New Insights on the Formation and Breaking Mechanism of Convective Cyclonic Cones in the South Adriatic Pit during Winter 2018

Abstract

The deepwater formation in the northern part of the South Adriatic Pit (Mediterranean Sea) is investigated using a unique oceanographic data set. In situ data collected by a glider along the Bari-Dubrovnik transect captured the mixing and the spreading/re-stratification phase of the water column in winter 2018. After a period of about two weeks from the beginning of the mixing phase, a homogeneous convective area of ∼ 300 m depth breaks up due to the baroclinic instability process in cyclonic cones made of geostrophically adjusted fluid. The base of these cones is located at the bottom of the mixed layer and they extend up to the theoretical critical depth Z_c. These cones, with a diameter of the order of internal Rossby radius of deformation (∼ 6 km) populate the ∼ 110-km wide convective site, develop beneath it and have a short life time of weeks. Later on, the cones extend deeper and intrusion from deep layers makes their inner core denser and colder. These observed features differ from the long-lived cyclonic eddies sampled in other ocean sites and formed at the periphery of the convective area in a post-convection period. So far, to the best of our knowledge, only theoretical studies, laboratory experiments and model simulations have been able to predict and describe our observations and no other in-situ information has yet been provided. The deepwater formation in the northern part of the South Adriatic Pit (Mediterranean Sea) is investigated using a unique oceanographic data set. In situ data collected by a glider along the Bari-Dubrovnik transect captured the mixing and the spreading/re-stratification phase of the water column in winter 2018. After a period of about two weeks from the beginning of the mixing phase, a homogeneous convective area of ∼ 300 m depth breaks up due to the baroclinic instability process in cyclonic cones made of geostrophically adjusted fluid. The base of these cones is located at the bottom of the mixed layer and they extend up to the theoretical critical depth Z_c. These cones, with a diameter of the order of internal Rossby radius of deformation (∼ 6 km) populate the ∼ 110-km wide convective site, develop beneath it and have a short life time of weeks. Later on, the cones extend deeper and intrusion from deep layers makes their inner core denser and colder. These observed features differ from the long-lived cyclonic eddies sampled in other ocean sites and formed at the periphery of the convective area in a post-convection period. So far, to the best of our knowledge, only theoretical studies, laboratory experiments and model simulations have been able to predict and describe our observations and no other in-situ information has yet been provided.