SATELLITE ASSESSMENT OF MISSISSIPPI RIVER PLUME VARIABILITY - CAUSES AND PREDICTABILITY

The Mississippi River is the largest river in North America and 6th la rgest worldwide in terms of discharge. In this study, 5 years (1989-19 93) of NOAA Advanced Very High Resolution Radiometer satellite data we re used to investigate the variability of the Mississippi River sedime nt plume and the environmental forcing factors responsible for its var iability. Plume variability was determined by extracting information o n plume area and plume length from 112 cloudl-free satellite images. C orrelation and multiple regression techniques were used to quantify th ese relationships for possible predictive applications. River discharg e and wind forcing were identifed as the main factors affecting plume variability. Seasonal and interannual variabilities in plume area were similar in magnitude and corresponded closely with large changes in r iver discharge. However, day-to-day variability in plume size and morp hology was more closely associated with changes in the wind field. The plume parameters bst predicted by the multiple regression models were plume area, east and west of the delta. Predictive models were improv ed by separating the data into summer and winter seasons. The best pre dictive model for the western area was obtained during summer when 64% of plume variability was explained by river discharge, wind speed, an d the east-west wind component. The best model for the eastern plume a rea was obtained during summer when river discharge, the north-south a nd east-west wind components explained 70% of plume variability. The b est model for the offshore extent of the sediment plume was obtained d uring summer when 53% of plume variability was explained by the east-w est wind component, river discharge, and wind speed. All plume measure ments were maximized by eastward winds from slightly different directi ons. During winter, the area and length of the western plume was addit ionally enhanced by offshore winds associated with winter storms. Anti cyclonic curvature of tile plume west of the delta was observed in 42% of the satellite images. This circulation pattern was observed primar ily in association with westward winds.