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- Title
Seasonal and Interannual Variability in the Sea Surface Temperature Front in the Eastern Pacific Ocean.
- Authors
Yuntao Wang; Jin Liu; Hailong Liu; Pengfei Lin; Yeping Yuan; Fei Chai
- Abstract
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. Plain Language Summary Oceanic fronts delineate the boundaries of different water masses and frontal zones are associated with intensive dynamics and high levels of nutrients. The eastern Pacific Ocean is characterized by abundant fronts, which are important for supplying fishery resources. In this study, 15 years of satellite observations of sea surface temperature are used to identify the frequency of frontal occurrence, namely, frontal probability (FP), and its associated variability. High FP distributes generally near the coast and decreases with offshore distance. In coastal regions, high FP is driven mainly by the local wind such that the equatorward wind stress forces coastal upwelling, which generates fronts. Frontal activities are generally enhanced during local summer when upwelling-favorable wind prevails. In mid-latitude regions, the fronts generated nearshore migrate offshore with propagation speeds close to the speed of Rossby waves. In the tropical Pacific Ocean, trade winds drive strong divergence, which induces upwelling that subsequently drives fronts. Large interannual variability is also modulated by the El Niño-Southern Oscillation. Frontal activities are suppressed during El Niño years and elevated during La Niña years because of the corresponding wind dynamics.
- Subjects
PACIFIC Ocean; OCEAN temperature; WIND pressure; OCEAN waves; OCEANOGRAPHY
- Publication
Journal of Geophysical Research. Oceans, 2021, Vol 126, Issue 2, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2020JC016356