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Author name code: ortiz
ADS astronomy entries on 2022-09-14
author:"Ortiz, Ada" AND (aff:"Barcelona" OR aff:"Oslo") -aff:"Valencia"
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Title: High-resolution observations of the solar photosphere,
chromosphere, and transition region. A database of coordinated IRIS
and SST observations
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson,
M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.;
Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques,
V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.;
Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.;
Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.;
Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski,
M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P.
2020A&A...641A.146R Altcode: 2020arXiv200514175R
NASA's Interface Region Imaging Spectrograph (IRIS) provides
high-resolution observations of the solar atmosphere through ultraviolet
spectroscopy and imaging. Since the launch of IRIS in June 2013, we
have conducted systematic observation campaigns in coordination with
the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides
complementary high-resolution observations of the photosphere and
chromosphere. The SST observations include spectropolarimetric imaging
in photospheric Fe I lines and spectrally resolved imaging in the
chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present
a database of co-aligned IRIS and SST datasets that is open for
analysis to the scientific community. The database covers a variety
of targets including active regions, sunspots, plages, the quiet Sun,
and coronal holes.
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Title: Ellerman bombs and UV bursts: reconnection at different
atmospheric layers
Authors: Ortiz, Ada; Hansteen, Viggo H.; Nóbrega-Siverio, Daniel;
Rouppe van der Voort, Luc
2020A&A...633A..58O Altcode: 2019arXiv191010736O
The emergence of magnetic flux through the photosphere and into
the outer solar atmosphere produces, amongst other dynamical
phenomena, Ellerman bombs (EBs), which are observed in the wings of
Hα and are due to magnetic reconnection in the photosphere below
the chromospheric canopy. Signs of magnetic reconnection are also
observed in other spectral lines, typical of the chromosphere or the
transition region. An example are the ultraviolet (UV) bursts observed
in the transition region lines of Si IV and the upper chromospheric
lines of Mg II. In this work we analyze high-cadence, high-resolution
coordinated observations between the Swedish 1m Solar Telescope (SST)
and the Interface Region Imaging Spectrograph (IRIS) spacecraft. Hα
images from the SST provide us with the positions, timings, and
trajectories of EBs in an emerging flux region. Simultaneous, co-aligned
IRIS slit-jaw images at 133 (C II, transition region), 140 (Si IV,
transition region), and 279.6 (Mg II k, core, upper chromosphere)
nm as well as spectroscopy in the far- and near-ultraviolet from the
fast spectrograph raster allow us to study the possible chromospheric
and transition region counterparts of those EBs. Our main goal is
to study the possible temporal and spatial relationship between
several reconnection events at different layers in the atmosphere
(namely EBs and UV bursts), the timing history between them, and the
connection of these dynamical phenomena to the ejection of surges in
the chromosphere. We also investigate the properties of an extended
UV burst and their variations across the burst domain. Our results
suggest a scenario where simultaneous and co-spatial EBs and UV bursts
are part of the same reconnection system occurring sequentially along
a vertical or nearly vertical current sheet. Heating and bidirectional
jets trace the location where reconnection takes place. These results
support and expand those obtained from recent numerical simulations
of magnetic flux emergence. <P />The movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936574/olm">https://www.aanda.org</A>
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Title: Ellerman bombs and UV bursts: transient events in chromospheric
current sheets
Authors: Hansteen, V.; Ortiz, A.; Archontis, V.; Carlsson, M.; Pereira,
T. M. D.; Bjørgen, J. P.
2019A&A...626A..33H Altcode: 2019arXiv190411524H
Context. Ellerman bombs (EBs), observed in the photospheric wings
of the Hα line, and UV bursts, observed in the transition region Si
IV line, are both brightenings related to flux emergence regions and
specifically to magnetic flux of opposite polarity that meet in the
photosphere. These two reconnection-related phenomena, nominally formed
far apart, occasionally occur in the same location and at the same
time, thus challenging our understanding of reconnection and heating
of the lower solar atmosphere. <BR /> Aims: We consider the formation
of an active region, including long fibrils and hot and dense coronal
plasma. The emergence of a untwisted magnetic flux sheet, injected 2.5
Mm below the photosphere, is studied as it pierces the photosphere
and interacts with the preexisting ambient field. Specifically, we
aim to study whether EBs and UV bursts are generated as a result of
such flux emergence and examine their physical relationship. <BR />
Methods: The Bifrost radiative magnetohydrodynamics code was used
to model flux emerging into a model atmosphere that contained a
fairly strong ambient field, constraining the emerging field to
a limited volume wherein multiple reconnection events occur as
the field breaks through the photosphere and expands into the outer
atmosphere. Synthetic spectra of the different reconnection events were
computed using the 1.5D RH code and the fully 3D MULTI3D code. <BR
/> Results: The formation of UV bursts and EBs at intensities and
with line profiles that are highly reminiscent of observed spectra
are understood to be a result of the reconnection of emerging flux
with itself in a long-lasting current sheet that extends over several
scale heights through the chromosphere. Synthetic spectra in the Hα
and Si IV 139.376 nm lines both show characteristics that are typical
of the observations. These synthetic diagnostics suggest that there
are no compelling reasons to assume that UV bursts occur in the
photosphere. Instead, EBs and UV bursts are occasionally formed at
opposite ends of a long current sheet that resides in an extended bubble
of cool gas. <P />The movie associated to Fig. 3 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201935376/olm">https://www.aanda.org</A>
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Title: Chromospheric Heating due to Cancellation of Quiet Sun
Internetwork Fields
Authors: Gošić, M.; de la Cruz Rodríguez, J.; De Pontieu, B.; Bellot
Rubio, L. R.; Carlsson, M.; Esteban Pozuelo, S.; Ortiz, A.; Polito, V.
2018ApJ...857...48G Altcode: 2018arXiv180207392G
The heating of the solar chromosphere remains one of the most
important questions in solar physics. Our current understanding is that
small-scale internetwork (IN) magnetic fields play an important role
as a heating agent. Indeed, cancellations of IN magnetic elements in
the photosphere can produce transient brightenings in the chromosphere
and transition region. These bright structures might be the signature
of energy release and plasma heating, probably driven by the magnetic
reconnection of IN field lines. Although single events are not expected
to release large amounts of energy, their global contribution to the
chromosphere may be significant due to their ubiquitous presence
in quiet Sun regions. In this paper, we study cancellations of IN
elements and analyze their impact on the energetics and dynamics of
the quiet Sun atmosphere. We use high-resolution, multiwavelength,
coordinated observations obtained with the Interface Region Imaging
Spectrograph and the Swedish 1 m Solar Telescope (SST) to identify
cancellations of IN magnetic flux patches and follow their evolution. We
find that, on average, these events live for ∼3 minutes in the
photosphere and ∼12 minutes in the chromosphere and/or transition
region. Employing multi-line inversions of the Mg II h and k lines,
we show that cancellations produce clear signatures of heating in the
upper atmospheric layers. However, at the resolution and sensitivity
accessible to the SST, their number density still seems to be one
order of magnitude too low to explain the global chromospheric heating.
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Title: Chromospheric heating due to internetwork magnetic flux
cancellations
Authors: Gosic, Milan; de la Cruz Rodriguez, Jaime; De Pontieu, Bart;
Bellot Rubio, Luis; Ortiz, Ada; Esteban Pozuelo, Sara
2017SPD....4810404G Altcode:
The heating of the solar chromosphere is one of the most intriguing
unanswered problems in solar physics. It is believed that this
phenomenon may significantly be supported by small-scale internetwork
(IN) magnetic fields. Indeed, cancellations of IN magnetic flux
patches might be an efficient way to transport flux and energy from
the photosphere to the chromosphere. Because of this, it is essential
to determine where they occur, the rates at which they proceed, and
understand their influence on the chromosphere. Here we study the
spatial and temporal evolution of IN cancelling patches using high
resolution, multiwavelength, coordinated observations obtained with
the Interface Region Imaging Spectrograph (IRIS) and the Swedish
1-m Solar Telescope (SST). Employing multi-line inversions of the
Mg II h&k lines we show that cancelling events, while occurring
ubiquitously over IN regions, produce clear signatures of heating in
the upper atmospheric layers. Using the RADYN code we determine the
energy released due to cancellations of IN elements and discuss about
their impact on the dynamics and energetics of the solar chromosphere.
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Title: Emergence of Granular-sized Magnetic Bubbles Through the
Solar Atmosphere. III. The Path to the Transition Region
Authors: Ortiz, Ada; Hansteen, Viggo H.; Bellot Rubio, Luis Ramón;
de la Cruz Rodríguez, Jaime; De Pontieu, Bart; Carlsson, Mats;
Rouppe van der Voort, Luc
2016ApJ...825...93O Altcode: 2016arXiv160400302O
We study, for the first time, the ascent of granular-sized magnetic
bubbles from the solar photosphere through the chromosphere into the
transition region and above. Such events occurred in a flux emerging
region in NOAA 11850 on 2013 September 25. During that time, the
first co-observing campaign between the Swedish 1-m Solar Telescope
(SST) and the Interface Region Imaging Spectrograph (IRIS) spacecraft
was carried out. Simultaneous observations of the chromospheric Hα
656.28 nm and Ca II 854.2 nm lines, plus the photospheric Fe I 630.25
nm line, were made with the CRISP spectropolarimeter at the Spitzer
Space Telescope (SST) reaching a spatial resolution of 0.″14. At
the same time, IRIS was performing a four-step dense raster of the
emerging flux region, taking slit jaw images at 133 (C II, transition
region), 140 (Si IV, transition region), 279.6 (Mg II k, core, upper
chromosphere), and 283.2 nm (Mg II k, wing, photosphere). Spectroscopy
of several lines was performed by the IRIS spectrograph in the far-
and near-ultraviolet, of which we have used the Si IV 140.3 and the
Mg II k 279.6 nm lines. Coronal images from the Atmospheric Imaging
Assembly of the Solar Dynamics Observatory were used to investigate
the possible coronal signatures of the flux emergence events. The
photospheric and chromospheric properties of small-scale emerging
magnetic bubbles have been described in detail in Ortiz et al. Here
we are able to follow such structures up to the transition region. We
describe the properties, including temporal delays, of the observed
flux emergence in all layers. We believe this may be an important
mechanism of transporting energy and magnetic flux from subsurface
layers to the transition region and corona.
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Title: Emergence of Granular-sized Magnetic Bubbles through the
Solar Atmosphere. II. Non-LTE Chromospheric Diagnostics and Inversions
Authors: de la Cruz Rodríguez, Jaime; Hansteen, Viggo; Bellot-Rubio,
Luis; Ortiz, Ada
2015ApJ...810..145D Altcode: 2015arXiv150303846D
Magnetic flux emergence into the outer layers of the Sun is a
fundamental mechanism for releasing energy into the chromosphere and
the corona. In this paper, we study the emergence of granular-sized
flux concentrations and the structuring of the corresponding physical
parameters and atmospheric diagnostics in the upper photosphere and
in the chromosphere. We make use of a realistic 3D MHD simulation of
the outer layers of the Sun to study the formation of the Ca ii 8542
line. We also derive semi-empirical 3D models from non-LTE inversions of
our observations. These models contain information on the line-of-sight
stratifications of temperature, velocity, and the magnetic field. Our
analysis explains the peculiar Ca ii 8542 Å profiles observed in the
flux emerging region. Additionally, we derive detailed temperature
and velocity maps describing the ascent of a magnetic bubble from the
photosphere to the chromosphere. The inversions suggest that, in active
regions, granular-sized bubbles emerge up to the lower chromosphere
where the existing large-scale field hinders their ascent. We report
hints of heating when the field reaches the chromosphere.
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Title: Emergence of Granular-sized Magnetic Bubbles through the
Solar Atmosphere. I. Spectropolarimetric Observations and Simulations
Authors: Ortiz, Ada; Bellot Rubio, Luis R.; Hansteen, Viggo H.;
de la Cruz Rodríguez, Jaime; Rouppe van der Voort, Luc
2014ApJ...781..126O Altcode: 2013arXiv1312.5735O
We study a granular-sized magnetic flux emergence event that occurred
in NOAA 11024 in 2009 July. The observations were made with the CRISP
spectropolarimeter at the Swedish 1 m Solar Telescope achieving a
spatial resolution of 0.”14. Simultaneous full Stokes observations of
the two photospheric Fe I lines at 630.2 nm and the chromospheric Ca
II 854.2 nm line allow us to describe in detail the emergence process
across the solar atmosphere. We report here on three-dimensional
(3D) semi-spherical bubble events, where instead of simple magnetic
footpoints, we observe complex semi-circular feet straddling a few
granules. Several phenomena occur simultaneously, namely, abnormal
granulation, separation of opposite-polarity legs, and brightenings at
chromospheric heights. However, the most characteristic signature in
these events is the observation of a dark bubble in filtergrams taken
in the wings of the Ca II 854.2 nm line. There is a clear coincidence
between the emergence of horizontal magnetic field patches and the
formation of the dark bubble. We can infer how the bubble rises through
the solar atmosphere as we see it progressing from the wings to the
core of Ca II 854.2 nm. In the photosphere, the magnetic bubble shows
mean upward Doppler velocities of 2 km s<SUP>-1</SUP> and expands at a
horizontal speed of 4 km s<SUP>-1</SUP>. In about 3.5 minutes it travels
some 1100 km to reach the mid chromosphere, implying an average ascent
speed of 5.2 km s<SUP>-1</SUP>. The maximum separation attained by the
magnetic legs is 6.”6. From an inversion of the observed Stokes spectra
with the SIR code, we find maximum photospheric field strengths of 480 G
and inclinations of nearly 90° in the magnetic bubble interior, along
with temperature deficits of up to 250 K at log τ = -2 and above. To
aid the interpretation of the observations, we carry out 3D numerical
simulations of the evolution of a horizontal, untwisted magnetic flux
sheet injected in the convection zone, using the Bifrost code. The
computational domain spans from the upper convection zone to the lower
corona. In the modeled chromosphere, the rising flux sheet produces a
large, cool, magnetized bubble. We compare this bubble with the observed
ones and find excellent agreement, including similar field strengths
and velocity signals in the photosphere and chromosphere, temperature
deficits, ascent speeds, expansion velocities, and lifetimes.
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Title: Dimming of the 17th Century Sun
Authors: Foukal, Peter; Ortiz, Ada; Schnerr, Roald
2011ApJ...733L..38F Altcode: 2011arXiv1103.5442F
Reconstructions of total solar irradiance (TSI) rely mainly on linear
relations between TSI variation and indices of facular area. When these
are extrapolated to the prolonged 15th-17th century Spörer and Maunder
solar activity minima, the estimated solar dimming is insufficient to
explain the mid-millennial climate cooling of the Little Ice Age. We
draw attention here to evidence that the relation departs from linearity
at the lowest activity levels. Imaging photometry and radiometry
indicate an increased TSI contribution per unit area from small network
faculae by a factor of 2-4 compared with larger faculae in and around
active regions. Even partial removal of this more TSI-effective network
at prolonged minima could enable climatically significant solar dimming,
yet be consistent with the weakened but persistent 11 yr cycle observed
in Be 10 during the Maunder Minimum. The mechanism we suggest would
not alter previous findings that increased solar radiative forcing is
insufficient to account for 20th century global warming.
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Title: Dimming of the 17th Century Sun
Authors: Foukal, Peter V.; Ortiz, A.; Schnerr, R.
2011SPD....42.0702F Altcode: 2011BAAS..43S.0702F
Reconstructions of total solar irradiance (TSI) rely mainly on linear
relations between TSI variation and indices of facular area. When these
are extrapolated to the prolonged 15<SUP>th</SUP> - 17<SUP>th</SUP>
century Spörer and Maunder solar activity minima, the estimated solar
dimming is insufficient to explain the mid- millennial climate cooling
of the Little Ice Age. We draw attention here to evidence that the
relation departs from linearity at the lowest activity levels. Imaging
photometry and radiometry indicate an increased TSI contribution per
unit area from small network faculae by a factor of 2-4 compared to
larger faculae in and around active regions. Even partial removal of
this more TSI - effective network at prolonged minima could enable
climatically significant solar dimming, yet be consistent with the
weakened but persistent 11- yr cycle observed in Be 10 during the
Maunder Minimum. The mechanism we suggest would not alter previous
findings that increased solar radiative forcing is insufficient
to account for 20<SUP>th</SUP> century global warming. This work
was supported at Heliophysics, Inc. by NASA grants NNX09AP96G and
NNX10AC09G.
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Title: Dimming of the 17th Century Sun
Authors: Foukal, Peter V.; Ortiz, A.; Schnerr, R.
2011AAS...21822423F Altcode: 2011BAAS..43G22423F
Reconstructions of total solar irradiance (TSI) rely mainly on linear
relations between TSI variation and indices of facular area. When these
are extrapolated to the prolonged 15<SUP>th</SUP> - 17<SUP>th</SUP>
century Spörer and Maunder solar activity minima, the estimated solar
dimming is insufficient to explain the mid- millennial climate cooling
of the Little Ice Age. We draw attention here to evidence that the
relation departs from linearity at the lowest activity levels. Imaging
photometry and radiometry indicate an increased TSI contribution per
unit area from small network faculae by a factor of 2-4 compared to
larger faculae in and around active regions. Even partial removal of
this more TSI - effective network at prolonged minima could enable
climatically significant solar dimming, yet be consistent with the
weakened but persistent 11- yr cycle observed in Be 10 during the
Maunder Minimum. The mechanism we suggest would not alter previous
findings that increased solar radiative forcing is insufficient to
account for 20<SUP>th</SUP> century global warming.
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Title: Upflows in the Central Dark Lane of Sunspot Light Bridges
Authors: Rouppe van der Voort, L.; Bellot Rubio, L. R.; Ortiz, A.
2010ApJ...718L..78R Altcode: 2010arXiv1006.4578R
We use high spatial and spectral resolution observations obtained with
the CRisp Imaging SpectroPolarimeter at the Swedish 1 m Solar Telescope
to analyze the velocity profile of granular light bridges (LBs) in
a sunspot. We find upflows associated with the central dark lanes of
the LBs. From bisectors in the Fe I 630.15 nm line we find that the
magnitude of the upflows varies with height, with the strongest upflows
being deeper in the atmosphere. Typical upflow velocities measured from
the 70% bisector are around 500 m s<SUP>-1</SUP> with peaks above 1 km
s<SUP>-1</SUP>. The upflows in the central dark lane are surrounded by
downflows of weaker magnitude, sometimes concentrated in patches with
enhanced velocities reaching up to 1.1 km s<SUP>-1</SUP>. A small
spatial offset between the upflows and the continuum dark lane is
interpreted as a line-of-sight effect due to the elevated nature of the
dark lane and the LB above the umbral surroundings. Our observations
show that the central dark lane in granular LBs is not equivalent to
the intergranular lanes of normal photospheric granulation that host
convective downflows. These results support recent MHD simulations of
magneto-convection in sunspot atmospheres.
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Title: Downflows in Sunspot Umbral Dots
Authors: Ortiz, A.; Bellot Rubio, L. R.; Rouppe van der Voort, L.
2010ApJ...713.1282O Altcode: 2010arXiv1003.1897O
We study the velocity field of umbral dots (UDs) at a resolution
of 0farcs14. Our analysis is based on full Stokes measurements of a
pore taken with the Crisp Imaging Spectro-Polarimeter at the Swedish
1 m Solar Telescope. We determine the flow velocity at different
heights in the photosphere from a bisector analysis of the Fe I 630 nm
lines. In addition, we use the observed Stokes Q, U, and V profiles
to characterize the magnetic properties of these structures. We find
that most UDs are associated with strong upflows in deep photospheric
layers. Some of them also show concentrated patches of downflows at
their edges, with sizes of about 0farcs25, velocities of up to 1000
m s<SUP>-1</SUP>, and enhanced net circular polarization signals. The
downflows evolve rapidly and have lifetimes of only a few minutes. These
results appear to validate numerical models of magnetoconvection in
the presence of strong magnetic fields.
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Title: Spectropolarimetry with CRISP at the Swedish 1-m Solar
Telescope
Authors: Ortiz, A.; Rouppe van der Voort, L. H. M.
2010ASSP...19..150O Altcode: 2009arXiv0902.4150O; 2010mcia.conf..150O
CRISP (Crisp Imaging Spectro-polarimeter), the new spectropolarimeter
at the Swedish 1-m Solar Telescope, opens a new perspective in solar
polarimetry. With better spatial resolution (0.13″) than Hinode in
the Fe I 6302 Å lines and similar polarimetric sensitivity reached
through postprocessing, CRISP complements the SP spectropolarimeter
onboard Hinode. We present some of the data that we obtained in our
June 2008 campaign and preliminary results from LTE inversions of a
pore containing umbral dots.
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Title: Latitudinal Variation of the Solar Photospheric Intensity
Authors: Rast, Mark P.; Ortiz, Ada; Meisner, Randle W.
2008ApJ...673.1209R Altcode: 2007arXiv0710.3121R
We have examined images from the Precision Solar Photometric
Telescope (PSPT) at the Mauna Loa Solar Observatory (MLSO) in search
of latitudinal variation in the solar photospheric intensity. Along
with the expected brightening of the solar activity belts, we have
found a weak enhancement of the mean continuum intensity at polar
latitudes (continuum intensity enhancement ~0.1%-0.2%, corresponding
to a brightness temperature enhancement of ~2.5 K). This appears to be
thermal in origin and not due to a polar accumulation of weak magnetic
elements, with both the continuum and Ca II K intensity distributions
shifted toward higher values with little change in shape from their
midlatitude distributions. Since the enhancement is of low spatial
frequency and of very small amplitude, it is difficult to separate from
systematic instrumental and processing errors. We provide a thorough
discussion of these and conclude that the measurement captures real
solar latitudinal intensity variations.
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Title: Solar cycle evolution of the contrast of small photospheric
magnetic elements
Authors: Ortiz, Ada
2005AdSpR..35..350O Altcode:
Solar irradiance variations produced on the solar rotation time-scale
are known to be driven by the passage of active regions while, during
the last years, the origin of variations on the solar cycle time-scale
has been under debate. Nowadays, there is an agreement that the magnetic
network has an important contribution to these long-term variations,
although it has not been fully quantified. This important role
motivated us to study its physical properties along the solar cycle,
such as contrast and population. We combine magnetograms and intensity
images from the MDI instrument on board the SOHO spacecraft to analyze
the radiative properties of small magnetic elements. We determine the
contrast of faculae and network elements as a function of position over
the disk, magnetic flux and time, finding that these elements exhibit a
very different center-to-limb variation of the contrast. This implies
that their contribution to irradiance variability is distinct. By
extending this analysis through the rising phase of solar cycle 23,
we conclude that the functional dependence of the contrast of small
elements results to be time independent, implying that the physical
properties of the underlying flux tubes may not vary with time. We
decompose magnetograms into two structures identifying both faculae and
network features and we examine their populations along the solar cycle.
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Title: Excess facular emission from an isolated active region during
solar minimum: the example of NOAA AR 7978
Authors: Ortiz, A.; Domingo, V.; Sanahuja, B.; Fröhlich, C.
2004JASTP..66...67O Altcode: 2004JATP...66...67O
The facular contribution to solar irradiance variations on the short
time scale is studied by analyzing a simple case of an isolated active
region that crossed the solar disk during the 1996 minimum of activity,
NOAA AR 7978. Its passage during several Carrington rotations,
specifically from rotation 1911 to 1916, allows us to analyze the
evolution of the angular distribution of the excess radiance of
the facular region using SOHO/VIRGO and MDI data. We associate this
evolution with the evolution of the extent corresponding to the isolated
active region as well as with the aging of the region itself. Finally,
we evaluate the total (i.e. in all directions) emission of this facular
region and its spectral and temporal evolution.
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Title: Solar irradiance variations induced by faculae and small
magnetic elements in the photosphere
Authors: Ortiz, A.
2003PhDT.........1O Altcode:
This PhD thesis studies the variability of the solar irradiance (total
and spectral) induced by small magnetic elements present in the solar
photosphere, both on the short and long time-scales. The aim of this
work is to contribute to a better knowledge of the influence of this
small elements to solar variability, specially on the solar cycle
time-scale. Data from the MDI and VIRGO instruments on board the SOHO
spacecraft have been used. Several algorithms have been developed in
order to correct instrumental effects from the data, converting them
from level 0 (raw data) to level 2 (scintifically useful) data. <P
/>We have analyzed the evolution of an isolated active region (NOAA AR
7978) during the 1996 minimum in order to determine its contribution
to solar irradiance variations. We have also studied the contrast
of small photospheric magnetic elements as well as its dependence
on position, magnetic signal and solar cycle evolution. From these
analysis we conclude that: 1) the contrast center-to-limb variation
of active region faculae and the magnetic network are very different,
and thus their contribution to irradiance variability is very different;
2) the contrast of these elements does not change with the solar cycle,
therefore we suggest that the physical properties of the underlying flux
tubes do not vary with time; 3) the network presents a positive contrast
at all positions over the disk and it is the dominant population along
the cycle, therefore, it has a significant contribution to the long-term
variations and has to be taken into account.
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Title: Modelling solar irradiance variations: separate models for
the network and active region faculae
Authors: Wenzler, T.; Solanki, S. K.; Fluri, D. M.; Frutiger, C.;
Fligge, M.; Ortiz, A.
2002ESASP.508..231W Altcode: 2002soho...11..231W
In order to determine to what extent solar surface magnetism
affects solar irradiance we need to reconstruct the irradiance from
magnetograms. This process requires the use of model atmospheres. Here
we present two model atmospheres describing faculae in active regions
and the network. The models have been constructed such that they
reproduce various data sets simultaneously.
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Title: On the intensity contrast of solar photospheric faculae and
network elements
Authors: Ortiz, A.; Solanki, S. K.; Domingo, V.; Fligge, M.;
Sanahuja, B.
2002A&A...388.1036O Altcode: 2002astro.ph..7008O
Sunspots, faculae and the magnetic network contribute to solar
irradiance variations. The contribution due to faculae and the network
is of basic importance, but suffers from considerable uncertainty. We
determine the contrasts of active region faculae and the network,
both as a function of heliocentric angle and magnetogram signal. To
achieve this, we analyze near-simultaneous full disk images of
photospheric continuum intensity and line-of-sight magnetic field
provided by the Michelson Doppler Interferometer (MDI) on board
the SOHO spacecraft. Starting from the surface distribution of
the solar magnetic field we first construct a mask, which is then
used to determine the brightness of magnetic features, and the
relatively field-free part of the photosphere separately. By sorting
the magnetogram signal into different bins we are able to distinguish
between the contrasts of different concentrations of magnetic field. We
find that the center-to-limb variation (CLV) of the contrast changes
strongly with magnetogram signal. Thus, the contrasts of active region
faculae (large magnetogram signal) and the network (small signal)
exhibit a very different CLV, showing that the populations of magnetic
flux tubes that underly the two kinds of features are different. The
results are compatible with, on average, larger flux tubes in faculae
than in the network. This implies that these elements need to be treated
separately when reconstructing variations of the total solar irradiance
with high precision. We have obtained an analytical expression for
the contrast of photospheric magnetic features as a function of both
position on the disk and spatially averaged magnetic field strength,
by performing a 2-dimensional fit to the observations. We also provide
a linear relationship between magnetogram signal and the mu =cos (theta
), where theta is the heliocentric angle, at which the contrast is
maximal. Finally, we show that the maximum contrast per unit magnetic
flux decreases rapidly with increasing magnetogram signal, supporting
earlier evidence that the intrinsic contrast of magnetic flux tubes
in the network is higher.
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Title: Variation of the facular and network contrast during the
rising phase of cycle 23
Authors: Ortiz, A.; Domingo, V.; Sanahuja, B.; Solanki, S. K.
2002ESASP.508..185O Altcode: 2002soho...11..185O
Magnetic activity contributes to solar irradiance variations, both on
short and long time-scales. While sunspots and active region faculae
are the dominant contributors to irradiance changes on time-scales of
days to weeks, the origin of the long-term increase of the irradiance
between activity minimum and maximum (~0.1%) is still debated. It
has been proposed that the small-scale magnetic elements composing the
enhanced and quiet network contribute substantially to this increase. To
contribute to this debate, we attempt to see if there is a change in
the radiative properties of these elements along the solar cycle,
and to evaluate such a change. We use near-simultaneous full disk
magnetograms and images of the photospheric continuum intensity provided
by MDI/SOHO. We have studied the center-to-limb variations (CLV) of the
contrast as a function of magnetic strength and we are now analyzing how
the noise level of the images changes throughout time, as a preliminary
step towards an analysis of the temporal irradiance variations.
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Title: An Example of Isolated Active Region Energy Evolution: NOAA
AR 7978
Authors: Ortiz, A.; Domingo, V.; Sanahuja, B.; Sánchez, L.
2000ESASP.463..395O Altcode: 2000sctc.proc..395O
The facular contribution to solar irradiance variations on the short
time scale is studied by analysing a simple case of an isolated
active region, NOAA AR7978, during the minimum of 1996. We focus on
the relationship between the temporal evolution of the active region
surface magnetic field, its physical characteristics and the total
facular energy emission, using VIRGO/SOHO and MDI/SOHO data sets.
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Title: On the Contrast of Faculae and Small Magnetic Features
Authors: Ortiz, A.; Solanki, S. K.; Fligge, M.; Domingo, V.;
Sanahuja, B.
2000ESASP.463..399O Altcode: 2000sctc.proc..399O
Sunspots, faculae and the magnetic network contribute to solar
irradiance variations. The contribution due to faculae and the network
is important for understanding solar irradiance variations, but suffers
from considerable uncertainty. We focus our study on the faculae and
the network which produce an increase in the irradiance. Data from
the Michelson Doppler Interferometer (MDI) are employed. Starting from
the surface distribution of the solar magnetic field we build a mask
to detect bright features and study their contrast dependence on limb
angle and magnetic field. By sorting the magnetic field strength into
different bins we can distinguish between different associated bright
features. We find that the contrast of active region faculae and the
network exhibits different centre to limb variations, implying that
they need to be treated separately when reconstructing variations of
the total solar irradiance.
