34 DISTANT EFFECTS - Tt was expected that, following the lerge CASTIE explosions, effects at distant locations would be found in the F region, similar ‘n nature to those attributed to a disturbance emanating from IVY Mike, starting at a time corresponding to a velocity of about 13in/min. The presence of such a disturbance might be manifested in the iono~ grams in various ways, principally by the appearance of som sort cf oblique echo, that is, a signal which leaves the recorder anu returns to it over a path oblique to the earth (instead of vertically), in- dicating that a portion of the reflecting layer is effectively tilted and not concentric with the earth's surface. Instead of a direct oblique echo, however, one is more likely to find a return which has traversed two or more hups with intermediate reflections from the earth's surface or from sporadic-E ionization. Breaking up of the reflecting layer into several strata might also be seen, possibly ine dicating a horizontal movement of ions accompanying the moving dise turbance. Since all of these irregularities occur naturally from time to time, toe likelihood of their resulting from a shot-causéi disturbance must be judged by their magnitude, duration, and particulerly by their temporal consistency. It is also advisable to note the free quency of. natural irregularities for the season and the time of day involved. , 3 ohel 4t Guan Careful study of the Guam lonosphere records for the period following each shot by 2 to 10 hours reveals that, although the possibility of a disturbance in the F region was indicated several hours after each of the five largest shotc, mark2a and continuing | irregularities were present only after th ‘three largest shots, and these were fairly consistent in time of apy: ::rance relative to shot tims. After each of Shots and 2, there se. “1d to bs a period of relatively miner effects,2/starting shortly af.-r the expected tins of arrival (ETA) based on a velocity of 13 km/m:, then an interval when the F2 layer appeared quite normal, and finaliy a period of une usual Cisturbance. After Shot 5 there were clearly two distinct periods of uwmsual disturbance. Re-examination of Shot VWike ionograms revealed that two veriods of marked effects had oce’rred then also, Table 3.3 gives a survey of these overall results, 2/Although these effects were ratuer weak, their appearance at this time and for several consecutive records seems to be significant when compared with this result of examining the records for 29 normal days din April; f4x instances cf oblique echoes found between 0600 and 0800 hours, none of which extended into two consecutive ionograms,. 51 SECRET nee ’ oe maenernemes