Research into the aeronomical and plasma physical aspects of high power, high frequency ionospheric modification is the principal thrust of the HAARP program. One aspect of the modification process is the generation of new wave energy at low frequencies. An extensive suite of ground-based diagnostic instruments for studying the modification and wave generation processes will complement the RF heating facility at Gakona, Alaska.

One of the instruments being considered for the diagnostic facility is an imaging riometer capable of examining the perturbed region with sufficient spatial and temporal resolution to aid in characterizing the ionospheric parameters that are critical for understanding and controlling the conversion of HF heater power to other forms. To realize the full potential of this instrument it should be located several miles from the heater site in order to minimize electromagnetic interference from the RF transmitters.

A prototype of the HAARP imaging riometer has been designed and deployed at the Gakona HAARP site. To date, it has been used mainly to observe the naturally-occurring auroral absorption activity prevalent at this site. Midnight and midday absorption events associated with magnetospheric substorms are common features at this subauroral location.

A new feature, intense, often localized, short-duration absorption spikes, occurring around the dusk meridian, has been encountered. The spatial and temporal morphology of these spikes, and their relationship to substorm processes, are subjects of current study.

The work at the University of Maryland has been carried out with support from the High Frequency Active Auroral Research Program (HAARP) through subcontract No. 1011-91-01 from APTI. The contributions to this project by H. Breden, J. Etter, P. Flores, J. Giganti, E. Knouse, D. Papadopoulous, L. Pharr, J. Touart, and R. Wood of the University of Maryland are greatly appreciated. We also acknowledge the helpful contributions of R. Jacobsen, M. McCarrick, R. Shanny, R. Short, and L. Shulman of APTI and J.V. Olson of the University of Alaska, Fairbanks.

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Carpenter, D.L., B.L.\ G...
 ...rn Scandinavia, {\it J.\ Atmos.\ Terr.\ Phys., 44}, 1025, 1982.

Allan T. Weatherwax