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Measurements of the horizontal and vertical wind component by a crosswind scintillometer during foehn, the chinooklike downslope windstorm in the Alps, are presented. Because of the sparsity of vertical velocity measurements in the immediate vicinity, the scintillometer calibration is checked mainly with horizontal wind measurements. Then it is assumed that the calibration is the same for both components. The concept was tested during the Mesoscale Alpine Programme field campaign in the autumn of 1999, during which two scintillometers were deployed. Strong, long-lasting, quasi-stationary downward motions on the order of 5 m s−1 and horizontal wind speeds of over 30 m s−1 were detected during strong foehn phases within the valley. Aircraft measurements of various transects near the light paths are compared with two crosswind evaluation techniques. One of them, the slope method, tends to overestimate the actual wind speed by about 20%, whereas the peak technique gives values that are about 10% too ...

In the framework of the project ‘Windbank’, wind field patterns in an area of 30 km×30 km in the Swiss Plateau between the Alps and the Jura were measured with 22 temporary meteorological stations and two SODARs during 4 months in 1997. Hourly averages from this high resolution network were combined with meteorological information from routine stations and from a weather prediction model. This data-set comprises all available parameters influencing the complex wind flow in the investigated area between the Alps and the Jura. A cluster analysis for this data-set lead to 12 classes with a high separation quality. It is demonstrated, that an on-line acquisition of meteorological data from routine stations and from a weather prediction model can be used to diagnose the recent wind field class with a probability of 96% to hit the correct wind field class. This diagnosis reveals wind fields with a very high spatial resolution in a very short time. Consequently, it is useful as a contribution to a decision support system for safety management after accidental releases of nuclear or chemical air pollutants. Further, a method is outlined to use the weather prediction model to forecast the wind field class. An average probability of 79% to hit the correct wind field classes for a forecast time of up to 24 h is evaluated.

The Mesolcina Valley campaign was an important part of the VOTALP project. Its main goals were the study of the effects of thermal wind systems on horizontal and vertical ozone transport over various distances, and on local production of ozone in an Alpine valley. The field measurements took place in the Mesolcina Valley in southern Switzerland in July and August 1996. The Mesolcina Valley is typical for the Alps for its size and its rural character, and contains an important traffic route. Ground-based and airborne instruments were deployed to obtain a four-dimensional chemical and physical picture of the valley atmosphere and the surroundings. Field measurements were complemented by numerical modeling studies. An overview of the campaign, its geographic background, and the measurement plan is given together with selected highlights of the results obtained so far. A synoptic-climatological approach tries to evaluate the representativeness of the observation days. It was found that during the campaign representative data for typical ozone days were collected, while extreme events did not occur. The main results of the campaign are that very high pollutant concentrations at the Alpine crests are the effect of advective, larger-scale transport, mainly from the Alpine forelands. The valley is very effective in pumping air into elevated layers during the day, with the slope winds probably carrying the bulk of the air volume to higher levels. Up to five times the valley volume may be exported during one upwind phase. Net local production is estimated to be approximately 3–8 ppb h −1 of ozone, but seems to be compensated by dry deposition. This indicates that the Alpine valleys may be important net sinks of air pollutants, which may lead to negative impacts on the Alpine ecosystems.

Several large-aperture scintillometers were built at the Paul Scherrer Institute with the aim to measure wind over complex terrain. A prototype instrument was tested over flat ground, and the performance of six analyzing techniques was evaluated by comparing them with conventional anemometers. Next, a set of five improved scintillometers was used in an experiment over complex terrain. This experiment represents a unique opportunity for evaluating scintillometer performance by comparing their results to sodar, aircraft, and ground station measurements. The results complement and partly contradict the observations previously published; the so-called peak technique is the most reliable and frequency techniques fail to provide faithful results in many cases. The measurements demonstrate that scintillometry is useful and reliable for wind and turbulence measurements over complex terrain.

As a contribution to the terrestrial ecosystem research initiative (TERI) within Framework IV of the EU, ECOMONT aims at investigating ecological effects of land-use changes in European terrestrial mountain ecosystems. The project is carried out by nine European partners in six composite landscapes in the Eastern Alps, the Swiss Alps, the Spanish Pyrenees and the Scottish Highlands. An analysis of structures and processes in the context of land-use changes is performed, scaling from the leaf to the landscape level. The following research topics are being investigated: spatial distribution of vegetation and soil in the composite experimental sites; physical and chemical soil properties, soil organic matter (SOM) status and turnover; canopy structure; water relations of ecosystems and hydrology of catchment areas; micro-climate and energy budget of ecosystems; gas exchange of single plants, ecosystems and gas exchange between the composite experimental sites and the atmosphere; potential risks through land-use changes. In order to link biodiversity with ecosystem functioning and to ensure a profound analysis of the ecosystem processes at the level of composite landscapes, a specific up-scaling approach is applied in ECOMONT combining empirical field studies and mathematical modelling. At each level of integration the results of the modelling approach are validated by direct field measurements. This will be shown on the example of the bottom up approach for the gas exchange processes. The experimental up-scaling starts from measurements of the gas exchange of single leaves using fully climatised CO2/H2O porometers, proceeds to the canopy level using Bowen-ratio and Eddy-correlation techniques, and finally to the gas exchange of composite landscapes using a scintillation anemometer system/differential optical absorption spectroscopy system (SCIDAR/DOAS) equipment in combination with a instrumented aircraft flying at a constant height above the landscape. A hierarchy of process-based models is used to link the gas exchange processes at the different scales: a single leaf model based on a biochemical model of photosynthesis, a newly developed multi-species canopy model taking into account multiple light scattering and non-uniform distribution of leaves, and a landscape model providing a pixel by pixel integration.

First results of the European project “ECOMONT” are presented. In a field campaign on Monte Bondone near Trento, Italy, fluxes of H 2 O and CO 2 over a composite ecosystem area were measured with scintillation anemometers and an instrumented aircraft. The turbulent fluxes from the aircraft data are discussed. The budget of the fluxes from the aircraft data is evaluated and compared to the scintillation mass fluxes. The budget is formulated for an air volume above a horizontal triangle over a heterogeneous ecosystem of a few square kilometers in the Alps. The budget is based on data obtained from aircraft measurements on different heights. The H 2 O-budget consists of four terms: a divergence of the vertical turbulent flux of −1.08 g m −3 h −1 , an increase of water vapour with time of +0.25 g m −3 h −1 , an advection of dry air of +2.80 g m −3 h −1 and a subsidence of wet air of −1.97 g m −3 h −1 . Additionally, exchange rates for H 2 O and CO 2 with the vegetation are estimated.

During the years 1989–1991, ozone was measured at four sites around Arosa (Switzerland). One of these sites was identical with that, where surface ozone was measured in the 1950s (Gotz and Volz, 1951; Perl, 1965). Comparison of both old and recent data indicates that surface ozone concentrations at Arosa have increased by a factor of approximately 2.2. The increase shows a seasonal variation with a relative increase of more than a factor of three in December and January. The results are discussed in the context of measurements made at other times, locations and altitudes. The comparison indicates that the increase in ozone levels at Arosa has most likely occured between the fifties and today. The measurements additionally suggest that photochemical ozone production in the free troposphere has significantly contributed to the observed ozone trends in winter.

Understanding migration is important for the adequate use of biological resources. A new level of understanding is demonstrated with cereal pathogens recognized to be obligate nomads of the atmosphere. From basic reasoning, a hypothesis is put forward: virulence complexity, i.e. the number of virulences per pathogen genotype, is expected to increase in the direction of predominant winds. The hypothesis was confirmed by all of a variety of data from own investigations and from the literature and by modelling. For instance, virulence complexity of cereal mildews and rusts increased from western to eastern Europe and as far as Siberia by approximately one to two virulences per 1,000 km. The impact of our findings for general population genetics and gene flow across Europe and Asia and for further geographical areas is supposed to be considerable and worth elucidating further. Obligate nomad is a novel term that appears to be advantageous in several respects of population biology and life. Therefore, the consideration of obligate nomadism is extended to a spectrum of cases including plants, fungi and animals, as well as to neonomads and invasive plant species as a consequence of our present traffic and civilization. Most often obligate nomads are forced to migrate as substrates are ephemeral and ecological niches exist for a short period of time only. Chances and risks for health and the use of biological resources are discussed.

Shimmering of distant objects on a hot day or the twinkling of stars is familiar to most people. These visual effects, known as scintillation, are caused by the drift of refractive-index irregularities in the atmosphere. Analysis of scintillation phenomena provide a method for remotely sensing the atmosphere, since this effect is related to turbulence and wind. Optical remote sensing is an appealing method to measure wind in complex terrain. A scintillometer was built at the authors' institute, with the aim to measure wind across an Alpine valley. In a first step, they tested this instrument over a flat ground and compared its performance with conventional anemometers. Different methods of evaluation can be used. They investigated 6 different methods, and the results of these tests are reported.

The methodology of evaluating the exchange rates of CO2 and water vapor between vegetation and the atmosphere is presented. The two gases are measured with a short open path, fast responding infrared absorption gas analyzer. To determine the turbulent fluxes due to large scale eddies, high resolution wind measurements are obtained with a five-hole pressure sonde and a fast GPS (Global Positioning System) receiver. Measurements taken over Monte Bodone near Trento, Italy, a plateau in the Alps, are evaluated. The CO2 and water vapor budgets for the air layer above a few square kilometers were calculated and exchange rates for H2O and CO2 with the vegetation were estimated.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A simple layout for a DOAS system based on a commercially available spectrometer with CCD-detector is presented. The open-path light beam over several kilometers is controlled automatically to maintain an optimal beam alignment. The DOAS system is operated in parallel with a scintillation anemometer (scidar), which optically measures the path averaged crosswind. This arrangement provides fluxes of atmospheric constituents under the constrain of homogeneous concentrations along the light paths. In the framework of the EU-project 'VOTALP' 5 combined systems were used to evaluate the budget of NO2, O3, formaldehyde, toluene and SO2 fluxes in the Mesolcina valley in Switzerland. Two scidar/DOAS systems were set up in different heights across the northern end of the valley, two across the southern end and one parallel to the valley sidewall. Beam lengths ranged from 0.6 to 2.7 km. Results of the flux measurements are presented.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A He-Ne laser based profiler for atmospheric wind measurements across a laser beam is compared to an instrument using incoherent infrared light from a photodiode tranmitter. Both optical crosswind profilers use the scintillation of the light source to measure the average wind across the light path. Several techniques to derive the wind velocity from the normalized time- lagged covariance function of two narrow spaced receivers are tested. Nine conventional wind sensors were placed along a 1 km long test path to get a reference wind distribution for the instruments. The tests performed over a wide variety of different weather situations with low to high wind velocities and different turbulent conditions reveal a good performance of the IR scintillometer.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spectrometers from the Swedish company OPSIS were used to measure trace gas concentrations of NO 2, NO, SO 2 and ozone in rural sites. Simultaneous measurements with conventional gasanalyzers from the Californian company MonitorLabs were used to check possible cross-sensitivities of the DOAS system to other atmospheric gases. Considering the fundamental difference between long path integral and single point measurement the comparability of both systems is good with correlation coefficients better than 0.94 for a few thousend data pairs of each of the four gases.