Ae me at a A A ABSTRACT During Opsration CASTIE, two ionosphere recorders were operated in the Marshall Islands — at Site Elmer, about 200 miles west of Bikini Atoll, and at Rongerik Atoll, about 150 miles east of Bikini «= . in order to study the effects of the detonations on the ionosphere. Normal data from existing stations at Maul and Adak and special data furnished by existing stations at Guam and Okinawa were examined for effects at distances of 1,400 to 3,000 miles. Severe absorption was observed 200 miles west of all. multimegaton shots, lasting several hours, presumably due to ionization caused by radioactive material carried by high-level winds. Turbulence in the E region after each major shot was indicated by the diffuse sporadic-£ returns at Rongerik. Also, for shots of megaton range, an effect on the F2 laysr similar to that first found following Shot Mike of Operation IVY was observed, its natwme varying from shot to shot. This phenomenon is apparently far more complex than originally assumed, but it is still attributed to the large-scale convection resulting from the conversion of blast-wave energy into heat in the upper atmos~ phere. Lonospheric disturbances, apparently resulting from the three largest explosions, were found up to 2,600 miles away, with indicated velocities of about § to 16 kn/min. 5-6 SECRET