1,092 research outputs found
Polarimetric Properties of Flux-Ropes and Sheared Arcades in Coronal Prominence Cavities
The coronal magnetic field is the primary driver of solar dynamic events.
Linear and circular polarization signals of certain infrared coronal emission
lines contain information about the magnetic field, and to access this
information, either a forward or an inversion method must be used. We study
three coronal magnetic configurations that are applicable to polar-crown
filament cavities by doing forward calculations to produce synthetic
polarization data. We analyze these forward data to determine the
distinguishing characteristics of each model. We conclude that it is possible
to distinguish between cylindrical flux ropes, spheromak flux ropes, and
sheared arcades using coronal polarization measurements. If one of these models
is found to be consistent with observational measurements, it will mean
positive identification of the magnetic morphology that surrounds certain
quiescent filaments, which will lead to a greater understanding of how they
form and why they erupt.Comment: 22 pages, 8 figures, Solar Physics topical issue: Coronal Magnetis
On the structure and evolution of a polar crown prominence/filament system
Polar crown prominences are made of chromospheric plasma partially circling
the Suns poles between 60 and 70 degree latitude. We aim to diagnose the 3D
dynamics of a polar crown prominence using high cadence EUV images from the
Solar Dynamics Observatory (SDO)/AIA at 304 and 171A and the Ahead spacecraft
of the Solar Terrestrial Relations Observatory (STEREO-A)/EUVI at 195A. Using
time series across specific structures we compare flows across the disk in 195A
with the prominence dynamics seen on the limb. The densest prominence material
forms vertical columns which are separated by many tens of Mm and connected by
dynamic bridges of plasma that are clearly visible in 304/171A two-color
images. We also observe intermittent but repetitious flows with velocity 15
km/s in the prominence that appear to be associated with EUV bright points on
the solar disk. The boundary between the prominence and the overlying cavity
appears as a sharp edge. We discuss the structure of the coronal cavity seen
both above and around the prominence. SDO/HMI and GONG magnetograms are used to
infer the underlying magnetic topology. The evolution and structure of the
prominence with respect to the magnetic field seems to agree with the filament
linkage model.Comment: 24 pages, 14 figures, Accepted for publication in Solar Physics
Journal, Movies can be found at http://www2.mps.mpg.de/data/outgoing/panesar
3D MHD Flux Emergence Experiments: Idealized models and coronal interactions
This paper reviews some of the many 3D numerical experiments of the emergence
of magnetic fields from the solar interior and the subsequent interaction with
the pre-existing coronal magnetic field. The models described here are
idealized, in the sense that the internal energy equation only involves the
adiabatic, Ohmic and viscous shock heating terms. However, provided the main
aim is to investigate the dynamical evolution, this is adequate. Many
interesting observational phenomena are explained by these models in a
self-consistent manner.Comment: Review article, accepted for publication in Solar Physic
Observable Social Cognition – A Rating Scale: an interview-based assessment for schizophrenia
Individuals with schizophrenia consistently show impairments in social cognition (SC). SC has become a potential treatment target due to its association with functional outcomes. An alternative method of assessment is to administer an observer-based scale incorporating an informant’s “first hand” impressions in ratings
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
Progressive transformation of a flux rope to an ICME
The solar wind conditions at one astronomical unit (AU) can be strongly
disturbed by the interplanetary coronal mass ejections (ICMEs). A subset,
called magnetic clouds (MCs), is formed by twisted flux ropes that transport an
important amount of magnetic flux and helicity which is released in CMEs. At 1
AU from the Sun, the magnetic structure of MCs is generally modeled neglecting
their expansion during the spacecraft crossing. However, in some cases, MCs
present a significant expansion. We present here an analysis of the huge and
significantly expanding MC observed by the Wind spacecraft during 9 and 10
November, 2004. After determining an approximated orientation for the flux rope
using the minimum variance method, we precise the orientation of the cloud axis
relating its front and rear magnetic discontinuities using a direct method.
This method takes into account the conservation of the azimuthal magnetic flux
between the in- and out-bound branches, and is valid for a finite impact
parameter (i.e., not necessarily a small distance between the spacecraft
trajectory and the cloud axis). Moreover, using the direct method, we find that
the ICME is formed by a flux rope (MC) followed by an extended coherent
magnetic region. These observations are interpreted considering the existence
of a previous larger flux rope, which partially reconnected with its
environment in the front. These findings imply that the ejected flux rope is
progressively peeled by reconnection and transformed to the observed ICME (with
a remnant flux rope in the front part).Comment: Solar Physics (in press
Observations of Coronal Mass Ejections with the Coronal Multichannel Polarimeter
The Coronal Multichannel Polarimeter (CoMP) measures not only the
polarization of coronal emission, but also the full radiance profiles of
coronal emission lines. For the first time, CoMP observations provide
high-cadence image sequences of the coronal line intensity, Doppler shift and
line width simultaneously in a large field of view. By studying the Doppler
shift and line width we may explore more of the physical processes of CME
initiation and propagation. Here we identify a list of CMEs observed by CoMP
and present the first results of these observations. Our preliminary analysis
shows that CMEs are usually associated with greatly increased Doppler shift and
enhanced line width. These new observations provide not only valuable
information to constrain CME models and probe various processes during the
initial propagation of CMEs in the low corona, but also offer a possible
cost-effective and low-risk means of space weather monitoring.Comment: 6 figures. Will appear in the special issue of Coronal Magnetism,
Sol. Phy
COMPOSITION AND VARIATION OF FATTY ACIDS AMONG GROUNDNUT CULTIVARS IN UGANDA
Groundnuts ( Arachis hypogaea L.) contain approximately 44-56% oil
made up of fatty acids. Oleic and linoleic acids comprise about 80% of
fatty acids in groundnuts. Groundnuts with >80% oleic are beneficial
health-wise and also improve groundnut quality, flavour, and extended
shelf-life, which is beneficial to traders. In Uganda, however, little
is known about the fatty acids content of commercially available
cultivars. This study was undertaken to determine the fatty acid
composition of the most recently released commercially available
groundnut cultivars in Uganda. Eleven groundnut genotypes were profiled
for different fatty acids using gas chromatography (GC). Data were
recorded in percentages from chromatographs and totaled up to about
100%. Oleic to linoleic ratios (O/L) and iodine values were calculated
from fatty acid data. Groundnut genotypes tested differed significantly
(P<0.05) in oleic, linoleic, palmitic, behenic, gadoleic, arachidic
and palmitoleic acids. Oleic acid was highest in Lot 197 line, and
linoleic acid was lowest in the same line. Oleic acid was lowest in
Serenut 7 (43.19%) and linoleic acid was highest in the same line
(33.45%). The lowest iodine value was observed in 197 (84.14); and the
highest in Serenut 9T (96.59). Significant correlations (P<0.001)
were observed between most of the fatty acids, except between arachidic
versus gadoleic, stearic and gamma linoleic.L\u2019Arachide ( Arachis hypogaea L.) contient approximativement
44-55% d\u2019huile faites d\u2019acides gras. Les acides
ol\ue9ique et linol\ue9ique constituent environ 80% des acides gras
dans l\u2019arachide. Les arachides avec plus de 80%
d\u2019ol\ue9iques sont b\ue9n\ue9fiques pour la sant\ue9 et
aussi am\ue9liorent la qualit\ue9 de l\u2019arachide, le
go\ufbt, et une longue dur\ue9e de conservation, avantageux pour
les commer\ue7ants. En Ouganda, toutefois, tr\ue8s peu
d\u2019informations sont disponibles concernant la teneur en acides
gras des cultivars commercialement disponibles. Cette \ue9tude a
\ue9t\ue9 entreprise pour d\ue9terminer la composition en acide
gras de la majorit\ue9 des cultivars d\u2019arachides r\ue9cemment
lib\ue9r\ue9s et commercialement disponibles en Ouganda. Onze
g\ue9notypes d\u2019arachide ont \ue9t\ue9 profil\ue9s pour
les diff\ue9rents acides gras en utilisant le gaz chromatographie
(GC). Les donn\ue9es ont\ua0\ue9t\ue9 collect\ue9es des
chromatographes en pourcentages et additionn\ue9es jusqu\u2019\ue0
environ 100%. Les rapports d\u2019ol\ue9iques au linol\ue9iques
(O/L) et les valeurs d\u2019iode ont \ue9t\ue9 calcul\ue9es
\ue0 partir des donn\ue9es des acides gras. Les g\ue9notypes
d\u2019arachide test\ue9s ont \ue9t\ue9 significativement
(P<0,05) diff\ue9rents en acides ol\ue9ique, linol\ue9ique,
palmitique, b\ue9h\ue9nique, gadol\ue9ique, arachidique et
palmitoleique. L\u2019acide ol\ue9ique \ue9tait le plus
\ue9lev\ue9 dans la lign\ue9e Lot 197, et l\u2019acide
linol\ue9ique \ue9tait le plus faible dans la m\ueame
lign\ue9e. L\u2019acide ol\ue9ique \ue9tait le plus faible en
Serenut 7 (43,19%) et l\u2019acide linol\ue9ique \ue9tait le plus
\ue9lev\ue9 dans la m\ueame lign\ue9e (33,45%). La plus faible
valeur de l\u2019iode \ue9tait observ\ue9e dans 197 (84,14)\ua0;
et la valeur la plus \ue9lev\ue9e dans Serenut 9T (96,59). Des
corr\ue9lations significatives (P<0,001) \ue9taient
observ\ue9e entre la majorit\ue9 des acides gras, sauf entre
l\u2019acide arachidique contre les acides gadol\ue9ique,
st\ue9arique et gamma linol\ue9ique
Coronal Diagnostics from Narrowband Images around 30.4 nm
Images taken in the band centered at 30.4 nm are routinely used to map the
radiance of the He II Ly alpha line on the solar disk. That line is one of the
strongest, if not the strongest, line in the EUV observed in the solar
spectrum, and one of the few lines in that wavelength range providing
information on the upper chromosphere or lower transition region. However, when
observing the off-limb corona the contribution from the nearby Si XI 30.3 nm
line can become significant. In this work we aim at estimating the relative
contribution of those two lines in the solar corona around the minimum of solar
activity. We combine measurements from CDS taken in August 2008 with
temperature and density profiles from semiempirical models of the corona to
compute the radiances of the two lines, and of other representative coronal
lines (e.g., Mg X 62.5 nm, Si XII 52.1 nm). Considering both diagnosed
quantities from line ratios (temperatures and densities) and line radiances in
absolute units, we obtain a good overall match between observations and models.
We find that the Si XI line dominates the He II line from just above the limb
up to ~2 R_Sun in streamers, while its contribution to narrowband imaging in
the 30.4 nm band is expected to become smaller, even negligible in the corona
beyond ~2 - 3 R_Sun, the precise value being strongly dependent on the coronal
temperature profile.Comment: 26 pages, 11 figures; to be published in: Solar Physic
Triggering an eruptive flare by emerging flux in a solar active-region complex
A flare and fast coronal mass ejection originated between solar active
regions NOAA 11514 and 11515 on July 1, 2012 in response to flux emergence in
front of the leading sunspot of the trailing region 11515. Analyzing the
evolution of the photospheric magnetic flux and the coronal structure, we find
that the flux emergence triggered the eruption by interaction with overlying
flux in a non-standard way. The new flux neither had the opposite orientation
nor a location near the polarity inversion line, which are favorable for strong
reconnection with the arcade flux under which it emerged. Moreover, its flux
content remained significantly smaller than that of the arcade (approximately
40 %). However, a loop system rooted in the trailing active region ran in part
under the arcade between the active regions, passing over the site of flux
emergence. The reconnection with the emerging flux, leading to a series of jet
emissions into the loop system, caused a strong but confined rise of the loop
system. This lifted the arcade between the two active regions, weakening its
downward tension force and thus destabilizing the considerably sheared flux
under the arcade. The complex event was also associated with supporting
precursor activity in an enhanced network near the active regions, acting on
the large-scale overlying flux, and with two simultaneous confined flares
within the active regions.Comment: Accepted for publication in Topical Issue of Solar Physics: Solar and
Stellar Flares. 25 pages, 12 figure
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