The variability of currents in the Yucatan Channel: Analysis of results from a numerical ocean model

a near-surface maximum (4-year) mean of around 1.5 m s � 1 and SD � 0.4 m s � 1 . Three (return) outflow regions are identified, one in the upper layer (thickness � 600 m) on the eastern third of the Channel, with mean near the surface of about 0.2 m s � 1 and SD � 0.14 m s � 1 , and two deep outflow cores, along the western and eastern slopes of the Channel, with (Mean, SD) � (0.17, 0.05) and (0.09, 0.07) m s � 1 , respectively. The total modeled Channel transport varies from 16 to 34 Sv (1 Sverdrup = 10 6 m 3 s � 1 ) with a mean around 25 Sv. The above velocity and transport values agree quite well with observations by Maul et al. [1985], Ochoa et al. [2001], and Sheinbaum et al. [2002]. The deep return transport below 800 m was found to correlate with changes in the Loop Current extension area, in agreement with the observational analysis by Bunge et al. [2002]. The EOF mode#1 of the along-channel currents contains 50% of the total energy. It is surface-trapped, is 180� out of phase across the channel, and correlates well (correlation coefficient g � 0.8) with the cross-channel vacillations of the LC frontal position. The EOF mode#2 contains 18% of the energy, and its structure mimics that of the mean flow: dominated by two vertically more coherent regions that are 180� out of phase across the Channel. The mode is dominated by two periods, approximately 11 months and 2 months respectively, and correlates (g � 0.7) with the upper-channel inflow transport. The third and fourth modes, together, account for 18% of the total energy. Their combined time series correlates (g � 0.66) with the deep current over the sill, and is dominated by fluctuations with a period � 205 days coincident with the dominant low-frequency fluctuations inherent in Maul et al.’s [1985] sill measurement. Thus the dominant mode of flow fluctuations in the Yucatan Channel is caused by LC cross-frontal movements which may not be directly related to LC eddy-sheddings, while higher modes correspond to transport fluctuations that affect eddy-sheddings, and to bottom-trapped current fluctuations, the cause of which has yet to be fully uncovered. INDEX TERMS: 4255 Oceanography: General: Numerical modeling; 4512 Oceanography: Physical: Currents; 4520 Oceanography: Physical: Eddies and mesoscale processes;

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