631 research outputs found
Relating near-Earth observations of an interplanetary coronal mass ejection to the conditions at its site of origin in the solar corona
A halo coronal mass ejection (CME) was detected on January 20, 2004. We use solar remote sensing data (SOHO, Culgoora) and near-Earth in situ data (Cluster) to identify the CME source event and show that it was a long duration flare in which a magnetic flux rope was ejected, carrying overlying coronal arcade material along with it. We demonstrate that signatures of both the arcade material and the flux rope material are clearly identifiable in the Cluster and ACE data, indicating that the magnetic field orientations changed little as the material traveled to the Earth, and that the methods we used to infer coronal magnetic field configurations are effective
How Can Active Region Plasma Escape into the Solar Wind from below a Closed Helmet Streamer?
Recent studies show that active-region (AR) upflowing plasma, observed by the
EUV-Imaging Spectrometer (EIS), onboard Hinode, can gain access to open
field-lines and be released into the solar wind (SW) via magnetic-interchange
reconnection at magnetic null-points in pseudo-streamer configurations. When
only one bipolar AR is present on the Sun and it is fully covered by the
separatrix of a streamer, such as AR 10978 in December 2007, it seems unlikely
that the upflowing AR plasma can find its way into the slow SW. However,
signatures of plasma with AR composition have been found at 1 AU by Culhane et
al. (2014) apparently originating from the West of AR 10978. We present a
detailed topology analysis of AR 10978 and the surrounding large-scale corona
based on a potential-field source-surface (PFSS) model. Our study shows that it
is possible for the AR plasma to get around the streamer separatrix and be
released into the SW via magnetic reconnection, occurring in at least two main
steps. We analyse data from the Nan\c{c}ay Radioheliograph (NRH) searching for
evidence of the chain of magnetic reconnections proposed. We find a noise storm
above the AR and several varying sources at 150.9 MHz. Their locations suggest
that they could be associated with particles accelerated during the first-step
reconnection process and at a null point well outside of the AR. However, we
find no evidence of the second-step reconnection in the radio data. Our results
demonstrate that even when it appears highly improbable for the AR plasma to
reach the SW, indirect channels involving a sequence of reconnections can make
it possible.Comment: 26 pages, 10 figures. appears in Solar Physics, 201
Recommended from our members
iBBiG: iterative binary bi-clustering of gene sets
Motivation: Meta-analysis of genomics data seeks to identify genes associated with a biological phenotype across multiple datasets; however, merging data from different platforms by their features (genes) is challenging. Meta-analysis using functionally or biologically characterized gene sets simplifies data integration is biologically intuitive and is seen as having great potential, but is an emerging field with few established statistical methods. Results: We transform gene expression profiles into binary gene set profiles by discretizing results of gene set enrichment analyses and apply a new iterative bi-clustering algorithm (iBBiG) to identify groups of gene sets that are coordinately associated with groups of phenotypes across multiple studies. iBBiG is optimized for meta-analysis of large numbers of diverse genomics data that may have unmatched samples. It does not require prior knowledge of the number or size of clusters. When applied to simulated data, it outperforms commonly used clustering methods, discovers overlapping clusters of diverse sizes and is robust in the presence of noise. We apply it to meta-analysis of breast cancer studies, where iBBiG extracted novel gene set—phenotype association that predicted tumor metastases within tumor subtypes
Flows and Non-thermal Velocities in Solar Active Regions Observed with the Extreme-ultraviolet Imaging Spectrometer on Hinode: A Tracer of Active Region Sources of Heliospheric Magnetic Fields?
From Doppler velocity maps of active regions constructed from spectra
obtained by the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft we observe large areas of outflow (20-50 km/s) that can persist for
at least a day. These outflows occur in areas of active regions that are faint
in coronal spectral lines formed at typical quiet Sun and active region
temperatures. The outflows are positively correlated with non-thermal
velocities in coronal plasmas. The bulk mass motions and non-thermal velocities
are derived from spectral line centroids and line widths, mostly from a strong
line of Fe XII at 195.12 Angstroms. The electron temperature of the outflow
regions estimated from an Fe XIII to Fe XII line intensity ratio is about
1.2-1.4 MK. The electron density of the outflow regions derived from a density
sensitive intensity ratio of Fe XII lines is rather low for an active region.
Most regions average around 7E10+8 cm(-3), but there are variations on pixel
spatial scales of about a factor of 4. We discuss results in detail for two
active regions observed by EIS. Images of active regions in line intensity,
line width, and line centroid are obtained by rastering the regions. We also
discuss data from the active regions obtained from other orbiting spacecraft
that support the conclusions obtained from analysis of the EIS spectra. The
locations of the flows in the active regions with respect to the longitudinal
photospheric magnetic fields suggest that these regions might be tracers of
long loops and/or open magnetic fields that extend into the heliosphere, and
thus the flows could possibly contribute significantly to the solar wind.Comment: one tex file, 11 postscript figure file
Flows in the solar atmosphere due to the eruptions on the 15th July, 2002
<p>Which kind of flows are present during flares? Are they compatible with the present understanding of energy release and which model best describes the observations? We analyze successive flare events in order to answer these questions. The flares were observed in the magnetically complex NOAA active region (AR) 10030 on 15 July 2002. One of them is of GOES X-class. The description of these flares and how they relate to the break-out model is presented in Gary & Moore (2004). The Coronal Diagnostic Spectrometer on board SOHO observed this active region for around 14 h. The observed emission lines provided data from the transition region to the corona with a field of view covering more than half of the active region. In this paper we analyse the spatially resolved flows seen in the atmosphere from the preflare to the flare stages. We find evidence for evaporation occurring before the impulsive phase. During the main phase, the ongoing magnetic reconnection is demonstrated by upflows located at the edges of the flare loops (while downflows are found in the flare loops themselves). We also report the impact of a filament eruption on the atmosphere, with flows up to 300 km s<sup>-1</sup> observed at transition-region temperatures in regions well away from the location of the pre-eruptive filament. Our results are consistent with the predictions of the break out model before the impulsive phase of the flare; while, as the flare progresses, the directions of the flows are consistent with flare models invoking evaporation followed by cooling and downward plasma motions in the flare loops.</p>
Recommended from our members
A Single Dose of Nicotine Enhances Reward Responsiveness in Nonsmokers: Implications for Development of Dependence
Background: Tobacco smoking, driven by the addictive properties of nicotine, is the most prevalent preventable cause of death in the Western world. Accumulated evidence suggests that nicotine may increase appetitive responding for nondrug incentives in the environment. Methods: To test this hypothesis, we conducted a randomized, double-blind, placebo-controlled, crossover study of the effect of a single dose of transdermal nicotine on reward responsiveness in 30 psychiatrically healthy nonsmokers. A novel signal detection task in which correct responses were differentially rewarded in a 3:1 ratio was used to assess the extent to which participants modulated their behavior as a function of reward. Results: Despite expected adverse effects such as nausea, nicotine significantly increased response bias toward the more frequently rewarded condition, at the expense of accuracy, independent of effects on attention or overall vigilance. Additionally, response bias on placebo was greater in participants who received nicotine in the first session, indicating that an effect of nicotine on reward responsiveness or reward-based learning persisted for at least 1 week. Conclusions: These findings suggest that a single dose of nicotine enhances response to non-drug-related rewards in the environment, with lasting effects. This effect may contribute to reinforcement of early smoking behavior and development of nicotine dependence.Psycholog
EUV emission lines and diagnostics observed with Hinode/EIS
Quiet Sun and active region spectra from the Hinode/EIS instrument are
presented, and the strongest lines from different temperature regions
discussed. A list of emission lines recommended to be included in EIS
observation studies is presented based on analysis of blending and diagnostic
potential using the CHIANTI atomic database. In addition we identify the most
useful density diagnostics from the ions covered by EIS.Comment: 14 pages, 3 figures, submitted to PASJ Hinode first results issu
Multi-wavelength observations and modelling of a canonical solar flare
This paper investigates the temporal evolution of temperature, emission
measure, energy loss and velocity in a C-class solar flare from both an
observational and theoretical perspective. The properties of the flare were
derived by following the systematic cooling of the plasma through the response
functions of a number of instruments -- RHESSI (>5 MK), GOES-12 (5-30 MK),
TRACE 171 A (1 MK) and SOHO/CDS (~0.03-8 MK). These measurements were studied
in combination with simulations from the 0-D EBTEL model. At the flare on-set,
upflows of ~90 km s-1 and low level emission were observed in Fe XIX,
consistent with pre-flare heating and gentle chromospheric evaporation. During
the impulsive phase, upflows of ~80 km s-1 in Fe XIX and simultaneous downflows
of 20 km s-1 in He I and O V were observed, indicating explosive chromospheric
evaporation. The plasma was subsequently found to reach a peak temperature of
~13 MK in approximately 10 minutes. Using EBTEL, conduction was found to be the
dominant loss mechanism during the initial ~300s of the decay phase. It was
also found to be responsible for driving gentle chromospheric evaporation
during this period. As the temperature fell below ~8 MK, and for the next
~4,000s, radiative losses were determined to dominate over conductive losses.
The radiative loss phase was accompanied by significant downflows of <40 km s-1
in O V. This is the first extensive study of the evolution of a canonical solar
flare using both spectroscopic and broad-band instruments in conjunction with a
hydrodynamic model. While our results are in broad agreement with the standard
flare model, the simulations suggest that both conductive and non-thermal beam
heating play important roles in heating the flare plasma during the impulsive
phase of at least this event.Comment: 10 pages, 7 figures, 2 tables. Accepted for publication in A&
Strongly Blueshifted Phenomena Observed with {\it Hinode}/EIS in the 2006 December 13 Solar Flare
We present a detailed examination of strongly blueshifted emission lines
observed with the EUV Imaging Spectrometer on board the {\it Hinode} satellite.
We found two kinds of blueshifted phenomenon associated with the X3.4 flare
that occurred on 2006 December 13. One was related to a plasmoid ejection seen
in soft X-rays. It was very bright in all the lines used for the observations.
The other was associated with the faint arc-shaped ejection seen in soft
X-rays. The soft X-ray ejection is thought to be an MHD fast-mode shock wave.
This is therefore the first spectroscopic observation of an MHD fast-mode shock
wave associated with a flare.Comment: 18 pages, 1 table, 6 figures. ApJ, accepte
Simultaneous Observations of the Chromosphere with TRACE and SUMER
Using mainly the 1600 angstrom continuum channel, and also the 1216 angstrom
Lyman-alpha channel (which includes some UV continuum and C IV emission),
aboard the TRACE satellite, we observed the complete lifetime of a transient,
bright chromospheric loop. Simultaneous observations with the SUMER instrument
aboard the SOHO spacecraft revealed interesting material velocities through the
Doppler effect existing above the chromospheric loop imaged with TRACE,
possibly corresponding to extended non-visible loops, or the base of an X-ray
jet.Comment: 14 pages, 10 figures, accepted by Solar Physic
- …