Ocean Science www.ocean-sci.net 1812-0784 1812-0792 5 4 2009 10.5194/os-5-461-2009 http://www.ocean-sci.net/5/461/2009/ http://www.ocean-sci.net/5/461/2009/os-5-461-2009.html http://www.ocean-sci.net/5/461/2009/os-5-461-2009.pdf 461 473 2009-10-26 A nested Atlantic-Mediterranean Sea general circulation model for operational forecasting P. Oddo oddo@bo.ingv.it M. Adani N. Pinardi C. Fratianni M. Tonani D. Pettenuzzo Gruppo Nazionale di Oceanografia Operativa, Istituto Nazionale di Geofisica e Vulcanologia, Via Aldo Moro 44, 40128 Bologna, Italy Centro Interdipartimentale per la Ricerca in Scienze Ambientali, Università di Bologna Ravenna, Italy A new numerical general circulation ocean model for the Mediterranean Sea has been implemented nested within an Atlantic general circulation model within the framework of the Marine Environment and Security for the European Area project (MERSEA, Desaubies, 2006). A 4-year twin experiment was carried out from January 2004 to December 2007 with two different models to evaluate the impact on the Mediterranean Sea circulation of open lateral boundary conditions in the Atlantic Ocean. One model considers a closed lateral boundary in a large Atlantic box and the other is nested in the same box in a global ocean circulation model. Impact was observed comparing the two simulations with independent observations: ARGO for temperature and salinity profiles and tide gauges and along-track satellite observations for the sea surface height. The improvement in the nested Atlantic-Mediterranean model with respect to the closed one is particularly evident in the salinity characteristics of the Modified Atlantic Water and in the Mediterranean sea level seasonal variability. 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