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  • From: StatFizSzeminar <statfiz AT>
  • To: fizinfo AT
  • Subject: [Fizinfo] Stat Fiz Szeminarium
  • Date: Fri, 24 Feb 2012 18:35:17 +0100
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ELTE Institute of Physics

A HELYSZÍN: Északi tömb 4.70

Henk A. Dijkstra Lecture Series
on Nonlinear Physical Oceanography

1 March (Thu), 16:15-17:45

The use of implicit models to understand the physics of the
climate system

Abstract: Over the last decades a hierarchy of implicit
ocean-climate models has been developed making use of
sophisticated linear systems solvers (e.g., MRILU) and
generalized eigenproblem solvers (e.g. JDQZ). In this
presentation, I will give an overview of what one has learned
from these models regarding the physics of the climate system
(a few examples), describe the current capabilities of these
models and discuss their (potential) future development.

Ref: H.A. Dijkstra, Nonlinear Physical Oceanography, 2nd
edition, Springer, 2005.

2 March (Fri), 11:15-12:45

A nonlinear theory of Kuroshio path variability

Abstract: The bimodal behavior of the path of the Kuroshio in
the North Pacific has fascinated physical oceanographers since
indications of this phenomenon were found. Why would a western
boundary current switch between a large-meander and a
small-meander state and back? Why does this phenomenon not
appear in other western boundary currents, such as the Gulf
Stream? For the Kuroshio, both large- and small meander states
can persist over a period ranging from a few years to a decade.
With the analysis of satellite data and those of in situ
measurements, quite a detailed description of the different
states and their transition behavior is now available. There is
still, however, no consensus on which processes cause the
low-frequency variability in the Kuroshio. It appears that
direct interpretation of the observations often has been based
on mechanisms involving external causes (such as atmospheric
forcing) and linear ocean dynamics while ocean modelers have
tended to suggest mechanisms which involve elements of
nonlinear ocean dynamics. A theory of the Kuroshio path
variability should explain at least (i) why the Kuroshio can be
in different states and provide a mechanism for the different
spatial patterns of these states, and explain (ii) the physics
of the transition time scale between the two states. Based on a
(stochastic) dynamical systems analysis of a hierarchy of
models (quasi-geostrophic, shallow-water, primitive equations),
a nonlinear theory will be presented which is able to provide
answers to the issues (i-ii) above.

Ref: S. Pierini, Dijkstra, H.A. and A. Riccio, A nonlinear
theory of the Kuroshio Extension Bimodality, J. Phys.
Oceanography 39, 2212-2229 , (2009).

2 March (Fri), 16:15-17:45

North Atlantic Multidecadal Variability: a synthesis view

Abstract: A dynamical systems framework, in many ways similar
to that for El Nino/Southern Oscillation, is presented to
understand the multidecadal variability in the North Atlantic.
A so-called minimal primitive equation model is first used to
represent the multidecadal variability in the North Atlantic
climate system. Within this minimal model, we identify a normal
mode of multidecadal variability that can destabilize the
background climate state through a so-called Hopf bifurcation.
Next, it is argued that noise is setting the amplitude of the
sea surface temperature variability associated with this
normal mode. Finally, it will argued that the mechanism found
in the minimal model is responsible for the multidecadal
variability in GCMs and in available observations.

Ref: L. M. Frankcombe, A. von der Heydt, H. A. Dijkstra, North
Atlantic Multidecadal Climate Variability: An investigation of
dominant time scales and processes, J. Climate, 23, 3626-3638,

3 March (Sat), 11:15-12:45

Will the Atlantic Ocean Circulation collapse before the end of
this century?

Abstract: The Atlantic Ocean, in particular its Meridional
Overturning Circulation (MOC), is sensitive to the patterns of
atmospheric forcing, in particular to that of the freshwater
flux. Relatively small changes in atmospheric conditions can
therefore lead to a spectacular reduction (collapse) of the
Atlantic MOC. As the time scale of a collapse is only a few
decades, the associated changes in heat transport may have a
large impact on European climate and society. In the latest
IPCC assessment (AR4), climate models project that changes in
freshwater input due to global warming will only lead to at
most 10% change in the strength of the Atlantic MOC at the end
of this century. However, there have been recent developments
which indicate that the Atlantic MOC may be more sensitive
than these models suggest. These new results will be the main
focus of this presentation.

Ref: Huisman, S., M. den Toom, Dijkstra, H. A. and S.
Drijfhout. An indicator of the multiple equilibria regime of
the Atlantic Meridional Overturning Circulation. J. Phys.
Oceanography, 40, 551-567, (2010).

1117 Budapest, Pázmány P. sétány 1/A (Northern Block)
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  • [Fizinfo] Stat Fiz Szeminarium, StatFizSzeminar, 02/24/2012

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