UPPER -WIND OBSERVATIONS AND RESULTS OBTAINED ON CRUISE VII 



OF THE CARNEGIE 



INTRODUCTION 



Early in 1928 the Department of Terrestrial Mag- 

 netism of the Carnegie Institution of Washington decided 

 to make pilot-balloon observations as opportunity per- 

 mitted on cruise VII of the Carnegie . The immediate 

 consideration which led to the initiation of an upper - 

 wind program was that the Carnegie's proposed sailing 

 route lay across rarely visited parts of the oceans, 

 where no upper -air data had been obtained. The value 

 of such upper -wind observations in the navigation of 

 flying craft over the ocean, as well as in the elucidation 

 of problems of the atmospheric circulation over the 

 earth's surface, was obviously great. 



Since the study of upper -air currents lay outside the 

 geophysical program of the Department, government or- 

 ganizations engaged in aerological investigations were 

 consulted with regard to equipment and procedure. The 

 Bureau of Aeronautics, United States Navy Department; 

 the Meteorological Service of the Signal Corps and the 

 Air Corps of the United States War Department; and the 

 Aerological Division of the United States Weather Bu- 

 reau cooperated generously. Each of these organiza- 

 tions was liberal with advice, and the use of the best 

 aerological equipment at its command. 



The Carnegie received a shipboard theodolite at 

 Panama, Canal Zone, and on October 27, 1928 observed 

 the first flight in the Gulf of Panama. Throughout the 

 cruise in the Pacific the officers took advantage each 



day of any opportunity of skies comparatively free from 

 clouds to make a flight. The only part of the cruise 

 without observations was from July 3 to 21, 1929, in the 

 northern Pacific about latitude 50° north, when fog, low 

 clouds, and almost uninterrupted foul weather would 

 have prevented the observer following the balloons for 

 more than two minutes. Only 5 of the 171 flights in the 

 Pacific were made in higher latitudes than 40° north. 

 The remaining 166 flights were made as follows: equa- 

 tor to 20° north, 23 flights; 20° north to 40° north, 47 

 flights; equator to 20° south, 79 flights; and from 20° to 

 40° south, 17 flights. Of 110 flights within the tropics, 

 29 were made north and 81 south of the equator. Thus, 

 the majority of the observations were inside the trade- 

 wind regions, where a comparatively small number of 

 observations reveals the typical air movements charac- 

 teristic of the locality more clearly than an equal num- 

 ber of observations made in temperate or polar regions. 

 The balloons were observed to the following heights: 

 171 balloons at the surface, 153 at 1 km, 112 at 2 km, 90 

 at 3 km, 76 at 4 km, 58 at 5 km, 38 at 6 km, 23 at 7 km, 

 14 at 8 km, 10 at 9 km, 5 at 10 km, 3 at 11 km, 2 at 12 

 km, and 1 at 12.5 km. The observers followed one-half 

 the flights to 3.5 km, and in the highest flight, no. 77, on 

 the afternoon of March 18, 1929 an extreme height com- 

 puted to be 12.8 km was attained. 



EQUIPMENT USED IN UPPER-WIND OBSERVATIONS ON THE CARNEGIE 



The usual pilot-balloon apparatus and observational 

 procedure have been greatly modified for use on board 

 battleships and large ocean liners, where, almost ex- 

 clusively, such observations have been made. The small 

 size of the Carnegie (her displacement tonnage being on- 

 ly 568 tons), and her lively ship motion, rendered it im- 

 perative to obtain good equipment, and also to attempt 

 expedients which would not be necessary on larger ves- 

 sels. 



Shipboard Theodolite 



During 1927 and 1928 the Bureau of Aeronautics of 

 the United States Navy Department, developed and had 

 manufactured (by Keuffel and Esser, Brooklyn, N. Y.) 

 shipboard theodolites, which included numerous modifi- 

 cations from earlier types. The first of these theodo- 

 lites available. Aero 1928 U.S.N. No. 15, was loaned to 

 the Carnegie in October 1928. Subsequently the Bureau 

 of Aeronautics replaced this theodolite with an improved 

 model, which was employed in all flights after leaving 

 San Francisco on September 4, 1929. 



Both shipboard theodolites embraced a principle 

 similar to the sextant, differentiating them sharply from 

 the land pilot-balloon theodolite. The observer kept the 

 balloon in view in the vertical plane by rotating a small 

 reflecting prism aro\md a horizontal axis, the angle of 



prism rotation measuring the balloon's elevation above 

 the horizon line in an exactly analogous manner to meas- 

 uring the altitude of a star with a marine sextant. When 

 the balloon and the horizon line were brought into coin- 

 cidence, the correct angle of elevation was read off the 

 scale. No further adjustment of the setting was neces- 

 sary from instant to instant to correct for pitch and roll 

 of the ship, as both horizon and balloon shifted together 

 in the field of view. 



The optical arrangement is shown in figure 1 (p. 47) 

 and the theodolite in figure 2 (p. 47). The magnification 

 of the optical system is eight power and the field covers 

 6°. 



When the horizon line was indistinct, either because 

 of atmospheric obscurity or night, the observer could 

 employ an artificial horizon formed by an ingenious 

 small bubble device. On the cruise from Panama to San 

 Francisco, however, flights were restricted to fair 

 weather, during which the observer found the natural 

 horizon much easier for the eye than the artificial. In 

 usuig the natural horizon the balloon was seen between 

 two parts of a horizontal line, whereas the bubble gave a 

 reference only on one side. 



The red and yellow color filters on numerous flights 

 increased the visibility of the pearly surface of the bal- 

 loon against a background of blue or whitish-blue sky. 

 The routine use of a filter was found desirable for cutting 

 down the scattered light from both the sky and the sur- 



