141 research outputs found
Hot prominence detected in the core of a Coronal Mass Ejection: III. Plasma filling factor from UVCS Lyman- and Lyman- observations
This work deals with the study of an erupting prominence embedded in the core
of a CME and focuses on the derivation of the prominence plasma filling factor.
We explore two methods to measure the prominence plasma filling factor that are
based on the combination of visible-light and ultraviolet spectroscopic
observations. Theoretical relationships for resonant scattering and collisional
excitation are used to evaluate the intensity of the H I Lyman-{\alpha} and
Lyman-{\beta} lines, in two prominence points where simultaneous and cospatial
LASCO-C2 and UVCS data were available. Thermodynamic and geometrical parameters
assumed for the calculation are provided by both observations and the results
of a detailed 1D non-LTE radiative-transfer model of the prominence, developed
in our previous work (Heinzel 2016). The filling factor is derived from the
comparison between the calculated and the measured intensities of the two
lines. The results are then checked against the non-LTE model in order to
verify the reliability of the methods. The resulting filling factors are
consistent with the model in both the prominence points when the separation of
the radiative and collisional components of the total intensity, required to
estimate the filling factor, is performed using both the line intensities. An
exploration of the parameter space shows that the results are weakly sensitive
to the plasma velocity, but they depends more strongly on the assumed kinetic
temperatures. The combination of visible-light and ultraviolet Lyman-{\alpha}
and Lyman-{\beta} data can be used to approximately estimate the geometrical
filling factor in erupting prominences, but the proposed techniques are
reliable only for emission that is optically thin in the lines considered,
condition that is not in general representative of prominence plasma
Kinematics of a compression front associated with a Coronal Mass Ejection
On 2014 November 1st a solar prominence eruption associated with a C2.7 class ïŹare and a type II radio burst resulted in a fast partial halo Coronal Mass Ejection (CME). Images acquired in the extreme UV (EUV) by SDO/AIA and PROBA-2/SWAP, and in white light (WL) by SOHO/LASCO show a bright compression front expanding ahead of the CME. The main goal of this work was to infer the location and timing of the shock formation in the corona. A comparison between the starting frequency of the type II emission and the frequencies derived from the inferred coronal density distribution, allowed us to identify a region located northward of the CME as the most probable site for shock formation
Detection of Solar Coronal Mass Ejections from Raw Images with Deep Convolutional Neural Networks
Coronal Mass Ejections (CMEs) are massive releases of plasma from the solar corona. When the charged material is ejected towards the Earth, it can cause geomagnetic storms and severely damage electronic equipment and power grids. Early detection of CMEs is therefore crucial for damage containment. In this paper, we study detection of CMEs from sequential images of the solar corona acquired by a satellite. A low-complexity deep neural network is trained to process the raw images, ideally directly on the satellite, in order to provide early alerts
Signatures of impulsive localized heating in the temperature distribution of multi-stranded coronal loops
We study the signatures of different coronal heating regimes on the
differential emission measure (DEM) of multi-stranded coronal loops by means of
hydrodynamic simulations. We consider heating either uniformly distributed
along the loops or localized close to the chromospheric footpoints, in both
steady and impulsive conditions. Our simulations show that condensation at the
top of the loop forms when the localized heating is impulsive with a pulse
cadence time shorter than the plasma cooling time, and the pulse energy is
below a certain threshold. A condensation does not produce observable
signatures in the global DEM structure. Conversely, the DEM coronal peak is
found sensitive to the pulse cadence time. Our simulations can also give an
explanation of the warm overdense and hot underdense loops observed by TRACE,
SOHO and Yohkoh. However, they are unable to reproduce both the transition
region and the coronal DEM structure with a unique set of parameters, which
outlines the need for a more realistic description of the transition region.Comment: 31 pages, 7 figure
Comparing extrapolations of the coronal magnetic field structure at 2.5 solar radii with multi-viewpoint coronagraphic observations
The magnetic field shapes the structure of the solar corona but we still know
little about the interrelationships between the coronal magnetic field
configurations and the resulting quasi-stationary structures observed in
coronagraphic images (as streamers, plumes, coronal holes). One way to obtain
information on the large-scale structure of the coronal magnetic field is to
extrapolate it from photospheric data and compare the results with
coronagraphic images. Our aim is to verify if this comparison can be a fast
method to check systematically the reliability of the many methods available to
reconstruct the coronal magnetic field. Coronal fields are usually extrapolated
from photospheric measurements typically in a region close to the central
meridian on the solar disk and then compared with coronagraphic images at the
limbs, acquired at least 7 days before or after to account for solar rotation,
implicitly assuming that no significant changes occurred in the corona during
that period. In this work, we combine images from three coronagraphs
(SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) observing the Sun from different
viewing angles to build Carrington maps covering the entire corona to reduce
the effect of temporal evolution to ~ 5 days. We then compare the position of
the observed streamers in these Carrington maps with that of the neutral lines
obtained from four different magnetic field extrapolations, to evaluate the
performances of the latter in the solar corona. Our results show that the
location of coronal streamers can provide important indications to discriminate
between different magnetic field extrapolations.Comment: Accepted by A&A the 20th of May, 201
AntarctiCor: Solar Coronagraph in Antarctica for the ESCAPE Project
The Antarctica solar coronagraph âAntarctiCorâ for the âExtreme Solar Coronagraphy Antarctic Program Experimentâ âESCAPEâ comprises an internally-occulted coronagraph based on the externally-occulted ASPIICS coronagraph for the ESA formation-ïŹying PROBA-3 mission. This paper describes the AntarctiCor design for ground-based observations from the DomeC Antarctica plateau of the polarized broad-band (591 nm ± 5 nm) K-corona and of the narrowband (FWHM = 0.5 nm), polarized emission of the coronal green-line at 530.3 nm. The science goal of these observations is to map the topology and dynamics of the coronal magnetic ïŹeld, addressing coronal heating and space weather questions
The Heliospheric Space Weather Center: A novel space weather service
The Heliospheric Space Weather Center project is the result of the synergy between the Aerospace Logistics Technology Engineering Company (ALTEC S.p.A.) and the INAF-Astrophysical Observatory of Torino, both located in Turin, Italy. The main goal of this project is to provide space weather medium and short-term forecast, by combining remote-sensing and in situ open data with novel data analysis technologies, giving to scientists the possibility of designing, implementing, and validating space-weather algorithms using extensive data sets
Using a Differential Emission Measure and Density Measurements in an Active Region Core to Test a Steady Heating Model
The frequency of heating events in the corona is an important constraint on
the coronal heating mechanisms. Observations indicate that the intensities and
velocities measured in active region cores are effectively steady, suggesting
that heating events occur rapidly enough to keep high temperature active region
loops close to equilibrium. In this paper, we couple observations of Active
Region 10955 made with XRT and EIS on \textit{Hinode} to test a simple steady
heating model. First we calculate the differential emission measure of the apex
region of the loops in the active region core. We find the DEM to be broad and
peaked around 3\,MK. We then determine the densities in the corresponding
footpoint regions. Using potential field extrapolations to approximate the loop
lengths and the density-sensitive line ratios to infer the magnitude of the
heating, we build a steady heating model for the active region core and find
that we can match the general properties of the observed DEM for the
temperature range of 6.3 Log T 6.7. This model, for the first time,
accounts for the base pressure, loop length, and distribution of apex
temperatures of the core loops. We find that the density-sensitive spectral
line intensities and the bulk of the hot emission in the active region core are
consistent with steady heating. We also find, however, that the steady heating
model cannot address the emission observed at lower temperatures. This emission
may be due to foreground or background structures, or may indicate that the
heating in the core is more complicated. Different heating scenarios must be
tested to determine if they have the same level of agreement.Comment: 16 pages, 9 figures, accepted to Ap
Decomposing the misery index: A dynamic approach
YesThe misery index (the unweighted sum of unemployment and inflation
rates) was probably the first attempt to develop a single statistic to measure the level
of a populationâs economic malaise. In this letter, we develop a dynamic approach to
decompose the misery index using two basic relations of modern macroeconomics:
the expectations-augmented Phillips curve and Okunâs law. Our reformulation of the
misery index is closer in spirit to Okunâs idea. However, we are able to offer an improved
version of the index, mainly based on output and unemployment. Specifically,
this new Okunâs index measures the level of economic discomfort as a function of
three key factors: (1) the misery index in the previous period; (2) the output gap in
growth rate terms; and (3) cyclical unemployment. This dynamic approach differs
substantially from the standard one utilised to develop the misery index, and allow
us to obtain an index with five main interesting features: (1) it focuses on output,
unemployment and inflation; (2) it considers only objective variables; (3) it allows
a distinction
between short-run and long-run phenomena; (4) it places more
importance
on output and unemployment rather than inflation; and (5) it weights
recessions
more than expansions
- âŠ