在孟加拉湾由地转流引起的地面混合
Surface Mixing by Geostrophic Flows in the Bay of Bengal
摘要：
在孟加拉湾的混合，驱动测高派生的每日地转表面流，研究在亚季节时间尺度。Hovmiller和波数-频率图与功率谱证实了流动的多尺度性质。带的平流立即带来了混乱的性质混合在海湾通过反复的应变和示踪剂场的反射。一个主要的发现是混合是局部的，即，的规模，并没有跨越整个盆地。事实上，有限时间李雅普诺夫指数（FTLE），相对色散（RD）和有限大小李雅普诺夫指数（FSLE）在所有季节的地图是补丁与最小分散在海湾的内部。海湾的不均匀搅拌反映在FTLE的长尾直方图中，其在较长的时间间隔内变得更加拉伸。一周平流的定量分析表明，平均FTLE位于0.15-0.16 $day^{-1}$附近，而极端值几乎达到0.5 $day^{-1}$。平均在海湾，RD最初呈指数增长，这是其次是一个幂律的规模之间约100和250 $km$，最后过渡到涡流扩散制度。这些发现被FSLE证实;此外，低于250 $km$，提取尺度依赖的扩散系数，而高于250 $km$，涡流扩散系数范围从$6 \times 10^3$ - $10^4$ $m^2/s$。最后，结合卫星盐度资料，对一次季风后淡水混合事件进行了分析。在这里，FTLEs和FSLEs允许运输障碍的识别，并阐明如何漩涡帮助保存淡水的身份。
英文摘要：
Mixing in the Bay of Bengal, driven by altimetry derived daily geostrophic surface currents, is studied on subseasonal timescales. Hovm{ö}ller and wavenumber-frequency diagrams with power spectra confirm the multiscale nature of the flow. Advection of bands immediately brings out the chaotic nature of mixing in the Bay via repeated straining and filamentation of the tracer field. A principal finding is that mixing is local, i.e., of the scale of the eddies, and does not span the entire basin. Indeed, Finite Time Lyapunov Exponent (FTLE), Relative Dispersion (RD) and Finite Size Lyapunov Exponents (FSLE) maps in all seasons are patchy with minima scattered through the interior of the Bay. Non-uniform stirring of the Bay is reflected in long tailed histograms of FTLEs, that become more stretched for longer time intervals. Quantitatively, advection for a week shows the mean FTLE lies near 0.15-0.16 $day^{-1}$, while extremes reach almost 0.5 $day^{-1}$. Averaged over the Bay, RD initially grows exponentially, this is followed by a power-law at scales between approximately 100 and 250 $km$, which finally transitions to an eddy-diffusive regime. These findings are confirmed by FSLEs; in addition, below 250 $km$, a scale dependent diffusion coefficient is extracted, while above 250 $km$, eddy-diffusivities range from $6 \times 10^3$ - $10^4$ $m^2/s$. Finally, with satellite salinity data, these Lagrangian tools are used in the analysis a single post-monsoonal fresh water mixing event. Here, FTLEs and FSLEs allow the identification of transport barriers, and elucidate how eddies help preserve the identity of fresh water.
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