Radar Angels and Their Relationship to Meteorological Factors
Abstract
From a year-long study of radar angels, carried out near Stockholm, Sweden, with a 10-cm vertically-pointing pulse radar, tropograms, or time-height records 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. The employment of ultrasensitive, high-resolution radars with scanning antennas in studies of layer angels has greatly amplified the meteorological significance of these echoes, and, consequently, radar meteorology has been extended to investigations of meteorological processes in the clear atmosphere. A brief resume of recent experimental work on radar backscattering from clear air concludes this report in order to illustrate the application of radar methods in clear-air research and to summarize characteristic features of clear-air structures observed with radar.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1970
- Accession Number
- AD0707663
Entities
People
- Hans Ottersten