5.2 Wind-Driven Currents 



Effect of Wind on Tidal Currents 



The results presented in the above did not contain any wind-driven 

 effect. During our study, wind data were collected at several meteorological 

 stations surrounding the Mississippi Sound. The wind during the 5-day period 

 between 20 Sept. and 25 Sept. 1980 was generally quite mild (~ 10 mph) from 



the southeast. To examine the effect of wind on the currents, we carried out 



2 

 a three-day simulation from 20 Sept. using a uniform wind stress of 1 dyne/cm 



from the southeast. As shown in Figure 5.26, the southeasterly wind caused 



water to pile up within the Mississippi Sound at (I ,J)=(22,62), outside 



Pascagoula Harbor along the northern shore. The wind resulted in a set-up of 



0.4 ft. The wind set-up at (I ,J) = (30,56), however, is only 0.2 ft. due to 



the shielding effect of the Horn Island. 



The influence of wind on the current also depends on the location. 

 Figure 5.27 shows the along-shore velocity at 2 locations over the 3-day 

 period. At (33,28), off Cat Island, the presence of the wind did not have an 

 appreciable effect on the tidal current. At (26,88), within the pass between 

 the Mississippi Sound and the Mobile Bay, the wind caused significant flow 

 from the Mobile Bay into the Sound. This resulted in a significantly larger 

 bottom shear stress, which leads to the reduction in the amplitude of the 

 tide-driven currents. 



Currents Driven by Southeasterly Wind 



2 



Currents driven by an impulsive wind stress of 1 dyne/cm from the 



southeast are computed by the three-dimensional hydrodynamic model. As shown 

 in Figure 5.28, the near-surface currents after 1 day simulation time are 

 generally less than 30 cm/sec. The near-bottom currents are 50% smaller. 



107 



