A climatology of the northern Adriatic Sea's response to bora and river forcing

Abstract

A new northern Adriatic climatology characterizes salinity and temperature fields associated with response to strong riverine input and bora wind forcing acting on variable ambient stratification. Time series of key forcing variables, specifically Po River discharge and wind velocity in bora pathways, combined with a measure of time‐variable ambient stratification, indicate the dominant dynamics (e.g., bora winds acting on an unstratified northern Adriatic or strong Po River outflow into an unstratified basin). These indicators define an averaging scheme which organizes archived temperature and salinity profiles into groupings based on common dynamics, providing climatological characterizations of response to bora forcing and the differing basin responses to strong and weak Po discharge into strong and weak ambient stratification. The resulting maps demonstrate that the offshore penetration of Po waters depends strongly on outflow strength and ambient stratification. The climatology reveals buoyant Po River waters spreading in a surface layer throughout much of the northern basin during periods of strong ambient stratification, with little dependence on outflow strength. In contrast, during unstratified periods, outflow strength determines whether the river waters penetrate into the basin (strong outflow) or remain trapped over the Italian shelf (weak outflow). In addition, separation of oceanographic data into periods of strong bora winds reveals the formation of a freshwater filament in the resulting salinity fields. This feature extends into the open sea, separating two pools of higher salinity water. Significance testing of the mode‐maps with climatological averages indicate that the mode‐based maps are statistically robust within the 95% confidence interval in areas of energetic mesoscale activity such as those regions subject to direct riverine or wind forcing.