Seasonal and interannual variability of the northern Adriatic surface fluxes

Coastal meteorological data and sea surface temperature collected over a 27-year interval (1966–1992) have been used to evaluate seasonal cycle and interannual variability of surface heat, water and buoyancy fluxes at three locations in the northern Adriatic (Trieste, Rovinj and Mali Lo inj). Annual averages of downward heat and water fluxes and upward buoyancy flux ranged between −7 W m−2 and 3 W m−2, 0.3 mm day−1 and 0.8 mm day−1, and −0.4×10−8 m2 s−3 and 0.2×10−8 m2 s−3, respectively. Seasonal cycle of buoyancy flux depended almost entirely on surface heat exchange. Considerable spatial variations of fluxes, controlled by evaporation and to a less extent by sensible heat flux, have been observed at seasonal time scale. The finding was supported by an error analysis, which included estimation of random error (due to uncertainties in basic observations and in method of computation), estimation of the error due to averaging and correction for the use of coastal data while computing open-sea fluxes. Short time series (8 November 1992–21 February 1993) of hourly measurements at two nearby locations (Rovinj and Pula) have been used to show that spatial variability in air–sea forcing was even more pronounced at hourly and daily time scales. In order to discuss long-term variations of surface fluxes, monthly values computed for the 1966–1992 interval were considered. By relating the extreme values of surface fluxes to global meteorological conditions the reliability of our computation was confirmed. In addition, an attempt has been made to relate the interannual variability of the northern Adriatic surface fluxes to the winter dense-water formation processes and to the changes in temperature, salinity and density of water found in the bottom layer of central Adriatic between 1966 and 1980.