The large-scale processes preconditioning the winter deep-water formation in the northwestern Mediterranean Sea are investigated with a primitive equation numerical model where convection is parameterized by a non-penetrative convective adjustment algorithm. The ocean is forced by momentum and buoyancy fluxes that have the gross features of mean winter forcing found in the MEDOC area. The wind-driven barotropic circulation appears to be a major ingredient of the preconditioning phase of deep-water formation. After three months, the ocean response is dominated by a strong barotropic cyclonic vortex located under the forcing area, which fits the Sverdrup balance away from the northern coast. In the vortex center, the whole water column remains trapped under the forcing area all winter. This trapping enables the thermohaline forcing to drive deep-water formation efficiently. Sensitivity studies show that beta effect and bottom topography play a paramount role and confirm that deep convection occurs only in areas that combine a strong surface thermohaline forcing and a weak barotropic advection so that water masses are submitted to the negative buoyancy fluxes for a much longer time. In particular, the impact of the Rhone Deep Sea Fan on the barotropic circulation dominates the beta effect: the barotropic flow is constrained to follow the bathymetric contours and the cyclonic vortex is shifted southward so that the fluid above the fan remains quiescent. Hence, buoyancy fluxes trigger deep convection above the fan in agreement with observations. The selection of the area of deep-water formation through the deflection of the barotropic circulation by the topography seems a more efficient mechanism than those associated with the wind-driven barotropic vortex. This is due to its permanency, while the latter may be too sensitive to time and space variations of the forcing.
机构:
Northwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Liang, Chao
Liu, Chiyang
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Northwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Liu, Chiyang
Xie, Xinong
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China Univ Geosci, Coll Marine Sci & Technol, Wuhan 430074, Peoples R China
Southern Marine Sci & Engn Guangdong Lab Zhuhai, Zhuhai 519082, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Xie, Xinong
Yu, Xiaohang
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China Univ Geosci, Coll Marine Sci & Technol, Wuhan 430074, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Yu, Xiaohang
He, Yunlong
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China Univ Geosci, Coll Marine Sci & Technol, Wuhan 430074, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
He, Yunlong
Chen, Hui
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Sun Yat Sen Univ, Sch Marine Sci, Zhuhai 519082, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Chen, Hui
Zhou, Zhan
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China Natl Offshore Oil Corp, Zhanjiang Branch, Zhanjiang 524057, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Zhou, Zhan
Tian, Dongmei
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China Univ Geosci, Coll Marine Sci & Technol, Wuhan 430074, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Tian, Dongmei
Lu, Biyu
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China Univ Geosci, Coll Marine Sci & Technol, Wuhan 430074, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Lu, Biyu
Mi, Honggang
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China Natl Offshore Oil Corp, Zhanjiang Branch, Zhanjiang 524057, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Mi, Honggang
Li, Mingjun
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China Natl Offshore Oil Corp, Zhanjiang Branch, Zhanjiang 524057, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Li, Mingjun
Zhang, Hui
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China Natl Offshore Oil Corp, Zhanjiang Branch, Zhanjiang 524057, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China
Zhang, Hui
Yang, Yunliu
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China Univ Geosci, Coll Marine Sci & Technol, Wuhan 430074, Peoples R ChinaNorthwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China