Radio Refractivity Gradient in Lower Troposphere & Its Influence on Transhorizon Radiowave Propagation

Abstract

Based on recent radiosonde data from the India Meteorological Department, which have better accuracy than data available upto 1967, refractivity gradients for three years (1968-70) over the Indian subcontinent have been determined. The influence of high refractivity gradients usually observed in the lower troposphere on radio wave field strength and variability over transhorizon paths is discussed. The gradients in the lower layers, particularly upto an altitude of 250 m were found to be much higher than values determined from the difference between surface refractivity (N_s) and refractivity at 1 km (<i>N</i>₁). A significant percent of these were ducting gradients. Field strength observations over three typical transhorizon paths, which were characterized by high level and wide variability for a significant percentage of time, were found to be consistent with these refractivity gradients.