Dr. Fabio Lepreti: Research

Transport processes in turbulent plasmas (2002- )

(In collaboration with V. Carbone and P. Veltri)

Statistical properties of solar flares (2000 - 2002)

(In collaboration with V. Carbone and P. Veltri)

Structure and dynamics of the solar photosphere (1998 - 2002)

(In collaboration with V. Carbone, L. Primavera, A. Vecchio, F. Berrilli, G. Consolini, E. Pietropaolo)

Particle transport and acceleration
in stochastic environments (2003- )

(In collaboration with L. Vlahos, V. Carbone, K. Arzner, H. Isliker)

(In collaboration with L. Vlahos, V. Carbone, K. Arzner, H. Isliker)

- Our aim is to study transport and acceleration process in stochastic environments. Different models will be implemented in order to reproduce some of the basic properties of turbulent plasmas and the motion of test particles in such systems will be investigated, to the aim of characterizing diffusion properties and studying particle acceleration. We are also interested in developing numerical codes providing the time evolution and the spectra of radiation emitted by charged particles moving in a turbulent environment. As an application of this work, we would like to compare the results obtained from our models with the observations of high energy radiation produced by solar flares.

Transport processes in turbulent plasmas (2002- )

(In collaboration with V. Carbone and P. Veltri)

- We are currently investigating the problem of
transport control in electrostatic turbulence by means of test-particle simulations.
We found that a barrier for the transport, that is, a region of space where
transport is significantly reduced, can be generated by randomizing the phases
of the turbulent fields. In other words, this corresponds to the annihilation
of coherent structures, which are present on all scales, without actually
decreasing the turbulence level.

Statistical properties of solar flares (2000 - 2002)

(In collaboration with V. Carbone and P. Veltri)

- Statistical properties of solar flares have
been studied through the analysis of X-ray bursts produced by flares. We
showed that the probability distribution of time intervals between successive
bursts (also called
*waiting times*) is not in agreement with a poisson process. In fact, we found that the waiting time distribution (WTD) for soft X-ray bursts detected by GOES satellites can be reproduced by a Lévy function, which is characterized by a power law tail at large waiting times. This result indicates that the physical process underlying solar flares is statistically self-similar in time and that long range correlations are present.

Structure and dynamics of the solar photosphere (1998 - 2002)

(In collaboration with V. Carbone, L. Primavera, A. Vecchio, F. Berrilli, G. Consolini, E. Pietropaolo)

- This project has been carried on by using data acquired by the Italian Panoramic Monochromator (IPM) installed at the THEMIS telescope, located at the Teide observatory of the Instituto de Astrofisica de Canarias (IAC). Intensity and velocity photospheric velocity field have been analyzed through multifractal methods. This approach allowed us to evidence that the intensity fluctuations, which are particularly strong at the bundaries of the granules, tend to concentrate on smaller and smaller spatial scales with increasing photospheric heights.
- The dynamics of photospheric motions has been
investigated for the first time by means of the Proper Orthogonal Decomposition
(POD), a technique which is also used, for example, to analyze the behavior
of coherent structures in turbulent flows.
By applying this method to line of sight, photospheric
velocity dataprovided by the THEMIS-IPM system, we found that the most two
energetic modes are due to granulation, while the next two modes (in order
of decreasing energy) describe the contribution of the "5-min" acoustic
oscillations (
*p*-modes).