H cabana wy atomic cloud. Disturpances in the trade winds modify the prevailing eastnortheast flow for periods of,a few days but the effect is to enlarge the trade wind cloud rather than alter the general westward drift. It is possible, however, to reduce the probability of contaminatian in some areas affected bythe Ivy debris by scheduling future tests in different months. Figure 5.1, 5.2, and 5.3 show the monthly average trade wind flow at the surface as of the first of January, March, May, duly, September, and November, Ths shaded portions Gack the areas of mixing between the trade winds of northern and southern hemispheres - areas of increased precipitation and generally disturbed weather. Disturbed weather does not affect the entire shaded area simultaneously, for the storminess is, generally, confined to narrow and intermittent bands (often two east-west _ bands roughly parallel) perhaps only 100 miles wide. The areas indicated on the figures include the normal north-south range of this intermittent band of storminess and seasonal variation of rainfall is the result of the seasonal movenant of this disturbed weather zone. ‘These figures present climatology that might be useful for : general planning. For exanple, the probability of rainout -hezard is maximized in the shaded areas. The second map of Figure 5.3 corresponds to the time of Operation IVY and illustrates the prevailing flow from Eniwetok to southern Asia. This was corroborated by the radiological data. The second map of Figure 5.2 on the other hand, illustrates the fact that the fallout and rainout at Guam, the Philippine Islands and southeastern Ania would be minimized in late sumer. In addition to fallout from the trade wind Layer, the total activity could be greatly increased by superimposing material from ‘the upper troposphere. Such superposition might be caused by a current of "deep easterlies". Occasionally, the winds at Eniwetok ‘blow from the east throughout the troposphere - from the surface to 55,000 feet. Bomb debris that stabilized in the troposphere in such a situation would move toward the west with little stretching .go that the amount of radioactivity available for fallout and Sonata rainout would be relatively large. Showers are more frequent over islands so it would be possible for a long column of this concentrated debris to move over an island such as Guam and be scavenged by rain. The meteorological conditions necessary for the "Vertical shear in disturbances is more pronounced than in the undisturbed trades, producing a greater than normal cross-stream stretching of the atomic cloud, - 30-