maxima of the comparison period and critical frequencies were consistentiy leas than the frequency minima. However, the extreme rise in virtual height which occurred after Shots 1 and 2 and Shot Mike (Operation IVY) was not observed at. Rongerik following Shot 4. If there was a region of mrked upward displacement of the F2 layer resulting from Shot 4, as seems likely, then it occurred above another geographical location. Ths most pronounced evidence of | abnormal conditions occurred in the Jonograms recorded during the per= iod from plus 40 min, when the F2 layer emerged from absorptive obscuration, to about plus 11/2 hr. The weak and irregular echoes from plus 40 to plus 55 min are shown in Fig. 3.16. A series of ‘Lonograms from plus 57 to plus 70 minshows an F2 return apparently — rising to 500 ln (Fig. 3.17). _ 7 Kn cet pp cae “ab Sete Eee: 800 ere? ‘ x2 A dda “2B Se Er it EERE: ‘ ~*~ 45.+40M 600 - 400 200 qa + a fi THEE an: beck: bict ? ome 0 ra POPE 46+ 42M oe 800 OY 49.536 i ee Sart 600 400 200 dina fninn KM i pepe 800 Bik 47.4456q Fe i Fie op Ks 600 § ph pore 2 00 tmmerer a ow 2 : : Pi: Be Bo s * pe are bent 0 ~ ene te een 80.455M a: aa. eer mi 5. sh at : a me : | TTS i oe 3 4 Ria be i 6 60 eek ee OL 8 te te“se Figo 3.16 « Ionospheric Resords at, Rongerik Following Shot 4 ty 40 to 55 min, Showing Weak and Irregular F2 Echoes 43 SECRET