56 INSTRUCTIONS TO MARINE METEOROLOGICAL OBSERVERS 



Under certain conditions supplemental data are also required. 

 They may be sent in any one of three forms, as indicated by the first 

 figure of the first group. The first form, which has only two groups, 

 is sometimes used by ships reporting to the Weather Bureau; the 

 first figure of the first group in this case is always 6. The order of 

 symbols - is as follows : 



6KDkCN T.dsAWCH 



The second form, Avith three groups, is quite generally used in 

 sending radio reports to the meteorological services of certain other 

 nations. Here the first figure of the first group is always 3. The 

 order of symbols - is as follows : 



3ClCmChN TJvDkWN^ d,v,app 



A third form is occasionally required, the first figure of the first 

 group of which is always 9. The order of symbols ^ is as follows : 



9SKDkW CNNuATd 



No matter what form of supplemental data is used, it is always 

 preceded by the four Universal Groups. 



If one or more figures of a group cannot be given, owing to lack 

 of observation, or to failure of, or damage to, instruments, each miss- 

 ing figure should be replaced by the letter X. 



The following information will serve as a guide to the obtaining 

 and reporting of supplemental data: 



Barometric fendeiici/ (A). — This ({uantity, representing the approx- 

 imate amount and general character of the change of the barometer 

 in the 3 hours prior to the observation, is expressed in the radio 

 message by a single figure, in accordance with the table given below. 

 It is obtained either from the record traced out by a barograph or 

 from two readings of a barometer made at the hour of observation 

 and 3 hours ])rior to it. respectively. The amount of the tendency is 

 simply the difference between the barometric readings observed at 

 these two instants of time. The character of the tendency is de- 

 scribed as "steady", "rising", or "falling", depending u])on whether 

 the net change is zero, positive, or negative. 



Symbol A — Barometric tendency 



Code 

 figures 



Barometric tendency 



Barometer steady. (Has not fallen or risen more than 0.01 inch (}/2 millibar) in 



last 3 hours.) 

 Barometer rising slowly; (Has ri.sen 0.03\o 0.04 inch (1 to IJ-^'millibars) in last 



3 hours.) 

 Barometer rising. (Has risen 0.06 to 0.10 inch (2 to 314 millibars) in last 3 



hours.) 

 Barometer rising quickly. (Has risen 0.12 to 0.18 inch (4 to G millibars) in last 



3 hours.) 

 Barometer rising very rapidly. (Has risen more than 0.18 inch (fi millibars) in 



last 3 hours.) 

 Barometer fallin;< slowly. (Has fallen 0.03 to 0.04 inch (1 to IH millibars) in 



last 3 hours.) 

 Barometer falling. (Has fallen 006 to 0.10 inch (2 to 3}n millibars) in last 3 



hours.) 

 Barometer falling quickly. (Has fallen 0.12 to 0.18 inch (4 to 6 millibars) in last 



3 hours.) 

 Barometer fallin? very rapidly. (Has fallen more than 0.18 inch (6 millibars) in 



last 3 hours.) 



' For meaning of these symbols, see headings of sections which follow. 



