Spatial and Seasonal Variations of Submesoscale Eddies in the Eastern Tropical Pacific Ocean

The spatial and seasonal variations of submesoscale eddy activities in the eastern tropical Pacific Ocean (2°–12°N, 95°–165°W) are investigated based on a 1/10° ocean general circulation model (OGCM). In the studied region, it is found that motions shorter than 500 km are subject to submesoscale dynamics with an O(1) Rossby number and Richardson number and a −2 spectral slope for kinetic energy, suggesting that submesoscale eddies there can be well resolved by the model. Enhanced submesoscale eddy kinetic energy (SMKE) is found in the surface mixed layer centered at 5°N. A complete SMKE budget analysis suggests that the submesoscale eddies in the surface mixed layer are generated mainly by the barotropic instability and secondarily by the baroclinic instability. The nonlinear interactions lead to a significant forward energy cascade in the submesoscale range and play an important role in balancing the energy budget. As a response to the change of energy input through barotropic instability, the SMKE exhibits a pronounced seasonal cycle with the largest and smallest values occurring in boreal autumn and spring. Furthermore, the strong seasonal cycle plays an important role in modulating the seasonality of mixed layer depth (MLD). In particular, the restratification induced by the strong submesoscale eddies between July and October makes important contribution to the shoaling of MLD in this season.