d. Compute direction of vector sum from c to estimate wind 

 direction. 



38. The distribution of the hourly winds with respect to direction is 

 shown as a wind rose (Figure 18). The wind rose shows the distribution of 

 winds in 16 directional sectors as a percent of all winds. The bars in each 

 direction are broken into 10-mph intervals. 



39. The distributions of wind speed and duration relating to return 

 period are presented in Figure 19. Figure 19 shows combined data from all 

 sectors (0-360 deg). The curves represent the visual best fit to the data. 

 From these curves, the wind speed for a given return period can be obtained. 

 In general, these curves should not be extrapolated beyond twice the period 

 of record (37 years). 



Puffin Island Data 



40. The Puffin Island anemometer is part of the ACDCP. Puffin Island 

 is located 1.5 miles offshore in Chiniak Bay. The anemometer is located at an 

 elevation of 23 m (island elevation) plus 6.1 m (elevation of sensor above the 

 island). The anemometer supplied about 16 months of usable data starting late 

 in 1981. The anemometer was not working in October and November of I98I nor 

 in October of 1982, months when major storms are expected. The anemometer was 

 also out during other extreme events, so the data for extreme events are un- 

 reliable. The observations were 1-hr averages at 3-hr intervals. 



Data adjustments 



41. Again, the raw data were adjusted using the method presented in 

 CETN-I-5. The adjustments included: 



a. Correction to 10-m level. 



b. Adjustment of overland readings to overwater readings. 



c Correction for nonconstant coefficient of drag. 



d. Correction for instability due to air-sea temperature differ- 

 ences for directions where the fetch is greater than 10 miles 

 (an unstable condition was assumed, since no temperature data 

 were available) . 



A calibration correction factor of I.06 was also applied as recommended by the 

 Alaska District. An additional adjustment was made to account for the influ- 

 ence of the island height and shape on the airflow (Simiu and Scanlon 1978). 



43 



