Satellite assessment of Mississippi River plume variability: causes and predictability.
Walker, N.D., 1996.
The Mississippi River is the largest in North America and 6th largest worldwide in terms of discharge. In this study, 5 years (1989-1993) of NOAA Advanced Very High Resolution Radiometer satllite data were used to investigate the variability of the Mississippi River sediment plume and the environmental forcing factors responsible for its variability. Plume variability was determined by extracting information on plume area and plume length from 112 cloud-free satellite images. Correlation and multiple regression techniques were used to quantify these relationships for possible predictive applications. River discharge and wind forcing were identified 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 river discharge. However, day-to-day variability in plume size and morphology was more closely associated with changes in the wind field. The plume parameters best predicted by the multiple regression models were plume area, east and west of the delta. Predictive models were improved by separating the data into summer and winter seasons. The best predictive model for the western area was obtained during summer when 64% of plume variability was explained by river discharge, wind speed, and the east-west wind component. The best model for the eastern plume area was obtained during summer when river discharge, the north-south and east-west wind components explained 70% of plume variability. The best model for the offshore extent of the sediment plume was obtained during summer when 53% of plume variability was explained by the east-west wind component, river discharge, and wind speed. All plume measurements were maximized by eastward winds from slightly different directions. During winter, the area and length of the western plume was additionally enhanced by offshore winds associated with winter storms. Anticyclonic curvature of the plume west of the delta was observed in 42% of the satellite images. This circulation pattern was observed primarily in association with westward winds.