156 research outputs found
Dissipative dynamics of western boundary currents
We investigate the steady barotropic circulation patterns driven by inflow-outflow boundary conditions on a rectangular β-plane domain. An inertial jet enters the domain in the southwest corner and a broad eastward outflow is prescribed at the eastern boundary. On the western wall there is no mass flux and no slip.With weak viscosity, ν the western boundary jet ?overshoots? northward, beyond the latitude band of the eastern outflow. As the viscosity is reduced the length of this overshoot increases as ν−2/3, before the jet gradually peels away from the western wall, plunges southward and eventually turns eastward. Away from the wall the current forms a damped stationary Rossby wave, as described by Moore in 1963.The initial northward overshoot and southward plunge is a distinct dynamical regime, and not merely the first and largest undulation of the Rossby wave. For instance the zonal length scale of the overshoot is just the Munk scale, (ν/β)1/3 and inertia, planetary vorticity and viscosity are all important at leading order in the dynamical balance as ν → 0. All of the streamlines pass through this dissipative region and most of the Lagrangian potential vorticity alterations occur here, rather than in the Rossby wave.The preceeding scenario applies only when the northern boundary is distant, so that the overshoot peels away from the western wall before striking the northwest corner of the domain. If the jet reaches the northern boundary it drives an inertial recirculating gyre in the corner
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Eddy saturation and frictional control of the Antarctic Circumpolar Current
The Antarctic Circumpolar Current is the strongest current in the ocean and has a pivotal impact on ocean stratification, heat content, and carbon content. The circumpolar volume transport is relatively insensitive to surface wind forcing in models that resolve turbulent ocean eddies, a process termed “eddy saturation.” Here a simple model is presented that explains the physics of eddy saturation with three ingredients: a momentum budget, a relation between the eddy form stress and eddy energy, and an eddy energy budget. The model explains both the insensitivity of circumpolar volume transport to surface wind stress and the increase of eddy energy with wind stress. The model further predicts that circumpolar transport increases with increased bottom friction, a counterintuitive result that is confirmed in eddy-permitting calculations. These results suggest an unexpected and important impact of eddy energy dissipation, through bottom drag or lee wave generation, on ocean stratification, ocean heat content, and potentially atmospheric CO2
The role of ocean gateways in the dynamics and sensitivity to wind stress of the early Antarctic Circumpolar Current
The date of inception of the Antarctic Circumpolar Current is debated due to uncertainty in the relative opening times of Drake Passage and the Tasman Seaway. Using an idealized eddy-resolving numerical ocean model, we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current. We find that overlapping continental barriers do not impede a circumpolar transport in excess of 50Sv, as long as a circumpolar path can be traced around the barriers. However, the presence of overlapping barriers does lead to an increased sensitivity of the current's volume transport to changes in wind stress. This change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress. Specifically, when the pressure drop across continents is the main balancing sink of momentum, the zonal volume transport is sensitive to changes in wind stress. Changes in zonal volume transport take place via altering the depth-independent part of the circumpolar transport rather than that arising from thermal wind shear. In such a scenario, isopycnals continue to slope steeply across the model Southern Ocean, implying a strong connection between the deep and surface oceans. This may have consequences for the meridional overturning circulation and its sensitivity to wind stress
Destabilization of the thermohaline circulation by transient perturbations to the hydrological cycle
We reconsider the problem of the stability of the thermohaline circulation as
described by a two-dimensional Boussinesq model with mixed boundary conditions.
We determine how the stability properties of the system depend on the intensity
of the hydrological cycle. We define a two-dimensional parameters' space
descriptive of the hydrology of the system and determine, by considering
suitable quasi-static perturbations, a bounded region where multiple equilibria
of the system are realized. We then focus on how the response of the system to
finite-amplitude surface freshwater forcings depends on their rate of increase.
We show that it is possible to define a robust separation between slow and fast
regimes of forcing. Such separation is obtained by singling out an estimate of
the critical growth rate for the anomalous forcing, which can be related to the
characteristic advective time scale of the system.Comment: 37 pages, 8 figures, submitted to Clim. Dy
Ensemble Dynamics and Bred Vectors
We introduce the new concept of an EBV to assess the sensitivity of model
outputs to changes in initial conditions for weather forecasting. The new
algorithm, which we call the "Ensemble Bred Vector" or EBV, is based on
collective dynamics in essential ways. By construction, the EBV algorithm
produces one or more dominant vectors.
We investigate the performance of EBV, comparing it to the BV algorithm as
well as the finite-time Lyapunov Vectors. We give a theoretical justification
to the observed fact that the vectors produced by BV, EBV, and the finite-time
Lyapunov vectors are similar for small amplitudes.
Numerical comparisons of BV and EBV for the 3-equation Lorenz model and for a
forced, dissipative partial differential equation of Cahn-Hilliard type that
arises in modeling the thermohaline circulation, demonstrate that the EBV
yields a size-ordered description of the perturbation field, and is more robust
than the BV in the higher nonlinear regime. The EBV yields insight into the
fractal structure of the Lorenz attractor, and of the inertial manifold for the
Cahn-Hilliard-type partial differential equation.Comment: Submitted to Monthly Weather Revie
A mathematical framework for critical transitions: normal forms, variance and applications
Critical transitions occur in a wide variety of applications including
mathematical biology, climate change, human physiology and economics. Therefore
it is highly desirable to find early-warning signs. We show that it is possible
to classify critical transitions by using bifurcation theory and normal forms
in the singular limit. Based on this elementary classification, we analyze
stochastic fluctuations and calculate scaling laws of the variance of
stochastic sample paths near critical transitions for fast subsystem
bifurcations up to codimension two. The theory is applied to several models:
the Stommel-Cessi box model for the thermohaline circulation from geoscience,
an epidemic-spreading model on an adaptive network, an activator-inhibitor
switch from systems biology, a predator-prey system from ecology and to the
Euler buckling problem from classical mechanics. For the Stommel-Cessi model we
compare different detrending techniques to calculate early-warning signs. In
the epidemics model we show that link densities could be better variables for
prediction than population densities. The activator-inhibitor switch
demonstrates effects in three time-scale systems and points out that excitable
cells and molecular units have information for subthreshold prediction. In the
predator-prey model explosive population growth near a codimension two
bifurcation is investigated and we show that early-warnings from normal forms
can be misleading in this context. In the biomechanical model we demonstrate
that early-warning signs for buckling depend crucially on the control strategy
near the instability which illustrates the effect of multiplicative noise.Comment: minor corrections to previous versio
SDS-PAGE-Based Quantitative Assay for Screening of Kidney Stone Disease
Kidney stone disease is a common health problem in industrialised nations. We developed a SDS-PAGE-based method to quantify Tamm Horsfall glycoprotein (THP) for screening of kidney stone disease. Urinary proteins were extracted by using ammonium sulphate precipitation at 0.27 g salt/mL urine. The resulted pellet was dissolved in TSE buffer. Ten microliters of the urinary proteins extract was loaded and separated on 10% SDS-PAGE under reducing condition. THP migrated as single band in SDS-PAGE. The assay reproducibility and repeatability were 4.8% CV and 2.6% CV, respectively. A total of 117 healthy subjects and 58 stone patients were tested using this assay, and a distinct cut-off (P < 0.05) at 5.6 μg/mL THP concentration was used to distinguish stone patients from healthy subjects. The sensitivity and specificity of the method were 92.3% and 83.3%, respectively
Coupled atmosphere–mixed layer ocean response to ocean heat flux convergence along the Kuroshio Current Extension
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Climate Dynamics 36 (2011): 2295-2312, doi:10.1007/s00382-010-0764-8.The winter response of the coupled atmosphere-ocean mixed layer system to
anomalous geostrophic ocean heat flux convergence in the Kuroshio Extension is
investigated by means of experiments with an atmospheric general circulation model
coupled to an entraining ocean mixed layer model in the extra-tropics. The direct
response consists of positive SST anomalies along the Kuroshio Extension and a
baroclinic (low-level trough and upper-level ridge) circulation anomaly over the North
Pacific. The low-level component of this atmospheric circulation response is weaker in
the case without coupling to an extratropical ocean mixed layer, especially in late winter.
The inclusion of an interactive mixed layer in the tropics modifies the direct coupled
atmospheric response due to a northward displacement of the Pacific Inter-Tropical
Convergence Zone which drives an equivalent barotropic anomalous ridge over the North
Pacific. Although the tropically-driven component of the North Pacific atmospheric
circulation response is comparable to the direct response in terms of sea level pressure
amplitude, it is less important in terms of wind stress curl amplitude due to the mitigating
effect of the relatively broad spatial scale of the tropically-forced atmospheric
teleconnection.We gratefully acknowledge
financial support from NOAA’s Office of Global Programs (grant to C. Deser and Y.-O.
Kwon). Y.-O. Kwon is also supported through the Claudia Heyman Fellowship of the
WHOI Ocean Climate Change Institute
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