D. . = smallest value on curve, and sometimes, 

 J mm 



D. = secondary maximum; a value at least 0.025 greater 



■' than minimum values between it and D. 



J max 



The curves for each station were classified into six groups (Fig. 5) 

 identified by numbers 1 to 6: 



(1) ^]rnax occurring at 1200 or 1600 hours; or at 2000 hours if the 

 next highest point is at 1600 hours; D. - D. . > 0.1, 



and no D. 



jsm 



J max , J mm 



(21 Same as number 1, except that D. - D. . < 0.1. 



^ -^ ^ jmax 3 mm — 



(3) D^^g^^ occurring at 0800 hours; or at 2000 hours, but only if the 



next highest point is not at 1600 hours; D. - D. . < 0.1, 



° ^ max imm — 



and no D. . j j 



jsm 



(41 Same as number 3 except that D. - D. . > 0.1. 

 ^ -^ ^ J max jmm 



(51 D. and D. both occurring, 

 jmax jsm 



(6) Anything that does not fit into groups 1 to 5. 



The curve groups classify diurnal variation by time of occurrence of 

 maximum, occurrence of secondary maxima, and amount of variation between 

 the highest and lowest values. The typical curves for the six-curve 

 groups are shown in Figure 5. Curves resulting from an idealized land- 

 sea breeze system would fall into one of the first four groups. Groups 

 1 and 2 have a day or early evening maximum (expected for wave height) ; 

 groups 3 and 4 have a morning or late evening maximum (possible for period 

 distribution) . 



Wave height curve groups for each station in June, July, and August 

 are listed in Table 1. Group 1 or 2 curves were found at 88 percent 

 of the stations in June, 94 percent in July, and 82 percent in August. 

 There does not appear to be any pattern to the exceptions. 



As a check of significance, 100 D^ curves of the types shown in Figure 

 5 were artificially generated by randomly choosing sets of four numbers 

 from the pooled Dj numbers found for summer months at the COSOP stations; 

 57 fell into groups 1 or 2. This suggests that the approximately 88 per- 

 cent occurrence of groups 1 or 2 actually observed was not a chance 

 occurrence. 



Groups 1 or 2 should be representative of the diurnal variation in 

 wave height because the daytime onshore sea breeze should increase the 

 height. The effect should be more significant where wave heights are 

 normally quite low. The same onshore wind is expected to decrease the 

 period by generating waves with shorter than average periods because of 



