Rio de la Plata estuary response to wind variability in synoptic to intraseasonal scales: Barotropic response

The first long-period acoustic Doppler current profiler series collected in two locations of the Rio de la Plata estuary are explored for barotropic current variability and its connection to wind variability in synoptic to intraseasonal timescales. Wind-driven currents can be explained in terms of two modes, resulting of the estuary's geometry. The first one prevails for winds with a cross-river component, whereas the second dominates when they blow along the estuary axis. Even though both modes imply that barotropic currents develop in a phase lag with the wind that depends on the location, northeasterly and southwesterly winds generate stronger currents than southeasterly and northwesterly winds. Barotropic response to winds occurs in around 6 hours, and an equilibrium regime is reached for processes with temporal scales more than 4 days. The temporal scales of estuarine variability replicate the wind ones, with activity in bands around 2-8, 10-12, and 18-25 days. Therefore the estuary reaches an equilibrium regime with most of atmospheric processes from synoptic to intraseasonal scales. Intraseasonal variability can be significant and even act in the same direction as the synoptic one, with important effects on circulation. These features imply that the estuary has "weather'' and "climate'' as the atmosphere does. Our results suggest that conditions classically thought as characteristic of "summer'' or "winter'' likely occur during any season with high variability. This result has important implications for those coastal species that spawn in the estuary, as they require specific conditions for their successful reproduction, and on estuary's predictability.