the limited fetch. However, the plots of the period ratios fell almost 

 equally into groups 1 to 4. Visual observation of the wave period is 

 difficult, especially if more than one wave train is present. If the 

 height of the swell is large, then the superimposed smaller sea breeze- 

 generated waves may not be visible to the observer, and the shorter period 

 waves would not appreciably alter the observed period of the swell, 

 although it might add to the observed height. 



V. EXPOSURE AND ANNUAL HEIGHT 



The orientation and exposure of a station's coastline affect both the 

 wave climate and the sea breeze. For this reason, the coastal exposure 

 of the observing station was compared with the diurnal variation in wave 

 height for the 17 COSOP stations. Two measures of exposure were defined 

 by measuring the size of the overwater arc swept by a 30- or 300-mile 

 radius centered on the station. Small islands were ignored, and large 

 islands were subtracted from the arc. The resulting sector, measured in 

 degrees, was taken as the exposure of the station (Kohler, 1972). The 

 COSOP stations were grouped in four categories by the size of the sector 

 measured from National Ocean Survey charts, and the absolute diurnal 

 variation in wave height was averaged for stations in each exposure 

 category (Table 2). 



Table 2. Absolute diurnal variation for coastal exposure groupings. 

 Exposure group Number of Mean absolute diurnal variation 

 stations July June/July/August 

 (ft] (ft) 



30-miIe land limited 



>180° 4 



157° to 180° 5 



135° to 156° 5 



<I35° 3 



300-mile land limited 



>162° 2 



126° to 162° 7 



90° to 125° 4 



<90° 4 



0.100 



0.111 



0.112 



0.138 



0.132 



0.145 



0.165 



0.160 



0.115 



0.132 



0.137 



0.145 



0.168 



0.164 



0.133 



0.113 



The average absolute diurnal variation for June, July, and August 

 appears to depend on exposure (Table 2). As the 30-mile land-limited 

 exposure increases, the absolute diurnal variation decreases. The 300- 

 mile exposure shows a similar trend except for the group with minimum 

 exposure. If the observed variations are directly related to the sea 



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