These studies suggest that upwelling-favorable wind forcing is the primary mechanism for the offshore dispersal of many buoyant coastal plumes. 2001 Sanders and Garvine 2001 Hallock and Marmorino 2002 Johnson et al. ![]() Observational studies have shown that alongshore winds that oppose the buoyant coastal current (upwelling-favorable winds) can cause the buoyant water to separate from the coast, spread offshore, and eventually disperse if the winds are strong enough ( Fong et al. The theory, modified to allow for time-variable wind stress, also reproduces the observed response of the buoyant coastal plume from Chesapeake Bay during an 11-day period of upwelling winds in August 1994.īuoyant discharge from rivers or estuaries typically turns to the right (Northern Hemisphere) and forms a buoyant coastal plume that can flow tens to hundreds of kilometers alongshore before dispersing. The theory reproduces results from 20 numerical model runs by Fong and Geyer, including their estimates of the plume-average entrainment rate (correlations greater than 0.98 and regression coefficients approximately 1 for plume characteristics and 1.7 for the entrainment rate). ![]() Here t s = 2 A o/( Ri c U E) is the time for entrainment to double the cross-sectional area of the plume A o at the onset of the wind forcing, where U E is the Ekman transport. The theory predicts that, for t̂ ≡ t/ t s, the plume density anomaly decreases as (1 + t̂) −1, the thickness increases as (1 + t̂) 1/3, the width increases as (1 + t̂) 2/3, and the plume average entrainment rate decreases as (1 + t̂) −2/3. The theory provides estimates of the buoyant plume characteristics and offshore displacement as a function of time t, given the wind stress, the characteristics of the buoyant plume prior to the onset of the wind forcing, and a critical value for the bulk Richardson number (Ri c). ![]() The primary assumption is that competition between wind-driven vertical mixing and lateral buoyancy forcing in the region where the isopycnals slope upward to intersect the surface results in continual entrainment at the offshore edge of the plume. To better understand the response of a buoyant coastal plume to wind-induced upwelling, a two-dimensional theory is developed that includes entrainment.
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