Investigating the role of abyssal stratification in the propagation of vorticity throughout the water column: a Mediterranean example (Ionian Sea)

Analysis of in situ data from the Ionian Sea revealed the presence of variability with tidal periodicity in the deep layer, suggesting that the deep variability is actually related to the whole water column. The observations were made from 1999 to 2003, during the years of adjustment to the Eastern Mediterranean Transient, a major climate event that occurred at the end of the 80s. During the observation period, the Ionian deep layers were characterized by the presence of a stable water mass, the Ionian Abyssal Water, whose presence could be a key condition for catching such variability in the deep and for studying the role of the stratification on the propagation of the perturbation throughout the water column. The observed mean structure of the stratification suggests that a 4-layer scheme should be sufficient to have a realistic yet simple representation. To study how much and under which conditions a vorticity input can propagate, a quasi-geostrophic equation has been considered, with 4 coupled layers of arbitrary thickness and density, simulated with a custom-designed algorithm. This case study aims to give more insight into how energy stored by the deep layers can be released along the entire water column, contributing to the climate variability of the Mediterranean Sea.