803 research outputs found
Plasma diagnostics of an EIT wave observed by Hinode/EIS and SDO/AIA
We present plasma diagnostics of an EIT wave observed with high cadence in
Hinode/EIS sit-and-stare spectroscopy and SDO/AIA imagery obtained during the
HOP-180 observing campaign on 2011 February 16. At the propagating EIT wave
front, we observe downward plasma flows in the EIS Fe XII, Fe XIII, and Fe XVI
spectral lines (log T ~ 6.1-6.4) with line-of-sight (LOS) velocities up to 20
km/s. These red-shifts are followed by blue-shifts with upward velocities up to
-5 km/s indicating relaxation of the plasma behind the wave front. During the
wave evolution, the downward velocity pulse steepens from a few km/s up to 20
km/s and subsequently decays, correlated with the relative changes of the line
intensities. The expected increase of the plasma densities at the EIT wave
front estimated from the observed intensity increase lies within the noise
level of our density diagnostics from EIS XIII 202/203 AA line ratios. No
significant LOS plasma motions are observed in the He II line, suggesting that
the wave pulse was not strong enough to perturb the underlying chromosphere.
This is consistent with the finding that no Halpha Moreton wave was associated
with the event. The EIT wave propagating along the EIS slit reveals a strong
deceleration of a ~ -540 m/s2 and a start velocity of v0 ~ 590 km/s. These
findings are consistent with the passage of a coronal fast-mode MHD wave,
pushing the plasma downward and compressing it at the coronal base.Comment: Accepted for ApJ Letter
The onset and association of CMEs with sigmoidal active regions
Previous studies of active regions characterised by Soft X-ray S or inverse-S morphology [Canfield et al., 1999], have found these regions to possess a higher probability of eruption. In such cases, CME launch has been inferred using X-ray proxies to indicate eruption. Active regions observed during 1997, previously categorised as both sigmoidal and eruptive [Canfield, 1999], have been selected for further study, incorporating SoHO-LASCO, SoHO-EIT and ground based H-alpha data. Our results allow re-classification into three main categories; sigmoidal, non-sigmoidal and active regions appearing sigmoidal due to the projection of many loops. Although the reduced dataset size prevents a statistical measure of significance, we note that regions comprising a single S (or inverse-S) shaped structure are more frequently associated with a CME than those classed as non-sigmoidal. This motivates the study of a larger dataset and highlights the need for a quantitative observational definition of the term "sigmoid"
The Effectiveness of Peer to Peer Mentoring in Reducing Symptoms of Depression and Anxiety in College Students
University counseling centers are struggling against resource constraints to meet the rising demand for mental health care. Peer-based mentoring programs offer the potential for an alternative approach to mitigate the increasing demand for treatment and improve overall psychological well-being among college students. However, research investigating peer mentoring programs on college campuses is lacking. This study evaluates program feasibility and potential effectiveness in reducing anxiety and depression symptoms among college students that underwent a 4-week peer mentoring program. Results from this preliminary study indicate peer-based programs may be more effective in reducing symptoms of depression (especially anhedonic depression) compared to anxiety. These data support that peer-based programs may be a promising alternative resource that can be offered at most colleges and universities
Spectroscopic analysis of interaction between an EIT wave and a coronal upflow region
We report a spectroscopic analysis of an EIT wave event that occurred in
active region 11081 on 2010 June 12 and was associated with an M2.0 class
flare. The wave propagated near circularly. The south-eastern part of the wave
front passed over an upflow region nearby a magnetic bipole. Using EIS raster
observations for this region, we studied the properties of plasma dynamics in
the wave front, as well as the interaction between the wave and the upflow
region. We found a weak blueshift for the Fe XII {\lambda}195.12 and Fe XIII
{\lambda}202.04 lines in the wave front. The local velocity along the solar
surface, which is deduced from the line of sight velocity in the wave front and
the projection effect, is much lower than the typical propagation speed of the
wave. A more interesting finding is that the upflow and non-thermal velocities
in the upflow region are suddenly diminished after the transit of the wave
front. This implies a significant change of magnetic field orientation when the
wave passed. As the lines in the upflow region are redirected, the velocity
along the line of sight is diminished as a result. We suggest that this
scenario is more in accordance with what was proposed in the field-line
stretching model of EIT waves.Comment: 13 pages, 7 figures, accepted for publication in Ap
Establishing a Connection Between Active Region Outflows and the Solar Wind: Abundance Measurements with EIS/Hinode
One of the most interesting discoveries of the X-ray Telescope and EUV
Imaging Spectrometer (EIS) on board the Hinode solar observatory is the
presence of persistent high temperature high speed outflows from the edges of
active regions. Measurements by EIS indicate that the outflows reach velocities
of 50 km/s with spectral line asymmetries approaching 200 km/s. It has been
suggested that these outflows may lie on open field lines that connect to the
heliosphere, and that they could potentially be a significant source of the
slow speed solar wind. A direct link has been difficult to establish, however.
In this letter, we use EIS measurements of spectral line intensities that are
sensitive to changes in the relative abundance of Si and S as a result of the
first ionization potential (FIP) effect, to measure the chemical composition in
the outflow regions of AR 10978 over a period of 5 days in December 2007. We
find that Si is always enhanced over S by a factor of 3--4. This is generally
consistent with the enhancement factor of low FIP elements measured in-situ in
the slow solar wind by non-spectroscopic methods. Plasma with a slow wind-like
composition was therefore flowing from the edge of the active region for at
least 5 days. Furthermore, on December 10--11, when the outflow from the
western side was favorably oriented in the Earth direction, the Si/S ratio was
found to match the value measured a few days later by ACE/SWICS. These results
provide strong observational evidence for a direct connection between the solar
wind, and the coronal plasma in the outflow regions.Comment: Version to be published in ApJ
On the nature of spectral line broadening in solar coronal dimmings
We analyze the profiles of iron emission lines observed in solar coronal
dimmings associated with coronal mass ejections, using the EUV Imaging
Spectrometer on board Hinode. We quantify line profile distortions with
empirical coefficients (asymmetry and peakedness) that compare the fitted
Gaussian to the data. We find that the apparent line broadenings reported in
previous studies are likely to be caused by inhomogeneities of flow velocities
along the line of sight, or at scales smaller than the resolution scale, or by
velocity fluctuations during the exposure time. The increase in the amplitude
of Alfv\'en waves cannot, alone, explain the observed features. A
double-Gaussian fit of the line profiles shows that, both for dimmings and
active region loops, one component is nearly at rest while the second component
presents a larger Doppler shift than that derived from a single-Gaussian fit.Comment: 16 pages, 11 figures - Accepted for publication in Ap
Spectroscopic signatures related to a sunquake
© 2015. The American Astronomical Society. All rights reserved.. The presence of flare-related acoustic emission (sunquakes (SQs)) in some flares, and only in specific locations within the flaring environment, represents a severe challenge to our current understanding of flare energy transport processes. In an attempt to contribute to understanding the origins of SQs we present a comparison of new spectral observations from Hinode's EUV imaging Spectrometer (EIS) and the Interface Region Imaging Spectrograph (IRIS) of the chromosphere, transition region, and corona above an SQ, and compare them to the spectra observed in a part of the flaring region with no acoustic signature. Evidence for the SQ is determined using both time-distance and acoustic holography methods, and we find that unlike many previous SQ detections, the signal is rather dispersed, but that the time-distance and 6 and 7 mHz sources converge at the same spatial location. We also see some evidence for different evolution at different frequencies, with an earlier peak at 7 mHz than at 6 mHz. Using EIS and IRIS spectroscopic measurements we find that in this location, at the time of the 7 mHz peak the spectral emission is significantly more intense, shows larger velocity shifts and substantially broader profiles than in the location with no SQ, and there is a good correlation between blueshifted, hot coronal, hard X-ray (HXR), and redshifted chromospheric emission, consistent with the idea of a strong downward motion driven by rapid heating by nonthermal electrons and the formation of chromospheric shocks. Exploiting the diagnostic potential of the Mg ii triplet lines, we also find evidence for a single large temperature increase deep in the atmosphere, which is consistent with this scenario. The time of the 6 mHz and time-distance peak signal coincides with a secondary peak in the energy release process, but in this case we find no evidence of HXR emission in the quake location, instead finding very broad spectral lines, strongly shifted to the red, indicating the possible presence of a significant flux of downward propagating Alfvén waves
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