90 MANUAL OF MARINE METEOROLOGICAL OBSERVATIONS 



9450. WAVE GROUP. The symbols for the direction (d^d^), period 

 (Pw), and height (H^) of the waves combine to form the wave group 

 "idwdwPwHw/' where "l" is the group indicator. 



Example: The coded wave group "12768" is decoded as follows: 



1 Group indicator. 

 27 Waves are coming from the west (270°), 



6 Wave period of 12 to 13 seconds. 



8 Wave height of 13 feet. 



9451. When more than one wave system is observed, code each system 

 separately: 



Example: The coded wave groups "12939 and 12157" are decoded as 

 follows: 



(a) Sea waves group: 



1 Group indicator. 



29 The sea is from 290°. 



3 Period of sea waves is 6 seconds. 



9 Height of sea waves is 14 feet. 



(b) Swell group: 



1 Group indicator. 



21 Swell direction is from 210°. 



5 Period of swell is 10 seconds. 



7 Height of swell is 12 feet. 



9452. When the sea is CALM, or when no waves are present, the wave 

 group is coded (100X0) as follows: 



(a) Calm sea. 



1 Group indicator. 



00 Calm, wind direction indeterminate. 



X Period of waves calm, or indeterminate. 



Height of waves less than 1 foot. 



