466 research outputs found
Dissipative Quasigeostrophic Motion under Temporally Almost Periodic Forcing
The full nonlinear dissipative quasigeostrophic model is shown to have a
unique temporally almost periodic solution when the wind forcing is temporally
almost periodic under suitable constraints on the spatial square-integral of
the wind forcing and the parameter, Ekman number, viscosity and the
domain size. The proof involves the pullback attractor for the associated
nonautonomous dynamical system
Noise-Sustained currents in quasigeostrophic turbulence over topography
We study the development of mean structures in a nonlinear model of large
scale ocean dynamics with bottom topography and dissipation, and forced with a
noise term. We show that the presence of noise in this nonlinear model leads to
persistent average currents directed along isobaths. At variance with previous
works we use a scale unselective dissipation, so that the phenomenon can not be
explained in terms of minimum enstrophy states. The effect requires the
presence of both the nonlinear and the random terms, and can be though of as an
ordering of the stochastic energy input by the combined effect of nonlinearity
and topography. The statistically steady state is well described by a
generalized canonical equilibrium with mean energy and enstrophy determined by
a balance between random forcing and dissipation. This result allows predicting
the strengh of the noise-sustained currents. Finally we discuss the relevance
that these noise-induced currents could have on real ocean circulation.Comment: 11 pages REVTeX. Includes 4 figures using epsf. Related material in
http://www.imedea.uib.es/Nonlinear and http://www.imedea.uib.es/Oceanograph
Local and Nonlocal Dispersive Turbulence
We consider the evolution of a family of 2D dispersive turbulence models. The
members of this family involve the nonlinear advection of a dynamically active
scalar field, the locality of the streamfunction-scalar relation is denoted by
, with smaller implying increased locality. The dispersive
nature arises via a linear term whose strength is characterized by a parameter
. Setting , we investigate the interplay of
advection and dispersion for differing degrees of locality. Specifically, we
study the forward (inverse) transfer of enstrophy (energy) under large-scale
(small-scale) random forcing. Straightforward arguments suggest that for small
the scalar field should consist of progressively larger eddies, while
for large the scalar field is expected to have a filamentary structure
resulting from a stretch and fold mechanism. Confirming this, we proceed to
forced/dissipative dispersive numerical experiments under weakly non-local to
local conditions. For , there is quantitative agreement
between non-dispersive estimates and observed slopes in the inverse energy
transfer regime. On the other hand, forward enstrophy transfer regime always
yields slopes that are significantly steeper than the corresponding
non-dispersive estimate. Additional simulations show the scaling in the inverse
regime to be sensitive to the strength of the dispersive term : specifically,
as decreases, the inertial-range shortens and we also observe that
the slope of the power-law decreases. On the other hand, for the same range of
values, the forward regime scaling is fairly universal.Comment: 19 pages, 8 figures. Significantly revised with additional result
Intergyre transport in a wind-driven, quasigeostrophic double gyre: An application of lobe dynamics
We study the flow obtained from a three-layer, eddy-resolving quasigeostrophic ocean circulation model subject to an applied wind stress curl. For this model we will consider transport between the northern and southern gyres separated by an eastward jet. We will focus on the use of techniques from dynamical systems theory, particularly lobe dynamics, in the forming of geometric structures that govern transport. By âgovernâ, we mean they can be used to compute Lagrangian transport quantities, such as the flux across the jet. We will consider periodic, quasiperiodic, and chaotic velocity fields, and thus assess the effectiveness of dynamical systems techniques in flows with progressively more spatio-temporal complexity. The numerical methods necessary to implement the dynamical systems techniques and the significance of lobe dynamics as a signature of specific âeventsâ, such as rings pinching off from a meandering jet, are also discussed
Predictability of the Burgers dynamics under model uncertainty
Complex systems may be subject to various uncertainties. A great effort has
been concentrated on predicting the dynamics under uncertainty in initial
conditions. In the present work, we consider the well-known Burgers equation
with random boundary forcing or with random body forcing. Our goal is to
attempt to understand the stochastic Burgers dynamics by predicting or
estimating the solution processes in various diagnostic metrics, such as mean
length scale, correlation function and mean energy. First, for the linearized
model, we observe that the important statistical quantities like mean energy or
correlation functions are the same for the two types of random forcing, even
though the solutions behave very differently. Second, for the full nonlinear
model, we estimate the mean energy for various types of random body forcing,
highlighting the different impact on the overall dynamics of space-time white
noises, trace class white-in-time and colored-in-space noises, point noises,
additive noises or multiplicative noises
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