Werner K. Graber

Trends in surface ozone concentrations at Arosa (Switzerland)

Abstract 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.

Scintillometer Wind Measurements over Complex Terrain

Abstract 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.

Comparison of Horizontal and Vertical Scintillometer Crosswinds during Strong Foehn with Lidar and Aircraft Measurements

Abstract 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 ...

Real time modelling as an emergency decision support system for accidental release of air pollutants

In the framework of the project ‘Windbank’, wind field patterns in an area of 30km×30km 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 24h is evaluated.

Multi-parcel lagrangian model for quantification of influence of alpine air mass exchange on photo-oxidant production

Abstract The Swiss plateau, embedded between the Jura and the Alps, has high population density with strong anthropogenic emissions. The main processes leading to exchange of air masses between the Swiss plateau and the Alps are the thermally produced valley winds transporting pollution into the Alpine valleys during the day and their respective backflush during the night. During a cloudless summer day, about 40% of the whole air mass under the mixing height over the Swiss plateau is exchanged with Alpine air masses. In the present case study for 29 July 1993, the dynamics including this exchange process is calculated on three different scales by means of wind trajectories. The valley wind systems are described on a grid with a resolution of 500 m using scale-related parameterizations for each relevant physical process. The regional wind field and the long-range trajectories are obtained from different models, taking into account the general weather pattern. The chemistry is calculated in the framework of a Lagrangian model using the CBM IV mechanism. The anthropogenic emissions over the Swiss plateau as well as the biogenic hydrocarbons emitted by the forests are considered. Both emission inventories are given on a grid with a 5 km resolution. While moving over the ground, emissions and depositions of the species are simulated, taking into account mixing and exchange with air parcels of the upper layer. The results show a clear overall NO x limited ozone production situation in the Swiss plateau and a marginal influence of biogenic VOC emisions. Only south of the Alps and near the northeastern border the VOC decrease could lead to a substantial reduction of the ozone levels under weather conditions represented in this study.

Airborne Migration of Obligate Nomads Demonstrates Gene Flow Across Eurasia

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.

Scidar: laser- and LED-based wind sensing by scintillation detection and ranging

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.

Evaluation of CO2, water vapor, and their turbulent exchange rates with an airborne open-path infrared gas analyzer

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.