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The Impact of the Chromosphere on Numerical Models of the Convection Zone-to-Corona System

Author(s): W. P. Abbett

Institution(s): UC Berkeley


This review will provide an overview of recent progress toward simulating the magnetic and energetic connection between the convection zone and corona with a particular emphasis on the effect of the chromosphere on the coupled system. We will discuss the challenges inherent in modeling the dynamics and energetics of the chromosphere, then review what 3D MHD simulations of the atmosphere are able to tell us about about the transport of magnetic flux and energy from below the visible surface into the low atmosphere and corona. We will explore how the dynamic chromosphere affects the structure and non-potentiality of the overlying coronal field, and what implications this may have to force-free models based on photospheric magnetograms.

Connecting the photosphere to the corona : Reconstructing the Solar Coronal Magnetic Field

Author(s): T. Amari (1), F. Delyon (1), F. Alauzet (2), A. Canou (3)-(1), Z. Mikic (4), J.J Aly (5), SOLIS/Team and Stanford SDO/HMI Team

Institution(s): (1)CNRS, Centre de Physique Th\'eorique de l'Ecole Polytechnique, F-91128 Palaiseau Cedex, (2)INRIA - Projet Gamma.Domaine de Voluceau - Rocquencourt - B.P. 105.78153 Le Chesnay Cedex (France) (3) Institut d'Astrophysique Spatiale, Bâtiment 121, Universite Paris Sud, 91405 ORSAY Cedex, France. (4) Predictive Science Inc., San Diego, CA 92121, USA (5)AIM - Unite Mixte de Recherche CEA - CNRS - UniversiteParis VII - UMR 7158, Centre d'Etudes de Saclay, F-91191 Gif sur Yvette Cedex, France


The low solar corona is dominated by the magnetic field which is created inside the sun by a dynamo process and then emerges into the atmosphere. This magnetic field plays an important role in most structures and phenomena observed at various wavelengths such as prominences, small and large scale eruptive events, and continuous heating of the plasma, and therefore it is important to understand its three-dimensional properties in order to elaborate efficient theoretical models. Unfortunately, the magnetic field is difficult to measure locally in the hot and tenuous corona. But this can be done at the level of the cooler and denser photosphere, and several instruments with high resolution vector magnetographs are currently available (THEMIS, Imaging Vector Magnetograph (IVM), the Advanced Stokes Polarimeter (ASP)), SOLIS, HINODE , Solar Dynamics Observatory (SDO), or will be shortly available and future programmed missions such as , SOLAR-ORBITER. This has lead solar physicists to develop an approach which consists in reconstructing the coronal magnetic field from boundary data given on the photosphere. We will present our recent progress and results to solve this problem at the scale of active regions or larger ones such as full disk or synoptic scales, for which the large amount of data as well as their sparsity on the solar disk, require to develop particular strategies. We will also illustrate the interest of the reconstruction for characterizing the magnetic environments of prominences, emerging sub-photospheric structures and the pre-eruptive ones.

The Role of Topology in the Energetics of the Coupled Solar Atmosphere

Author(s): Spiro K. Antiochos

Institution(s): NASA/GSFC


The defining physical property of the solar atmosphere is that the magnetic field dominates the plasma. This property implies that magnetic topology plays the central role in determining the structure and energetics of the atmosphere. For example, the formation of observed coronal loops, the explosive energy release in flares and coronal mass ejections, and the creation of the solar wind are all controlled by the topological constraints imposed on the plasma by the magnetic field. In this presentation I discuss how magnetic topology leads to the formation of the structures and dynamics observed in the solar atmosphere including the wind. Not surprisingly, the most important process for driving the dynamics is magnetic reconnection, which acts to break many of the topological constraints. Reconnection, however, preserves some of the topology, in particular, helicity. This turns out to have major implications for the coupled atmosphere. In this presentation, I will also discuss the implications of the topological constraints on observations from SDO and Hinode. This work was supported, in part, by the NASA TR&T and SR&T Programs.

Forecast of the total and solar irradiance based on HMI/SDO magnetograms and solar surface magnetic flux transport models

Author(s): Luis Eduardo A. Vieira, Thierry Dudok de Wit, Matthieu Kretzschmar, Mehmet Karaca

Institution(s): LPC2E/CNRS and University of Orleans


The evolution of the outer layers of the Sun drives the energy flux through the Heliosphere. Therefore, the ionized and neutral components of planetary environments are significantly affected by changes in the Sun. While the total solar irradiance is the main external source of heat to the Earth’s couple atmospheric/oceanic system, the emission in different regions of the spectrum affects the composition and the thermal structure of different layers of the Earth's atmosphere. Consequently, near real-time monitoring and forecast of the solar irradiance is a key element of weather and space weather programs. Here we present a model to reconstruct and predict the solar irradiance based on HMI/SDO magnetograms and solar surface magnetic flux transport models. We find that we can obtain reliable reconstructions of the level of the total and spectral irradiance up to one month. The preliminary results, uncertainties and operational issues are discussed in details. This work is supported by the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement n° 218816 (SOTERIA project) and 261948 (ATMOP Project). A prototype of the forecast model is available at:

Force-free Magnetic Fields and Electric Currents inferred from Coronal Loops and Stereoscopy

Author(s): Markus J. Aschwanden, P. Boerner, C.J.Schrijver, and A. Malanushenko

Institution(s): Solar and Astrophysics Lab., LMSAL, ATC


Force-free magnetic fields are considered to be a natural state of the low plasma-beta corona. There exist about a dozen of numerical nonlinear force-free field (NLFFF) computation codes that are able to caclulate a divergence-free and force-free solution of the magnetic field, by extrapolation from a lower boundary condition that is specified with 3D vector magnetograph data. However, significant differences in the solutions have been found among the different NLFFF codes, as well as in comparison with stereoscopically triangulated 3D coordinates of coronal loops, exhibiting field misalignment angles of 20-40 degrees. Each calculation of a NLFFF solution is computing-intensive and no code is fast enough to enable forward-fitting to observations. Here we derive an analytical approximation of NLFFF solutions that is accurate to second order and can efficiently be used for forward-fitting to coronal loops. We demonstrate the accurcay of the NLFFF forward-fitting code by reproducing the Low and Lou (1990) analytical model withg an accuracy of <5 degres. Further, we show examples of fitted NLFFF solutions to STEREO observations of coronal loops. Future NLFFF fits are expected based on line-of-sight magnetograms and automated loop tracings only, without requiring vector field and STEREO data.

Inversion tools for chromospheric lines

Author(s): A. Asensio Ramos

Institution(s): Instituto de Astrofisica de Canarias


Chromospheric lines are usually formed in non-local thermodynamical equilibrium conditions. The radiation that we see with our telescopes in a point of the solar atmosphere strongly depends on what are the physical conditions in very distant regions. This highly complicates the extraction of thermodynamical and magnetic information from the observations. In this talk I discuss the complexity of the inversion of chromospheric spectral lines, how to deal with them and the main differences with the inversion of photospheric spectral lines: non-locality and the presence of magnetic structures. I present the tools we have to extract information from the relatively optical thin lines of He I and from the optically thick Ca II infrared lines. I will also discuss some extensions to these tools that I consider we need to develop in the future.

The Prominence/Coronal Cavity Connection: using Hinode, AIA, and IRIS to explore the source of quiet-Sun CMEs

Author(s): Thomas Berger

Institution(s): LMSAL


The Hinode and SDO/AIA missions have revolutionized our view of prominences and coronal cavities. Hinode/SOT observations have established that quiescent prominences are extremely dynamic structures with constant filamentary downflows, rising magnetic "bubbles" that lead to Rayleigh-Taylor instability flows, and various MHD wave modes. SDO/AIA has shown that coronal cavities have helical magnetic topology and that quiescent prominences and coronal cavities should be viewed as elements of a single magnetic system: magnetic flux ropes in the corona, by far the largest coherent magnetic structures on the Sun and the source of all quiet-Sun CMEs. In this talk we review the Hinode/SOT and SDO/AIA observations of prominences and coronal cavities to demonstrate the unification of these previously disparate topics. We conclude with a look at possible measurements using IRIS to further our understanding of this complex chromospheric/coronal magnetic system.

Synoptic measurements of chromospheric and prominence magnetic fields with the Chromosphere Magnetometer ChroMag

Author(s): Bethge, C. (1), de Wijn, A.G. (2), McIntosh, S.W. (3), Tomczyk, S. (4), Casini, R. (5)

Institution(s): High Altitude Observatory


The Chromosphere Magnetometer is part of the Coronal Solar Magnetism Observatory (COSMO) proposed by the High Altitude Observatory (HAO) in collaboration with the University of Hawaii and the University of Michigan. Routine measurements of chromospheric and coronal magnetic fields are vital if we want to understand fundamental problems like the energy and mass balance of the corona, the onset and acceleration of the solar wind, the emergence of CMEs, and how these phenomena influence space weather. ChroMag is designed as a Lyot-type filtergraph polarimeter with an FOV of 2.5 solar radii, i.e., it will be capable of both on-disk and off-limb polarimetric measurements. The Lyot filter - currently being built at HAO - is tunable at a fast rate, which allows to determine line-of-sight velocities. This will be done in the spectral lines of H alpha at 656.3 nm, Fe I 617.3 nm, Ca II 854.2 nm, He I 587.6 nm, and He I 1083.0 nm at a high cadence of less than 1 minute, and at a moderate spatial resolution of 2 arcsec. ChroMag data will be freely accessible to the community, along with inversion tools for an easier interpretation of the data. A protoype instrument for ChroMag is currently being assembled at HAO and is expected to perform first measurements at the Boulder Mesa Lab in Summer 2012. We present an overview of the ChroMag instrument and the current status of the protoype.

Large scale MHD model of the solar corona above time dependent HMI/SDO magnetograms

Author(s): Bingert S., Peter H.

Institution(s): Max Planck Institute for Solar System Research


The SDO spacecraft provides a unique tool to observe the solar atmosphere simultaneously in the photosphere and the corona. The magnetic field and the energy transport couples the whole system, which requires a model that describes the atmosphere all the way from the photosphere into the corona. We present the results of a large scale three dimensional magneto-hydrodynamic model of the solar corona, that is driven by the (time variable) magnetic field in the photosphere as observed by HMI/SDO. The results of the 3D MHD model are then used to synthesize the coronal emission and is directly compared to AIA/SDO observations. The domain of the numerical model spans over 100x100 Mm^2 in horizontal directions and reaches a height of 80 Mm, thus containing the full (small) active region. The spatial resolution is sufficient to resolve thin loops and fine structure in the transition region and corona. This large scale model includes all needed physics, such as anisotropic heat conduction and radiative loss to account for a proper coronal pressure. Based on the data we also derive basic parameters, e.g. the energy flux through the domain or the structure and energy content of the coronal magnetic field.

To the top of the photosphere

Author(s): Robert Cameron

Institution(s): Max Plack Institute for Solar System Research


We will discuss the interaction of convection and magnetic fields in the solar photosphere. In particular we will concentrate on the broad range of time and spatial scales over which structures are generated and evolve. The importance of waves, vortices and braiding of the magnetic footpoints will be mentioned, as well as future problems which need to be tackled.

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Last Updated on Tuesday, 24 January 2012 13:45