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Author name code: aiouaz
ADS astronomy entries on 2022-09-14
author:"Aiouaz, Tayeb"
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Title: Relentless Reconnections at Boundaries of Supergranular
Network Lanes
Authors: Aiouaz, T.
2008ESPM...12.2.80A Altcode:
Doppler-shift properties of the solar transition region (TR) and low
corona are investigated in relation to the underlying chromospheric
supergranular network, with particular regard to the role of the
magnetic field. EUV line properties were obtained from a large raster
scan of the solar transition region and corona acquired by the UV/EUV
spectrometer SUMER on board SOHO. The observed regions include an
equatorial coronal hole, as well as surrounding quiet Sun areas. I
present correlations between the chromospheric network, and the N IV
(765.15 Å), O IV (790.19 Å), S V (786.50 Å), O V (760.45 Å) Doppler
shifts in quiet Sun and coronal hole. <P />It is established that the
maximum inflow (redshift) at transition region temperatures appears
statistically toward the center of the network lanes in the quiet
Sun areas and toward the boundary of the network lanes in the coronal
hole part. Furthermore, while the strong red-shifts in the TR lines
complement spatially blue-shifts from the low corona (Ne VIII, 770.41
Å) in a puzzle-like pattern, bi-directional flows (i.e. cospatial
strong red/blue-shits in the TR/Corona) appear predominantly in the
coronal hole. The bi-directional flows happen almost systematically
at boundaries of magnetic field concentrations when compared to the
reconstructed magnetogram from a MDI/SOHO series. <P />These results
allow to propose for the first time a coherent interpretation involving
a single driver for almost thirty years of unexplained statistical
Doppler shift variations in the transition region and corona for quiet
Sun and coronal hole. The proposed scenario involves reconnections
between the strong network magnetic field and continuously advected
weak field from the supergranular cell interior.
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Title: Evidence of Relentless Reconnections at Boundaries of
Supergranular Network Lanes in Quiet Sun and Coronal Hole
Authors: Aiouaz, T.
2008ApJ...674.1144A Altcode:
Doppler-shift properties of the solar transition region (TR) and low
corona are investigated in relation to the underlying chromospheric
supergranular network, with particular regard to the role of the
magnetic field. EUV line properties were obtained from a large
raster scan of the solar chromosphere, transition region, and corona
acquired by the SUMER spectrometer on board SOHO. The observed region
includes an equatorial coronal hole, as well as surrounding quiet-Sun
areas. The chromospheric supergranular network pattern is enhanced
using a filter defined previously by Aiouaz and coworkers applied to
a Lyman continuum image. The filtered continuum image and Dopplergrams
are used to produce dispersion plots. We find correlations between the
chromospheric network, and the N IV (765.15 Å), O IV (790.19 Å),
S V (786.50 Å), O V (760.45 Å) Doppler shifts in quiet Sun and
coronal hole. It is established that the maximum inflow (redshift)
at transition region temperatures appears statistically toward the
center of the network lanes in the quiet-Sun areas and toward the
boundary of the network lanes in the coronal hole. Furthermore, while
the strong redshifts in the TR lines complement spatially blueshifts
from the low corona (Ne VIII 770.41 Å) in a puzzle-like pattern,
bidirectional flows (i.e., cospatial strong red- and blueshifts in the
TR/Corona) appear predominantly in the coronal hole. The bidirectional
flows congregate almost systematically at boundaries of magnetic field
concentrations seen in SOHO MDI magnetograms. These results support a
coherent interpretation of almost 30 years of unexplained statistical
Doppler-shift variations in the transition region and corona for quiet
Sun and coronal hole. The proposed scenario involves reconnections
between the strong network magnetic field and continuously advected
weak field from the supergranular cell interior.
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Title: Role of Magneto-Convection in Plasma Dynamic and Energy
Balance Above the Supergranular Network
Authors: Aiouaz, T.
2008ASPC..383..173A Altcode:
The current project aims to model the upper solar atmosphere taking
in account the magnetic complexity of the supergranulation pattern. <P
/>The result of a potential field extrapolation is used as the initial
condition for the magnetic field <P />in the framework of a forward 3D
MHD model including the calculation of EUV emission lines. <P />The MHD
model describes the solar atmosphere from the high chromosphere to the
lower solar corona above a synthetic supergranular cell. <P />I present
preliminary results on the relation between the magnetic topology,
the thermodynamic properties of the plasma (e.g., flow, temperature,
density) and the EUV intensity as calculated from the synthetic
emission lines. <P />Signatures of the magnetic field concentration
is to be found in the corona in the density and temperature structure,
and thus in emissivity and intensity, while the magnetic field is almost
homogeneous. <P />This model succeeds in reproducing for the first time
the supergranular pattern as observed with a spectrometer in the EUV.
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Title: The correlation between coronal Doppler shifts and the
supergranular network
Authors: Aiouaz, T.; Peter, H.; Lemaire, P.
2007A&A...466..689A Altcode:
No abstract at ADS
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Title: Expansion of the Supergranular Magnetic Network through the
Solar Atmosphere
Authors: Aiouaz, T.; Rast, M. P.
2006ApJ...647L.183A Altcode:
The solar magnetic field has its footpoints in the photosphere,
extends through the chromosphere, and is thought to expand through
the transition region and into the corona. It is organized by fluid
motions to form strong flux concentrations within the boundaries of
the supergranular convection cells. These boundaries are the network
lanes observed in line emission, and they display increasing width with
height through the solar atmosphere. The network field concentrations
are surrounded by a mixed-polarity internetwork magnetic field on the
scale of granulation. We use a potential magnetic field extrapolation
of synthetic photospheric magnetograms to study the magnetic network
topology and the effects of a mixed-polarity background field on
the network expansion with height through the solar atmosphere. We
find that the expansion of the network boundary with height deviates
significantly from the funnel expansion model. Moreover, we find that
the background magnetic field has a considerable effect on the filling
factor of the network area with height, even though the background
flux is strictly equal to zero.
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Title: Expansion of the supergranular magnetic network through the
solar atmosphere
Authors: Aiouaz, T.; Rast, M. P.
2006IAUS..233..161A Altcode:
The solar magnetic field that extends through the chromosphere is
thought to expand through the transition region into the corona. The
strong flux concentrations are located within the boundaries
of supergranular convection cells. These boundaries form network
lanes, observed in emission lines as bright lanes with varying width
throughout the solar atmosphere. These network field concentrations
are surrounded by mixed-polarity magnetic field with a scale of the
granule diameter, as suggested by observations. We use potential
magnetic field extrapolations on synthetic magnetograms to study
the magnetic network topology and the effects of background magnetic
field on the network expansion through the solar atmosphere. We find
that the background magnetic field has a considerable effect on the
ratio of network area over field of view. Furthermore we find that the
expansion of the network boundaries with height deviate significantly
from well-assumed funnel model expansion.
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Title: Forward modeling of coronal funnels
Authors: Aiouaz, T.; Peter, H.; Keppens, R.
2005A&A...442L..35A Altcode:
We propose a forward modeling approach of coronal funnels to investigate
the outer layers of the solar atmosphere with respect to their
thermodynamical properties and resulting emission line spectra. We
investigate the plasma flow out of funnels with a new 2D MHD time
dependent model including the solar atmosphere all the way from
the chromosphere to the corona. The plasma in the funnel is treated
in the single-fluid MHD approximation including radiative losses,
anisotropic thermal conduction, and two different parameterized heating
functions. We obtain plasma properties (e.g. density, temperature
and flow speed) within the funnel for each heating function. From
the results of the MHD calculation we derive spectral profiles of a
low corona emission line (Ne VIII, 770 Å). This allows us e.g. to
study the Doppler shifts across the funnel. These results indicate a
systematic variation of the Doppler shifts in lines formed in the low
corona depending on the heating function used. The line shift above
the magnetic field concentration in the network is stronger than in the
inter-network in both cases. However, for one of the heating functions,
the maximum blue-shift (outflow) is not to be found in the very center
of the funnel but in the vicinity of the center. This is not the case
of the second heating function where the maximum is well aligned with
the centre of the funnel. This model directly relates for the first
time the form of the heating function to the thermodynamic and spectral
properties of the plasma in a funnel.
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Title: Relation of the Chromospheric Network to Coronal Funnels and
the Solar Wind
Authors: Aiouaz, T.; Peter, H.; Keppens, R.
2005ESASP.592..135A Altcode: 2005ESASP.592E..20A; 2005soho...16E..20A
No abstract at ADS
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Title: The correlation between coronal Doppler shifts and the
supergranular network
Authors: Aiouaz, T.; Peter, H.; Lemaire, P.
2005A&A...435..713A Altcode:
We examine properties of line profiles as found with large raster
scans of the solar corona acquired by the UV spectrometer SUMER on
board SOHO. The observed regions include an equatorial coronal hole,
a polar coronal hole, as well as surrounding quiet Sun areas. In
order to reveal the network and remove strong local brightenings,
a filter is applied to a continuum image. The filtered continuum
image, the intensity image and the dopplergram are used to produce
“scatter diagrams” (dispersion plots). We find correlations
between the chromospheric network, the Ne VIII (770 Å) intensity
and the Ne VIII (770 Å) Doppler shift in quiet Sun areas and in
coronal holes. We establish that the maximum outflow (blue-shift) at
low corona temperatures does not appear in the centre of the network
but rather near network boundaries. Furthermore the maximum blue-shift
seems to appear in the dark regions in Ne VIII line intensity, which
is in agreement with Wilhelm (2000). The opposite correlation appears
for very low intensities (less than half of the average intensity),
revealing in these regions a lack of energy to either accelerate the
solar wind or produce any detectable radiation. The absence of magnetic
field concentration in these regions in a reconstructed magnetogram
from a MDI/SOHO series seems to confirm the lack of energy.
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Title: On the Outflow at Solar Corona Heights
Authors: Aiouaz, T.; Peter, H.; Lemaire, P.
2004ESASP.575..331A Altcode: 2004soho...15..331A
No abstract at ADS
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Title: Forward Modelling of Coronal Funnels
Authors: Aiouaz, T.; Peter, H.; Keppens, R.
2004ESASP.575..337A Altcode: 2004soho...15..337A
No abstract at ADS
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Title: Dynamics and Properties of Coronal Funnels
Authors: Aiouaz, T.; Peter, H.; Lemaire, P.; Keppens, R.
2004ESASP.547..375A Altcode: 2004soho...13..375A
Coronal funnels are open magnetic structures connecting the chromosphere
with the solar corona [5, 3]. We investigate the stationary plasma
flow out of funnels with a 2D- MHD model. The funnel area function is
derived from a magnetic field model and the funnel is approximately 10
Mm high and 20 Mm wide. The energy balance includes radiative losses,
thermal conduction, and a parametrized heating function. We adjust the
parameters to the quantities measured in the lower solar corona. We
obtained 2D plasma properties (e.g. density, temperature, flow speed,
etc.) within the funnel. From the results of the MHD calculation we
synthesize emision profiles of various lines formed in the transition
region from the chromosphere to the corona. This allows us to study
e.g. the Doppler shifts at various temperatures across the funnel
and thus enables a detailed comparison of the model results with
observations. For this we investigate SUMER data and study Doppler
shifts perpendicular to the chromospheric network for different emission
lines, where a tessalation technique is used to derive the outlines of
the chromospheric network. In this paper typical results are presented
for the Ne VIII(770.4 Å) line. Preliminary results show that these
model caclulations compare well to the observations.
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Title: Dynamics and Properties of Coronal Funnels
Authors: Aiouaz, T.; Peter, H.; Lemaire, Philippe; Keppens, Rony
2003ANS...324....7A Altcode: 2003ANS...324..B01A
No abstract at ADS
