A Feature Oriented Regional Modeling System for the North Brazil Current Rings Migration after Retroflection

摘要

Southeast of the Trinidad-Venezuela region, the North Brazil Current (NBC) retroflects and forms about 5-8 ringsrnannually. The ensemble of trajectories of rings extends offshore of the 500 m isobath, with a mean translation speed ofrnapproximately 14 km/day and a mean length scale of about 100 km (Goni and Johns, 2001, 2003). At least two distinct ringrntypes exist: surface-intensified and thermocline-intensified, with differences evident in both azimuthal velocity and waterrnmasses. This paper presents a recent implementation of an operational modeling system for this region. The key to thisrnmodeling effort is to implement the feature oriented regional modeling methodology for the NBC rings with an advancedrninitialization scheme to incorporate the varying ring structure, shape, and associated currents made possible by regularrnsurveillance and deployment of instruments into the ring. Multiple observations provide input and guidance to the ring initialrnconditions for the feature model system.rnBased on previous studies and data, a water-mass based feature model system for two distinct NBC rings is developed.rnThe parametric models for temperature and salinity are built to capture the main features observed in vertical structure ofrnthose rings. For example, in the case of the thermocline-intensified ring, different empirical-analytical functions with tunablernparameters are used to represent (i) the thermocline shoaling up in the intermediate depth of the ring, (ii) the dipping down inrnthe inshore and offshore edges, and (iii) the presence of the maximum salinity water at 50-100 m. These feature models arernfirst calibrated with available sea surface temperature (SST) data and then melded with background climatology in a featureorientedrnmultiscale objective analysis to develop a three-dimensional description of the regional ocean.rnThe feature oriented scheme is used to initialize an operational forecasting system using the Harvard Ocean PredictionrnSystem (HOPS) framework. Implementation, calibration, and validation of this system were carried out for multiple casernstudies during 2006 and 2007 when a number of drifter data sets were available. A hindcast study for 27 January 2010 isrnused for verifying the forecast system in a semi-operational mode. A fully operational system was launched in July 2010.