valley atmosphere and the mixing-layer height were observed continuously by SODAR and ceilometer measurements. The winter-time weather conditions were characterized by exceptionally low temperature and high amount of snow in the valley. This resulted in the development of very stable cold pools with low wind speeds and accordingly high air pollution burden. During several periods the air pollutants accumulated from day to day and frequent exceedances of NO 2 and PM 10 thresholds were detected. Furthermore it could be concluded that the emission situation was not unusually high during these periods, at least concerning road traffic as the dominant source for nitrogen oxides. Analysis confirms that the typical weather phenomena associated with stable high-pressure regimes are the main factor for the observed pollution burden. During foehn and cold front passages, which interrupted these high pressure periods, concentration levels generally decrease at the valley ground and increase at the slope. Analysis reveals that this is a consequence of vertical mixing due to the influence of mountain specific wind systems, like thermally driven and quasi-periodic valley or slope winds. NO 2 concentration levels are a matter of concern regarding annual mean values as well as -previously not recorded -exceedances of the half-hourly threshold in severe winter conditions. Compared to previous investigations an increased NO 2 /NO x ratio was observed during the measurement campaign which is related to enhanced NO 2 emissions from road traffic in consequence to fleet composition and emission changes.
Ceilometer backscatter information is evaluated by comparison with parallel measurements. Data ar... more Ceilometer backscatter information is evaluated by comparison with parallel measurements. Data are presented from two years of combined ceilometer and RASS measurements at the same site and from comparison with a nearby (60 km) radiosonde for largerscale humidity information. This evaluation is designed to make MLH monitoring from ceilometer data more reliable. Finally, the detection of volcanic ash clouds with ceilometers is addressed.
An attempt is made to correlate the mixing heights, derived from ceilometer and Sodar measurement... more An attempt is made to correlate the mixing heights, derived from ceilometer and Sodar measurements, to those simulated by different atmospheric boundary-layer parameterization schemes. The comparison is performed at two sites (one suburban and one rural) close to Munich, Germany for two spring and two winter days. It is found that, under convective conditions, the mixing height determined, by both Sodar and ceilometer, corresponds to the middle or the top of the entrainment zone, respectively, as calculated from the eddy-viscosity profiles. Under stable conditions, the measured mixing height is related to the height where eddy viscosities attain their minimum values (Sodar) or to the height of residual mechanical turbulence (ceilometer). During a foehn case with weak turbulence, the measured mixing height from both Sodar and ceilometer is better inferred by considering the eddy-viscosity profiles during daytime and the height of the low-level jet during nighttime.
An observational dataset from a wintertime field campaign in the Inn Valley, Austria, is analysed... more An observational dataset from a wintertime field campaign in the Inn Valley, Austria, is analysed in order to study mechanisms of air pollution transport in an Alpine valley. The results illustrate three types of mechanisms: transport by a density current, backand-forth transport by valley winds, and transport by slope winds. The first type is associated with an air mass difference along the valley. Cooler air located in the lower part of the valley behaves like a density current and produces the advection of pollutants by upvalley winds. In the second type, strong horizontal gradients in pollution concentrations exist close to ground. Multiple wind reversals result in a back-and-forth transport of pollutants by weak valley winds. In the third type, upslope winds during daytime decrease low-level pollution concentrations and cause the formation of elevated pollution layers.
The typical features of a summer smog episode in the highly complex terrain of the Province of Bo... more The typical features of a summer smog episode in the highly complex terrain of the Province of Bolzano (Northern Italy) were investigated by numerical modelling with two non-hydrostatic models, ground-based monitoring stations, and vertical profiling with two sodars and an ultra-light aircraft. High ozone concentrations are most likely to appear in situations where the local circulation in the valleys is decoupled from the synoptic flow above during anticyclonic weather regimes. Both models (MM5 and TVM) produced similar results and were able to simulate the local winds in the valleys. A comparison of the measured data to the model simulation results made an evaluation of the performance of the two models in such complex terrain possible. Both models proved to be suitable for the simulation of the meteorological conditions during such summer smog episodes in complex terrain. r
The occurrence of nocturnal secondary ozone maxima was investigated by ground-level meteorologica... more The occurrence of nocturnal secondary ozone maxima was investigated by ground-level meteorological and air quality measurements in an urban park in Essen, Germany, during 29 individual summer measurement campaigns between May 1995 and September 1997. In addition, during an intensive measurement campaign in May 1997, SODAR measurements of wind and turbulence were made. The spatial and temporal distribution of nocturnal ozone maxima within the measurement network of the Environmental Protection O$ce of North Rhine}Westphalia was also analysed. Two case studies of nocturnal secondary ozone maxima are discussed in more detail. They represent two di!erent types of this phenomenon, associated with a nocturnal low-level jet (LLJ) and the passage of a front, respectively. In both cases, the nocturnal increase in ozone concentration was accompanied by a signi"cant increase in the standard deviation of the vertical wind speed across the lower stable boundary layer, indicating enhanced vertical mixing. During the LLJ case, ozone maxima were observed at 33% of the stations of the Environmental Protection O$ce network at approximately the same time. In the case of the front, the time of the ozone concentration rise could be allocated to the time of the passage of the front, moving from northwest to southeast across the study area. For the "rst time, the measurements presented here document turbulent mixing induced by shear forces in the whole layer between the core of the LLJ and the ground surface during secondary nocturnal ozone maxima.
A comparison of the determination of boundary-layer structures by a SODAR, by a RASS, and by a ce... more A comparison of the determination of boundary-layer structures by a SODAR, by a RASS, and by a ceilometer is presented. One important structure is the mixing-layer height (MLH). The comparison is focused on 3 days with an evolution of a convective boundary layer over a larger city in Germany. The three instruments give information that partly agree and partly complement each other. By this, a picture of the diurnal evolution of the vertical structure of this urban boundary layer is presented. The ceilometer gives information on the aerosol content of the air and the RASS provides a direct measurement of the vertical temperature distribution in the boundary layer. The RASS and the ceilometer add information on the moisture structure of the boundary layer that is not detected by the SODAR. On the other hand this comparison validates known techniques by which the MLH is derived from SODAR data. Especially the temperature information from the RASS agrees well with lifted inversions derived from the analysis of the SODAR data. The ceilometer, being the smallest instrument, has a potential to be used in future MLH studies. r
The spatial structure and the progression speed of the first ash layer from the Icelandic Eyjafja... more The spatial structure and the progression speed of the first ash layer from the Icelandic Eyjafjallajökull volcano which reached Germany on 16/17 April is investigated from remote sensing data and numerical simulations. The ceilometer network of the German Meteorological Service was able to follow the progression of the ash layer over the whole of Germany. This first ash layer turned out to be a rather shallow layer of only several hundreds of metres thickness which was oriented slantwise in the middle troposphere and which was brought downward by large-scale sinking motion over Southern Germany and the Alps. Special Raman lidar measurements, trajectory analyses and in-situ observations from mountain observatories helped to confirm the volcanic origin of the detected aerosol layer. Ultralight aircraft measurements permitted the detection of the arrival of a second major flush of volcanic material in Southern Germany. Numerical simulations with the Eulerian meso-scale model MCCM were able to reproduce the temporal and spatial structure of the ash layer. Comparisons of the model results with the ceilometer network data on 17 April and with the ultralight aircraft data on 19 April were satisfying. This is the first example of a model validation study from this ceilometer network data.
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