Contributions of incoherent-scatter radar measurements at Arecibo for the improvement of IRI

In the years 1974 to 1977 the incoherent-scatter radar at Arecibo made high resolution measurements of electron density in time and altitude, under the I29 program. This program ran on monthly basis and each observing run was for about 36 hours, consisting of two daytime periods and the intervening night. Electron density was measured from 100 to 500 km with a single 24 μs pulse which provided an altitude resolution of 3.6 km. These measurements provided very accurate values of hmF2, h0.5, E-F valley parameters and topside Ne gradient thereby providing important inputs for the improvement of IRI. This paper gives a summary of these inputs.