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Wind and turbulence

 
We work on theoretical and practical aspects of the wind field and turbulence in canopies (i.e within forests and in urban environments) as well as in complex terrain. We develop experimental and numerical methods to visualize, understand, and predict the flow and the associated exchange of energy and trace gases over these complex surfaces.

Storm damage

Sturmschäden

Storms are currently the main natural hazard to forests in Europe. The last once-in-a-century storm "Lothar", which occurred in Southwest Germany on 26.12.1999 caused in the forests of Baden-Württemberg approximately 30 million m3 of damaged timber volume. The financial loss for forestry was estimated at 770 milion Euros. At the Chair of Environmental Meteorology a high-resolution empirical storm damage model was developed to simulate the damage caused by extreme storm events (Schindler et al., 2016).

The frequency and dynamics of future winter storm events across Europe is of great importance to several sectors of society and economic sectors. Extreme winter storms have caused over $60 billion in damage throughout Europe since 1980. However, individual, model-based projections of the future storm are subject to great uncertainties, Mölter et al. (2016) summarized a large number of current studies. Using the effective tendency  of winter storms, we were able to show that the results of the evaluated studies point to an intensification of the storm frequency and impact over central and western Europe. Based on current state of knowledge, it can be also assumed that the intensity of the winter storm will weaken in southern Europe.

Pressure pumping and trace gas exchange

High-precision differential air pressure measurements were conducted in the below canopy space of a Scots pine forest and in the forest soil to investigate small air pressure fluctuations and their effect on soil gas flux. In addition to air pressure measurements, tracer gas concentration in the soil and airflow characteristics above and below the canopy were measured. Results suggest that air pressure fluctuations in the frequency range of 0.01 Hz to 0.1 Hz are strongly dependent on above-canopy wind speed. While amplitudes of the observed air pressure fluctuations (<10 Pa) increase significantly with increasing above-canopy wind speed, the periods decrease significantly with increasing above-canopy speed. These air pressure fluctuations are associated with the pressure-pumping effect in the soil. A pressure-pumping coefficient was defined, which describes the strength of the pressure-pumping effect. During the measurement period, pressure-pumping coefficients up to 0.44 Pa/s were found. The dependence of the pressure-pumping coefficient on mean above-canopy wind speed can be described well with a polynomial fit of second degree. The knowledge of this relation simplifies the quantification of the pressure-pumping effect in a Scots pine forest considerably, since only the mean above-canopy wind speed has to be measured. In addition, empirical modeling revealed that the pressure-pumping coefficient explains the largest fraction of the variance of tracer gas cocentration in the topsoil (Mohr et al., 2016).

Wind energy potential

In the future energy mix of Germany, wind energy will play a significant role. However, the usable wind energy is very variable, therefore the assessment of suitable locations for wind turbines is of fundamental importance. Particularly in regions with complex terrain the small-scale estimation of the average annual wind energy yield is a challenge. At the Chair of Environmental Meteorology a novel methodology has been developed that allows for the assessment of the annual wind energy yield at very small scales.


Recent publications on "Wind and turbulence"