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ÈAzimuthal variation of various physical quantities in the corona at a radial point 1.04 The x-axis represents the coronal posi- R _ . tion angles from the north pole (zero) toward the east. Prominent plumes are marked as " " P.ÏÏ from SOHO (Hassler et al. 1997 ; Noci et al. 1997 ; Wilhelm et al. 1998). It can be seen that the drop in width is proportional to the brightness of the plume. The maximum drop in the line width is up to 18%. There is a plumelike brightening seen at the pole, albeit with large line widths and Doppler velocities. The detailed examination of the line proÐles in this region shows some evidence of multiple components that needs further study. Wilhelm et al. (2000) also Ðnd signatures of multi-Gaussian components in the coronal hole line proÐles.
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The distribution of emission-line intensities, Doppler velocities, and line widths in a polar coronal hole and nearby regions are obtained from the spectroscopic observations carried out on 1998 November 3 at the Norikura Solar Observatory, Japan. The coronal red line [Fe X] λ6374 that is prominent at coronal hole temperatures is used for the study...
Contexts in source publication
Context 1
... general anticorrelation between the intensity and the line width in the coronal hole region can be noted in Figure 5. This is due to the narrower line width in the plumes than in the interplume regions, which is the well-known result The x-axis represents the coronal posi- R _ . ...
Context 2
... may be seen from Figure 5 that there is also an anti- correlation between the line intensity and the Doppler velocity. As discussed earlier, the line-of-sight Doppler velocity is difficult to interpret because of the uncertain projection e †ects of the coronal structures. ...
Context 3
... the available reports indicate that the plumes have low or no bulk velocities (Wang 1994 ;Wilhelm et al. 1998 ;Hassler et al. 1999). The negative correlation between the intensity and Doppler velocity, similar to that between the intensity and line width, seen in Figure 5, agrees well with the above reports. ...
Citations
... Besides, different line widths are found in different structures of a coronal hole . For example, Raju et al. (2000) found that line widths are narrower in plumes than in inter-plume regions. ...
The non-thermal broadening of spectral lines formed in the solar corona is often used to seek the evidence of Alfv\'en waves propagating in the corona. To have a better understanding of the variation of line widths at different altitudes, we measured the line widths of the strong Fe \textsc{xii} 192.4 \mbox{\AA}, 193.5 \mbox{\AA}, 195.1 \mbox{\AA} and Fe \textsc{xiii} 202.0 \mbox{\AA} in an off-limb southern coronal hole up to 1.5 $R_\odot$ observed by the \textit{Extreme Ultraviolet Spectrometer} (EIS) on board the \textit{Hinode} satellite. We compared our measurements to the predictions from the Alfv\'en Wave Solar Model (AWSoM) and the SPECTRUM module. We found the Fe \textsc{xii} and Fe \textsc{xiii} line widths first increase monotonically below 1.1 $R_\odot$, then keep fluctuating between 1.1 - 1.5 $R_\odot$. The synthetic line widths of Fe \textsc{xii} and Fe \textsc{xiii} below 1.3 $R_\odot$ are notably lower than the observed ones. We discuss several possible sources of this discrepancy and suggest that some other heating mechanisms besides the dissipation of the Alfv\'en waves are required to understand the coronal heating and solar wind acceleration from coronal holes below 1.3 $R_\odot
... These solar winds carry energetic particles into the interplanetary space and play a fundamental role in governing space weather. Raju et al., [38] studied the physical conditions of coronal holes and the nearby regions by exploiting the SOHO/EIT and Norikura Solar Observatory data. They found that the nonthermal velocity in the coronal ISSN: 2456-7108 Available online at Journals.aijr.in ...
The present article is the successor of Solar Dynamical Processes I. The previous article was focused on the Sun, its magnetic field with an emphasis on various dynamical processes occurring on the Sun, e.g. sunspots, prominence and bright points which in turn plays a fundamental role in regulating the space weather. This article is emphasized on the solar dynamical processes and develop an extensive understanding of the various phenomena involved in their origin. The article also covers various models and hypothesis put forward by pioneer scientists on the basis of their observation by space-borne and ground-based instruments. This article shade light over a wide range of dynamical processes e.g., solar flares, coronal mass ejections, solar jets and coronal holes. Solar jets, the small-scale transient activities are found to have association with the other transient activities (e.g., mini-flares and mini-filaments). Flares as well as the coronal mass ejections are responsible for releasing a large amount of high energy charged particles and magnetic flux into the interplanetary space, and are being considered as the main drivers of space weather.
... Hassler et al. (1997), using SUMER data, report a broader line width in interplume regions, with respect to plumes. This result has been confirmed by further studies, from either groundbased coronagraph data (Raju et al., 2000), or from data acquired by space-borne experiments like SUMER (see, e.g., Banerjee et al., 1998Banerjee et al., , 2000b and CDS (see, e.g., Banerjee et al., 2000aBanerjee et al., , 2001O'Shea et al., 2003). A summary of the plume/interplume line widths can be found in Table 2 of Wilhelm (2012). ...
Polar plumes are thin long ray-like structures that project beyond the limb of the Sun polar regions, maintaining their identity over distances of several solar radii. Plumes have been first observed in white-light (WL) images of the Sun, but, with the advent of the space era, they have been identified also in X-ray and UV wavelengths (XUV) and, possibly, even in in situ data. This review traces the history of plumes, from the time they have been first imaged, to the complex means by which nowadays we attempt to reconstruct their 3-D structure. Spectroscopic techniques allowed us also to infer the physical parameters of plumes and estimate their electron and kinetic temperatures and their densities. However, perhaps the most interesting problem we need to solve is the role they cover in the solar wind origin and acceleration: Does the solar wind emanate from plumes or from the ambient coronal hole wherein they are embedded? Do plumes have a role in solar wind acceleration and mass loading? Answers to these questions are still somewhat ambiguous and theoretical modeling does not provide definite answers either. Recent data, with an unprecedented high spatial and temporal resolution, provide new information on the fine structure of plumes, their temporal evolution and relationship with other transient phenomena that may shed further light on these elusive features.
The nonthermal broadening of spectral lines formed in the solar corona is often used to seek evidence of Alfvén waves propagating in the corona. To have a better understanding of the variation of line widths at different altitudes, we measured the line widths of the strong Fe xii 192.4, 193.5, and 195.1 Å and Fe xiii 202.0 Å in an off-limb southern coronal hole up to 1.5 R ⊙ observed by the Extreme Ultraviolet Spectrometer on board the Hinode satellite. We compared our measurements to the predictions from the Alfvén Wave Solar Model (AWSoM) and the SPECTRUM module. We found that the Fe xii and Fe xiii line widths first increase monotonically below 1.1 R ⊙ and then keep fluctuating between 1.1 and 1.5 R ⊙ . The synthetic line widths of Fe xii and Fe xiii below 1.3 R ⊙ are notably lower than the observed ones. We found that the emission from a streamer in the line of sight significantly contaminates the coronal hole line profiles even up to 1.5 R ⊙ both in observations and simulations. We suggest that either the discrepancy between the observations and simulations is caused by insufficient nonthermal broadening at the streamer in the AWSoM simulation or the observations are less affected by the streamer. Our results emphasize the importance of identifying the origin of the coronal EUV emission in off-limb observations.
The eclipse-observed emission lines formed in the upper solar atmosphere can be used to diagnose the atmosphere dynamics which provides an insight to the energy balance of the outer atmosphere. In this paper, we analyze the spectra formed in the upper chromospheric region by a new instrument called Fiber Arrayed Solar Optic Telescope (FASOT) around the Gabon total solar eclipse on November 3, 2013. The double Gaussian fits of the observed profiles are adopted to show enhanced emission in line wings, while red-blue (RB) asymmetry analysis informs that the cool line (about \(10^{4}~\mbox{K}\)) profiles can be decomposed into two components and the secondary component is revealed to have a relative velocity of about \(16\mbox{--}45~\mbox{km}\,\mbox{s}^{-1}\). The other profiles can be reproduced approximately with single Gaussian fits. From these fittings, it is found that the matter in the upper solar chromosphere is highly dynamic. The motion component along the line-of-sight has a pattern asymmetric about the local solar radius. Most materials undergo significant red shift motions while a little matter show blue shift. Despite the discrepancy of the motion in different lines, we find that the width and the Doppler shifts both are function of the wavelength. These results may help us to understand the complex mass cycle between chromosphere and corona.
Distributions of the Doppler velocities (V), widths (Δλ), and intensities (W) have been obtained based on the λ6374 and λ5303 spectra observed with the Large Coronograph at Sayan Observatory above active regions and their surroundings. The average Doppler velocities in both lines are ±5 km/s; a decrease and stabilization of these velocities with increasing W demonstrate the effect of magnetic fields. The dispersion of V for λ6374 in the zones with decreased W is substantially larger than such a dispersion for λ5303, the Δλ values are larger in these zones respectively. This is explained by the fact that the profile shape is affected by the plasma structuring degree along the line of sight controlled by the magnetic field topology in the regions where these lines glow: the field should be open and closed in the red and green coronas, respectively.
This article describes the history of Norikura Solar Observatory over
sixty years, and introduces its main instruments and research
highlights. The observatory was closed in 2009, and utilization of the
facility and the site in future is being sought.
The relative Doppler velocities and linewidths in a polar coronal hole and
the nearby quiet-Sun region have been obtained from the {\it Solar and
Heliospheric Observatory} (SOHO)/{\it Coronal Diagnostic Spectrometer} (CDS)
observations using emission lines originating at different heights in the solar
atmosphere from the lower transition region (TR) to the low solar corona. The
observed region is separated into the network and the cell interior and the
behavior of the above parameters were examined in the different regions. It has
been found that the histograms of Doppler velocity and width are generally
broader in the cell interior as compared to the network. The histograms of
Doppler velocities of the network and cell interior do not show significant
difference in most cases. However, in the case of the quiet Sun, the Doppler
velocities of the cell interior are more blueshifted than those of the network
for the lowermost line He {\sc ii} 304 {\AA}, and an opposite behavior is seen
for the uppermost line Mg {\sc ix} 368 {\AA}. The histograms of line width show
that the network--cell difference is more prominent in the coronal hole. The
network has significantly larger linewidth than the cell interior for the
lowermost TR line He {\sc ii} 304 {\AA} for the quiet Sun. For coronal hole,
this is true for the three lower TR lines He {\sc ii} 304 {\AA}, O {\sc iii}
599 {\AA}, and O {\sc v} 630 {\AA}. Also obtained are the correlations between
the relative Doppler velocity and the width. A mild positive correlation is
found for the lowermost transition region line He {\sc ii} 304 {\AA} which
further decreases or become insignificant for the intermediate lines. For the
low coronal line, Mg {\sc ix} 368 {\AA}, the correlation becomes strongly
negative.
Relative Doppler velocities and spectral linewidths in a coronal hole and in the quiet Sun region outside have been obtained
from Solar and Heliospheric Observatory (SOHO)/Coronal Diagnostic Spectrometer (CDS) observations. Five strong emission lines in the CDS wavelength range (namely,
O iii 599Å, O v 630Å, Ne vi 562.8Å, He ii 304Å, and Mg ix 368Å), whose formation temperatures represent different heights in the solar atmosphere from the lower transition region
to the inner corona, have been used in the study. As reported earlier, relative velocities in the coronal hole are generally
blueshifted with respect to the quiet Sun, and the magnitude of the blueshifts increases with height. It has been found that
the polar coronal hole has larger relative velocities than the equatorial extension in the inner corona. Several localized
velocity contours have been found mainly on network brightenings and in the vicinity of the coronal hole boundary. The presence
of velocity contours on the network may represent network outflows whereas the latter could be due to localized jets probably
arising from magnetic reconnection at the boundary. All spectral lines have larger widths in the coronal hole than in the
quiet Sun. In O v 630Å an extended low-linewidth region is seen in the coronal hole – quiet Sun boundary, which may indicate fresh mass transfer
across the boundary. Also polar coronal holes have larger linewidths in comparison with the equatorial extension. Together
with larger relative velocities, this suggests that the solar wind emanating from polar hole regions is faster than that from
equatorial hole regions.
The coronal green line (Fe XIV 5303 A) profiles were obtained from
Fabry-Perot interferometric observations of the solar corona during the total
solar eclipse of 21 June 2001 from Lusaka, Zambia. The instrumental width is
about 0.2 A and the spectral resolution is about 26000. About 300 line profiles
were obtained within a radial range of 1.0-1.5 R\odot and position angle
coverage of about 240\circ. The line profiles were fitted with single Gaussian
and their intensity, Doppler velocity, and line width have been obtained. Also
obtained are the centroids of the line profiles which give a measure of line
asymmetry. The histograms of Doppler velocity show excess blueshifts while the
centroids reveal a pre-dominant blue wing in the line profiles. It has been
found that the centroids and the Doppler velocities are highly correlated. This
points to the presence of multiple components in the line profiles with an
excess of blueshifted components. We have then obtained the(Blue-Red) wing
intensity which clearly reveals the second component, majority of which are
blueshifted ones. This confirms that the coronal green line profiles often
contain multicomponents with excess blueshifts which also depend on the solar
activity. The magnitude of the Doppler velocity of the secondary component is
in the range 20-40 km s-1 and they show an increase towards poles. The possible
explanations of the multicomponents could be the type II spicules which were
recently found to have important to the coronal heating or the nascent solar
wind flow, but the cause of the blue asymmetry in the coronal lines above the
limb remains unclear.
