accurate th. ’ feet and may be in error by as much as +1,000 feet. When making prints from the o sative, an overexposure can result in the disappearance of some detail in the surge ou By superimposing the time sequence of Surge outlines for a given shot, a few such photographic disappearances become apparent. Since the base surge should not retract from a region where it is once photographically detected, the largest photographically determined boundary is always continued into later time; these maintained boundaries are indicated as dashed lines in the transit plots (Appendix F) to be described later. Times cannot be more accurate than +2 seconds, a limitation determined by the accuracy with which the gamma records can be related to the photographic data. Therefore, the analysis presented, while useful for the purposes of this report, must be substantiated by repetition with final reduced photographic information (Reference 91). These limitations also apply to other sections of this re- port (especially Section 3.3.4) where the position of the visible boundary is used. On the basis of both radiological and photographic evidence, the base surge may be generally described as a low torus-shaped cloud that expands radially as it is transported downwind. Al- though roughly circular in outline, definite lobes or irregularities can be observed in the aerial photographs and are suggested by the final isodoSe patterns (Figures 3.103 and 3.105). Such irregularities are probably caused by nonsymmetrical interaction of the explosion bubble with the surface or by local retardation due to turbulence resulting from Surface obstructions such as the target ships or the atoll reef. On both shots, the base surge did not exceed an altitude of about 2,000 feet; thus, after cessation of energetic radial expansion, surge movement is controlled by local surface winds. Difficulties caused by incomplete knowledge of local wind speed and direction are met by assuming that the photographically determined center X (Appendix F) represents the true surge center up to the last reliable photographically determined position (3.5 minutes for Wahoo and 6.0 minutes for Umbrella), after which the surge center is assumed to move in accordance with the official Task Force surface winds (15 knots from 090° . T for Wahoo and 20 knots from 050° T for Umbrella). AS will be substantiated in detail later, the downwind gamma dose rate records for Wahoo suggest the generation of at least two base surges after Wahoo, forming a series of roughly concentric expanding toroids. Such a complex Surge structure could result from a sequence of interactions between the explosion bubble and the water surface, a postulate that is supported by photographic evidence showing secondary plumes rising above an already well developed base surge at about 26 seconds (Reference 88). A similar phenomena (with perhapstertiary plumes) was photographically recorded after Shot Wigwam, the only other deep-water nuclear detonation for which such data is available (Reference 14). Additional plume development may be presumed to have created a second base surge in a manner similar to primary surge genesis. The multiple surges so formed might mix or remain as partially or wholly separate cloud masses. Aerial photographs of the Wahoo surge at times greater than 2 minutes show two concentric rings of cloud separated by an annulus of relatively clear air. The center of the inner surge ring contains a number of irregular clouds. Prior to 2 minutes, white water masks any inter- nal details of the base surge. Thus, both the dose rate records and later aerial photography favor the hypothesis that at least a primary and a secondary base surge did exist and that these surges were at least partially separate. For Umbrella, however, a single base surge torus seems adequate for an analysis of the gamma doSe rate records. Aerial photographs show a Single base surge toroid witha nearly cloud-free center. Very diffuse remnants of the Um- brella column moving centrally but above the surface base surge are apparent in some photographs, ” A Schematic representation of the more complex Wahoo surge is presented in Figure 3.63 together with a number of additional terms and symbols needed for a description of photographically distihguishabie surge features or the manner of base surge passage over a given Station. For greater simplicity of presentation, the surge is illustrated as stationary while the coracles are indicated as moving through it. The nine different types of transit illustrated together with their letter designators are self-explanatory. Use of these letter designators permits a maximum condensation of descriptive material and pertinent data. The -designators 120 Page 121 was deleted. 8