96. 1984 versus prior years. Variation of the monthly mean visibility 

 during 1984 was similar to prior years (Figure 38) . Unusually good visibility 

 during February and March was because of the mild wave conditions and the 

 predominantly onshore, southerly winds. 



97. All years combined. Figure 39 shows the distribution of daily 

 values for 1980 through 1984. For 121 days a year, the visibility at the FRF 

 can be expected to be less than 1 m; while for 82 days a year, the visibility 

 can be expected to exceed 3 m. 



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Figure 38. Comparison of mean surface water visibility 



Density 



98. 



Present year. Daily density values show large daily variations 

 (Figure 40). Table 10 gives the monthly means for the year. Some density 

 values were low during the spring and summer; however, the means did not fol- 

 low a consistent pattern. The very low density values during August and on 

 2 September were neither times of heavy rain fall nor times of abnormally high 

 water temperatures. These values tend to occur when the wave angles are very 

 large, approaching from north-northeast. This may create a southerly flow 

 along the coast that brings relatively fresh water from the Chesapeake Bay as 

 far south as the FRF; on numerous occasions plumes of fresh water from the bay 

 have been observed moving south past the FRF. 



99. 1984 versus prior years. The mean monthly water density through- 

 out 1984 was much lower than for prior years, especially during April and 

 August (Figure 41). Since water temperature did not show a corresponding dif- 

 ference, the reason for the difference is unknown. 



100. All years combined. The distribution of daily surface water den- 

 sity for 1981 through 1984 is shown in Figure 42. Density values lower than 



66 



