Numerical simulations of the Mediterranean sea outflow: impact of the entrainment parameterization in an isopycnic coordinate ocean model Matheos P. Papadakis a , Eric P. Chassignet a, * , Robert W. Hallberg b a RSMAS/MPO, 4600 Rickenbacker Causeway, University of Miami, Miami, FL 33149-1098, USA b NOAA/GFDL, Princeton, NJ 08542, USA Received 15 February 2002; received in revised form 16 September 2002; accepted 16 September 2002 Abstract Gravitycurrententrainmentisessentialindeterminingthepropertiesoftheinterioroceanwatermasses that result from marginal sea overflows. Although the individual entraining billows will be unresolvable in large-scale ocean models for the foreseeable future, some large-scale simulations are now being carried out that do resolve the intermediate scale environment which may control the rate of entrainment. Hallberg [Mon.Wea.Rev.128(2000)1402]hasrecentlydevelopedanimplicitdiapycnalmixingschemeforisopycnic coordinateoceanmodelsthatincludestheRichardsonnumberdependententrainmentparameterizationof Turner [J. Fluid Mech. 173 (1986) 431], and which may be capable of representing the gravity current evolution in large-scale ocean models. The present work uses realistic regional simulations with the Miami Isopycnic Coordinate Ocean Model (MICOM) to evaluate ability of this scheme to simulate the entrain- mentthatisobservedtooccurinthebottomboundarycurrentsdownstreamoftheMediterraneanoutflow. These simulations are strikingly similar to the observations, indicating that this scheme does produce re- alisticmixingbetweentheMediterraneanoutflowandtheNorthAtlanticCentralWater.Sensitivitystudies identify the critical Richardson number below which vigorous entrainment occurs as a particularly important parameter. Some of these experiments also show meddies detaching from the Mediterranean undercurrent at locations that appear to be highly influenced by topographic features. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Mediterranean sea outflow; Meddies; Entrainment; Isopycnic coordinate; Ocean modelling * Corresponding author. Tel.: +1-305-361-4041; fax: +1-305-361-4696. E-mail address: echassignet@rsmas.miami.edu (E.P. Chassignet). 1463-5003/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1463-5003(02)00042-2 Ocean Modelling 5 (2003) 325–356 www.elsevier.com/locate/omodol