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There are 123 abstracts


State-of-the-art of non-LTE diagnostics: observations and simulations

Author(s): Mats Carlsson

Institution(s): Institute of Theoretical Astrophysics

Abstract:

Advanced MHD simulations combined with non-LTE diagnostics are revolutionizing our view of chromospheric dynamics and heating. We will discuss how well synthetic observables compare with observations, how diagnostic codes can be used to derive physical information about the atmosphere, what is missing in current calculations and the consequences of current assumptions. Examples will focus on often used or to-be-used diagnostics of chromospheric lines, such as Ca II 8542, H-alpha and Mg II h/k.




Opportunities and challenges in determining the chromospheric magnetic field using He I 10830

Author(s): Rebecca Centeno

Institution(s): High Altitude Observatory

Abstract:

Determining the magnetic structure of the Solar Chromosphere entails all sorts of observational, theoretical and computational challenges. Within the observational approach, the first step in the inference of Chromospheric magnetic fields is to measure the imprints that these fields leave on the spectral line radiation. This already poses a problem due to the intrinsic weakness of the polarization signatures and the highly dynamic nature of the Chromosphere. The second hurdle is to interpret the spectral line radiation. This usually involves using a spectral line inversion code, i.e., a non-linear iterative algorithm that requires solving the radiative transfer equation coupled to the statistical equilibrium equations (a problem that has a non-linear iterative nature in itself!) at each iterative step. Due to its peculiar formation mechanism, the He I 10830 A multiplet offers a series of advantages that allow us to skip some of these obstacles. I will show some of the findings of the past decade that prove the enormous diagnostic potential of this triplet and I will argue why it should be considered as one of the Rosetta Stones for understanding Chromospheric magnetism.




Active region emergence sites observed with HMI

Author(s): Rebecca Centeno

Institution(s): High Altitude Observatory

Abstract:

One of the advantages of SDO/HMI is the consistent quality and uninterrupted nature of the data that it provides. We take advantage of this to study the emergence of active regions from the moment that the magnetic fields show their first imprints on the solar surface. Flux emergence sites are characterized by moving dipolar features (MDFs) that appear in between the main footpoints of an AR. In longitudinal magnetograms, MDFs show an inverse polarity configuration with respect to that of the active region. The vector magnetic field and line-of-sight velocity measurements of HMI allow us to track the dynamic and magnetic properties of these features and understand their movements in terms of the bending and straightening of magnetic field lines.




Data-Driven Modeling of the Evolution of Active Regions and Coronal Holes

Author(s): Cheung, M. C. M. (1), DeRosa, M. L. (1)

Institution(s): (1) Lockheed Martin Solar & Astrophysics Laboratory, Palo Alto, CA, USA

Abstract:

We present results from numerical simulations of the evolution of solar Active Regions (ARs) and Coronal Holes (CHs). The simulations use the magnetofrictional method, which solves the induction equation to drive magnetic configurations toward force-free states in response to photospheric changes. The method is applied to modeling energy build-up in ARs and morphological changes in CHs. Comparisons with AIA data will be presented.




Observational signatures of simulated reconnection in solar photosphere

Author(s): Danilovic,S.

Institution(s): MPS Germany

Abstract:

Recent IMaX/Sunrise observations reveal many short-lived high velocity flows that appear at very small scales everywhere in the quiet Sun. The flows usually appear close to the patches of opposite magnetic polarities. In some cases, the inversion result show localised temperature increase and strong downflows. Here, we confirm the hypothesis that some of the observed events are in fact produced by the reconnection of the emerging with the preexisting field. We concentrate on individual reconnection events in the realistic 3D MHD simulations and describe observational signatures that are likely to arise. The comparison of simulated with observed cases suggests that there might be currents sheets forming very low in the atmosphere. The retrieved temperatures and velocities imply that the observed events are much more energetic than the simulated cases.




White Light Coronal Velocity and Temperature Diagnostics

Author(s): Joseph M. Davila, Nelson Reginald, and O. C. St. Cyr

Institution(s): NASA Goddard Space Flight Center

Abstract:

During the March 2006 total solar eclipse we conducted an imaging experiment using the Imaging Spectrograph of Coronal Electrons (ISCORE) to determine the coronal electron temperature and its radial flow speed in the low solar corona. This technique required taking images of the solar eclipse through four broadband filters centered at 385.0, 398.7, 410.0 and 423.3 nm. The K-coronal temperature is determined from intensity ratios from the 385.0 and 410.0 nm filters, and the K-coronal radial flow speed is determined from intensity ratios from the 398.7 and 423.3 nm filters. The theoretical model for this technique assumes a symmetric corona devoid of any features like streamers that might alter the coronal symmetry. The model also requires an isothermal temperature and a uniform outflow speed all along the line of sight. We will call this the Constant Parameter Thomson Scattering Model (CPTSM). The latter assumption may sound unreasonable but in the symmetric corona with rapid fall of the electron density with height in the solar corona, the major contributions to the K-coronal intensity along a given line of sight comes from the plasma properties in the vicinity of the plane of the sky. But the pressing question is how is the derived plasma properties by ISCORE compare with the nature of the true corona. For this we turn to the CORHEL model by Predictive Science Inc. which used magnetogram data to create a realistic model of the solar corona that are made available through the Community Coordinated Modeling Center (CCMC) at GSFC. That team has consistently produced the expected coronal image days prior to many total eclipses where the major coronal features from their model matched actual coronal image on the day of the eclipse. Using the CORHEL model data we have calculated the K-coronal intensities at 385.0, 398.7, 410.0 and 423.3 nm using the electron density, plasma temperature (assumed to be electron temperature) and the flow speeds of the plasma along the line of sight in the CORHEL model and have calculated the temperature and radial flow speed sensitive intensity ratios. Next we identify the isothermal electron temperature and the radial flow speed in the CPTSM model that would match the temperature sensitive and radial flow speed sensitive intensity ratios from the CORHEL model and compare the CPTSM temperature and flow speed values with the corresponding values in the CORHEL model in the plane of the sky. These comparisons were made for Carrington Rotation 1977 with the CORHEL model of the solar corona rotated in intervals of 45 degrees with respect to the observer located at 1 AU. The average of the difference between the electron temperatures and the radial flow speed at 5 solar radii in the East-West direction were (underestimated by 0.02 MK or an error of 1.7%) and (overestimated by 22.km/sec or an error of 18%), respectively and in the South-North direction were (underestimated by 0.04 MK or an error of 3.2%) and (overestimated by 42 km/sec or an error of 21%), respectively.




NLTE inversions from a 3D MHD Chromospheric simulation

Author(s): J. de la Cruz Rodriguez (1), H. Socas-Navarro (2), M. Carlsson (3), J. Leenaarts (3)

Institution(s): (1) Department of Physics and Astronomy, Uppsala University, Sweden, (2) Instituto de Astrofisica de Canarias, Spain, (3) Institute of Theoretical Astrophysics, University of Oslo, Norway

Abstract:

The structure of the solar chromosphere is believed to be governed by magnetic fields, even in quiet Sun regions with a relatively weak field. Measuring the magnetic field of the solar chromosphere is an outstanding challenge for observers. Inversion codes allow for detailed interpretation of full-Stokes data from spectral lines formed in the chromosphere. However, the applicability of non-LTE inversions to infer physical conditions in the dynamic 3D solar chromosphere, has not yet been studied in detail. In this study, we use a snapshot from a 3D MHD simulation of quiet-sun, extending from the photosphere to the corona, to asses the reliability of non-LTE inversions to infer chromospheric quantities, especially the magnetic field.




What we can and cannot learn from seismology of the solar atmosphere

Author(s): I. De Moortel

Institution(s): University of St Andrews

Abstract:

During the last decade or so, new instruments have revealed a surprisingly large number of observations of oscillatory behaviour in the solar atmosphere. Both standing and propagating waves have now been detected in a variety of different structures with a wide range of instruments. After the initial euphoria in coronal seismology applications, the subject now needs to go through a period of consolidating and verifying results. So, what can we actually learn from coronal seismology? This talk will invite the community to debate future directions for both theoretical modelling and observational campaigns. How robust are the basic MHD waves models? Do they apply in the highly dynamical and structured solar atmosphere? What can we learn from numerical modelling? And what exactly can we deduce from the observations?




Coupling, damping and dissipation of magnetic waves in the chromosphere and corona

Author(s): I. De Moortel

Institution(s): University of St Andrews

Abstract:

In this talk I will give an overview of current (numerical) modelling of MHD waves and oscillations, emphasising in particular the process of mode coupling. Can models predict the observed damping rates and energy flux? How reliable are the comparisons between theory and observations? As observations of waves and oscillations become increasingly more detailed, it has become clear that the role of wave heating of the solar atmosphere has to be reassessed. I will highlight some of the recent modelling results as well as try to outline where future efforts are needed.




The Chromosphere and Prominence Magnetometer

Author(s): Alfred de Wijn, Christian Bethge, Scott McIntosh, Steven Tomczyk and Roberto Casini

Institution(s): High Altitude Observatory

Abstract:

ChroMag is an imaging polarimeter designed to measure on-disk chromosphere and off-disk prominence magnetic fields using the spectral lines of He I (587.6 and 1083 nm). It is part of the planned CoSMO suite, which includes two more instruments: a large 1.5-m refracting coronagraph for coronal magnetic field measurements, and the K-Coronagraph for measurement of the coronal density. ChroMag will provide insights in the energetics of the solar atmosphere, how prominences are formed, and how energy is stored and released in the magnetic field structure of the atmosphere. An essential part of the ChroMag program is a commitment to develop and provide community access to the ”inversion” tools necessary to interpret the measurements and derive the magneto-hydrodynamic parameters of the plasma. A prototype instrument is currently under construction at the High Altitude Observatory. We will present an overview of the ChroMag instrument concept, target science, and prototype status.





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Last Updated on Tuesday, 24 January 2012 13:45