Frontal structure of a river plume

Abstract

Field observations are reported of the frontal structure found along the boundary of the Connecticut River plume in Long Island Sound. The hydrography and the horizontal current field were determined in the vicinity of the front. The front separates ambient saltwater on the surface from the light brackish water of the plume. Beneath the surface an inclined frontal layer is found where static stability is a maximum. Isopycnals forming the frontal layer slope upward from a typical depth of 1 m and intersect the sea surface on a horizontal scale of 50 m. A sharp transition in surface color appears in the frontal zone. The primary motion relative to the front is manifested by a vigorous surface convergence from both sides. Sinking motion at the front is locally intense. Saltwater approaching the front is pressed downward beneath the pool of brackish water. The motion parallel to the front is much weaker and independent of density structure. The structure of a section of the front is destroyed by mixing over a period of several hours.