temperatures presented previously, but the temperature ranges varied inversely 

 from those of air temperature. July was a time of maximum range in water tem- 

 perature and minimum range in air temperature, while February's ranges were at 

 a minimum for water and a maximum for air. 



Sea Surface Visibility 



Month 1980 Temperature, °C m 



Jan 6.8 1.3 



Feb 3.5 1.4 



Mar 5.5 1.0 



Apr 11.2 2.5 



May 16.2 2.7 



Jun 18.5 3.9 



Jul 20.1 4.6 



Aug * 3.4 



Sep 22.1 2.9 



Oct 19.0 1.4 



Nov 13.2 1.0 



Dec 8.9 0.9 



" No measurement. 



126. Figure 24 shows the daily difference between the surface water 

 temperature and the air temperatures measured behind the dune 1.5 m above 

 ground. This temperature difference can be important to coastal engineers 

 when assessing storm surge and wave growth values because of the modification 

 of wind stress and, consequently, the transfer of momentum from the wind to 

 the sea surface. When the air is cooler than the water, increased turbulence 

 causes increased momentum transfer for a given wind speed; conversely, when 

 the air is warmer, a stable condition results and less momentum for a given 

 wind speed is transferred. The largest difference was 16° C which occurred 

 during August. During October through February, the water was warmer than 

 the air occasionally by more than 10° C. March and September are periods 



of transition, with warming and cooling of the coastal waters occurring 

 respectively. 



127. Visibility. Visibility in coastal nearshore waters depends on the 

 amount of salts, soluble organic material, detritus, living organisms, and in- 

 organic particles in the water. These dissolved and suspended materials 



61 



