 |
| Titel |
Ekman layers in the Southern Ocean: spectral models and observations, vertical viscosity and boundary layer depth |
| VerfasserIn |
S. Elipot, S. T. Gille |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1812-0784
|
| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 5, no. 2 ; Nr. 5, no. 2 (2009-05-14), S.115-139 |
| Datensatznummer |
250002418
|
| Publikation (Nr.) |
 copernicus.org/os-5-115-2009.pdf |
|
|
|
|
|
| Zusammenfassung |
Spectral characteristics of the oceanic
boundary-layer response to wind stress forcing are assessed by
comparing surface drifter observations from the Southern Ocean to a
suite of idealized models that parameterize the vertical flux of
horizontal momentum using a first-order turbulence closure scheme. The
models vary in their representation of vertical viscosity and boundary
conditions. Each is used to derive a theoretical transfer function
for the spectral linear response of the ocean to wind stress.
The transfer functions are evaluated using observational data.
The ageostrophic component of near-surface velocity is computed by subtracting
altimeter-derived geostrophic velocities from observed drifter velocities (nominally
drogued to represent motions at 15-m depth). Then the transfer function is
computed to link these ageostrophic velocities to observed wind stresses.
The traditional Ekman model, with infinite depth and constant vertical
viscosity is among the worst of the models considered in this study.
The model that most successfully describes the variability in the drifter
data has a shallow layer of depth O(30–50 m), in which the
viscosity is constant and O(100–1000 m2 s−1), with a no-slip bottom boundary
condition.
The second best model has a vertical viscosity with a surface value
O(200 m2 s−1), which increases
linearly with depth at a rate O(0.1–1 cm s−1) and a no-slip
boundary condition at the base of the boundary layer of depth O(103 m).
The best model shows little latitudinal or
seasonal variability, and there is no obvious link to wind stress or
climatological mixed-layer depth. In contrast, in the second best model,
the linear coefficient and the boundary
layer depth seem to covary with wind stress.
The depth of the boundary layer for this model is found to be unphysically large
at some latitudes and seasons, possibly
a consequence of the inability of Ekman models to remove
energy from the system by other means than shear-induced dissipation.
However, the Ekman depth scale appears to scale like the
climatological mixed-layer depth. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|