57 research outputs found
Magnetic pattern at supergranulation scale: the Void Size Distribution
The large-scale magnetic pattern of the quiet sun is dominated by the
magnetic network. This network, created by photospheric magnetic fields swept
into convective downflows, delineates the boundaries of large scale cells of
overturning plasma and exhibits voids in magnetic organization. Such voids
include internetwork fields, a mixed-polarity sparse field that populate the
inner part of network cells. To single out voids and to quantify their
intrinsic pattern a fast circle packing based algorithm is applied to 511
SOHO/MDI high resolution magnetograms acquired during the outstanding solar
activity minimum between 23 and 24 cycles. The computed Void Distribution
Function shows a quasi-exponential decay behavior in the range 10-60 Mm. The
lack of distinct flow scales in such a range corroborates the hypothesis of
multi-scale motion flows at the solar surface. In addition to the
quasi-exponential decay we have found that the voids reveal departure from a
simple exponential decay around 35 Mm.Comment: 6 pages, 8 figures, to appear in Astronomy and Astrophysic
JP3D compression of solar data-cubes: photospheric imaging and spectropolarimetry
Hyperspectral imaging is an ubiquitous technique in solar physics
observations and the recent advances in solar instrumentation enabled us to
acquire and record data at an unprecedented rate. The huge amount of data which
will be archived in the upcoming solar observatories press us to compress the
data in order to reduce the storage space and transfer times. The correlation
present over all dimensions, spatial, temporal and spectral, of solar data-sets
suggests the use of a 3D base wavelet decomposition, to achieve higher
compression rates. In this work, we evaluate the performance of the recent
JPEG2000 Part 10 standard, known as JP3D, for the lossless compression of
several types of solar data-cubes. We explore the differences in: a) The
compressibility of broad-band or narrow-band time-sequence; I or V stokes
profiles in spectropolarimetric data-sets; b) Compressing data in
[x,y,] packages at different times or data in [x,y,t] packages of
different wavelength; c) Compressing a single large data-cube or several
smaller data-cubes; d) Compressing data which is under-sampled or super-sampled
with respect to the diffraction cut-off
Multiple field-of-view MCAO for a Large Solar Telescope: LOST simulations
In the framework of a 4m class Solar Telescope we studied the performance of
the MCAO using the LOST simulation package. In particular, in this work we
focus on two different methods to reduce the time delay error which is
particularly critical in solar adaptive optics: a) the optimization of the
wavefront reconstruction by reordering the modal base on the basis of the
Mutual Information and b) the possibility of forecasting the wavefront
correction through different approaches. We evaluate these techniques
underlining pros and cons of their usage in different control conditions by
analyzing the results of the simulations and make some preliminary tests on
real data.Comment: 10 pages, 5 figures to be published in Adaptive Optics Systems II
(Proceedings Volume) Proceedings of SPI
A Probabilistic Approach to the Drag-Based Model
The forecast of the time of arrival of a coronal mass ejection (CME) to Earth
is of critical importance for our high-technology society and for any future
manned exploration of the Solar System. As critical as the forecast accuracy is
the knowledge of its precision, i.e. the error associated to the estimate. We
propose a statistical approach for the computation of the time of arrival using
the drag-based model by introducing the probability distributions, rather than
exact values, as input parameters, thus allowing the evaluation of the
uncertainty on the forecast. We test this approach using a set of CMEs whose
transit times are known, and obtain extremely promising results: the average
value of the absolute differences between measure and forecast is 9.1h, and
half of these residuals are within the estimated errors. These results suggest
that this approach deserves further investigation. We are working to realize a
real-time implementation which ingests the outputs of automated CME tracking
algorithms as inputs to create a database of events useful for a further
validation of the approach.Comment: 18 pages, 4 figure
The correlation of synthetic UV color vs Mg II index along the solar cycle
Modeling of planets' climate and habitability requires as fundamental input
the UV emission of the hosting star. \citet{lovric2017} employed SORCE/SOLSTICE
solar observations to introduce a UV color index which is a descriptor of the
UV radiation that modulates the photochemistry of planets atmospheres. After
correcting the SOLSTICE data for residual instrumental effects that produced
asymmetric signals during different phases of the cycles analyzed, the authors
found that the UV color index is linearly correlated with the Mg II index.In
this paper we employ an irradiance reconstruction technique to synthetize the
UV color and Mg II index with the purpose of investigating whether the
correction applied by \citet{lovric2017} to SORCE/SOLSTICE data might have
compensated for solar variations, and to investigate the physical mechanisms
that produce such a strong correlation between the UV color index and the solar
activity. Reconstructed indices reproduce very well the observations and
present the same strong linear dependence. Moreover our reconstruction, which
extends back to 1989, shows that the UV color - Mg II index relation can be
described by the same linear relation for almost three cycles, thus ruling out
an overcompensation of SORCE/SOLTICE data in the analysis of
\citet{lovric2017}. We suggest that the strong correlation between the indices
results from the fact that most of the Far- and Middle- UV radiation originates
in the chromosphere, where atmosphere models of quiet and magnetic features
present similar temperature and density gradients.Comment: Accepted in Ap
Pressure-gradient current at high latitude from Swarm measurements
The pressure-gradient current is among the weaker ionospheric current systems arising from plasma pressure variations. It is also called diamagnetic current because it produces a magnetic field which is oriented oppositely to the ambient magnetic field, causing its reduction. The magnetic reduction can be revealed in measurements made by low-Earth orbiting satellites flying close to ionospheric plasma regions where rapid changes in density occur. Using geomagnetic field, plasma density and electron temperature measurements recorded on board ESA Swarm A satellite from April 2014 to March 2018, we reconstruct the flow patterns of the pressure-gradient current at high-latitude ionosphere in both hemispheres, and investigate their dependence on magnetic local time, geomagnetic activity, season and solar forcing drivers. Although being small in amplitude these currents appear to be a ubiquitous phenomenon at ionospheric high latitudes characterized by well defined flow patterns, which can cause artifacts in the main field models. Our findings can be used to correct magnetic field measurements for diamagnetic current effect, to improve modern magnetic field models, as well as to understand the impact of ionospheric irregularities on ionospheric dynamics at small-scale sizes of a few tens of kilometers
Comprehensive Sun-to-Earth analysis of the Geoeffective Solar event of June 21, 2015: Effects on the Magnetosphere - Plasmasphere - Ionosphere system
A full-halo coronal mass ejection left the sun on June 21, 2015 from the active region NOAA 12371 encountering Earth on June 22, 2015, generating a G3 strong geomagnetic storm. The CME was associated with an M2 class flare observed at 01:42 UT, located near the center disk (N12E16). Using satellite data from solar, heliospheric, magnetospheric missions and ground-based instruments, we performed a comprehensive Sun-to-Earth analysis. In particular, we analyzed the active region evolution using ground-based and satellite instruments (BBSO, IRIS, HINODE, SDO/AIA, RHESSI -- Halpha, EUV, UV, X), the AR magnetograms, using data from SDO HMI, the relative particle data, using PAMELA instruments and the effects of
interplanetary perturbation on cosmic ray intensity. We also evaluated the 1-8 soft X-ray and low-frequenct ( 1 MHz) Type III radio burst time-integrated
intensity (or fluence) of the flare in order to make a prediction of the associated Solar Energetic Particle (SEP) event by using the model developed by \cite{Laurenza09}. Inaddition, using ground based observations from lower to higher latitudes (INTERMAGNET - EMMA, etc.), we reconstructed the ionospheric current system associated to the geomagnetic Sudden Commencement. Furthermore, SuperDARN measurements are used to image the global ionospheric polar convection during the SSC and during the principal phases of the geomagnetic storm. Moreover, we investigated the dynamics of the plasmasphere during the different phases of the geomagnetic storm by examining the time evolution of the radial profiles of the
equatorial plasma mass density derived from field line resonances detected at the EMMA network (1.5 L 6.5). Finally, we presented the general features of the
geomagnetic response to the CME, by applying innovative data analysis tools that allow to investigate the time variation of ground-based observations of the Earth's
magnetic field during the associated geomagnetic storm
A New Method for Detecting Solar Atmospheric Gravity Waves
Internal gravity waves have been observed in the Earth's atmosphere and
oceans, on Mars and Jupiter, and in the Sun's atmosphere. Despite ample
evidence for the existence of propagating gravity waves in the Sun's
atmosphere, we still do not have a full understanding of their characteristics
and overall role for the dynamics and energetics of the solar atmosphere. Here
we present a new approach to study the propagation of gravity waves in the
solar atmosphere. It is based on calculating the three-dimensional
cross-correlation function between the vertical velocities measured at
different heights. We apply this new method to a time series of co-spatial and
co-temporal Doppler images obtained by SOHO/MDI and Hinode/SOT as well as to
simulations of upward propagating gravity wave packets. We show some
preliminary results and outline future developments.Comment: 11 pages, 6 figure
Single and Synergistic Effects of Fenbendazole and Metronidazole Against Subclinical Infection by Giardia duodenalis in Non-Human Primates in a Zoological Garden in Southern Italy
The aim of this study was to assess the single and synergistic effects of fenbendazole (Fenb) and metronidazole (Metro) for the treatment of Giardia duodenalis infection in different species of non-human primates (NHPs) housed in a zoological garden of southern Italy. Moreover, the study also aimed to better define the circulation of G. duodenalis zoonotic assemblages in NHP and the potential occurrence of zoonotic transmission between the staff from the zoo and NHP. Briefly, six species that belonged to four families (Lemuridae, Cercopithecidae, Atelidae, and Hylobatidae) of NHP and housed in six cages (CG) were identified as Giardia positive and divided into two groups. Group F (N = 16 animals) was treated with Fenb (50 mg/kg, every 24 h for 5 consecutive days) and Group M (N = 7 animals) was treated with Metro (25 mg/kg, two times a day for 5 consecutive days). After the first round of therapy, all the animals were retreated for 5 days by inverting the drugs in each group. On each sampling day [study days (SDs) 3-24], the samples were tested for the presence of Giardia cysts using the FLOTAC technique. Multiple fecal tests for the antigen detection of Giardia, such as rapid ELISA and direct immunofluorescence (IFA), were performed at each sampling point only on samples that resulted in positive for Giardia cysts with FLOTAC. The efficacy of Fenb ranged from 30 to 67% and for Metro ranged from 82 to 96%. The results showed the synergistic effects of Metro and Fenb (98-100%) over the combination of Fenb and Metro (52-90%) against the infection by Giardia in NHPs. The overall k agreement between FLOTAC and IFA was reached 0.858 (p = 0.0001). In contrast, all the samples had a negative antigen result when using ELISA. At molecular analysis, six samples were confirmed positive for Giardia by nested PCR. Only two positive samples were successfully sequenced that showed 100% of identity with assemblage B. All the samples from the humans included in the study resulted in negative for Giardia cysts. Overall, the study emphasizes the need for regular monitoring of Giardia infections in NHP housed in zoos by traditional diagnostic tools combined with molecular characterization of the parasite
Chromospheric Heating by Acoustic Waves Compared to Radiative Cooling: II -- Revised Grid of Models
Acoustic and magnetoacoustic waves are considered to be possible agents of
chromospheric heating. We present a comparison of deposited acoustic energy
flux with total integrated radiative losses in the middle chromosphere of the
quiet Sun and a weak plage. The comparison is based on a consistent set of
high-resolution observations acquired by the IBIS instrument in the Ca II 854.2
nm line. The deposited acoustic-flux energy is derived from Doppler velocities
observed in the line core and a set of 1737 non-LTE 1D hydrostatic
semi-empirical models, which also provide the radiative losses. The models are
obtained by scaling the temperature and column mass of five initial models VAL
B-F to get the best fit of synthetic to observed profiles. We find that the
deposited acoustic-flux energy in the quiet-Sun chromosphere balances 30-50 %
of the energy released by radiation. In the plage, it contributes by 50-60 % in
locations with vertical magnetic field and 70-90 % in regions where the
magnetic field is inclined more than 50 degrees to the solar surface normal.Comment: 9 pages, 8 figure
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