Dynamics and oceanic response of the Madeira tip‐jets

• Published in: Quarterly journal of the Royal Meteorological Society 2020-10, Vol.146 (732), p.3048-3063
• Main Authors: Alves, José M.R., Caldeira, Rui M.A., Miranda, Pedro M.A.
• Format: Article
• Language: English
• Subjects: Anticyclones; Atmosphere; Atmospheric circulation; Atmospheric forcing; Dynamics; Eddies; Jets; Madeira island; Mixed layer depth; numerical modelling; Oceanic eddies; Oceanic response; Oceans; ocean–atmosphere interaction; Surface temperature; tip‐jets; Upper ocean; Variability
• ISSN: 0035-9009; 1477-870X
• DOI: 10.1002/qj.3825

Madeira island is a well‐known source of atmospheric and oceanic eddy activity, with relevant downstream impact in both media. Previous studies focused on the dynamics of the island wake environment, suggesting the relevance of different atmosphere–ocean interactions in its maintenance. Here, results from one summer (two months) of fully coupled atmosphere–ocean high‐resolution simulations are used to explore such interactions and to further understand the dynamics of Madeira's wake. Those results, validated against available in situ and remote‐sensing data, indicate that the atmospheric and ocean circulations near Madeira are dominated by the variability of two quasi‐permanent features, its tip‐jets, and more so by the variability of its eastern jet. While both jets are of comparable magnitude and present similar intraseasonal variability at the multi‐week time‐scale, they are associated with qualitatively different forcing. The jets dominate the atmosphere forcing over the upper ocean, leading to enhanced mixing and deeper mixed‐layer depth. Oceanic eddies are more frequent in the east jet region, as shedding anticyclones, confirming observational evidence. A comparison with a similar one‐way coupled atmospheric simulation indicates that atmosphere–ocean feedbacks are relevant to the coastal surface temperature. Isolated islands with a steep orography exert a significant impact on the regional circulation. Madeira island is one of such islands often within a flow regime characterized by a strong perturbation of the low‐level wind (as shown in the figure) associated with the generation of atmospheric and oceanic vortices. It is suggested that such variability occurs within a quasi‐permanent double tip‐jet, and that the east jet has a more relevant impact on the ocean.