Incoherent scatter observations of an artificially modified ionosphere

Abstract

The launch of NASA's HEAO‐C satellite by an Atlas/Centaur rocket on September 20, 1979, provided the first “experiment of opportunity” to test incoherent scatter radar techniques for the diagnostic study of a chemically‐induced modification of the ionosphere. The cause of the disturbance was the rocket's exhaust cloud of H2 and H2O molecules that cause a rapid recombination of the F region plasma at heights above 250 km. The launch from the Kennedy Space Center (28°N, 81°W) was monitored by the incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) using low elevation angle observations over ranges exceeding 2000 km. The experiment employed various pulse lengths, integration times and scanning modes to explore optimization methods for an upcoming series of Space Shuttle induced ionospheric hole experiments. The results from the HEAO‐hole campaign include the first unambiguous observations of a gas expansion “snowplow effect,” the derivation of local and height‐integrated plasma recombination rates, and the full spatial, temporal, and dynamical morphologies of a large‐scale ionospheric hole. The campaign succeeded in demonstrating that incoherent scatter radars can play a primary role in space plasma physics “active experiments” during the next decade.