The mid-depth circulation of the northwestern tropical Atlantic observed by floats

A comprehensive analysis of velocity data from subsurface floats in the northwestern tropical Atlantic at two depth layers is presented: one representing the Antarctic Intermediate Water (AAIW, pressure range 600–1050 dbar), the other the upper North Atlantic Deep Water (uNADW, pressure range 1200–2050 dbar). New data from three independent research programs are combined with previously available data to achieve blanket coverage in space for the AAIW layer, while coverage in the uNADW remains more intermittent. Results from the AAIW mainly confirm previous studies on the mean flow, namely the equatorial zonal and the boundary currents, but clarify details on pathways, mostly by virtue of the spatial data coverage that sets float observations apart from e.g. shipborne or mooring observations. Mean transports in each of five zonal equatorial current bands is found to be between 2.7 and 4.5 Sv. Pathways carrying AAIW northward beyond the North Brazil Undercurrent are clearly visible in the mean velocity field, in particular a northward transport of 3.7 Sv across 16°N between the Antilles islands and the Mid-Atlantic Ridge. New maps of Lagrangian eddy kinetic energy and integral time scales are presented to quantify mesoscale activity. For the uNADW, mean flow and mesoscale properties are discussed as data availability allows. Trajectories in the uNADW east of the Lesser Antilles reveal interactions between the Deep Western Boundary Current (DWBC) and the basin interior, which can explain recent hydrographic observations of changes in composition of DWBC water along its southward flow.     

全球Argo实时海洋观测网建设及应用进展

为了使各国政府、部门管理人员和科技工作者了解国际Argo计划的实施进展,以及帮助广大民众认识实施Argo计划的重要性和已经取得的初步成果,国际Argo信息中心、国际Argo科学组和国际Argo资料管理组联合编写了一本科普宣传册,题为“Argo,一个观测实时海洋的剖面浮标网”,经翻译、整理成文,以帮助国内读者深入了解和认识这一新世纪的重大国际观测计划。文章从陈述开展海洋观测的重要性和实施Argo计划的必要性着手,系统介绍了全球Argo实时海洋观测网建设的现状和Argo资料应用研究所取得的初步成果,以及Argo计划的发展前景等。     

Lagrangian floats as sea floor imaging platforms

There is a persistent need for high resolution photographic images of the sea floor and associated biota for marine habitat classification and fisheries stock assessment. This paper presents a novel low cost Lagrangian imaging platform that offers high quality images with reduced operational demands in comparison to existing methodologies such as diver surveys, drop cameras, ship towed systems and dedicated remote or autonomous underwater vehicles. The platform consists of a recently developed bottom following Lagrangian float fit with down looking stereo cameras and strobe lighting. The float can use active ballasting to perform constant altitude photographic drift surveys in coastal waters over varying bathymetry. Images from the float can be used to create large photomosaics, stereographic bathymetry estimates and image-derived current measurements. Test data are presented to demonstrate the operation of the Lagrangian float and summarize the data products.     

Statistics from Lagrangian observations

We review statistical analyses of Lagrangian data from the ocean. These can be grouped into studies involving single particles and those with pairs or groups of particles. Single particle studies are the most common. The prevalent analysis involves binning velocities geographically to estimate the Eulerian means and lateral diffusivities. However single particle statistics have also been used to study Rossby wave propagation, the influence of bottom topography and eddy heat fluxes. Other studies have used stochastic models to simulate dispersion, calculated Lagrangian frequency spectra and examined the relation between Lagrangian and Eulerian integral scales. Studies involving pairs of particles are fewer, and the results are not well-established yet. There are indications that pair separations grow exponentially in time below the deformation radius, as is also the case in the stratosphere. The behavior at larger scales is less clear, indicating either a turbulent cascade or dispersion by the sheared large-scale circulation. In addition, three or more particles can be used to measure relative vorticity and divergence.