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Reconciling Lagrangian Diffusivity and Effective Diffusivity in Contour-Based Coordinates
Qian, Yu-Kun; Peng, Shiqiu1,2; Liang, Chang-Xia
AbstractThe present study reconciles theoretical differences between the Lagrangian diffusivity and effective diffusivity in a transformed spatial coordinate based on the contours of a quasi-conservative tracer. In the transformed coordinate, any adiabatic stirring effect, such as shear-induced dispersion, is naturally isolated from diabatic cross-contour motions. Therefore, Lagrangian particle motions in the transformed coordinate obey a transformed zeroth-order stochastic (i.e., random walk) model with the diffusivity replaced by the effective diffusivity. Such a stochastic model becomes the theoretical foundation on which both diffusivities are exactly unified. In the absence of small-scale diffusion, particles do not disperse at all in the transformed contour coordinate. Besides, the corresponding Lagrangian autocorrelation becomes a delta function and is thus free from pronounced overshoot and negative lobe at short time lags that may be induced by either Rossby waves or mesoscale eddies; that is, particles decorrelate immediately and Lagrangian diffusivity is already asymptotic nomatter how small the time lag is. The resulting instantaneous Lagrangian spreading rate is thus conceptually identical to the effective diffusivity that only measures the instantaneous irreversible mixing. In these regards, the present study provides a new look at particle dispersion in contour-based coordinates.
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Document Type期刊论文
Affiliation1.Chinese Acad Sci, South China Sea Inst Oceanol, State Key Lab Trop Oceanog, Guangzhou, Guangdong, Peoples R China
2.Qingdao Natl Lab Marine Sci & Technol, Lab Reg Oceanog & Numer Modeling, Qingdao, Shandong, Peoples R China
3.Univ Chinese Acad Sci, Beijing, Peoples R China
4.South China Sea Marine Predict Ctr, State Ocean Adm, Guangzhou, Guangdong, Peoples R China
Recommended Citation
GB/T 7714
Qian, Yu-Kun,Peng, Shiqiu,Liang, Chang-Xia. Reconciling Lagrangian Diffusivity and Effective Diffusivity in Contour-Based Coordinates[J]. JOURNAL OF PHYSICAL OCEANOGRAPHY,2019,49(6):1521, 1539.
APA Qian, Yu-Kun,Peng, Shiqiu,&Liang, Chang-Xia.(2019).Reconciling Lagrangian Diffusivity and Effective Diffusivity in Contour-Based Coordinates.JOURNAL OF PHYSICAL OCEANOGRAPHY,49(6),1521.
MLA Qian, Yu-Kun,et al."Reconciling Lagrangian Diffusivity and Effective Diffusivity in Contour-Based Coordinates".JOURNAL OF PHYSICAL OCEANOGRAPHY 49.6(2019):1521.
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