Interferometry investigations of blob-like sporadic E plasma irregularity using the Chung-Li VHF radar

Radar echoes from 3-m plasma irregularities of ionospheric sporadic E (E-s) layer are analyzed and investigated in this article by using the Chung-Li VHF radar. The interferometry result indicates that the E-s echoes extendin g from about 109-122 km altitude are extremely aspect sensitive with enormo usly narrow aspect angle of +/-0.25 degrees. After reconstructing the three -dimensional structure of the echoes, we find that the object responsible f or the radar returns is an isolated and solid blob-like plasma structure wi th elliptical cross section. The average lengths of the major and minor axe s of the cross section are, respectively, 8.7 and 6.4 km, in which the majo r axis is primarily parallel to north-south direction and minor axis lies i n east-west direction. A comparison between the so-called trace velocity V- t deduced from the bulk displacement of the plasma structure projected on t hree mutually orthogonal planes and the true velocity V-a estimated from th e least-squares fit is also made. We find that for the present case in aver age V-a is systematically larger than V-t by a factor of 2. In addition, in terferometry analysis shows that the positive slope of the echoes structure (range rate) in the range-time-intensity plot and the negative Doppler fre quency shift of the echoes are attributed to the westward motion of the pla sma structure. This result strongly suggests that it is inappropriate to in fer the dynamic behavior of the E-s irregularities only from the informatio n in the range-time-intensity plot and the Doppler spectra, without acquiri ng the actual angular position and true velocity of the targets. (C) 2001 E lsevier Science Ltd. All rights reserved.