ABSTRACT



      Using a realistic, high-resolution, climatologically forced numerical simulation of the Atlantic Ocean, Fratantoni et al. (1995, 2000) concluded that North Brazil Current (NBC) rings account for approximately 1/5 to 1/4 of the northward transport within the Atlantic meridional overturning cell (MOC). Goni and Johns (2001) used TOPEX/POSEIDON altimeter data to determine that NBC rings may instead carry more than 1/3 of the MOC transport. A reasonable and logical next step toward resolving this discrepancy is to combine these two methods by assimilating satellite altimeter data into a realistic numerical ocean model. In this approach, a high-resolution, realistically-forced, global ocean circulation model similar to the Atlantic model used by Fratantoni et al. (1995, 2000) provides a dynamical analysis of the assimilated sea surface height data measured not only by the TOPEX/POSEIDON satellite altimeter, but also ERS-2. The model used in this study is the 1/16° global Naval Research Laboratory (NRL) Layered Ocean Model (NLOM), a descendant of the model developed by Hurlburt and Thompson (1980). This model is currently running in real-time using real-time Fleet Numerical Meteorology and Oceanography Center (FNMOC) surface stresses and thermal forcing. Even when it is not constrained by the assimilation of observed data, the model realistically simulates the position, strength, and sea surface height mean and variability patterns of observed current systems. This includes the currents of the tropical Atlantic. The total number and temporal distribution of large anticyclones produced by the model in the NBC region from 1993 through 1998 are very similar to the results obtained by Goni and Johns (2001) for the same time period. The number of these rings actually shed by the NBC retroflection is in agreement with both Goni and Johns (2001) and Fratantoni et al. (1995,2000).