1,721,124 research outputs found
Stellar turbulent convection: the multiscale nature of the solar magnetic signature
Full text linkThe multiscale dynamics associated with turbulent convection present in physical systems governed by very high Rayleigh numbers still remains a vividly disputed topic in the community of astrophysicists, and in general, among physicists dealing with heat transport by convection. The Sun is a very close star for which detailed observations and estimations of physical properties on the surface, connected to the processes of the underlying convection zone, are possible. This makes the Sun a unique natural laboratory in which to investigate turbulent convection in the hard turbulence regime, a regime typical of systems characterized by high values of the Rayleigh number. In particular, it is possible to study the geometry of convection using the photospheric magnetic voids (or simply voids), the quasi-polygonal quiet regions nearly devoid of magnetic elements, which cover the whole solar surface and which form the solar magnetic network. This work presents the most extensive statistics, both in the spatial scales studied (1-80 Mm) and in the temporal duration (SC 23 and SC 24), to investigate the multiscale nature of solar magnetic patterns associated with the turbulent convection of our star. We show that the size distribution of the voids, in the 1-80 Mm range, for the 317, 870 voids found in the 692 analyzed magnetograms, is basically described by an exponential function
A comparative test of different compression methods applied to solar images
No full textIn this work we conduct a comparative study on different data compression methods applied to high resolution images of the solar surface acquired at the Solar Dunn Telescope in Sacramento Peak with the IBIS (Interferometric Bidimensional Spectrometer) instrument. Our aim is to perform an estimation of the quality, efficiency and workload of the considered computing techniques both in the so-called lossless modality, where in the reconstruction phase there is no loss of information, and in lossy mode, where it should be possible to reach a high compression ratio at the expense of image information. In the latter case we quantify the quality with image analysis conventional methods and more specifically with the reconstruction of physical parameters through standard procedures used in this kind of observations. The considered methods constitute the most frequently adopted image compression procedures in a variety of fields of application; they exploit in different ways the properties of the Discrete Wavelet Transforms often coupled with standard entropy coders or similar coding procedures applied to the different bit planes in order to allow a progressive handling of the original image. In the lossless approach we found that all methods give a compression ratio around 2. For a lossy compression we reached a compression ratio of 8 (equivalent to a 2 bit per pixel) without any perceptual difference between original and reconstructed images, but with effects on the photometric accuracy. We also tested the performance of 3-D lossy methods for the compression of data-cubes. Maintaining the same data degradation level, those methods allows us to gain a 2x in the compression ratio over the 2-D methods
A new catalogue of solar flare events from soft X-ray GOES signal in the period 1986–2020
No full textSolar flares, along with other sun-originated events such as Coronal Mass Ejections, fast solar wind streams, and solar energetic particles, are among the most relevant events in Space Weather. Moreover, solar flares are the most energetic processes that occur in our solar system. The in-depth study of their occurrence statistics, both over extended periods or during individual solar cycles, allows us to improve and constrain the basic physical models of their origin. Increasing the number of detected events, especially those of lower intensity, and the number of physical parameters that describe the detected flares is, therefore, a mandatory goal. In this paper, we present a computationally efficient algorithm for the detection of solar flares in the soft-X solar flux provided by the GOES (NASA/NOAA) satellite constellation. Our code produces a new flare catalogue increasing the number of events with respect to the official GOES list. In addition to increasing the number of identified events, the catalogue contains information such as: an estimate of the total energy released, start and end time of the event, possible overlap with other events, background level of the GOES X-ray emission close to the revealed event. After a detailed description of the detection algorithm, we carry out a preliminary analysis of the flares reported in our catalogue and compare our results with the official list of GOES for the period from 1998 to 2020.(c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved
Magnetic energy balance in the quiet sun on supergranular spatial and temporal scales
Full text linkSmall-scale magnetic fields are ubiquitous in the quiet solar photosphere and may store and transfer huge amounts of energy to the upper atmospheric layers. For this reason, it is fundamental to constrain the energetics of the quiet Sun. By taking advantage of a 24 hr long magnetogram time series acquired by the Hinode mission without interruption, we computed, for the first time, the average rate of change of magnetic energy density on supergranular spatial and temporal scales. We found that the regions where this quantity is positive correspond with the longest magnetic field decorrelation times, with the latter being consistent with the timescales of magnetic energy density variation. This suggests that, on average, the energy provided by photospheric electric and magnetic fields and current density is effective in sustaining the magnetic fields in the network
First results from IBIS: Photosphere dynamics and network magnetic elements
No full textThe panoramic Interferometric BIdimensional Spectrometer IBIS, installed at the Dunn Solar Telescope of NSO-Sacramento Peak (NM), has been employed to investigate the interaction between photospheric flows and network magnetic elements in a supergranular cell near the solar disk center. High spectral resolution observations of the Fe I 709.0 nm and Fe II 722.4 nm spectral lines were used to compute vertical and horizontal velocities of the granulation field at two heights in the photosphere. The same data were used to compute spectral line parameters as core intensity or equivalent width. Monochromatic images on the wing of the Ca II 854.2 nm line are used as proxy of small network magnetic elements. The analysis of photospheric vertical velocities shows that segmented magnetic structures match downward velocities in the iron lines Doppler images. The identical magnetic regions correspond to low contrast features in Fe I 709.0 nm core intensity images. Finally, the horizontal divergence maps show that the supergranule edge is outlined by velocity convergences
High resolution observations of chromospheric network
No full textThere is an increasing evidence that primary driver of solar variability, on time scales of days up to the solar activity cycle length, is the evolution of magnetic field present on the solar surface. In this paper we investigate the correlation between the photospheric structures and emerging magnetic elements by means of high spectral resolution images containing network cells. We present the preliminary results derived from the analysis of observations carried out in the spectral lines Ca II 854.3 nm, Fe I 709.0 nm and Fe II 722.4 nm with the 2-D Interferometric Bidimensional Spectrometer IBIS installed at the DST - Dunn Solar Telescope, Sacramento Peak (NM)
Statistical Properties of Synthetic Nanoflares
No full textStatistical properties of flares are a powerful tool for addressing the upper solar atmosphere heating problem.We
simulate time series of synthetic flares by means of a dynamic model of the atmospheric magnetic field in which
magnetic loop footpoints are controlled by photospheric flows computed through a n-body algorithm. The n-body
simulation reproduces the behavior of a system where large spatial organization scales (i.e., mesogranulation) occur
from the interaction of small-scale advection flows (i.e., granulation). The frequency function of the emitted magnetic
energies obtained from the simulation is well approximated by a power law with index 2:4, while the frequency
function of the waiting times between emissions shows a Poisson-like behavior with a deviation for longer times. The
flare model yields a fairly intuitive interpretation ofmagnetic reconnection processes as magnetic field reconfigurations
triggered by passive advection of magnetic footpoints through photospheric space-temporal correlated flows
Analysis of Supergranulation Pattern: the Void Probability Function of Solar Magnetograms
No full textThe appearance of large scale magnetic fields on the non-active solar surface is dominated by the so-called magnetic network. In full disk images, the reticulated pattern of such a network outlines the boundaries of the supergranular cells and, presumably, it results from the organization of tiny magnetic elements caused by horizontal convective flows of photospheric plasma. The magnetic network, when observed at high spatial resolution, reveals its spatially intermittent nature. As a matter of fact, the reticulated pattern is substituted by a collection of, more or less, aligned or clustered magnetic features producing a highly branched and fractal pattern embodying isolated magnetic elements. Recent spectropolarimetric observations, from space and ground-based telescopes, revealed the presence in solar magnetograms of multiscale underdense magnetic regions, commonly called voids, which may be considered a relevant signature of the processes occurring on the surface of our star. A void searching algorithm is used to study the statistical properties of such voids as observed in MDI and HINODE magnetograms. A clear discrepancy is observed between distributions of voids diameters for solar magnetograms and for a pseudo-random distribution having comparable particle densities
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