arXiv subjects

E. Pietropaolo

Publications and source records attributed to E. Pietropaolo.

4 recordsLinked to original sources

arXiv2020

Optical design of the Tor vergata Synoptic Solar Telescope (TSST)

Synoptic full-disk solar telescope are fundamental instruments for present and future Solar Physics and Space Weather. They are typically used to study and monitor the solar activity by using high temporal cadence observations at different wavelength. The TSST (Tor vergata Synoptic Solar Telescope) is a new synoptic telescope composed of two spectral channels: an H$α$ (656.3 nm) telescope and a Magneto Optical Filter (MOF)-based telescope in the Potassium (KI D1) absorption spectral line at 769.9 nm. H$α$ observations are fundamental for the identification of flaring regions. The MOF-based telescope will produce line of sight magnetograms and dopplergrams of the solar photosphere, which are respectively used to study the magnetic field's geometry in active regions and dynamics of the solar atmosphere. In this work, we present an overview on the TSST and the optical design and characteristics of the MOF-based telescope, whose optical scheme is a double-Keplerian 80mm refractor with an aberration-free imaging lens.

astro-ph.IM↗

arXiv2017

Solar wind magnetic field background spectrum from fluid to kinetic scales

The solar wind is highly structured in fast and slow flows. These two dynamical regimes remarkably differ not only for the average values of magnetic field and plasma parameters but also for the type of fluctuations they transport. Fast wind is characterized by large amplitude, incompressible fluctuations, mainly Alfvénic, slow wind is generally populated by smaller amplitude and less Alfvénic fluctuations, mainly compressive. The typical corotating fast stream is characterized by a stream interface, a fast wind region and a slower rarefaction region formed by the trailing expansion edge of the stream. Moving {between these two regions}, from faster to slower wind, we observe the following behavior: a) the power level of magnetic fluctuations within the inertial range largely decreases, keeping the typical Kolmogorov scaling; b) at proton scales, for about one decade right beyond the high frequency break, the spectral index becomes flatter and flatter towards a value around -2.7; c) at higher frequencies, before the electron scales, the spectral index remains around -2.7 and, {based on suitable observations available for $4$ corotating streams}, the power level does not change, irrespective of the flow speed. All these spectral features, characteristic of high speed streams, suggest the existence of a sort of magnetic field background spectrum. This spectrum would be common to both faster and slower wind but, any time the observer would cross the inner part of a fluxtube channeling the faster wind into the interplanetary space, a turbulent and large amplitude Alfvénic spectrum would be superposed to it.

astro-ph.SR↗

arXiv2017

The dependence of the [FUV-MUV] colour on solar cycle

Solar UV variability is extremely relevant for the stratospheric ozone. It has an impact on Earth's atmospheric structure and dynamics through radiative heating and ozone photochemistry. Our goal is to study the slope of the solar UV spectrum in two UV bands important for the stratospheric ozone production. In order to investigate the solar spectral variability, we use SOLSTICE (the Solar Stellar Irradiance Comparison Experiment) data onboard Solar Radiation and Climate Experiment (SORCE) satellite. Data sets used are far UV (115-180nm) and middle UV (180-310nm), as well as the Mg II index (the Bremen composite). We introduce the SOLSTICE [FUV - MUV] colour to study the solar spectral characteristics, as well as analysis of the colour versus Mg II index. To isolate the 11-year scale variation, we used the Empirical Mode decomposition (EMD) on the data sets. The [FUV - MUV] colour strongly correlates with the Mg II index. More in detail, the [FUV - MUV] colour shows a time dependent behavior when plotted versus Mg II index. To explain this dependence we hypothesize an efficiency reduction of SOLSTICE FUV irradiance using an exponential aging law.

astro-ph.SR↗

arXiv2014

Radial evolution of intermittency of density fluctuations in the fast solar wind

We study the radial evolution of intermittency of density fluctuations in the fast solar wind. The study is performed analyzing the plasma density measurements provided by Helios 2 in the inner heliosphere between $0.3$ and $0.9$ AU. The analysis is carried out by means of a complete set of diagnostic tools, including the flatness factor at different time scales to estimate intermittency, the Kolmogorov-Smirnov test to estimate the degree of intermittency, and the Fourier transform to estimate the power spectral densities of these fluctuations. Density fluctuations within fast wind are rather intermittent and their level of intermittency, together with the amplitude of intermittent events, decreases with distance from the Sun, at odds with intermittency of both magnetic field and all the other plasma parameters. Furthermore, the intermittent events are strongly correlated, exhibiting temporal clustering. This indicates that the mechanism underlying their generation departs from a time-varying Poisson process. A remarkable, qualitative similarity with the behavior of plasma density fluctuations obtained from a numerical study of the nonlinear evolution of parametric instability in the solar wind supports the idea that this mechanism has an important role in governing density fluctuations in the inner heliosphere.

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