Clear evidence of obliauity appears in Fig. 3.18, particularly in the first two ionogiams (at plus 73 and 79 min), followed by indications of a return to normal (at plus 9 and 95 min). As illustrated by these oxamples, the F2 returns were very irregular. Interpretation in terms of a critical frequency and a minimum virtual height for the F2 Jayer was difficult or impossible. Furthermore, throughout much of this period, the lack of consistency from. me minute to the next indicated rapid changes in io distribution, presumably resulting ast from motion of the air molecules, : Despite the irregularities, an attempt was made to analyze the data recorded during this period. Ranges of height and frequency values for the variow groups of echoes in the F2 regi were plotted on work sheets. When these were examined, a tendency for the minimm SL+S7M 800 600 400 200 “= 52.+¢60M $$.+¢9M “400 + : ' 2 peeks tf “ za ae 3 ore ae ’ penne sof ub i oa GE, Be > rhebtd— age merida: ltd ob Ef 53.+63 + m Ferner = : a ine ee +4 s 29 <9 oot Boge os: o cpu oe 0 eh $4 ee Bhd oo - J 3 , pet ee hpinmebeed cpt fat f WW 56.+ 70M , ee ve oo , e Serr 4 os tt en Rasy is ¥E 7 epee 2 . i004 2 ee TE 3. Fos 4 6 ‘ & os 0 4 WNC Fig. 3.17 = Ionospheric Records at Rongerik Following Shot 4 by 57 to 70 min, Showing Echo Rising from 350 to 500 km Apparent Height a SECRET