RADAR ANGELS AND THEIR RELATIONSHIP TO METEOROLOGICAL FACTORS.
RESEARCH INST OF NATIONAL DEFENCE STOCKHOLM (SWEDEN)
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From a year-long study of radar angels, carried out near Stockholm, Sweden, with a 10-cm vertically-pointing pulse radar, tropograms, or time-heightrecords of angel activity, have been obtained together with information on meteorological parameters. Amplitude records of individual angel echoes have also been studied. Various types of radar angels are exemplified, and the seasonal variation and the height distribution of the angel activity is reviewed. Theoretical approaches to meteorological explanations of angel phenomena are discussed in terms of the consequences for the tropospheric refractive-index field. The statistical relationship between radar angels and meteorological parameters is presented, and explanations of the angel phenomena are offered. Layer angels, which are persistent, diffuse, layer-type echoes, occur due to backscattering from clear-air refractive-index perturbations associated with free convection, or with turbulent mixing induced by wind shear in zones of enhanced static stability. Dot angels, which are short-duration, coherent echoes from apparent point targets, are difficult to explain as reflections from invisible meteorological targets and are mainly caused by insects and birds. Author
- Active and Passive Radar Detection and Equipment