Stokes drift

During its periodic motion, a particle floating at the free surface of a water wave experiences a net drift velocity in the direction of wave propagation, known as the Stokes drift (Stokes 1847 Trans. Camb. Philos. Soc.8, 441-455). More generally, the Stokes drift velocity is the difference between the average Lagrangian flow velocity of a fluid parcel and the average Eulerian flow velocity of the fluid. This paper reviews progress in fundamental and applied research on the induced mean flow associated with surface gravity waves since the first description of the Stokes drift, now 170 years ago. After briefly reviewing the fundamental physical processes, most of which have been established for decades, the review addresses progress in laboratory and field observations of the Stokes drift. Despite more than a century of experimental studies, laboratory studies of the mean circulation set up by waves in a laboratory flume remain somewhat contentious. In the field, rapid advances are expected due to increasingly small and cheap sensors and transmitters, making widespread use of small surface-following drifters possible. We also discuss remote sensing of the Stokes drift from high-frequency radar. Finally, the paper discusses the three main areas of application of the Stokes drift: in the coastal zone, in Eulerian models of the upper ocean layer and in the modelling of tracer transport, such as oil and plastic pollution. Future climate models will probably involve full coupling of ocean and atmosphere systems, in which the wave model provides consistent forcing on the ocean surface boundary layer. Together with the advent of new space-borne instruments that can measure surface Stokes drift, such models hold the promise of quantifying the impact of wave effects on the global atmosphere-ocean system and hopefully contribute to improved climate projections.This article is part of the theme issue 'Nonlinear water waves'

Transcriptomic analysis of milk somatic cells in mastitis resistant and susceptible sheep upon challenge with Staphylococcus epidermidis and Staphylococcus aureus

<p>Abstract</p> <p>Background</p> <p>The existence of a genetic basis for host responses to bacterial intramammary infections has been widely documented, but the underlying mechanisms and the genes are still largely unknown. Previously, two divergent lines of sheep selected for high/low milk somatic cell scores have been shown to be respectively susceptible and resistant to intramammary infections by <it>Staphylococcus spp</it>. Transcriptional profiling with an 15K ovine-specific microarray of the milk somatic cells of susceptible and resistant sheep infected successively by <it>S. epidermidis </it>and <it>S. aureus </it>was performed in order to enhance our understanding of the molecular and cellular events associated with mastitis resistance.</p> <p>Results</p> <p>The bacteriological titre was lower in the resistant than in the susceptible animals in the 48 hours following inoculation, although milk somatic cell concentration was similar. Gene expression was analysed in milk somatic cells, mainly represented by neutrophils, collected 12 hours post-challenge. A high number of differentially expressed genes between the two challenges indicated that more T cells are recruited upon inoculation by <it>S. aureus </it>than <it>S. epidermidis</it>. A total of 52 genes were significantly differentially expressed between the resistant and susceptible animals. Further Gene Ontology analysis indicated that differentially expressed genes were associated with immune and inflammatory responses, leukocyte adhesion, cell migration, and signal transduction. Close biological relationships could be established between most genes using gene network analysis. Furthermore, gene expression suggests that the cell turn-over, as a consequence of apoptosis/granulopoiesis, may be enhanced in the resistant line when compared to the susceptible line.</p> <p>Conclusions</p> <p>Gene profiling in resistant and susceptible lines has provided good candidates for mapping the biological pathways and genes underlying genetically determined resistance and susceptibility towards <it>Staphylococcus </it>infections, and opens new fields for further investigation.</p

Turbulence structure in the upper ocean: a comparative study of observations and modeling

Observations of turbulent dissipation rates measured by two independent instruments are compared with numerical model runs to investigate the injection of turbulence generated by sea surface gravity waves. The nearsurface observations are made by a moored autonomous instrument, fixed at approximately 8 m below the sea surface. The instrument is equipped with shear probes, a highresolution pressure sensor, and an inertial motion package to measure time series of dissipation rate and nondirectional surface wave energy spectrum. A free-falling profiler is used additionally to collect vertical microstructure profiles in the upper ocean. For the model simulations, we use a one-dimensional mixed layer model based on a k–ε type second moment turbulence closure, which is modified to include the effects of wave breaking and Langmuir cells. The dissipation rates obtained using the modified k–ε model are elevated near the sea surface and in the upper water column, consistent with the measurements, mainly as a result of wave breaking at the surface, and energy drawn from wave field to the mean flow by Stokes drift. The agreement between observed and simulated turbulent quantities is fairly good, especially when the Stokes production is taken into account

Detection of Pacific Tropical Water variability by taut-line moorings in the western equatorial Pacific

http://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr99-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr01-k01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr02-k02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr02-k06_leg2/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-08_leg2/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr06-01/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr08-03/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr09-04/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr10-07/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr00-k07_leg1/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr03-k03_leg1/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr04-03_leg1/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr05-03_leg1/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr06-05_leg3/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr07-07_leg1/ehttp://www.godac.jamstec.go.jp/darwin/cruise/mirai/mr10-02/ehttp://www.godac.jamstec.go.jp/darwin/cruise/kaiyo/ky03-12/ehttp://www.godac.jamstec.go.jp/darwin/cruise/kaiyo/ky09-01_leg1/ehttp://www.godac.jamstec.go.jp/darwin/cruise/kaiyo/ky09-01_leg3/ehttp://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk04-02/