Author name code: ortiz ADS astronomy entries on 2022-09-14 author:"Ortiz, Ada" AND (aff:"Barcelona" OR aff:"Oslo") -aff:"Valencia" ------------------------------------------------------------------------ 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. Bibcode: 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. 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 Bibcode: 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.

The movies are available at https://www.aanda.org 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. Bibcode: 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.
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.
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.
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.

The movie associated to Fig. 3 is available at https://www.aanda.org 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. Bibcode: 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. 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 Bibcode: 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. 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 Bibcode: 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. 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 Bibcode: 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. 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 Bibcode: 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-1 and expands at a horizontal speed of 4 km s-1. 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-1. 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. Title: Dimming of the 17th Century Sun Authors: Foukal, Peter; Ortiz, Ada; Schnerr, Roald Bibcode: 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. Title: Dimming of the 17th Century Sun Authors: Foukal, Peter V.; Ortiz, A.; Schnerr, R. Bibcode: 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 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 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 20th century global warming. This work was supported at Heliophysics, Inc. by NASA grants NNX09AP96G and NNX10AC09G. Title: Dimming of the 17th Century Sun Authors: Foukal, Peter V.; Ortiz, A.; Schnerr, R. Bibcode: 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 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 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 20th century global warming. Title: Upflows in the Central Dark Lane of Sunspot Light Bridges Authors: Rouppe van der Voort, L.; Bellot Rubio, L. R.; Ortiz, A. Bibcode: 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-1 with peaks above 1 km s-1. 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-1. 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. Title: Downflows in Sunspot Umbral Dots Authors: Ortiz, A.; Bellot Rubio, L. R.; Rouppe van der Voort, L. Bibcode: 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-1, 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. Title: Spectropolarimetry with CRISP at the Swedish 1-m Solar Telescope Authors: Ortiz, A.; Rouppe van der Voort, L. H. M. Bibcode: 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. Title: Latitudinal Variation of the Solar Photospheric Intensity Authors: Rast, Mark P.; Ortiz, Ada; Meisner, Randle W. Bibcode: 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. Title: Solar cycle evolution of the contrast of small photospheric magnetic elements Authors: Ortiz, Ada Bibcode: 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. 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. Bibcode: 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. Title: Solar irradiance variations induced by faculae and small magnetic elements in the photosphere Authors: Ortiz, A. Bibcode: 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.

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. 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. Bibcode: 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. Title: On the intensity contrast of solar photospheric faculae and network elements Authors: Ortiz, A.; Solanki, S. K.; Domingo, V.; Fligge, M.; Sanahuja, B. Bibcode: 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. 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. Bibcode: 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. Title: An Example of Isolated Active Region Energy Evolution: NOAA AR 7978 Authors: Ortiz, A.; Domingo, V.; Sanahuja, B.; Sánchez, L. Bibcode: 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. Title: On the Contrast of Faculae and Small Magnetic Features Authors: Ortiz, A.; Solanki, S. K.; Fligge, M.; Domingo, V.; Sanahuja, B. Bibcode: 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.