46 INSTRUCTIONS FOR MAKING PILOT BALLOON OBSERVATIONS 



velocity. If the means are used, as in the graphical method, the 

 required velocity is obtained directly, the computation may be done 

 by slide rule. 



145. Foim No. 1117-Aer. is used for the tabulation of wind-aloft 

 data into velocity groups for each direction. Particular attention is 

 called to the fact that the second level on this form provides for data 

 at 500 meters above the surjace, while all other levels refer to sea level. 



146. The data for the level 500 meters above the surface are to be 

 entered regardless of the altitude of the station above sea level. For 

 some stations it will be necessary to take the data for this level from 

 Form No. lllOA-Aer. or Form No. 1115-Aer. However, the alti- 

 tudes of several stations are such that these data can be copied from 

 some one of the standard levels above sea level. The data may be so 

 copied when one of the standard levels above sea level is 50 meters or 

 less above or below the 500-meter level above surface. For example, 

 at stations with altitudes of 50 meters or less above sea level, the data 

 for the 500-meter level above surface are to be copied from the. 500- 

 meter level above sea level; while at stations with altitudes between 

 200 and 300 meters above sea level, the data for the 500-meter level 

 above surface are to be tabulated from those entered on Form No. 

 1124-Aer. for the 750-meter level above sea level, etc. 



147. Data for all levels, except as indicated for the 500-meter level 

 above surface, are to be taken from Form No. 1124-Aer. To tabulate 

 the data the number of velocity entries on Form No. 1124-Aer. oppo- 

 site each direction, falling within each of the five velocity groups, are 

 counted separately and the number counted entered in the appropriate 

 squares on Form No. 1117-Aer. For example, if the velocities oppo- 

 site "N" on Form No. 1124-Aer. are as follows: 2, 1, 6, 9, 4, 18, 11, 22, 

 the entries to be made opposite "N" on Form No. 1117-Aer. would be 

 as follows: Under (2-7), 3; under (8-14), 2; under (15-21), 1; and 

 under 021), 1. The same procedure is to be followed for each of 

 the other directions. All velocities of 1 meter per second or less, 

 including cahns, are then to be counted and entered in the lower 

 left-hand square under the heading "0-1." These data may also be 

 taken directly from Formslll4A-Aer. and 1114B-Aer. by countmg 

 the number of velocities in each velocity category for each direction. 

 The final step is to total the entries both vertically and horizontally 

 and to enter the combined total in the lower right-hand square. 

 This last entry should, of course, check with the "total number of 

 observations" appearing on Form No. 1124-Aer. 



148. Mailing forms to the central office. — At the conclusion of each 

 month all pilot-balloon forms are to be carefully checked and prepared 

 for mailing to the central office. All forms for the month (except 

 Form No. 1116-Aer.) are to be mailed not later than the 10th of the 

 following month. The last combined form (lllOA and 1115-Aer.) to 

 be included, will be the one having the graph (Form 1115) for the last 

 observation of the month and the data (Form lllOA) for the first 

 observation of the following month. DupHcate copies of Form No. 

 lllOA-Aer. are to be retained in the station file; also any other data 

 needed for special summaries, such as normal resultant winds, mean 

 wind roses, etc., are to be copied off the forms before mailing. 



149. Tables used in pilot-balloon work. — A brief description of the 

 tables which are used regularly in pilot-balloon work is given below. 



