Strong Long‐Lived Anticyclonic Mesoscale Eddies in the Balearic Sea: Formation, Intensification, and Thermal Impact. Issue 5 (21st May 2022)

• Record Type: Journal Article
• Authors: Aguiar, E.; Mourre, B.; Alvera‐Azcárate, A.; Pascual, A.; Mason, E.; Tintoré, J.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-05-21
• Subjects: eddy‐mean flow interactions -- Balearic sea -- Western Mediterranean Sea -- strong long‐lived eddies -- baroclinic/barotropic instability -- formation -- intensification -- thermal impacts; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017589
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Anticyclonic mesoscale eddies are often observed in the Balearic Sea (BS) toward the end of summer and autumn. In some years, these eddies become strong and persistent, modifying the local water mass properties. In this study, we analyze two of the most significant recent long‐lived anticyclonic eddies, occurring in 2010 and 2017, using data from a high‐resolution circulation model, altimetry and satellite‐borne sea surface temperature observations. These eddies lasted around 2 and 4 months, respectively, with a radius varying between 40 and 75 km. The generation and intensification mechanisms of these long‐lived anticyclonic eddies are studied by means of (a) energy conversion terms associated with eddy‐mean flow interaction and (b) model sensitivity tests. Results show that these eddies were formed and intensified through mixed barotropic and baroclinic instabilities. The former are produced under the action of intense northwesterly (NW) winds. The latter are related to the existence of an intense summer thermal front between the BS and the Gulf of Lion, and to northward inflows of relatively lower salinity waters. Both the wind events and the presence of the thermal front are necessary for the formation of the eddies. The intensification process varied between both events. While in 2010 it was driven by significant salinity gradients produced by northwards inflows, in 2017 it was produced by additional intense NW winds. Both long‐lived anticyclonic eddies created long‐lasting surface temperature anomalies up to 2.5°C, which have characteristics of local marine heatwaves. Plain Language Summary: Eddies are closed circular currents present in the oceans. They are important phenomena due to their capacity to isolate water masses, retain floating particles and modify ocean circulation. In the Western Mediterranean Sea there is a recognized area of anticyclonic eddy presence between Barcelona and the Balearic Islands, especially during late summer. Specifically, in 2010 and 2017 two such eddies were identified with lifetimes of 2 and 4 months, respectively. In this paper, we investigate why these eddies were so long and persistent in comparison with other years. Results confirm that these eddies are generated as a result of northwesterly (NW) winds events blowing over an area with two water masses of different temperature. In 2010, low salinity northward water inflows sustained this eddy during two months, while in 2017 the eddy remained active for a period of four months under the influence of additional intense NW winds. Both eddies created long‐lasting surface temperature anomalies, in particular in 2017, the sea surface temperature within the eddy influence area was 2.5°C warmer in comparison to other years. Key Points: Northwesterly (NW) wind events and the existence of the Pyrenees thermal front are both necessary for the formation of strong long‐lived Balearic Sea eddies Eddy intensification was driven by salinity gradients in 2010 and by additional NW wind events in 2017 Both events created long‐lasting surface temperature anomalies that have the characteristics of local marine heatwaves