Katharina Heinke Schlünzen

Viability and sunlight sensitivity of oak pollen and its implications for pollen-mediated gene flow

Pollen-mediated gene flow and the male reproductive success of wind-pollinated trees depend on the initial viability of the pollen and the changes that occur in its viability during transport in the atmosphere. The viability of Quercus robur pollen was determined before and during exposure to sunlight by in vitro germination and the fluorescein diacetate reaction (FCR) in 2002 and 2003, respectively. These experiments allowed us to calculate initial pollen viability and pollen sensitivity to sunlight. The germination test revealed a lower initial pollen viability (25–65%) than the FCR (53–92%). Following 9.5 h of irradiation the viability was reduced to 75–100% as determined by the in vitro germination test or to 40–70% as determined by the FCR. The actual values of initial pollen viability and pollen sensitivity to sunlight were used to define a range of values for modelling pollen dispersal using the mesoscale meteorological model METRAS. The deposition patterns of viable pollen varied by as much as a factor of 14 by changing the viability parameters in the range of the observed values. This suggests significant differences in male reproductive success. Variations in initial pollen viability have stronger effects on the gene-flow pattern than do variations in pollen sensitivity to sunlight. In particular, pollen distribution throughout the local environment is shaped by the initial pollen viability, while pollen sensitivity to sunlight mainly influences long-distance pollen dispersal.

Influence of thermal effects on street canyon circulations

A numerical study has been carried out to investigate the influence of large-scale thermal effects and strong local-scale temperature gradients near the ground on the circulation inside a street canyon. The results show that the dynamical forcing dominates the circulation inside a street canyon. But this forcing is influenced by the large-scale thermal stability. Thus, atmospheric stability indirectly controls the street canyon circulation. Small temperature gradients inside the street-canyon are neutralised by the external dynamical forcing. Strong temperature gradients inside the street-canyon show an impact on the street canyon circulation. While stable stratification reduces the circulation for the building configuration investigated, convective stratification seems to intensify it.

A model system for the assessment of ambient air quality conforming to EC directives

EC framework directive 96/62/EC and its daughter directives allow the use of models to evaluate ambient-air quality. The model system M-SYS has been developed for this purpose. M-SYS employs a hierarchy of mesoscale and microscale models for both, meteorology and chemistry, to calculate air quality metrics corresponding to the limit values of the EC daughter directives. Corresponding to the directives the model system delivers maps showing concentration distributions in different spatial resolution for the different subjects of protection. M-SYS results show the resolution dependence of maximum values. Concentration fields show a large variability on spatial scales smaller than the average spacing of air quality stations. These heterogeneities cannot be resolved by the operational air quality network. Commonly used interpolation techniques can also not capture these spatial patterns as long as they lack information on the small-scale variability of wind, turbulence, and chemical conversion. At traffic-orientated sites in the urban obstacle layer, particularly large heterogeneities are found which require the use of three-dimensional obstacle resolving models.

The effect of different k- closures on the results of a micro-scale model for the flow in the obstacle layer

A non-hydrostatic micro-scale model (MITRAS) is used to simulate the flow field over a beam. The model is run with a constant grid size of 1/5 times the beam height representing a relatively coarse resolution. Different types of k-epsilon closures are used, the standard k-epsilon closure and modified ones. A comparison of model results (mean values, turbulent kinetic energy and momentum fluxes) with wind tunnel data confirms the finding of earlier studies performed with models of higher resolution, that the standard k-epsilon closure overestimates the turbulent kinetic energy in stagnation points. The comparison with wind tunnel data reveals that the momentum fluxes are overestimated at stagnation points as well. A modification of the standard k-epsilon closure is introduced that reduces both, the modelled momentum fluxes and the turbulent kinetic energy at stagnation points.

Simulation of transport and chemical transformations in the atmospheric boundary layer: review on the past 20 years developments in science and practice

The scientific progress in simulating transport and chemical transformations of tracers in the atmospheric boundary layer is summarised, starting from the 1980s. An overview on the current status of boundary layer resolving transport models and their use in practice is given. Selected model results are presented in comparison to measured data. Some examples for the uncertainty of model results are discussed. Perspectives on future developments of transport models for the atmospheric boundary layer are given.