21.01.16 Kolloquium: Prof. Dr. Christoph Thomas
Prof. Dr. Christoph Thomas, Abteilung Mikrometeorologie, Universität Bayreuth
The near-surface layer impacts the abundance and quality of life on Earth through the transfer and mixing of light, heat, water, CO2, and other substances controlling the resources for humans, plants, and animals. While current theories and models well describe the dynamics of this layer during significant convention when synoptic forcing and/or solar radiation are substantial, they fail when airflows and turbulence are weak during calm, stable nights leaving model predictions uncertain. This nocturnal weak-wind regime occupies substantial fractions of time and our landscape, its physics are largely unknown, and has eluded thorough experimental investigation.
This presentation will give on overview of recent advancements in observing and understanding the weak-wind boundary layer. Special attention will be given to investigating so-called ‘submeso-scale’ motions, i.e. flow modes, that exist on scales larger than those of the isotropic and homogeneous turbulence, but smaller than those of synoptic meso-scale motions. Submeso-scale motions are ubiquitous and exist throughout the diurnal period, but exert a dominant forcing on transport and mixing only when winds are weak.
Innovative observational techniques include camera-recorded releases of machine-generated fog, larger sensor networks, and the laser-based fiber-optic distributed temperature sensing method. The latter is capable of delivering images of the thermal structure and the wind field over four orders of magnitude (decimeter to kilometer) at a resolution fine enough to resolve even individual larger turbulent motions, which we termed ‘Large Eddy Observation (LEO)’ in analogy to the modeling technique. Results from several field experiments will be presented hat span a wide range of surface conditions and topography.
20. Januar 2016