INSTRUCTIONS rOR MAKING PILOT BALLOON OBSERVATIONS 45 



When an observation is not entered on Form No. 1114A-Aer. the 

 ''No observation" note on the Form No. 1114A-Aer. for the previous 

 scheduled time will, for example, read as follows: "None — Low 

 clouds — Observation made at 8:20 a. m." The time of each delayed 

 observation entered on these forms is to be entered in red ink. In 

 entering the maximum altitude wind data on Form No. 1114A-Aer. the 

 following rules shall apply: 



1, For levels between surface and 1,000 meters mean sea level, in- 

 clusive, if the maximum altitude reached is 100 meters, or less, below 

 one of the standard levels, the wind data for the maximum altitude 

 shall be entered on Form No. 1114 for that standard level. 



2. For levels of 1,500 meters, or above, if the maximum altitude 

 reached is 250 meters, or less, below a standard level, the data for the 

 maximum altitude shall be entered for that standard level. 



139. In the "maximum altitude" column at the right-hand side of 

 Form No. 1114A-Aer. both the maximum altitude reached (to the 

 nearest meter) and the wind data at that level are to be entered, thus: 



5672, 14716, etc. 

 12—13 14—22 



140. When the maximum altitude reached is more than 10,000 

 meters above sea level, data for each 1,000-meter level above 10,000- 

 meters (11,000, 12,000, etc.) are to be entered on Form No. 1114B-Aer. 



141. Form No. 1116-Aer. is for station file and is designed to assist 

 in the preparation of wind-aloft reports as transmitted by teletype or 

 telegraph and to serve as a station record of such reports. 



142. Form No. 1124--Aer. is used for the tabulation of wind veloci- 

 ties according to directions and for the computation of resultant 

 winds (by those stations specifically instructed to do so). In the 

 columns under "Velocities" will be entered the individual velocities, 

 each quarter of a sheet representing one level. After the velocities 

 have been added and canceled, that is, the difference between dia- 

 metrically opposite directions obtained, these differences are multi- 

 plied by the sine and cosine values given on the form. The algebraic 

 sums and means of these products are then obtained. The resultant 

 wind direction and velocity may be obtained either graphically or 

 trigonometrically from these sums. 



143. Graphical method. — Set protractor of plotting board on zero if 

 the north component is plus, on 180° if it is minus, and plot its length 

 along the initial line; then set the protractor on 270° if the west com- 

 ponent is plus, on 90° if it is minus, and add its length along the ver- 

 tical line from the first point. The resultant direction and distance 

 is read from the protractor when the second point is brought on the 

 initial line. In order to obtain the resultant velocity, the distance 

 must be divided by the number of observations. In cases where the 

 means exceed 2.0, they may be used instead of the sums, and in this 

 case the velocity is given directly without dividing by the number of 

 observations. 



144. Trigonometric method. — Tan X = W/N, where N is the north 

 component and W the west component, and X the angle between 

 the north-south line and the resultant, or the bearing of the wind 

 requu-ed. Th e resultan t distance may be found by W/ sin X, 

 NJ cos X, or ■^/ N^ -{- W^. The resultant distance, of course, must be 

 divided by the number of observations to obtain the mean resultant 



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