Mobile version

Southern Ocean Eddy Diffusion

A new lateral surface eddy diffusion coefficient has been calculated from surface drifters and altimetric data.

A statistical analysis of surface drifter observations is used to compute eddy length and time scales and lateral eddy diffusion in the Southern Ocean.

Lateral eddy diffusion values of the order of 104 m².s-1 are found in the energetic western boundary currents north of the Antarctic Circumpolar Current (ACC) and secondary peaks show up where the ACC negotiates topography. The diffusivity shows an increase from the Antarctic continent to the ACC, a stable plateau within the ACC and either a decrease North of the ACC outside the western boundary region or further increase dominated by the western boundary currents.

Diffusivity is also calculated from simulated trajectories based on altimetric geostrophic velocities, with and without mean flow, as well as with simulated trajectories based on Ekman currents. Ekman currents at the drogue depth (15m) have only a small impact whereas the geostrophic currents dominate the eddy diffusivity. The mean flow acts as a weak barrier to mixing oustside the western boundary regions and tends to reduce the along stream eddy diffusion. Complementary statistical analyses confirm these results.

The surface drifter eddy diffusion is used to test a simple parameterization based on satellite altimetric observations of eddy kinetic energy (EKE). For EKE ≥ 150 cm².s-², the eddy diffusion = 1.35√EKELd m.s-1, where Ld is the first baroclinic Rossby radius. This parameterization holds in the energetic ACC, consistent with an eddy field in the “frozen field” regime, and fails over broader areas of weak eddy fields, where mixing is nevertheless fairly uniform and stable at about 1800 +/- 1000 m2.s-1.

Further information on the method and access to the eddy diffusion coefficient matrix.

Time (top) and length (middle) eddy scales and eddy diffusion coefficient (bottom) in the Southern Ocean, for both the cross-stream and along stream components. Credits JB. Sallée et al. (2008), JMR.

References:

  • Sallée, J.B.; Speer, K.; Morrow, R. and Lumpkin, R. (2008). An estimate of Lagragian eddy statistics and diffusion in the mixed layer of the Southern Ocean, Journ. of Marine Res., 2008, 66(4), 441-463

 

EnglishFrançaisEspañol
Rss feedsContactSitemapPartnersFAQGlossaryLexiconMobile
You must enable cookies in your browser preferences to save the modifications
You are using an older version of Internet Explorer, please update to take full advantage of Aviso+ features

Customize the home page

View all widgets
Reduce display
Public profile
User profile

Select/Deselect widgets

Discover AVISO+

Customizable home, reading tools, products search guide, etc.. Discover step by step the features of the new site AVISO+.

Customizable homepage

The new home page is composed of blocks called "widgets".

Rearrange the blocks with a "Click & Drop".

Hide a widget with the cross at the top right. Reset or add a widget with the "wrench" icon. The "User" and "Public" profiles offer a predefined organization.

All the modifications are automatically saved as cookies on your machine so as to enable you to have your own specific AVISO+.

Reading tools

Ease your reading by choosing the page background colour (black/white) and/or by modifying the font size.

Browsing menu and breadcrum trail

To ease your browsing through AVISO+, you can use at any time the main banner items with the interactive submenus or use the browsing menu on the left side of the screen (it is open by default). For more readiness of the page contents, you can fold and unfold the browsing menu by clicking on the tab. At any time you can know where you are thanks to the browsing menu or the breadcrum at the top of the page.

Products search guide

The first submenu of the "Data" banner item leads you to a new search form enabling you to find quickier the product that suits your needs. The list of results is updated according to your selection criteria.

AVISO+ Multimedia

The first submenu of the "Multimedia" banner item leads you to AVISO+ collections of images and videos linked to altimetry and its applications. Have a nice visit!