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**From**: StatFizSzeminar <statfiz AT glu.elte.hu>**To**: fizinfo AT lists.kfki.hu**Subject**: [Fizinfo] Stat Fiz Szeminarium - Helyesbites**Date**: Fri, 13 Apr 2018 13:22:34 +0200

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ELTE TTK Fizikai Intézet

STATISZTIKUS FIZIKAI SZEMINÁRIUM

PÁROS SZEMINÁRIUM

2018. április 18.

szerda, 11.00

Gábor Drótos

University of the Balearic

Islands and CSIC

"A coarse-grained finite-time description of

open flows, with an introduction

to the conceptof Lagrangian flow networks"

In fluid flows, or in the phase space of any dynamical

system, the time evolution of the trajectories can be

regarded as a transport phenomenon, described by the

Perron--Frobenius operator. Its discretized version gives

the amount of (phase space) volume transported from one

box of the domain to another. The recognition that this

discretized operator can be considered to be the connec-

tivity matrix of a weighted directed network, a Lagrangian

flow network, led to particularly successful applications

of this coarse-grained description. Beyond identifying

relationships between traditional quantifiers of chaos and

network characteristics, techniques developed for the inves-

tigation of networks, like community detection, have proven

to be remarkably useful from a dynamical systems point of

view, like for the identification of coherent regions.

The focus has so far been almost exclusively on volume-pre-

serving closed flows. In one of our research directions, we

study how characteristics of open flows can be defined in a

coarse-grained finite-time description. In particular, we

consider the escape rate and the fractal dimension beyond

the finite-time largest Lyapunov exponent, and illustrate

numerically that the Kantz--Grassberger relation, linking

these quantities on infinitesimally small spatial scales for

asymptotically long times, is approximately satisfied by the

coarse-grained finite-time counterparts of these quantities.

What is interesting is that these quantities have a spread

throughout the domain of the flow, but such that the Kantz-

Grassberger relation is approximately fulfilled.

2018. április 18.

szerda, 12.10

Tamás Bódai

University of Reading

"Linear response theory applied to

geoengineering"

We investigate in an intermediate-complexity cli-

mate model (I) the applicability of linear response

theory to a geoengineering problem and (II) the suc-

cess of the considered geoengineering method. The

geoengineering method is framed here as a special

optimal control problem, which leads mathematically

to the following inverse problem. A given rise in

carbon dioxide concentration would result in a

global climate change with respect to an appropriate

ensemble average of the surface air temperature. We

are looking for a suitable modulation of solar forcing

which can cancel out the said global change, or mod-

ulate it in some other desired fashion. It is rather

straightforward to predict this solar forcing, consid-

ering an infinite time period, and we will spell out an

iterative procedure suitable for numerical implementa-

tion that applies to finite time periods too.

Regarding (I), we find that under geoengineering, i.e.

the combined greenhouse and solar forcing, the actual

global mean surface temperature response asymptotically

is not zero, indicating that the linear susceptibility

is not determined correctly. This is due to a signifi-

cant quadratic nonlinearity of the response under system

identification achieved by a forced experiment. This non-

linear contribution can in fact be easily removed, which

results in much better estimates of the linear suscepti-

bility, and, in turn, in a five-fold reduction in a resi-

dual global mean surface temperature response under geo-

engineering. Regarding (II), however, we diagnose this

geoengineering method to result in a considerable spatial

variation of the surface temperature anomaly, reaching more

than 2 K at polar/high latitude regions upon doubling

the carbon dioxide concentration, even in the ideal case

when the geoengineering method was successful in cancel-

ing out the response in the global mean. In the same

time, a new climate is realised also in terms of e.g. an

up to 4 K cooler tropopause or drier/disrupted Tropics,

relative to unforced conditions.

https://arxiv.org/abs/1803.09606

1117, Budapest, Pázmány P. sétány 1/A, Északi tömb 2.54

honlap: http://glu.elte.hu/~statfiz

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**[Fizinfo] Stat Fiz Szeminarium - Helyesbites**,*StatFizSzeminar, 04/10/2018*- <Possible follow-up(s)>
**[Fizinfo] Stat Fiz Szeminarium - Helyesbites**,*StatFizSzeminar, 04/13/2018*

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