International Journal of Sustainable Energy and Environmental Research 2312-5764 2306-6253 10.18488/journal.13.2018.72.53.64 International Journal of Sustainable Energy and Environmental Research Determination of Refractivity Gradient and Modified Refractivity Gradient for Cross River State International Journal of Sustainable Energy and Environmental Research International Journal of Sustainable Energy and Environmental Research 06-2018 2018 06-2018 06-2018 7 2 53 64 10 Oct 2018 18 Dec 2018 In this paper, determination of refractivity gradient and modified refractivity gradient for Cross River state was carried out. The year 2013 Radiosonde meteorological data from Nigerian Meteorological Agency (NIMET) was used. Refractivity, modified refractivity, refractivity gradient and modified refractivity gradient were computed. The results showed that in the year 2013, Cross River state had maximum modified refractivity gradient (dM/dz) of 114.9 (M -units/Km) and it occurred in December whereas the minimum modified refractivity gradient (dM/dz) on 81.9 (M–units/Km) and it occurred in October . Also, in the year 2013, the maximum refractivity gradient (dN/dz) was -42.1 (N-units/Km) and it occurred in December whereas the minimum refractivity gradient (dN/dz) was -75.1 (N-units/Km) and it occurred in October. The standard refractivity gradient of -39 N-units and standard modified refractivity gradient of 118 M-units occurred in December at altitude of 103 meters. In all the months the atmospheric condition was in the normal state except in the month of October where superrefraction occurred.