Stability and Height dependant Investigation of Seasonal and Diurnal Cycles of Optical Turbulence in the Lower Atmospheric Boundary Layer

The optical turbulence, described by the structure function parameter of the refractive index Cn², a key parameter in describing the atmospheric influence on wave propagation, is investigated from the data of the long-term experiment VerTurM (Vertical Turbulence Measurements). The focus in this experiment was set on the vertical distribution of the optical turbulence in the lower atmospheric boundary layer. The VerTurM experiment includes measurements with a laser-scintillometer, four ultrasonic anemometers in different heights up to 64 m, and a SODAR-RASS-system (Sound Detection and Ranging - Radio acoustic sounding). At a measurement site in a rural flat landscape in north-western Germany, the experiment has been continuously performed since summer 2009. The influence of thermal and mechanical forces on the height dependency of Cn² is examined. Diurnal and seasonal behaviour of the strength of Cn2 is presented. The dependence on atmospheric stability in the atmospheric surface layer is analyzed. A special focus is set on the stable night-time boundary layer. Model comparisons are carried out and discussed.