Stability and height dependant variations of the structure function parameters in the lower atmospheric boundary layer investigated from measurements of the long-term experiment VERTURM (vertical turbulence measurements)

Abstract

Operation and design of electro-optical systems are affected by atmospheric optical turbulence quantified by the refractive index parameter C_n². Regarding wave propagation in the visible and infrared (IR), C_n² is a function of height, dependant on temperature, pressure, and the structure temperature function parameter C_n². The long-term experiment VerTurM (vertical turbulence measurements) was designed to characterize the vertical variations of optical turbulence up to 250 m in the lower atmospheric boundary layer for a moderate typical central European climate. Since May 2009 three independent measurement systems have been operated in a flat pasture site in north-western Germany. In the atmospheric surface layer at a tall tower sonic anemometer measurements are performed on four discrete heights between 4 and 64 m providing information about atmospheric stability and turbulence. C_n² is derived. From 30 to 250 m a SODAR-RASS system (Sound Detection and Ranging - Radio acoustic sounding system) yields every half an hour profiles of C_n². Additional direct measurements of C_n² have been performed near the ground using a scintillometer. First results of the three measurement systems are presented. Vertical profiles and stability dependence are analysed in respect of Monin- Obukhov-similarity theory (MOST). Differences in the measurement systems and the expected height variations are discussed.