1.2.3 Absorption A decrease in intensity of certain high-frequency signals, last~ - dng for about 1/2 hour, was attributed to abnormal absorption in the D region (about 50 to 80 km high) resulting from the heating effect of the shock wave and the consequent increase of collision frequency. This was observed following Shots Mike and King of IVY. It was con- cluded that this absorption, though significant, would probably not seriously hamper communications. 124 Other Effects Initiation of effects in the E region, due to local changes in ion density, was shown (in the TUMBLER-SNAPPER report) to coincide with the errival time of the compress:.onel wave (see Reference 2). Both Ewlayer and Flelayer effects of this nature were observed at Bikini for Shot King, which took place at Eniwetok and which was re- latively small compared with Mike and the majority of the CASTIZ shots. An increase in sporadic-E activity has almost always been fowd to follow atomic explosions. This appears to be another aspect of the effects dus to local changes in ion density, as it seems to be ine creased backscatter from a region that is "roughened" by turbulence. 19 SECRET