The eastward Equatorial Undercurrent (EUC) flows along the equator beneath the westward South Equatorial Current (SEC).  This study compares simulated EUC at 0°, 140°W from the 1/48° LLC4320 Global Ocean General Circulation Model against Acoustic Doppler Current Profiler (ADCP) measurements.  The simulated undercurrent is weaker, deeper, and exhibits lower variance than observed. This discrepancy stems from stronger stratification and smaller vertical velocity shear in the model, which lead to a larger-than-observed (more stable) gradient Richardson number. Sensitivity experiments using modified vertical mixing coefficients in a 1/12° LLC1080 configuration demonstrate that optimizing vertical mixing is critical for achieving a realistic EUC. Finally, applying these adjusted mixing coefficients to the 1/48° LLC4320 configuration yields a similar, systematic improvement in the simulated undercurrent.
The eastward Equatorial Undercurrent (EUC) flows along the equator beneath the westward South Equatorial Current (SEC).  This study compares simulated EUC at 0°, 140°W from the 1/48° LLC4320 Global Ocean General Circulation Model against Acoustic Doppler Current Profiler (ADCP) measurements.  The simulated undercurrent is weaker, deeper, and exhibits lower variance than observed. This discrepancy stems from stronger stratification and smaller vertical velocity shear in the model, which lead to a larger-than-observed (more stable) gradient Richardson number. Sensitivity experiments using modified vertical mixing coefficients in a 1/12° LLC1080 configuration demonstrate that optimizing vertical mixing is critical for achieving a realistic EUC. Finally, applying these adjusted mixing coefficients to the 1/48° LLC4320 configuration yields a similar, systematic improvement in the simulated undercurrent.