Plot: . ~ We proceed now to describe the method of constructing the isodese contours for the simpler case of the static hodograph. The static hodograph presents a plan view of the vertical structure of the forecast idnds at- zero tine and at the origin. Pig. 1 is s sample hodograph constructed fran data in Table I, The criticiens against the static hodograph are that 4t shold not be expected to persist unchanged even at the origin throuche cut the time of fall-out, end that it does not in princinle aprly at all ta points displaced fram the origin. These criticiems become mre imrortcnt as one attempts to forecast thd lowleval iscdose lines which are estahlished at considerable ¢istances: from tho origin and many hours after shot tins. The static hedograph does, however, provide 6 useful suide ond has the virtue that 2 plot can be prepared from it very quickly indeed. Using the sample hodocraph of Pig, 1 let us compute the dose index for point "P* at 40° and 60 nautical miles from ground sero. There will be two componente for "“P* and all other scints along the redius fron "Z* through *P". From the hodograph the intercept heights ond distances cre 79,000 2 and 45 miles at */.", and 39,000 %% and 73 ailee at". is nentioned above the total index for "FP" is the aum of the indices computed Let us consider first the index free intercept "/.".. Particles wiich fell at ".." on the surface start at 79,000 ft above Zero... «2 they fell tc 65,%O rt they travel westward approximately 75 miles... In fallins the next 5,000 f% they travel approximately 10 miles scuthwest; Thereafter ‘ner swing arcand through the scuth, travel castward between 50,000 and a£,1100 ft, gradually turn to the northeast, ond at about 15,000 ft settle ints the surface trades for the last 20 miles of westward travel to pcint “3, Sdnee the hodogreph is draw: for the convoniont rate of 5,000 ft per hour the particles arrive at %:." 15.8 hours after sero. Particles arriving at "P® from 79,000 ft mist spend a slightly longer tine in ecch altitudes layer; their trajectary is similar to that for the faster~falling particles but is expended, Thee relative time for particles to arrive at *P* camparad to "2" is given by the ratio of the vector sums or by the factor 60/45 = 1.33. The time in houre is therefore 21.3 hours. Now we have aseumed a rolationshir between fall rate and particle Ciameter given by Stoke's law. Srecifically, for land shots et the Pacific Proving Grounda, we assume that 75-aicron particles settle at 4,000 ft rer hour. Particles arriving at "P* from 79,000 ft settle at 3,740 ft per hour ond are therefore slightly smaller than 7§ microns. Stoke's law cives values 72.4 cicrons T2eb wicrons., Using equation (3) with the sumerical tha intercept 7." <f end 21.1 hours coe obtains a dese index at "P* from approximately 12.