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Alternative TitleDynamics of westward coastal current during the southwest monsoon in southern Sri Lanka
Thesis Advisor王卫强
Degree Grantor南海海洋研究所
Degree Name硕士
Degree Discipline物理海洋学
AbstractSouthern Sri Lanka contains multiple corals and seagrass ecosystems and is a good fishing grounds during the southwest monsoon due to the ocean upwelling. However, little is known about the circulation of the upper layer pattern onshore (<200m isobaths). The Acoustic Current Doppler Profiler (ADCP) data was collected onboard in July 2018, between 79°E - 82.3°E and 5.32°N - 7°N, south of Sri Lanka. The observations suggest that the Southwest Monsoon Current (SMC) flows eastward just south of Sri Lanka and it is separated from the coast by a ~ 50km wide branch of westward flow with speed 0.5 ms-1. Thereafter, the SMC gradually turns to the northeastward and part of SMC recirculate as Sri Lanka Dome (SLD) while another branch recirculates as anti-cyclonic vortex south of Sri Lanka, accompanied by an anticyclonic vortex east of the SMC. However, the climatology of south Sri Lanka coastal current (herein after known as SSLCC) show the variation from the observations in 2018. Therefore, this study has focused on the interannual variability of SSLCC and factors affecting the mechanism of SSLCC variation.Dynamics of the SSLCC the south of Sri Lanka (80?E-82?E, 5.5?N-6?N) were investigated by examining 26-year ECCO2 data (1992-2017) during the summertime. The analysis indicated that the variability is caused by the presence of Boreal Summer Intra-seasonal oscillation (BSISO). During the westward case, the BSISO signal intensifies the wind strength south of Sri Lanka, leading to changes in the strength of SMC and Sri Lanka Dome (SLD). Strong wind induces the cyclonic circulation around Sri Lanka and weakens the SMC. Thus, the western flank of SLD flow southward along the east coast of Sri Lanka and turns towards the west at the southern coast of Sri Lanka attaining its maximum speed. BSISO increases the wind speed which propagates Rossby wave signal rapidly across the bay. The upwelling Rossby wave signal which hit the east of SLD, induce the strength of SLD. During the eastward case, the BSISO is absent. Thus, the wind strength decreases in the south of Sri Lanka. As a result, the wind stress curl weakens, which would cause to weakening the cyclonic circulation. However, the SMC and its anti-cyclonic bend become stronger. Additionally, the downwelling Rossby wave hit south of Sri Lanka, which also weakened the cyclonic circulation. During this period, the baroclinic and barotropic instability, favorable for mean-eddy energy conversion, induced the anti-cyclonic circulation. Therefore, in brief, when the BSISO exist, the cyclonic circulation is prominent. When BSISO is absent, anti-cyclonic circulation is prevalent.Moreover, the Bay of Bengal (BoB) low saline water drifts south of Sri Lanka during the westward case. However, the southward low saline flux is absent along the Sumatra coast (or eastern boundary of BoB) towards the Equator. During the eastward case, there is a prominent southward low saline BoB water flux along the Sumatra coast. Furthermore, the study reveals that the source of eddy kinetic energy (EKE) is from the time-varying (turbulent) wind stress field in this region. Thus, strong EKE increase occurs when the cyclonic circulation is strong in the region. The key, new insight from this study is how the strength of wind influences on the circulation pattern around Sri Lanka and the path of low saline water transport in the summer.
Document Type学位论文
Recommended Citation
GB/T 7714
CHATHURIKA HEMAMALI WICKRAMAGE. 斯里兰卡南部西向沿岸流在西南季风期间的动力学研究[D]. 南海海洋研究所,2019.
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