Radio-Physical Features of Radar Reflections From a Clear Sky in the Millimeter Wavelength Range

Abstract

The features of the Doppler spectra of radar signals scattered by atmospheric inhomogeneities under clear sky conditions are studied. A technique for measuring the wind field in the millimeter wavelength range using a coherent radar is described. The results of measurements of the radar reflectivity Z under summer convection cannot be interpreted by the theory of Bragg scattering on inhomogeneities due to locally homogeneous isotropic turbulence. The experimental values can exceed the theoretical estimates by two orders of magnitude. An analysis of the fine structure of the Doppler spectra obtained under summer conditions indicates their large width, multi-peakedness, and spatial variability. The authors attribute these features to the formation of thermals, the structure of which is accompanied by closely spaced ascending and descending flows. The high level of radar reflectivity also confirms the convective version of signal generation, in which a large moisture difference in closely spaced ascending and descending layers at the thermal boundary forms eddies with large refractive index gradients.