Etudes et évaluation de processus océaniques par des hiérarchies ...

4.5. MEAN CIRCULATION AND STRUCTURES OF TILTED OCEAN DEEP CONVECTION109
808 J O U R N A L O F P H Y S I C A L O C E A N O G R A P H Y VOLUME 38
tel-00545911, version 1 - 13 Dec 2010
FIG. 1. Horizontally averaged temperature T h as a function of depth (vertical scale, m) and time (horizontal scale, h) in the different
experiments: (top left) E01, (top right) E31, (middle left) E03, (middle right) E33, (bottom left) E04, (bottom right) E34. Black lines
are isotemperature lines at every 5 10 3 K. The black lines in the left panels are the isolines corresponding to the red lines in the
right panels (nontilted experiment).
quantities. We carefully checked that the last 90 h are in
a statistically stationary state. 2
4. Results
2 Temperature increases during the convection process, so it is
not strictly speaking in a statistically stationary state; however,
when the total mean temperature is continuously subtracted,
which has no dynamical implications when using the Boussinesq
approximation and a linear equation of state, such a state is obtained.
For brevity we will thus call the entire process statistically
stationary, once the convective front has reached the bottom of
the domain.
A detailed discussion on the dynamics of a single
convective plume is published in Wirth and Barnier
(2006), where a special emphasis was put on the influence
of a nonvanishing angle between the directions of
gravity and the rotation vector (tilted convection).
Here, we emphasize on the dynamics of the convection
process in an ocean that is cooled homogeneously
at its surface. The resulting dynamics are those of an
ensemble of convective plumes. Because of the nonlinear
character of the convection process, the dynamics
of the turbulent plume ensembles cannot be derived
from the behavior of a single plume. We again have to
resort to numerical simulations to determine the basic
features of turbulent convection.
The time evolution of the horizontally averaged temperature
in all experiments is shown (in Fig. 1). After
the onset of cooling, a negative temperature anomaly
develops at the surface. In less than 12 h this unstable
situation leads to convective motion, and a convective