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You searched for subject:(southeast tropical Atlantic). Showing records 1 – 2 of 2 total matches.

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Texas A&M University

1. Xu, Zhao. Oceanic Origins of Southwest Tropical Atlantic Biases.

Degree: PhD, Oceanography, 2013, Texas A&M University

The SST bias in the tropical Atlantic exists in the early to latest generation of coupled general circulation models. The maximum bias is not on the equator but at 16°S, the cause of which has not been thoroughly studied. Newly released CMIP5 models provide a useful tool to investigate the contributions of different physical processes to the SST bias in this area in the coupled system. We tested three existing mechanisms and found that: 1) there is no significant relationship between the SST bias and surface heat flux bias; 2) deficient coastal upwelling is a contributing but not the sole source of the bias; and 3) the SST bias is correlated with temperature biases in the upstream equatorial region. The Angola-Benguela front is displaced southward by more than 10° in latitude in many CIMP5 models. Due to the huge temperature contrasts on two sides of the front, such a frontal displacement generates a very strong SST bias. The correlation between the SST bias and frontal location error in this region is significant at the 99% level, demonstrating that the SST bias in coupled GCMs is attributable to the models’ inability to reproduce a realistic position of the front and the consequent erroneous advection by the southward Angola current. This is due to both errors in the simulated surface wind field and systematic errors in ocean models. Ocean reanalysis datasets and a high-resolution regional model simulation suffer a similar pattern of SST biases. Although they produce a more realistic ocean circulation than coarser resolution simulations and alleviate some of the severe SST bias near the front, a warm bias overlies on a northward current to the south of the front, which actually comes from the north of the front through a subsurface passage. We identify a strong subsurface temperature bias caused by a too-deep and diffused simulated thermocline along the coast of Angola, originating from the equatorial thermocline, advected by the Angola Current and an undercurrent beneath the Benguela current, and then brought to the surface by the coastal upwelling along the Benguela coast, contributing to the warm SST bias south of the front. Advisors/Committee Members: Chang, Ping (advisor), Lin, Xiaopei (advisor), Saravanan, R. (committee member), Hetland, Robert (committee member).

Subjects/Keywords: GCM; Southeast Tropical Atlantic; SST bias; oceanic current

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APA (6th Edition):

Xu, Z. (2013). Oceanic Origins of Southwest Tropical Atlantic Biases. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/149583

Chicago Manual of Style (16th Edition):

Xu, Zhao. “Oceanic Origins of Southwest Tropical Atlantic Biases.” 2013. Doctoral Dissertation, Texas A&M University. Accessed January 18, 2021. http://hdl.handle.net/1969.1/149583.

MLA Handbook (7th Edition):

Xu, Zhao. “Oceanic Origins of Southwest Tropical Atlantic Biases.” 2013. Web. 18 Jan 2021.

Vancouver:

Xu Z. Oceanic Origins of Southwest Tropical Atlantic Biases. [Internet] [Doctoral dissertation]. Texas A&M University; 2013. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/1969.1/149583.

Council of Science Editors:

Xu Z. Oceanic Origins of Southwest Tropical Atlantic Biases. [Doctoral Dissertation]. Texas A&M University; 2013. Available from: http://hdl.handle.net/1969.1/149583


Texas A&M University

2. Li, Pin. Quantifying the Contribution of Mean Flow and Eddy Advection to the Warm SST Bias in the Southeast Tropical Atlantic Region.

Degree: PhD, Oceanography, 2018, Texas A&M University

In current-generation climate models, the warm sea surface temperature (SST) bias problem is most commonly seen in the eastern boundary upwelling systems (EBUSs), and is most pronounced and most prevalent in the Southeast Tropical Atlantic (SETA) region. Previous studies have shown that the coastal wind pattern in this region, namely the Benguela low-level coastal jet (BLLCJ), is of great importance for the generation of such SST bias, because the coastal ocean circulation is highly sensitive to the off-shore structure of the wind forcing. Using an eddy-resolving regional ocean model, we first show that the SST bias in the region is drastically reduced when forced with simulated winds from a high-resolution regional atmospheric model. We subsequently demonstrate that the SST bias is highly sensitive to the spatial structure of the wind stress curl (WSC). We also find that when the ocean model is forced by a realistic high-resolution wind, the ocean model resolution is of second order importance in reducing the SST bias. Furthermore, we use a double-time average (DTA) method to quantify the contribution of heat budget terms, and show that the horizontal advection contributes significantly to the SST bias. We then examined the question: To what extent do ocean eddies play a role in balancing the coastal ocean heat budget and affecting the SST bias? By experimenting with a submesoscale eddy-permitting regional ocean model, we show that ocean eddies in the Southeast Tropical Atlantic region are most energetic near the Angola-Benguela Front (ABF), the Lüderitz Upwelling Cell region and the Agulhas Leakage region. In these three regions, comparisons between the two model simulations forced with the low- vs high-resolution winds suggest that the SST bias is mainly generated by mean flow advection with ocean eddies playing the role of counteracting the warming induced by the mean flow advection in this region. Advisors/Committee Members: Chang, Ping (advisor), Lin, Xiaopei (committee member), Hetland, Robert (committee member), Stössel, Achim (committee member), Saravanan, Ramalingam (committee member).

Subjects/Keywords: Climate model; SST bias; southeast tropical Atlantic; Benguela low-level coastal jet; Angola Current; Benguela Current; upwelling; eddy advection

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Li, P. (2018). Quantifying the Contribution of Mean Flow and Eddy Advection to the Warm SST Bias in the Southeast Tropical Atlantic Region. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/174045

Chicago Manual of Style (16th Edition):

Li, Pin. “Quantifying the Contribution of Mean Flow and Eddy Advection to the Warm SST Bias in the Southeast Tropical Atlantic Region.” 2018. Doctoral Dissertation, Texas A&M University. Accessed January 18, 2021. http://hdl.handle.net/1969.1/174045.

MLA Handbook (7th Edition):

Li, Pin. “Quantifying the Contribution of Mean Flow and Eddy Advection to the Warm SST Bias in the Southeast Tropical Atlantic Region.” 2018. Web. 18 Jan 2021.

Vancouver:

Li P. Quantifying the Contribution of Mean Flow and Eddy Advection to the Warm SST Bias in the Southeast Tropical Atlantic Region. [Internet] [Doctoral dissertation]. Texas A&M University; 2018. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/1969.1/174045.

Council of Science Editors:

Li P. Quantifying the Contribution of Mean Flow and Eddy Advection to the Warm SST Bias in the Southeast Tropical Atlantic Region. [Doctoral Dissertation]. Texas A&M University; 2018. Available from: http://hdl.handle.net/1969.1/174045

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