D region HF radar echoes associated with energetic particle precipitation and pulsating aurora
- 1Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
- 2Department of Information and Communication Engineering, University of Electro-Communications, Tokyo, Japan
- 3National Institute of Polar Research, Tokyo, Japan
- 4Department of Communications Systems, University of Lancaster, Lancaster LA1 4WA, UK
Abstract. Milan et al. (2001) identified a class of narrow, slow-moving HF radar backscatter echoes which originate between altitudes of 80 and 100 km, the ionospheric D- and lower E-regions. These echoes appeared to be associated with the occurrence of pulsating aurora, which are known to be created by energetic electrons capable of penetrating to D region altitudes. In this study we show that these echoes are observed in tandem with enhancements in cosmic noise absorption (auroral absorption), additional evidence that energetic (>30 keV) particle precipitation is responsible for generating the irregularities from which a radar can scatter. In addition, we show that the D region backscatter echoes occur predominantly in the post-midnight sector during substorm recovery phase, in common with auroral absorption events and pulsating aurora.