Wind-driven upwelling in the Adriatic Sea: Coastal vs. open-sea processes

• Wind-driven upwelling was observed close to the Adriatic coast as well as offshore. • The coastal upwelling was controlled by interacting boundary and wind-curl effects. • The open-sea upwelling was primarily related to wind-curl effect. • All processes were influenced by a positive feedback mechanism. The paper concentrates on the east Adriatic and a ten-day (20–29 May 2017) interval when a research cruise has been carried out, when the bottom probes have been operating close to the coast, and for which the satellite data have been available. Meteorological modeling has shown that two pulses of northern winds occurred at the time. The shipborne CTD and ADCP data collected on 28 May 2017 revealed a dense-water dome, with the surface cyclonic circulation developed around it, at a distance of 15–20 km from the coast. The temperature bottom probes and SST satellite sensors pointed to a decrease of temperature on two occasions, around 21 and 25–27 May 2017, close to the coast. The coincidence of the wind pulses with these processes in the sea indicated that they could be interpreted in terms of the wind-driven open-sea and coastal upwelling. In order to verify the interpretation, a simple analytical model has been developed and a combination of meteorological and oceanographic numerical modeling, with the wind field decomposed into the curl and curl-free components using the Helmholtz-Hodge approach, has been utilized. The theory and numerical simulations showed that the open-sea upwelling was related to the wind-curl effect while the coastal upwelling was controlled by interaction of the boundary and wind-curl effects. The phenomena were influenced by a positive feedback mechanism, which is more pronounced in shallow basins than in deep basins. This suggests that comparative studies of upwelling phenomena in different basins may be useful.