Deep convection in the Greenland Sea: Experimental study of the preconditioning and mixing phases

• Main Author: Lherminier, Pascale
• Other Authors: Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris VI, Jean-Claude Gascard, PRojet Européen ESOP
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 1998
• Subjects: Deep Convection; Greenland Sea; float; Convection profonde; Mer du Groenland; flotteur; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Arctic; Greenland; Groenland; North Atlantic Deep Water; North Atlantic
• Online Access: https://tel.archives-ouvertes.fr/tel-00881646; https://tel.archives-ouvertes.fr/tel-00881646/document; https://tel.archives-ouvertes.fr/tel-00881646/file/Lherminier_these1998b.pdf

Several oceanographic research projects presently focus on deep convection in the Greenland Sea, which is considered an important source of North Atlantic Deep Water. Major results from studies of 1993 and 1994 winter data, obtained from isobaric floats drifting between 250 and 850 m depth, and from a comprehensive dataset including meteorological, hydrological and ice cover data, are presented here. The relatively mild 1994 winter only induced a partial deep convection in an ice free basin, where an anticyclonic eddy appeared as a better preconditionned site for deep mixing. This eddy seemed to come from an interaction between a surface advection of Modified Atlantic Water and a patch of cold Arctic Intermediate Water below, formed by previous convective events that could have occurred during the preceding winter. Neither the aspect of this feature nor its spatial and temporal stability could be directly related to inverse or direct cascades usually suggested as mechanisms in deep convection processes. In 1994, the mixed layer evolution was controlled by tridimensional turbulent dynamics, very dependent on the surface forcing and on the basin stratification, and strongly influenced by mesoscale structures. Correlated to the most intense air-sea fluxes of 1994 winter, the activation of the mixing phase was identified as a regime transition in the amplitudes and frequencies of water vertical velocities w. Using a high resolution non hydrostatic model, we showed that low frequency components of w measured by floats were most likely the effects of the arrangement of turbulent convective cells (plumes) generated by strong and sudden surface buoyancy losses. La convection profonde en Mer du Groenland, source importante des eaux profondes de l'Atlantique Nord, fait actuellement l'objet de recherches approfondies. Nous présentons ici les principaux résultats obtenus au cours des hivers de 1993 et 1994 à partir de mesures de flotteurs isobares dérivant entre 250 et 850 m de profondeur et d'un vaste ensemble de données ...