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- Title
The Impact of the Eastern Pacific Fresh and Warm Pools on the Bimodal Seasonality of Barrier Layers.
- Authors
Chi, Jianwei; Du, Yan; Qi, Jifeng; Wang, Minyang; Chen, Ruyan
- Abstract
Observations of Argo profiles and TAO/TRITON array confirm the significant seasonality of the barrier layer (BL) and temperature inversion (TI) in the northeastern tropical Pacific (NETP). Statistical result of the occurrence based on the Argo profiles reveals a bimodal variability of the BL, with two peaks in July and October. This bimodal seasonality of BL is attributed to the out‐of‐phase variations of the eastern Pacific fresh and warm pools. The fresh and warm pools both expand westward from May to July, when the Inter‐Tropical Convergence Zone (ITCZ) becomes intense and broad. Heavy rainfall is the dominant contributor to the extension of the fresh and warm pools, leading to a high frequency of thick BL (40%). This frequent thick BL provides a precondition for its another development after August. The fresh pool is stable from August to November, while the warm pool contracts sharply. The cold tongue becomes active due to a prevailing trade wind and horizontal advection transports surface cold water to the northeastern warm pool. This cold advection deepens the isothermal layer and contributes to a frequent TI (30%) and thick BL (46%). The results suggest that the ITCZ rainfall and northward cold advection from equator dominate the upper layer stratification of NETP in summer and autumn, respectively. Plain Language Summary: The marine barrier layer (BL) features strong salinity stratification at the base of a surface mixed layer insulating water exchange between the surface and subsurface. The formation mechanisms of the BL in the northeastern tropical Pacific are analyzed based on the observations of Argo floats and the TAO/TRITON array. The BLs show a bimodal seasonality with two peaks in July and October. The atmospheric forcing leads to extensions of the warm and fresh pools in the summer and causes the BL formation. Temperature inversions (TIs) occur frequently during the boreal autumn, with the surface temperature lower than the subsurface 1.82°C in October. The warm pool contracts sharply during autumn due to the development of the cold tongue, which causes frequent TIs and thickens the BLs. The out‐of‐phase changes in the warm and fresh pools result in bimodal seasonality and different formation mechanisms. Key Points: The bimodal barrier layer seasonality is due to the out‐of‐phase variabilities of the fresh and the warm poolsThe heavy rainfall and equatorial ocean dynamics dominate the upper layer stratification in summer and autumn, respectivelyThe cold transport by the cold tongue deepens the isothermal layer, contributing to the temperature inversion and thick barrier layer
- Subjects
TEMPERATURE inversions; HALOCLINE; RAINFALL; TRADE winds; OCEAN dynamics
- Publication
Journal of Geophysical Research. Oceans, 2023, Vol 128, Issue 3, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2022JC018876