TFS Starting Grant

Many physical and natural systems such as atmospheric winds, astrophysical plasmas and near-wall turbulence in magnetically confined fusion plasmas are characterized by large-amplitude, intermittent fluctuations. These can be recognized by skewed and flattened probability densities far from the normal distribution. As a result, descriptions and methods assuming normal statistics may fail or have very poor predictive powers. Simply estimating mean values and standard deviations does not capture the nature of these fluctuations and using such methods may lead to fatal underestimation of the likelihood of extreme events.

A promising way to model such fluctuations is to use the filtered Poisson process (FPP). This is a model for describing measurement time series as a superposition of uncorrelated pulses with fixed shape but randomly distributed amplitudes, arrival and duration times, or equivalently, the result of a characteristic response to pulse-like forcing. As such, it is a linear model for investigating and describing the statistical properties of non-linear systems. The model takes large-amplitude fluctuations directly into account. The UiT fusion energy research team has used the FPP for pioneering analysis of intermittent near-wall turbulent fluctuations in magnetically confined fusion plasmas, explaining several well-established experimental observations.

In this project proposal, the FPP will be put to the test as a general model for intermittent fluctuations. It is done in collaboration with several international teams providing state-of-the-art measurement and simulation time series from such wide areas as magnetically confined plasmas, cosmic dust particles in the solar wind, climate response to volcanic activity and atmospheric aerosols. Not only does the project aim to further basic science research in providing a universal model for intermittent fluctuations in physical systems, but also aims to answer several physics questions such as how fluctuation amplitudes and durations scale with plasma and machine parameters in magnetically confined plasmas, how cosmic dust is distributed in the inner heliosphere, whether the global temperature response due to volcanic eruptions is linear and the presence and effect of long-range correlations in atmospheric aerosols.