Speaker Arianna Marchionne
Title: Modeling Past Abrupt Climate Changes
Abstract:
ABSTRACT:  
According to Milankovitch theory of ice ages, glacial cycles are driven 
by variations in the insolation, i.e. the amount of the incoming solar 
radiation reaching the Earth. These variations are associated with variations 
of the Earth's orbit. Many attempts have been made to identify the influence 
of the orbital variations on Earths climate; however, the knowledge and 
tools needed to complete a unified theory for ice ages have not been 
developed yet.

Here, we focus on the climatic variations that have occurred over the 
last few million years. Paleoclimatic records show that the glacial cycles 
are linked to the orbitally driven variations in insolation. 
However, the relationship is far from linear, and insolation alone can 
not explain the climatic variability seen in the records.

Firstly, we discuss the possible dynamical mechanisms for linking the 
frequencies observed in the records to those present in the astronomical 
forcing. Using a general framework of conceptual dynamical models, which 
may or may not exhibit internal self-sustained oscillations, we introduce 
and discuss two distinct mechanisms for a periodic response at a different 
period to a periodic forcing. In one case, the system has the ability of 
maintaining internal oscillations. In the second case, the system is damped, 
so it does not possess self-sustained oscillations.

The distinction between the two scenarios mentioned above is un-derstood in 
terms of two phenomena in oscillating systems, namely the phenomenon of 
resonance and that of synchronisation. To avoid con-fusion between them, 
we illustrate the main differences, and present a listing of their 
characteristic properties. A Duffing and a Duffing-Van der Pol oscillator 
will be used for illustrative purposes.

Next, we address the analysis of nonlinear resonances in a weakly-damped 
Duffing oscillator. In addition to already known odd and even subharmonic 
resonances, we combine the physical concept of subharmonic resonances and 
mathematical con-cept of bifurcations to uncover a novel resonance type.