Abstract
Abstract. The CUTLASS (Co-operative UK Twin Located Auroral Sounding System) Finland HF radar, whilst operating in a high spatial and temporal resolution mode, has measured the ionospheric signature of a naturally occurring ULF wave in scatter artificially generated by the Tromsù Heater. The wave had a period of 100 s and exhibited curved phase fronts across the heated volume (about 180 km along a single radar beam). Spatial information provided by CUTLASS has enabled an m-number for the wave of about 38 to be determined. This high-m wave was not detected by the IMAGE (International Monitor for Auroral Geomagnetic Efects) network of ground magnetometers, as expected for a wave of a small spatial scale size. These observations over the first independent confirmation of the existence of the ground uncorrelated ULF wave signatures previously reported in measurements recorded from an HF Doppler sounder located in the vicinity of Tromsö. These results both demonstrate a new capability for geophysical exploration from the combined CUTLASS-EISCAT ionospheric Heater experiment, and provide a verification of the HF Doppler technique for the investigation of small scale ULF waves.Key words. Ionosphere (ionosphere – magnetosphere interactions) . Magnetospheric physics (magnetosphere – ionosphere interactions; MHD waves and instabilities)
Highlights
Pulsations with large azimuthal wave numbers, m, are a topic of considerable interest at present, in both theoretical and experimental studies
The CUTLASS observations presented here indicate that a high-m wave was detected in the radar backscatter which was not observed on the ground but was observed in the ionosphere by the DOPE (Doppler Pulsation Experiment) sounder
The line of sightows observed by CUTLASS were modulated by a ULF wave signature which appears as a series of bands or stripes during this interval
Summary
Pulsations with large azimuthal wave numbers (small azimuthal scale size), m, are a topic of considerable interest at present, in both theoretical and experimental studies. The CUTLASS observations presented here indicate that a high-m wave was detected in the radar backscatter which was not observed on the ground but was observed in the ionosphere by the DOPE (Doppler Pulsation Experiment) sounder. Wright and Yeoman (1999) reported HF Doppler observations of so-called uncorrelated waves, that is to say those which had an ionospheric signature without a corresponding ground magnetic signature. These authors suggested that these observations were a result of waves with small spatial scale sizes which were not visible to other instruments with a lower spatial resolu-.
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