Small-scale variations of radio refractive index in the troposphere. Part 1: Relationship to meteorological conditions

A description is given of results obtained from soundings made with a spaced-cavity balloon-borne refractometer and 10cm-band vertical-incidence radar. The experiments, carried out at Cardington, Beds., England, in 1964 and 1965, show that at heights up to 2km there is often considerable inhomogeneity in the refractive-index structure, even in nonanticyclonic conditions. Instantaneous differences in refractive index of 5 parts in 106 (5N units) were observed over distances of 11cm within discrete parcels of air in which the quotient of variance by scale size was unusually large, occasionally 10¿11m¿1. Such parcels were often located at or near the base of a layer of steep mean vertical gradient in refractive index associated with elevated inversions or isothermals. The results are discussed in relation to meteorological factors, such as wind shear and dynamic stability, and to theories of tropospheric scatter based on the concept of homogeneous turbulence.