Wind-induced offshore removal of plume waters

The dynamics of the Mississippi River plume are highly affected by the wind conditions in the NGoMregion, which determine the along-shelf and across-shelf transport of riverinewaters. Numerical experiments forced by realistic, high frequency winds demonstrate the variability of the Mississippi River plume due to variable wind forcing and the wind conditions that enhance the offshore exportation of plume waters and facilitate the interactions with the offshore eddy circulation.

Northern Gulf of Mexico Hybrid Coordinate Ocean Model (NGoM-HYCOM)
Wind-induced offshore removal of plume waters

A):Snapshots of model surface salinity from selected days depicting different states of the Mississippi River plume under varied (6-hourly) wind forcing: during a period of easterly, downwelling-favorable winds (upper), after a period of westerly, upwelling favorable winds (middle) and during a period of southerly winds. The magenta vectors show the average wind direction during each wind event. (B)Snapshots of sea surface salinity and surface velocity vectors at selected days after the period of southerly winds. A and C show the location of anticyclonicand cyclonic eddies, respectively. For each day, the average wind vector is presented on the upper-right corner of the plot.

Easterly, downwelling-favorable winds transport low-salinity waters towards the broader Louisiana-Texas shelf effectively insulates the coastal plume from the offshore circulation. Offshore removal of the plume is induced by events of westerly and southerly winds, when riverinewaters near the delta are transported towards and beyond the shelfbreakto the east of the delta. Once the plume is removed to the shelfbreakregion by the favorable wind conditions (B) , the plume can be effectively entrained by the offshore eddy circulation (cyclones and anticyclones)

Villy Kourafalou —
Rafael Schiller —