SUMMERTIME THERMOCLINE SALINITY MAXIMUM INTRUSIONS IN THE MID-ATLANTIC BIGHT

Mooring data with high vertical resolution have been combined with hyd rographic data to investigate the character of high salinity thermocli ne intrusions in the shelf water-slope water frontal zone in the south ern Mid-Atlantic Bight. The coincidence of current, temperature and sa linity data has allowed a detailed investigation of how the intrusion process is initiated. The data show that the time scale for both the o nset and duration of the intrusions is very short. Most intrusions at a single location seem to last no more than a day, while the onshore f low associated with many, but not all, intrusions accelerates very qui ckly attaining amplitudes of 10-20 cm s(-1). As has been noted in earl ier studies, there is a correlation between the intrusions and upwelli ng favorable winds, but the magnitude of the wind stress is not suffic ient to account for the onshore transport of the intrusions. The combi nation of current measurements with density profiles has allowed the c alculation of gradient Richardson numbers associated with the intrusio ns. These calculations show that during the strong onshore flow period s there is significant mixing at the boundaries of the intrusions. At other times when the high salinity water is being passively advected a long the shelf, there appears to be little shear turbulence at the int rusion boundaries. Continuous data coverage during the summer suggests that the intrusion process is actually fairly infrequent, apparently requiring an offshore preconditioning in which high salinity waters of the correct density are located just offshore in addition to upwellin g favorable winds.