Wind Speed and Direction 



31. Winds at the FRF are dominated by tropical maritime air masses 

 which create low to moderate, warm southern breezes; Arctic and Polar air 

 masses which produce cold winds from northerly directions; and smaller scale 

 cyclonic, low pressure systems, which originate either in the tropics (and 

 move north along the coast) or on land (and move eastward offshore). The dom- 

 inant wind direction changes with season, being generally from northern direc- 

 tions in the fall and winter and from southern directions in the spring and 

 summer. The annual resultant wind direction is from the north-northwest. It 

 is common for fall and winter storms (northeasters) to produce winds with 

 average speeds in excess of 15 m/sec. 



Measurement instrument 



32. Winds were measured on top of the laboratory building at an eleva- 

 tion of 19.1 m (Figure 2) using a Weather Measure Corporation (Sacramento, 

 Calif.) Skyvane Model W102P anemometer. Wind speed and direction data were 

 incorporated into the automated data collection and analysis program and were 

 collected continuously on a strip-chart recorder. The anemometer manufacturer 

 specifies an accuracy of ±0.45 m/sec below 13 m/sec and 3 percent at speeds 

 above 13 m/sec, with a threshold of 0.9 m/sec. Wind direction accuracy is 



±2 deg with a resolution of less than 1 deg. The anemometer is calibrated 

 semiannually at the National Bureau of Standards in Gaithersburg, Md., and is 

 within the manufacturer's specifications. 



33. Annual, seasonal, and monthly joint probability distributions of 

 wind speed versus direction were computed. Wind speeds were resolved into 

 3-m/sec intervals, while the directions were at 22.5-deg intervals (i.e. 

 16-point compass direction specifications) . These distributions are presented 

 as wind "roses," such that the length of the petal represents the frequency of 

 occurrence of wind blowing from the specified direction, and the width of the 

 petal is indicative of the speed in 3-m/sec intervals. Resultant directions 

 and speeds were also determined by vector averaging the data. 



Results 



34. Present year. Winds during the year blew primarily from the north- 

 eastern and southwestern quadrants as shown in Figure 6. The wind blew from 

 north through east-northeast 40.8 percent of the time and south-southwest 

 through west-southwest 26.5 percent of the time. Wind speed exceeded 10 m/sec 



21 



