HF echo types revisited: aspect angle attenuation effects
The high-spatial-resolution observations of the auroral E-region echoes by the Super Dual Auroral Radar Network (SuperDARN) HF radar at Pykkvibaer, Iceland considered in a previous study are re-examined. Both the spectral power and Doppler velocity of the E-region HF echoes exhibit strong depend...
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2009-08-01
|
| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/27/3065/2009/angeo-27-3065-2009.pdf |
| Summary: | The high-spatial-resolution observations of the auroral E-region echoes by
the Super Dual Auroral Radar Network (SuperDARN) HF radar at Pykkvibaer,
Iceland considered in a previous study are re-examined. Both the spectral
power and Doppler velocity of the E-region HF echoes exhibit strong
dependence on the slant range and expected off-perpendicular magnetic aspect
angle (aspect angle attenuation). We consider the aspect angle attenuation
effects in identification of spectral HF echo types. It is argued that echoes
with Doppler velocities close to the nominal value of the ion-acoustic speed
<I>C<sub>s</sub></I> (~350 m/s) and echoes with velocities greatly exceeding the <I>C<sub>s</sub></I>
(up to 600 m/s) are more related in their generation mechanisms than
previously thought. It is proposed to treat the echoes near the <I>C<sub>s</sub></I> as
aspect-angle-attenuated counterparts of the high-velocity echoes and that
both types are generated directly by the modified two-stream instability with
aspect angle attenuation resulting in the preferential phase velocity
saturation at the <I>C<sub>s</sub></I>. |
|---|---|
| ISSN: | 0992-7689 1432-0576 |