T. Hagfors

Max Planck Institut für Aeronomie, Katlenburg-Lindau, Germany

The first serious high power ionospheric modification work was initiated at Platteville, Colorado, by ESSA, Environmental Science Services Administration under the leadership of Bill Utlaut. Studies were made if HF heater induced air-glow, heater-induced spread F, wide band heater-induced absorption and heater created field-aligned ionization. This work was carried out in the late 60-ies.

It soon became clear that it would be highly desirable to include in the complement of diagnostic tools an incoherent scatter radar, a tool developed for ionospheric diagnostics in Arecibo Puerto Rico, and in Jicamarca, Peru, and later also at Millstone Hill in Massachusetts. Spurred by the work in Platteville Bill Gordon and others suggested that a heating capability be developed in connection with the Arecibo observatory by suspending an HF feed above the primary reflector allowing the incoherent scatter facility to be used to probe the heating effects. The talk describes the early development in Arecibo, and the improvement in observations and facilities which gradually took place with the construction of a separate heating facility until the heating work was cut short by hurricane George in September 1998. The Arecibo work has provided inspiration and ideas for heating work in Tromsö, and has also provided material for disputes about the interpretation of results. Some of the advance in understanding of the processes in ionospheric heating is due to comparison of results from the two facilities. Much work remains to be done to understand the effects on the state of the ionosphere on the processes taking place, and the hope is that the heating work will be able to continue in Tromsö and that it can be resurrected in Arecibo with new heater concepts which resemble the original ones abandoned in the past.