75 research outputs found
Energy Distribution of Micro-events in the Quiet Solar Corona
Recent imaging observations of EUV line emissions have shown evidence for
frequent flare-like events in a majority of the pixels in quiet regions of the
solar corona. The changes in coronal emission measure indicate impulsive
heating of new material to coronal temperatures. These heating or evaporation
events are candidate signatures of "nanoflares" or "microflares" proposed to
interpret the high temperature and the very existence of the corona. The energy
distribution of these micro-events reported in the literature differ widely,
and so do the estimates of their total energy input into the corona. Here we
analyze the assumptions of the different methods, compare them by using the
same data set and discuss their results.
We also estimate the different forms of energy input and output, keeping in
mind that the observed brightenings are most likely secondary phenomena. A
rough estimate of the energy input observed by EIT on the SoHO satellite is of
the order of 10% of the total radiative output in the same region. It is
considerably smaller for the two reported TRACE observations. The discrepancy
can be explained partially by different thresholds for flare detection. There
is agreement on the slope and the absolute value of the distribution if the
same method were used and a numerical error corrected. The extrapolation of the
power law to unobserved energies that are many orders of magnitude smaller
remains questionable. Nevertheless, these micro-events and unresolved smaller
events are currently the best source of information on the heating process of
the corona
From Forbidden Coronal Lines to Meaningful Coronal Magnetic Fields
We review methods to measure magnetic fields within the corona using the
polarized light in magnetic-dipole (M1) lines. We are particularly interested
in both the global magnetic-field evolution over a solar cycle, and the local
storage of magnetic free energy within coronal plasmas. We address commonly
held skepticisms concerning angular ambiguities and line-of-sight confusion. We
argue that ambiguities are in principle no worse than more familiar remotely
sensed photospheric vector-fields, and that the diagnosis of M1 line data would
benefit from simultaneous observations of EUV lines. Based on calculations and
data from eclipses, we discuss the most promising lines and different
approaches that might be used. We point to the S-like [Fe {\sc XI}] line (J=2
to J=1) at 789.2nm as a prime target line (for ATST for example) to augment the
hotter 1074.7 and 1079.8 nm Si-like lines of [Fe {\sc XIII}] currently observed
by the Coronal Multi-channel Polarimeter (CoMP). Significant breakthroughs will
be made possible with the new generation of coronagraphs, in three distinct
ways: (i) through single point inversions (which encompasses also the analysis
of MHD wave modes), (ii) using direct comparisons of synthetic MHD or
force-free models with polarization data, and (iii) using tomographic
techniques.Comment: Accepted by Solar Physics, April 201
Prominence-cavity regions observed using SWAP 174A filtergrams and simultaneous eclipse flash spectra
Images from the SWAP (Proba 2 mission) taken at 174A in the Fe IX/X lines are
compared to simultaneous slitless flash spectra taken during the last solar
total eclipse of July, 11th 2010. Many faint low excitation emission lines
together with the HeI and HeII Paschen Alpha chromospheric lines are recorded
on eclipse spectra where regions of limb prominences are obtained with
space-borne imagers. We consider a deep flash spectrum obtained by summing 80
individual spectra to show the intensity modulations of the continuum.
Intensity depressions are observed around the prominences in both eclipse and
SWAP images. The prominence cavities are interpreted as a relative depression
of plasma density, produced inside the corona surrounding the prominences.
Photometric measurements are shown at different scales and different,
spectrally narrow, intervals for both the prominences and the coronal
background.Comment: 22 pages, 14 figures, accepted to publish in Sol. Phy
Neutralisation of Local Haemorrhage Induced by the Saw-Scaled Viper Echis carinatus sochureki
The objective of the study is to investigate the anti-snake venom activities of a local plant, Hibiscus aethiopicus L. The H. aethiopicus was dried and extracted with ethanol. Different assays were performed according to standard techniques, to evaluate the plant’s acute toxicity and its antivenom activities. The results of evaluating the systemic acute toxicity of the H. aethiopicus extract using “oral and intra-peritoneal” route were normal even at the highest dose (24 g/kg) tested. All guinea pigs (n=3) when treated with venoms E. c. sochureki (75 μg) alone induced acute skin haemorrhage. In contrast, all guinea pigs (n=18) treated with both venom and the plant extract at a concentration between 500 and 1000 mg/kg showed no signs of haemorrhage. Moreover, all guinea pigs (n=18) treated with venom and the plant extract below 400 mg/kg showed acute skin haemorrhage. All guinea pigs treated with venom E. c. sochureki (75 μg) alone induced acute skin haemorrhage after both 24 and 32 hours. In contrast, all guinea pigs treated with both venom and the plant extract (administered independently) at concentrations between 500 and 1000 mg/kg showed no signs of haemorrhage after 32 hours. However, after 24 hours all tested guinea pigs showed less inhibition (<60%) compared to that obtained after 32 hours. The outcome of this study reflects that the extract of H. aethiopicus plant may contain an endogenous inhibitor of venom induced local haemorrhage
A high-latitude coronal mass ejection observed by a constellation of coronagraphs: Solar Orbiter/Metis, STEREO-A/COR2, and SOHO/LASCO
Context. A few days before the first perihelion of the Solar Orbiter nominal mission, which occurred on 2022 March 26, the Metis coronagraph on board Solar Orbiter detected a coronal mass ejection (CME) that was moving away from the far side of the Sun (with respect to Solar Orbiter) at high northern latitudes. The eruption was also seen by other spacecraft, in particular, by STEREO-A, which was in quadrature configuration with Solar Orbiter. Aims. We analyse the different views of the CME by a constellation of spacecraft with the purpose to determine the speed and acceleration of the CME, and to identify the source region of the CME. Methods. Considering the positions of various spacecraft on 2022 March 22, this CME happened to be within the field of view of STEREO-A/SECCHI, and it was visible over the limb from SOHO/LASCO. We present the results of the 3D reconstruction of the CME based on the graduated cylindrical shell model and of the identification of the possible origin of the CME using extreme-ultraviolet (EUV) observations by Solar Orbiter/EUI, STEREO-A/EUVI, and SDO/AIA. The observations in EUV are compared with the coronal magnetic structure obtained by the potential field source surface method. Results. The 3D reconstruction of the CME derives a central latitude of 29 N, a Stonyhurst longitude of 125, and an average radial speed at the apex of 322 ± 33 km s1 between 4 and 13 RȮ, which is probably not high enough to generate a shock wave. The estimated average acceleration of the CME is 16 ± 11 m s2 in the same range of distances from the Sun. This CME may be associated with the disappearance of a coronal cloud prominence, which is seen in the EUV by STEREO-A/EUVI and SDO/AIA, and is also associated with rapidly evolving emerging magnetic flux
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Sudden cardiac death athletes: a systematic review
Previous events evidence that sudden cardiac death (SCD) in athletes is still a reality and it keeps challenging cardiologists. Considering the importance of SCD in athletes and the requisite for an update of this matter, we endeavored to describe SCD in athletes. The Medline (via PubMed) and SciELO databases were searched using the subject keywords "sudden death, athletes and mortality". The incidence of SCD is expected at one case for each 200,000 young athletes per year. Overall it is resulted of complex dealings of factors such as arrhythmogenic substrate, regulator and triggers factors. In great part of deaths caused by heart disease in athletes younger than 35 years old investigations evidence cardiac congenital abnormalities. Athletes above 35 years old possibly die due to impairments of coronary heart disease, frequently caused by atherosclerosis. Myocardial ischemia and myocardial infarction are responsible for the most cases of SCD above this age (80%). Pre-participatory athletes' evaluation helps to recognize situations that may put the athlete's life in risk including cardiovascular diseases. In summary, cardiologic examinations of athletes' pre-competition routine is an important way to minimize the risk of SCD
Exploring the Solar Wind from Its Source on the Corona into the Inner Heliosphere during the First Solar Orbiter-Parker Solar Probe Quadrature
This Letter addresses the first Solar Orbiter (SO)–Parker Solar Probe (PSP) quadrature, occurring on 2021 January 18 to investigate the evolution of solar wind from the extended corona to the inner heliosphere. Assuming ballistic propagation, the same plasma volume observed remotely in the corona at altitudes between 3.5 and 6.3 solar radii above the solar limb with the Metis coronagraph on SO can be tracked to PSP, orbiting at 0.1 au, thus allowing the local properties of the solar wind to be linked to the coronal source region from where it originated. Thanks to the close approach of PSP to the Sun and the simultaneous Metis observation of the solar corona, the flow-aligned magnetic field and the bulk kinetic energy flux density can be empirically inferred along the coronal current sheet with an unprecedented accuracy, allowing in particular estimation of the Alfvén radius at 8.7 solar radii during the time of this event. This is thus the very first study of the same solar wind plasma as it expands from the sub-Alfvénic solar corona to just above the Alfvén surface
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