Tilts of Atmospheric Radar-Scattering Structures Measured by Long-Term Windprofiler Radar Studies and Implications for Understanding Radar-Scattering Processes and the Structure of Atmospheric Turbulence

Month-long and seasonally persistent apparent tilts in atmospheric radar scatterers have been measured with a network of 6 windprofiler radars over a periods of two and more years. The method used employs cross-correlations between vertical winds and horizontal winds measured with the radars. It is shown that large-scale apparent tilts which persisted for many weeks and months were not uncommon at many sites, with typical tilts varying from horizontal to 2o from horizontal. The azimuthal and zenithal alignment of the tilts depend on local orography as well as local seasonal atmospheric conditions. It is demonstrated that these apparent tilts are not true large-scale phenomena, but rather are a manifestation of coordinated motions within turbulent radar-scattering structures at scales of a few metres and tens of metres, with these structures themselves being defined by larger-scale and longer-term physical processes. Implications for interpretation of the nature of turbulent eddies, the accuracy of vertical wind measurements, and the nature of layering and scattering in the real atmosphere, are discussed. For the first time, a method which allows accurate measurement of the mean off-horizontal alignment of anisotropic turbulent eddies is introduced.