MicroPoem: experimental investigation of birch pollen emissions

Diseases due to aeroallergens constantly increased over the last decades and affect more and more people. Adequate protective and pre-emptive measures require both reliable assessment of production and release of various pollen species, and the forecasting of their atmospheric dispersion. Pollen forecast models, which may be either based on statistical knowledge or full physical transport and dispersion modeling, can provide pollen forecasts with full spatial coverage. Such models are currently being developed in many countries. The most important shortcoming in these pollen transport systems is the description of emissions, namely the dependence of the emission rate on physical processes such as turbulent exchange or mean transport and biological processes such as ripening (temperature) and preparedness for release. Thus the quantification of pollen emissions and determination of the governing mesoscale and micrometeorological factors are subject of the present project MicroPoem, which includes experimental field work as well as numerical modeling. The overall goal of the project is to derive an emission parameterization based on meteorological parameters, eventually leading to enhanced pollen forecasts. In order to have a well-defined source location, an isolated birch pollen stand was chosen for the set-up of a ‘natural tracer experiment', which was conducted during the birch pollen season in spring 2009. The site was located in a broad valley, where a mountain-plains wind system usually became effective during clear weather periods. This condition allowed to presume a rather persistent wind direction and considerable velocity during day- and nighttime. Several micrometeorological towers were operated up- and downwind of this reference source and an array of 26 pollen traps was laid out to observe the spatio-temporal variability of pollen concentrations. Additionally, the lower boundary layer was probed by means of a sodar and a tethered balloon system (also yielding a pollen concentration profile). In the present contribution a project overview is given and first results are presented. An emphasis is put on the relative performance of different sample technologies and the corresponding relative calibration in the lab and the field. The concentration distribution downwind of the birch stand exhibits a significant spatial (and temporal) variability. Small-scale numerical dispersion modeling will be used to infer the emission characteristics that optimally explain the observed concentration patterns

Mean Flow and Turbulence Characteristics in an Urban Roughness Sublayer

In this study, a detailed model of an urban landscape has been re-constructed inthe wind tunnel and the flow structure inside and above the urban canopy has beeninvestigated. Vertical profiles of all three velocity components have been measuredwith a Laser-Doppler velocimeter, and an extensive analysis of the measured meanflow and turbulence profiles carried out. With respect to the flow structure inside thecanopy, two types of velocity profiles can be distinguished. Within street canyons,the mean wind velocities are almost zero or negative below roof level, while closeto intersections or open squares, significantly higher mean velocities are observed.In the latter case, the turbulent velocities inside the canopy also tend to be higherthan at street-canyon locations. For both types, turbulence kinetic energy and shearstress profiles show pronounced maxima in the flow region immediately above rooflevel. Based on the experimental data, a shear-stress parameterization is proposed, inwhich the velocity scale, us, and length scale, zs, are based on the level and magnitude of the shear stress peak value. In order to account for a flow region inside the canopy with negligible momentum transport, a shear stress displacement height, ds, is introduced. The proposed scaling and parameterization perform well for the measured profiles and shear-stress data published in the literature. The length scales derived from the shear-stress parameterization also allowdetermination of appropriate scales for the mean wind profile. The roughnesslength, z0, and displacement height, d0, can both be described as fractions of the distance, zs - ds, between the level of the shear-stress peak and the shear-stress displacement height. This result can be interpreted in such a way that the flow only feels the zone of depth zs - ds as the roughness layer. With respect to the lower part of the canopy (z < ds) the flow behaves as a skimming flow. Correlations between the length scales zs and ds and morphometric parameters are discussed. The mean wind profiles above the urban structure follow a logarithmic windlaw. A combination of morphometric estimation methods for d0 and z0 with wind velocity measurements at a reference height, which allow calculation of the shear-stress velocity, u*, appears to be the most reliable and easiest procedure to determine mean wind profile parameters. Inside the roughnesssublayer, a local scaling approach results in good agreement between measuredand predicted mean wind profile

A Three-Dimensional Backward Lagrangian Footprint Model For A Wide Range Of Boundary-Layer Stratifications

We present a three-dimensional Lagrangian footprint model with the ability to predict the area of influence (footprint) of a measurement within a wide range of boundary-layer stratifications and receptor heights. The model approach uses stochastic backward trajectories of particles and satisfies the well-mixed condition in inhomogeneous turbulence for continuous transitions from stable to convective stratification. We introduce a spin-up procedure of the model and a statistical treatment of particle touchdowns which leads to a significant reduction of CPU time compared to conventional footprint modelling approaches. A comparison with other footprint models (of the analytical and Lagrangian type) suggests that the present backward Lagrangian model provides valid footprint predictions under any stratification and, moreover, for applications that reach across different similarity scaling domains (e.g., surface layer to mixed layer, for use in connection with aircraft measurements or with observations on high towers

On the efficiency and correction of vertically oriented blunt bioaerosol samplers in moving air

The aspiration efficiency of vertical and wind-oriented Air-O-Cell samplers was investigated in a field study using the pollen of hazel, sweet chestnut and birch. Collected pollen numbers were compared to measurements of a Hirst-type Burkard spore trap. The discrepancy between pollen counts is substantial in the case of vertical orientation. The results indicate a strong influence of wind velocity and inlet orientation relative to the freestream on the aspiration efficiency. Various studies reported on inertial effects on aerosol motion as function of wind velocity. The measurements were compared to a physically based model for the limited case of vertical blunt samplers. Additionally, a simple linear model based on pollen counts and wind velocity was developed. Both correction models notably reduce the error of vertically oriented samplers, whereas only the physically based model can be used on independent datasets. The study also addressed the precision error of the instruments used, which was substantial for both sampler type

Implementation of the 64-meter-diameter Antennas at the Deep Space Stations in Australia and Spain

The management and construction aspects of the Overseas 64-m Antenna Project in which two 64-m antennas were constructed at the Tidbinbilla Deep Space Communications Complex in Australia, and at the Madrid Deep Space Communications Complex in Spain are described. With the completion of these antennas the Deep Space Network is equipped with three 64-m antennas spaced around the world to maintain continuous coverage of spacecraft operations. These antennas provide approximately a 7-db gain over the capabilities of the existing 26-m antenna nets. The report outlines the project organization and management, resource utilization, fabrication, quality assurance, and construction methods by which the project was successfully completed. Major problems and their solutions are described as well as recommendations for future projects

THE NATURE OF TURBULENT KINETIC ENERGY IN A DEEP AND NARROW VALLEY UNDER CONVECTIVE (?) CONDITIONS

This contribution investigates the nature of turbulent kinetic energy (TKE) in a steep and narrow Alpine valley under fair-weather summertime conditions. The Riviera Valley in southern Switzerland has been chosen for a detailed case study, in which the evaluation of aircraft data (obtained from the MAP-Riviera field campaign) is combined with the application of high-resolution (350 m) large-eddy simulations using the model ARPS. The simulations verify what has already been observed on the basis of measurement data: TKE profiles scale surprisingly well if the convective velocity scale w٭ is obtained from the sun-exposed eastern slope rather than from the surface directly underneath the profiles considered. ARPS is then used to evaluate the TKE-budget equation, showing that, despite sunny conditions, wind shear is the dominant production mechanism. Therefore, the surface heat fluxes (and thus w٭) on the eastern slope do not determine the TKE evolution directly but rather, as we believe, indirectly via the interaction of thermally-driven crossvalley and along-valley flow. Excellent correlations between w2٭ and the up-valley wind speed solidify this hypothesis

A simple two-dimensional parameterisation for Flux Footprint Prediction (FFP)

Flux footprint models are often used for interpretation of flux tower measurements, to estimate position and size of surface source areas, and the relative contribution of passive scalar sources to measured fluxes. Accurate knowledge of footprints is of crucial importance for any upscaling exercises from single site flux measurements to local or regional scale. Hence, footprint models are ultimately also of considerable importance for improved greenhouse gas budgeting. With increasing numbers of flux towers within large monitoring networks such as FluxNet, ICOS (Integrated Carbon Observation System), NEON (National Ecological Observatory Network), or AmeriFlux, and with increasing temporal range of observations from such towers (of the order of decades) and availability of airborne flux measurements, there has been an increasing demand for reliable footprint estimation. Even though several sophisticated footprint models have been developed in recent years, most are still not suitable for application to long time series, due to their high computational demands. Existing fast footprint models, on the other hand, are based on surface layer theory and hence are of restricted validity for real-case applications. <br><br> To remedy such shortcomings, we present the two-dimensional parameterisation for Flux Footprint Prediction (FFP), based on a novel scaling approach for the crosswind distribution of the flux footprint and on an improved version of the footprint parameterisation of Kljun et al. (2004b). Compared to the latter, FFP now provides not only the extent but also the width and shape of footprint estimates, and explicit consideration of the effects of the surface roughness length. The footprint parameterisation has been developed and evaluated using simulations of the backward Lagrangian stochastic particle dispersion model LPDM-B (Kljun et al., 2002). Like LPDM-B, the parameterisation is valid for a broad range of boundary layer conditions and measurement heights over the entire planetary boundary layer. Thus, it can provide footprint estimates for a wide range of real-case applications. <br><br> The new footprint parameterisation requires input that can be easily determined from, for example, flux tower measurements or airborne flux data. FFP can be applied to data of long-term monitoring programmes as well as be used for quick footprint estimates in the field, or for designing new sites