Monthly variation of the gradient of radio refractive index over india

Based on the afternoon radio sonde data of 12 stations in India during the years 1956¿1960, radio climatic charts of the radio refractive index difference between surface and 850 mb have been prepared and briefly discussed. Some climatic characteristics of the difference of radio refractive index between surface and 850 mb and that between 850 and 700 mb levels have also been tabulated. The correlation coefficients between the surface value of refractive index and its simple difference from that at 1.5 kilometre have been studied for all the four seasons and their least squares straight line fit determined in order to facilitate the predictions of the gradient of refractive index.