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Interannual Variability of Barrier Layer in the Tropical Atlantic and Its Relationship with the Tropical Atlantic Modes

Xiao MaaSchool of Oceanography, Shanghai Jiao Tong University, Shanghai, China

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Hailong LiuaSchool of Oceanography, Shanghai Jiao Tong University, Shanghai, China

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Xidong WangbSouthern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China
cKey Laboratory of Marine Hazards Forecasting, Ministry of Natural Resources, Hohai University, Nanjing, China

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Abstract

This study reveals the role of the tropical Atlantic variability in modulating the barrier layer thickness (BLT) in their peak seasons. Based on reanalysis data during 1980–2016, statistical and dynamical analyses are performed to investigate the mechanism of BLT variability associated with the tropical Atlantic modes. The regions with significant correlation between BLT and tropical Atlantic modes are located in the northwest and southeast coasts of the tropical Atlantic, which are consistent with BLT maximum variability regions. In boreal spring, BLT decreases in the northwest because less latent heat release affected by weak trade wind related to the Atlantic Meridional Mode (AMM) shoals the iso-thermal layer depth (ITLD). In the south equatorial Atlantic, deepened mixed layer depth (MLD) is controlled by the decreasing fresh water input brought by a northward shift of the intertropical convergence zone (ITCZ) and further lead to a thinner BL. However, a shoaling MLD appears in the north equatorial Atlantic, which results from excessive freshwater input, causing a thick BL there. In boreal summer, positive runoff anomaly caused by the Atlantic Equatorial Mode (AEM) leads to upper warming of the tropical northwest Atlantic and a shallowing ITLD, favoring a thinner BL there. However, a southward shift of ITCZ brings more freshwater into the south equatorial Atlantic, inducing a shallowing MLD as well as a thicker BL. AEM-driven horizontal heat advection of the south equatorial current contributes to a thick ITLD at central southern tropical Atlantic and thus increases BLT.

Corresponding author: Hailong Liu, hailong.liu@sjtu.edu.cn

Abstract

This study reveals the role of the tropical Atlantic variability in modulating the barrier layer thickness (BLT) in their peak seasons. Based on reanalysis data during 1980–2016, statistical and dynamical analyses are performed to investigate the mechanism of BLT variability associated with the tropical Atlantic modes. The regions with significant correlation between BLT and tropical Atlantic modes are located in the northwest and southeast coasts of the tropical Atlantic, which are consistent with BLT maximum variability regions. In boreal spring, BLT decreases in the northwest because less latent heat release affected by weak trade wind related to the Atlantic Meridional Mode (AMM) shoals the iso-thermal layer depth (ITLD). In the south equatorial Atlantic, deepened mixed layer depth (MLD) is controlled by the decreasing fresh water input brought by a northward shift of the intertropical convergence zone (ITCZ) and further lead to a thinner BL. However, a shoaling MLD appears in the north equatorial Atlantic, which results from excessive freshwater input, causing a thick BL there. In boreal summer, positive runoff anomaly caused by the Atlantic Equatorial Mode (AEM) leads to upper warming of the tropical northwest Atlantic and a shallowing ITLD, favoring a thinner BL there. However, a southward shift of ITCZ brings more freshwater into the south equatorial Atlantic, inducing a shallowing MLD as well as a thicker BL. AEM-driven horizontal heat advection of the south equatorial current contributes to a thick ITLD at central southern tropical Atlantic and thus increases BLT.

Corresponding author: Hailong Liu, hailong.liu@sjtu.edu.cn
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