WEATHEE BUKEAU. 89 



Observations with two theodolites have been continued, whenever 

 opportunity afforded, in order to cheek the accuracy of the formula 

 for rate of ascent of balloons and the behavior of the balloons them- 

 selves at hi<i:]i altitudes. These observations have shown that the 

 revised rate of ascent formula o:ives extremely reliable results, ex- 

 cept when there are pronounced vertical movements in the atmos- 

 phere. Even then tlie error is appreciable only in the lower layers. 

 Cooperation. — Effective cooperation with the Army and Navy 

 meteorological services has been continued throughout the year. 

 Each of these services maintains a number of pilot-balloon stations, 

 Avhose primary purpose is to furnish data of immediate local in- 

 terest to aviators at fl,ying fields. These observations are also tele- 

 graphed to district forecast centers of the Weather Bureau for 

 use in issuing " Flying Weather " forecasts. They thus supple- 

 ment, in a very helpful way, the observations made at Weather 

 Bureau aerological stations. In addition to the stations in the 

 United States proper, the Navy maintains one at Santo Domingo, 

 Dominican Republic, and one at Coco Solo, Canal Zone, which, 

 togetlier with those of the Weather Bureau at San Juan, P. R., 

 and Key West, Fla., furnish information of value in connection 

 with the development and movement of hurricanes. A much larger 

 number of stations is necessary, however, to make this service as 

 effective as it should be. 



In the autumn of 1921, at the request of the director of the 

 Brazilian meteorological service and in cooperation with a repre- 

 sentative of that service, temporarily stationed in Washington, plans 

 for the organization of an aerological service in Brazil, patterned 

 after that in the United States, were outlined and satisfactorily 

 worked out. All necessary equipment was purchased, methods used 

 in this country were studied and adopted, and two trained observers 

 of the Weather Bureau were released, in order that they might be 

 employed by the Brazilian Government to get the service properly 

 inaugurated in that country. 



Central office. — All observations made at kite and balloon stations, 

 by the Army and Navy as well as by the Weather Bureau, are for- 

 warded to the central office of the Weather Bureau for final reduc- 

 tion and study. Data based upon these observations are furnished . 

 in answer to numerous inquiries not only from other government 

 departments, but from commercial aviation concerns as well. In 

 many cases reprints of special discussions and summaries were issued 

 in answer to these requests. 



Work has been continued on the preparation of a summary entitled, 

 '' An Aerological Survey of the United States." When completed, 

 this will contain the results of all free-air observations made in this 

 countr}^ jt^art .1, " Results of Observations by Means of Kites," 

 was completed and published during the past year. It contains 

 tables and figures showing monthly, seasonal, and annual values of 

 pressure, temperature, humidity, density, and wind at various heights 

 u}) to 5 kilometers. It also includes a detailed study of the behavior 

 of free-air winds, classified by months and seasons, by geographic 

 location and according to different wind directions at the surface. 

 Tables and figures are given, showing the frequency and amount of 

 clockwise and counterclockwise turning of winds, the frequency of 



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