Abstract
Abstract. Results are presented from the first two active experimental campaigns undertaken by the new SPEAR (Space Plasma Exploration by Active Radar) high-power system that has recently become operational on Spitzbergen, in the Svalbard archipelago. SPEAR's high-power beam was used to excite artificial enhancements in the backscatter detected by the ESR (EISCAT Svalbard Radar) parallel to the geomagnetic field, as well as coherent backscatter detected by both of the CUTLASS (Co-operative UK Twin Located Auroral Sounding System) coherent radars, in directions orthogonal to the geomagnetic field. The ESR detected both enhanced ion-lines as well as enhanced plasma-lines, that were sustained for the whole period when SPEAR was transmitting ordinary mode radio waves, at frequencies below the maximum F-region plasma frequency. On a number of occasions, coherent backscatter was also observed in one or in both of the CUTLASS radars, in beams that intersected the heated volume. Although the levels of enhanced backscatter varied considerably in time, it appeared that ion-line, plasma-line and coherent backscatter were all excited simultaneously, in contrast to what has typically been reported at Tromsø, during EISCAT heater operations. A description of the technical and operational aspects of the new SPEAR system is also included.
Highlights
High-power ground-based HF radio transmitters have played an important role, over the past few decades, in the investigation of nonlinear wave interactions in space plasmas
The striations are thought to be generated by a thermal parametric instability at the upper-hybrid resonance (UHR) height, they extend for several tens of kilometres along the geomagnetic field (Robinson, 1989)
The SPEAR beam was directed along the geomagnetic field, as was the EISCAT Svalbard Radar (ESR) radar
Summary
High-power ground-based HF radio transmitters (heaters) have played an important role, over the past few decades, in the investigation of nonlinear wave interactions in space plasmas. In April 2004 a new high-power HF facility began operations on the island of Spitzbergen in the Svalbard archipelago This new SPEAR (Space Plasma Exploration by Active Radar) facility, designed and built by the University of Leicester, in the UK, is intended to serve a number of scientific purposes. Its main role will be to carry out active space plasma experiments in the polar ionosphere and magnetosphere by exciting striations that can be used as targets for coherent scatter radar observation of otherwise unobservable dynamical processes (Yeoman et al, 1997), by stimulating Alfven wave resonances in the magnetosphere (Robinson et al, 2000; Wright et al, 2000) and, in addition, it will be able to function as a radar, by itself receiving backscatter from the ionosphere (low-power mode), in a manner similar to the CUTLASS radars, and possibly from the magnetosphere (high-power mode).
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