Proceedings with Extended Abstracts (single PDF file) - Radio ...

WHAT IS TURBULENCE SEEN BY VHF RADARS ?J. Röttger, Max-Planck-Institut, 37191 Katlenburg-Lindau, GermanyAt the 9 th Workshop on Technical and Scientific Aspects of MST Radar - MST9 - Hockingand Röttger (2001) had reviewed the structure of turbulence in the middle and loweratmosphere seen by and deduced from MF-, HF- and VHF-radars with special emphasis onsmall-scale features. Here I want to expand on this by recollecting some more historical ideason scattering and reflection and very initial VHF MST (mesosphere-stratosphere-troposphere)radar observations. I also like to address frequently asked questions, and elaborate on simplenew methods to improve our understanding of these echoes. Here are a few of these questions:(1) Can the ensemble of refractive index irregularities, causing VHF radar echoes, be describedby a Gaussian process ?(2) How much does intermittency, inhomogeneity and anisotropy affect the interpretation ofthe echoes and the deduction of atmospheric parameters ?(3) How coherent are the "scatterers" or “partial reflectors”, which lead to echoes from themesosphere, stratosphere and troposphere ?(4) What is "turbulent" and "non-turbulent" scatter or “specular-type” partial reflection ?(5) How deeply must (can) we investigate the microstructure of scattering/reflection processesto improve our understanding of VHF MST radar echoes and the applied analysis methodsand interpretations ?The first high-resolution spectra of VHF MST radar (Fig. 1) showed that there are strongmonochromatic lines on top of what one may regard as a weak Gaussian background spectrum.This lead to the assumption that partial specular-type reflection would have to be considered,as Atlas (1964) had suggested already. The question then came up: How sharp havethe gradients of radar reflectivity to be to create such strong echoes and what the reason forthese gradients could be. It was also noticed that there exists a high aspect sensitivity (Figs. 2aand 2b), which let conclude that there is a pronounced horizontal stratification of these gradientstructures.Gaussian ?Röttger and Liu, 1978Fig. 1 Spectra of early SOUSY VHF Radar observations,which were not regarded to be of Gaussian shape.449