INSTRUCTIOISrS FOR MAKING PILOT BALLOON OBSERVATIONS 41 



ward portion of the graph should be drawn in red ink and the seccond 

 upward portion in purple, green, or any other available color which 

 will distinguish it from the first portion of the graph. 



127. When the wind velocity is "calm" (i. e., less than 0.5 m. p. s.) 

 the corresponding portion of the d/irection graph Mdll be broken and 

 the word "calm" written in the space. If the surface wind is calm 

 when the balloon is released and the balloon ascends directly over- 

 head, the approximate time elapsing between the release and the time 

 the balloon is observed to start moving away from the vertical 

 position should be noted. The azimuth angle of the initial horizontal 

 movement should also be noted by quickly sighting the theodolite 

 on the balloon. The velocity graph should then be drawn vertically 

 along the zero line up to the altitude at which the first horizontal 

 movement of the balloon was observed to take place. The direction 

 graph should, in such cases, be started at the point where the velocity 

 graph first indicates a velocity of 0.5 m. p. s. In extracting data 

 from Form No. 1115-Aer. for entries to the nearest whole meter per 

 second on Form No. 1114-Aer., 0.4 m. p. s. or less will be recorded as 

 calm and 0.5 m. p. s. as 1 m. p. s. 



V. FORMS AND REDUCTION TABLES 



128. Forms used in pilot-balloon work. — The forms used in pilot- 

 balloon work are Nos. 1110-Aer. lllOA-Aer., and 1115-Aer. (com- 

 bined), 1113-Aer., 1114A-Aer., 1114B-Aer., 1116-Aer., 1117-Aer., 

 and 1124-Aer. 



129. Form No. 1 110 A- Aer. -This form, combined with Form No. 

 1 115-Aer., is used for the recording of all original data in any way con- 

 nected with the observation. (See table 1.) The headings must be 

 carefully made out and the remaining spaces filled in as far as data 

 are available. The station altitude to be entered at the top of this 

 form and on all other pilot-balloon forms is the altitude above sea 

 level of the theodolite platform. Particular attention is to be given 

 to the recording of the disappearance of the balloon. When it is 

 due to clouds, it should be distinctly stated whether the balloon dis- 

 appeared against, entered base of, or passed behind them. The exact 

 type of cloud should also be given in such cases, using the abbreviations 

 Ci, Cs, Cc, etc. The balloon data and the auxilliary meteorological 

 data are to be entered in complete form in each case. Clouds or 

 sky conditions are to be recorded in accordance with the inter- 

 national code for reporting clouds, i. e., in numbers from to 9 and 

 classified according to height (high, middle, or low). The surface 

 wind direction is to be recorded both to the nearest whole degree 

 and to one of the 16 compass points, i. e., 283° WNW. and the velocity 

 in meters per second and tenths. The temperatures (both dry and 

 wet-bulb readings) are to be recorded to the nearest tenth degree, 

 Centigrade. For conversion from Fahrenheit to Centigrade, see table 

 4. Pressures are to be entered to the nearest tenth millibar, table 6 

 being used to make the conversion from inches. Form No. IIIOA- 

 Aer. will be rendered only when the observation reaches at least 1,000 

 feet above the surface. 



130. Note that the ascension numbers on Form No. lllOA-Aer. 

 are always one greater than those of the graphs (Form No. 1115-Aer.), 

 on the reverse side of the form. In inaugurating pilot-balloon observa- 



