UV VEL0CITY RT TIME = 72.0 H0URS RND DEPTH = 1.0 



X 3 



20 KM 



2.65E+01 ICM/SECJ 



Figure 7 . 



Tide-Driven Horizontal Velocities at 1 m Depth in the 

 Vicinity of the Mississippi Sound at hr, 

 23 Sept., 1980. 



Wind-Driven Currents off the Mississippi Coast 



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 was generally quite mild (- 5 m/sec) from the 

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

 out a three-day simulation from 20 Sept., using a uniform wind stress 

 of 1 dyne/cm^ from the Southeast. The southeasterly wind caused water 

 to pile up within the Mississippi Sound, with a set-up on the order of 

 12 cm along the Northern shore, and only 6 cm behind the barrier 

 islands. 



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

 Figure 8 shows the along-shore velocity at 2 locations over the 3-day 

 period. At Station 5, off Cat Island, the presence of the wind did not 

 have appreciable effect on the tidal current. At Station 6, within the 

 pass between the Mississippi Sound and the Mobile Bay, the wind caused 

 significant flow from the Mobil Bay into the Sound. This resulted in a 

 significantly larger bottom shear stress which leads to the reduction 

 in the amplitude of the tidal currents. 



Wind-driven currents in the Mississippi Sound depend strongly on 

 the wind direction. For example, assuming a uniform wind stress of 

 1 dyne/cm^ from the West, our model results showed relatively stronger 

 currents in the along-shore direction (Figure 9). Notice the 

 near-surface and near-bottom velocities differ not only in magnitude 

 but also in direction at some locations. This is partially associated 



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Sheng 



