Seasonal and Interannual Variability in the Sea Surface Temperature Front in the Eastern Pacific Ocean

Fifteen years of satellite observations of sea surface temperature (SST) are used to identify frontal activities in the eastern Pacific Ocean. The frontogenesis and variability of frontal activities are mainly determined by wind forces. Strong frontal activities are distributed mainly near the coast and decrease with increasing offshore distance. The seasonal cycle dominates the variability in the SST frontal probability (FP) in coastal regions, and large interannual variability is identified in the tropics. Coastal frontal activities are driven by the local wind such that the equatorward wind stress forces coastal upwelling, which brings subsurface cold water to the surface and induces fronts. Frontal activities are generally enhanced during local summer, when an upwelling‐favorable wind prevails. A prominent offshore migration pattern is identified for mid‐latitude regions, and the associated propagation speed is consistent with the wind‐induced offshore Ekman transport and mesoscale eddies. The coastal tropical Pacific is also characterized by a strong FP with large seasonal variability. The corresponding fronts result from the confluence between the boundary current and wind‐driven cold water as the wind jet passes through mountain gaps. The frontal activities near the equator are driven by wind‐induced tropical upwelling associated with a westward propagation at speeds close to the speed of Rossby waves. In the tropics, strong interannual variability in FP is identified that is, modulated by the El Niño‐Southern Oscillation. Frontal activities are suppressed during El Niño years because trade winds are characterized by strong convergence, which induces downwelling and subsequently reduces FP.