Barotropic tide and baroclinic waves observations in the Rio de la Plata Estuary

[ 1] The first long-period ADCP series collected in two locations of the salinity front of the Rio de la Plata estuary are explored for periods less than 30 hours. Barotropic velocity shows tidal and mean currents consistent with what is known about the estuarine circulation in tidal and seasonal scales. Baroclinic currents provide the first evidence of the occurrence of internal waves, which can account for half of the total variance. In the northernmost location, predominantly zonal oscillations with semidiurnal period, and oscillations with a dominant meridional component and diurnal period, are found. Whereas the first ones can be related to the semidiurnal tide, the second ones seem to be atmospherically forced by the land/sea breeze. In the southernmost location, more rotational oscillations are observed, with periods around the inertial and diurnal ones. Inertial oscillations could result from wind relaxation, whereas diurnal oscillations also seem to be forced by breeze. Wave activity in the diurnal band was less frequent in the northernmost than in the southernmost location. This can be attributed to less frequent favorable stratification conditions in that area during the observed period. Wave activity in the southernmost location resulted weaker during the observed fall than during the summer. This could be a typical feature given that in autumn both the number of storms destroying the thermohaline structure increases and land/sea breeze is less frequent. This suggests a likely seasonal cycle in the diurnal wave activity in this area, given that those unfavorable conditions are even more marked during winter.