A Salt Finger Tracer Release Experiment - Analysis

本课题组在北大西洋和加勒比海热带地区成功完成了为期两年的示踪剂和湍流野外研究，该地区容易发生盐指不稳定性。实验的初步结果是，在显示盐指现象的区域，被动示踪剂的垂直扩散系数是其他地方的4-5倍。热量的扩散率约为示踪剂的一半，能量耗散远小于剪切驱动混合所期望的，这是由于盐指混合所期望的。本项目是对现场研究数据的扩展分析，目的如下：准确确定示踪剂和热量在楼梯区域内外的垂直混合情况；评价剪切和盐指失稳在楼梯形成和维持以及增强混合中的作用；在易受盐指法影响的海洋区域建立热盐扩散系数的参数化方法，供数值模式使用；评价阶梯区混合增强对区域热盐输运和水体质量改变的作用；利用数值模型分析了示踪剂斑块的有效纬向弥散和示踪剂斑块的横向混合和搅拌；并公布研究结果。该项目将通过研究生培训、国际合作和对建模参数化的贡献产生更广泛的影响。

ABSTRACTOCE-0350743This research team successfully completed a two-year tracer and turbulence field study in the Tropical North Atlantic Ocean and Caribbean Sea, in an area prone to salt-finger instability. Preliminary results from the experiment are that the vertical diffusivity of the passive tracer in the area showing signs of salt-fingering was 4-5 times greater than elsewhere. Diffusivity for heat was about half that of the tracer, and that the energy dissipation was much smaller than would be expected for shear-driven mixing, both of which are expected for mixing due to salt fingers. This project is for the extended analysis of the data from the field study with the following objectives: to accurately determine the vertical mixing of tracer and heat within the staircase region and outside of it; to evaluate the roles of shear and salt finger instability in the formation and maintenance of staircases and the enhancement of mixing; to develop a parameterization of diffusivities of heat and salt in regions of the ocean susceptible to salt fingering for use in numerical models; to evaluate the role of enhanced mixing in the staircase region in regional transport of heat and salt and in water mass modification; to analyze the efficient zonal dispersion of the tracer patch, and lateral mixing and stirring of the tracer patch with the help of numerical models; and to publish the results of the research. The project will have broader impacts through the training of a graduate student, international collaborations and contribution to parameterizations for modeling.