The interpretation of stellar shadow‐bands as a consequence of turbulent mixing

Abstract

Abstract Recently published measurements of shadow‐band patterns produced by star‐light at ground level are analysed using the theory of wave‐propagation in a turbulent medium. The measured spatial and time spectra of the patterns can be described quantitatively by assuming that the optical inhomogeneities are produced by turbulent mixing in the earth's boundary‐layer and in shallow layers at heights around 8 km. Characteristics of the assumed turbulence in the upper air are estimated to be: mean height 8 km, layer depth 90–200 m, r.m.s. velocity fluctuation in wind direction 1·5‐2·0 m sec −1 , r.m.s. temperature fluctuation 0·2°C.