E region echoes observed with the Syowa HF radar under disturbed geomagnetic conditions

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E region radar echo parameters (echo power, Doppler velocity and spectral width) obtained with the Syowa Station HF radar under disturbed geomagnetic conditions are qualitatively analyzed to study how echoing region changes due to HF wave refraction caused by ionospheric disturbance. It is found that with increasing disturbance level, echo ranges become shorter because of wave refraction during propagation due to more enhanced D and E region electron density. When geomagnetic H component variation (ΔH) is less than about -900 nT, echoes are returned from the central E region where geomagnetic aspect angle is close to zero. When ΔH is very high (= - 1500nT), the echoes are backscattered from the D and lower E regions and their power, Doppler velocity and spectral width are largely suppressed. The results suggest that we must always consider, more or less, wave refraction effect in analyzing near-range E region HF radar echoes.
国立極地研究所の論文