Seasonal variability of turbid river plumes off central Chile based on high-resolution MODIS imagery

We have studied the seasonal variability of four turbid river plumes along the central Chilean coast using daily, high-resolution images of surface turbidity from MODIS (Moderate Resolution Imaging Spectroradiometer) in combination with measurements of wind, river flow, and hydrographic data. Atmospherically corrected MODIS data reveal strong seasonal variability in the areal extent of plume water, as well as in turbidity levels, which are significantly correlated with seasonality in river discharge. A seasonal climatology of turbid plume patterns shows individual plumes merging into an extensive body of turbid waters attached to the coast during fall (April-June)-winter (July-September) (occurs about 10% of days in fall-winter). During spring (October-December) and summer (January-March), the individual plumes remain distinct and occupy a smaller area close to the coast, when observed (evident on less than 30% of days in spring-summer). In spring-summer most plumes are detected for the northern rivers (Mataquito and Maule). When the plumes merge into a coastal band in fall-winter, a turbid area of more than 1000 km(2) is observed in the study area between 34.85 degrees S and 37.15 degrees S. This occurs following peaks in river discharge combined with the effect of strong southward (downwelling-favorable) winds. An analysis of key non-dimensional numbers shows that buoyancy dominates plume dynamics during summer, whereas inertial forcing associated with river outflow is more important in winter near the coast. Farther offshore (>10 km), the effects of rotation and wind tend to dominate the plume dynamics. (C) 2012 Elsevier Inc. All rights reserved.