糖心TV Complexity Science Events
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Please note that your event booking is for D1.07 only. The adjacent common room is a private area for the MathSys Centre that cannot used as part of your booking.
Complexity Forum: "Self-organized criticality: mechanisms and applications"
ABSTRACT:
This two part talk will discuss a practical application of the notion of
self-organized criticality (SOC) to atmospheric science followed by a discussion
of the theoretical foundations of the phenomenon of SOC in a more general context.
Part A : Non-equilibrium phase transitions and atmospheric convection.
Tropical rainfall can be viewed as an indicator of convection, an important and notoriously difficult process to parameterize in climate models. I will present an analysis of satellite data showing that atmospheric convection is well described by the terminology of non-equilibrium phase transitions. The atmospheric system is attracted by the critical point of the transition, making this an example of self-organized criticality. In climatology this is known as the "Quasi-Equilibrium hypothesis". Standard methods from critical phenomena are applicable with little modification: The finite-size scaling of order-parameter fluctuations indicates a diverging spatial correlation length near criticality; including tropospheric temperature in the analysis, a critical line in the temperature-moisture plane indicates that the transition is not purely controlled by saturation. The universality of the transition itself and of observables sensitive to the self-organization mechanism ("avalanches") will be discussed.
Part B (more technical): Universality in self-organized critical systems
It has been proposed that self-organized criticality is the result of coupling the tuning parameter of a phase transition to its order parameter. In sandpiles this amounts to coupling the particle density in a sandpile to the density of active sites, which is effectively achieved by bulk-conservation and open boundaries in conjunction with a slow drive. It will be shown that these conditions lead to criticality, but not to universality. This poses the question whether a) the mechanism is not responsible for SOC or b) SOC is fundamentally non-universal. The implications of b) would be severe since the study of systems as simple as sandpiles is largely justified by the universality hypothesis. Much of this is work in progress, and I will present the current state of the ongoing debate.