The Observations of Sporadic E Irregularities in Equatorial Anomaly Crest Zone by Using Chung-Li VHF Radar.

Abstract

With employing 52 MHz Chung-Li VHF radar, the ionospheric irregularities embedded in sporadic E layer in equatorial anomaly crest zone are observed. It shows that in general the echoes of sporadic E irregularities in association with plume-like structures are occurred in the height range from 99 km to 122 km and centered at around 108 km, quite consistent with the observations made by local HF ionosonde. Spectrally analyzing the radar returns indicates that the low-velocity type 1 (or type 3) and type 2 radar spectra are both observed and may appear simultaneously in the same Doppler spectrum. Their characteristics are estimated and discussed in the text. Differing from those obtained by using VHF radars situated in equatorial and auroral zone, the Doppler velocities of type 1 (or type 3) radar spectra observed here are generally within 95∼115 ms-1, fairly smaller than the former ones. The typical Doppler velocity and spectral width for type 2 radar spectra are within -150-160 ms-1 and 16-30 Hz, respectively. The average drift velocity of 3-meter irregularities deduced from type 2 spectra is also presented. It displays that the drift is toward the radar at the lower height, while away above approximately 104 km. Moreover, below the altitude of around 108 km the drift velocity varies substantially with height at the gradient of about 10 ms-1/km. Above that height, the drift velocity changes slightly with height. The plausible process corresponding to these two distinct behaviors of height variation of drift velocity are also discussed in this article.