Simulation of Mesoscale Variability in the Gulf of Mexico: Sensitivity Studies, Comparison with Observations, and Trapped Wave Propagation

Abstract

A primitive equation Gulf of Mexico model was used to examine variability of the Loop Current (LC) and Loop Current eddies (LCE). Realistic results were obtained for a certain range of values of the horizontal mixing coefficient: eddy paths were west and southwestward; eddy propagation speeds from 3 to 5 km day?1; the ratio of minor to major eddy axes about 0.8; eddy shedding periods from 200 to 500 days; eddy lifetimes from 100 to 200 days; eddy sizes from 200 to 400 km; and eddy swirl transports, as fractions of the specified inflow of 30 Sv, were from 0.55 to 0.85. On the other hand, the maximum vertical deepening of the 20°C isotherm was 15% to 50% less than that observed, resulting in weaker near-surface currents of about 0.65 m s?1, in comparison to observed values of 0.88 to 1.7 m s?1. A strong correlation between eddy shedding and decreasing or reversing lower-layer (below 750 m) transport in the Yucatan Channel is found. In the western Gulf, current variability is produced by eddy arrivals, as well as by forcing due to bottom-intensified topographic Rossby waves, which propagate along the slope from the east with a group velocity of about 12 km day?1 and periods of about 30?100 days. These waves are generally preceded by faster coastally trapped wave propagation, and all are produced by LC pulsation, eddy shedding, and westward propagation.