High-Resolution VHF Radar Sounding of the Troposphere and Stratosphere

Measurements of the fine structure of tropospheric and stratospheric refractivity variations with a vertically beamed pulsed VHF radar are presented. The scheme of radar operation and data acquisition by means of coherent detection and preintegration is described. Special emphasis is placed upon the evaluation of the fine structure through the application of pulse scanning, filtering, and signal deconvolution by means of contrast enhancement. These techniques yield a height resolution of about 30 m in the troposphere. Laminae or thin sheets of refractivity changes are regularly found in the troposphere and lower stratosphere. A cat´s eye turbulence structure of 100-m thickness, observed at 4.4-km height, is described in detail. It is concluded from the evaluation of the correlation function that scattering from turbulent refractivity fluctuations occurs in the middle of this layer whereas partial reflection from refractivity gradients dominates at the layer boundaries. Several mechanisms, such as the Kelvin-Helmholtz instability, wave-induced shear generation, or lateral convection, are discussed as possible origin of the refractivity structures revealed by VHF radar.