to changing wind conditions. As will be shown later, the response of the 

 shallow Mississippi Sound to an impulsive wind is relatively fast, such that 

 the flow within the Sound essentially reaches steady state before the end of 

 one day. Thus, we can examine the maximum possible current and bottom shear 

 stress within the Sound resulting from a given wind condition. To include the 

 effect of open Gulf circulation (e.g.. Loop Current) on the study area, an 

 entire Gulf model may be required to provide the necessary boundary 

 conditions. An alternative would be to measure the variation of major 

 variables along the open boundaries throughout the simulation period, 



2 



The response of bottom water to an impulsive wind stress of 3 dyne/cm 

 from the South is shown for three locations (B, C, and D, In Figure 4.9) in 

 Figure 4.12. Within the Sound (B), the bottom current has reached steady 

 state within an inertial period and hence the transient does not clearly show 

 the inertial period. The response at the offshore location (C) is somewhat 

 slower. At Location D, near the open boundary, the response is even slower, 

 as manifested by the distinctive inertial period in its oscillatory bottom 

 current. 



The mass fluxes, near-surface currents, near-bottom currents, and bottom 

 shear stresses caused by the same wind over the area are shown in Figure 4.13, 

 for a narrow coastal strip Including the Sound. Notice that there is an 

 appreciable difference between the surface currents and the bottom currents. 

 While the surface currents generally have an onshore component, the bottom 

 currents generally show an offshore component. High bottom shear stresses 

 prevail in the area between Horn Island, Ship Island, and the 

 Chandeleur Islands. The shear stresses due to the transient wind-driven 

 currents may be much greater than those due to the tidal currents, and hence 

 are more effective in causing resuspension of sediments. Results for other 

 wind directions can be found in Sheng (1981). 



70 



