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Spectroscopic Diagnostics and Heating of Active Region Cores

Author(s): Tripathi, D.(1); Mason, H.E.(2); Klimchuk, J.A.(3)

Institution(s): 1) Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007, India; 2) DAMTP, University of Cambridge, Cambridge CB3 0WA, England; 3) NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

Abstract:

It is widely believed that we are still far from spatially resolving the fundamental plasma structures in solar corona. Therefore, we must use spectroscopic diagnostic techniques such as emission measure distribution (EM(T)) and Doppler shifts that are not affected by spatial averaging. Using observations recorded by the Extreme ultraviolet Imaging Spectrometer we have studies emission measure (EM) distribution and Doppler shift in the moss and inter-moss regions. The EM distributions obtained for moss regions cab be reproduced by considering strong coronal condensation scenario suggesting bulk downflow of the plasma. Doppler shift measurements for the moss regions show that almost all the moss regions are red-shifted with velocities up to 15km/s with mean velocity of ~5 km/s. However, the uncertainty on the Doppler shift was large. The EM distributions obtained for inter-moss regions have power law slopes of approximately 2.4 coolward of the peak. We compare the EM for inter-moss region with that obtained from nanoflare model using EBTEL (Enthalpy-Based Thermal Evolution of Loops). Our results suggest that the EM distribution for both the moss as well as inter-moss regions and Doppler shift in the moss regions can be explained by nanoflare heating. IRIS will provide a better account of the Doppler shift in the moss regions, which will dramatically enhance our understanding of the heating of active region core.




Observables for Measuring the Outer-Atmospheric Magnetic Field from Chromosphere to Corona

Author(s): Trujillo Bueno et al.

Institution(s): IAC

Abstract:

The basic idea of optical pumping, for which Alfred Kastler received the 1966 Nobel Prize in physics, is that the absorption and scattering of light that is near-resonant with an optical transition can produce large population imbalances among the magnetic sublevels of atomic ground states as well as in excited states. The degree of this radiatively-induced atomic level polarization, which is very sensitive to the presence of magnetic fields, can be determined by observing the intensity and polarization of the scattered or transmitted spectral line radiation. Probably, the most important point for solar physics is that the outer solar atmosphere is indeed an optically pumped vapor and that the polarization of the emergent spectral line radiation can be exploited for detecting magnetic fields that are too weak and/or too tangled so as to produce measurable Zeeman polarization signals. Here we present several radiative transfer simulations of the linear polarization produced by optical pumping in selected FUV and EUV lines of the solar atmosphere, showing that their sensitivity to the Hanle effect is very suitable for magnetic field measurements in the upper chromosphere and transition region of the Sun. These results suggest that solar magnetometry using the spectral lines of optically pumped atoms in the chromosphere, transition region and corona should be a high-priority goal for large aperture solar telescopes, such as ATST, EST and SOLAR-C.




MHD waves in photosphere

Author(s): Saku Tsuneta

Institution(s): NAOJ

Abstract:

We report the observations of the magnetohydrodynamic (MHD) waves propagating along magnetic flux tubes in the solar photosphere. We identified multiple isolated strong peaks in the power spectra of the line-of-sight (LOS) magnetic flux, the LOS velocity, and the intensity for many different magnetic concentrations. The observation is performed with the spectro-polarimeter of the Solar Optical Telescope aboard the Hinode satellite. The oscillation periods are located in 3-9 minutes. These peaks correspond to the magnetic, the velocity, and the intensity fluctuations. Phase differences between the LOS magnetic flux and the LOS velocity have striking concentrations at around -90°. We suggest that the observed fluctuations are due to the superposition of the ascending wave and the descending longitudinal (sausage-mode) and/or transverse (kink-mode) MHD waves reflected at chromosphere/corona boundary (standing wave). Even with such reflected waves, the residual leaky Poynting flux is estimated to be 2.7 × 10(6) erg cm(-2) s(-1).




The RH suite of radiative transfer programs: a tutorial

Author(s): Han Uitenbroek

Institution(s): National Solar Observatory/Sacramento Pek

Abstract:

The RH suite of radiative transfer programs derives its name from the Rybicky-Hummer multi-level accelerated lambda iteration (MALI) formalism it employs for the general solution on Non-LTE problems in a given atmospheric model. The suite provides separate programs for Non-LTE solutions in 1-D, 2-D, and 3-D Cartesian, and spherical geometry, including the effects of partial frequency redistribution (PRD) and Zeeman-induced polarization. The code is flexible through the use of structured input files, and allows for the calculation of both atomic and molecular diagnostics. I will give a short tutorial on the structure of the code, the principles on which it is build, how to set up simple problems, and how to use the IDL-based graphical user interface to look at output results. The code is available for download for those interested in using it.




The role of magnetic braiding and MHD wave dynamics in the heating of the Sun's outer atmosphere

Author(s): A. A. van Ballegooijen

Institution(s): SAO

Abstract:

The solar corona is thought to be heated by dissipation of magnetic disturbances that propagate up from the Sun's convection zone. Two types of disturbance have often been considered: (1) twisting and braiding of coronal field lines as a result of random footpoint motions in the photosphere, and (2) MHD waves launched by such motions. One difficulty with the former is that coronal observations with Hinode/XRT and other imaging instruments show little evidence for braided fields. Furthermore, quasi-static braiding models predict that in active regions the misalignment angles of the braided field lines relative to the potential field should be large (~20 degrees), which is not consistent with coronal loop observations. We suggest that the braiding occurs on small transverse length scales in the corona (a few Mm or less), and must involve small misalignment angles (at most a few degrees). We argue that the braiding is dominated by small-scale footpoint motions occurring inside the kilogauss flux tubes in the photosphere (size < 100 km). Results from 3D MHD simulations of braided fields in coronal loops are presented. According to these models the footpoint motions cause Alfven waves to be launched into the system. The waves strongly reflect at the transition region, which leads to counter-propagating Alfven waves and turbulence in the chromospheric parts of the flux tube. Such turbulence has a major effect on the properties of the Alfven waves injected into the corona: the wave periods and transverse scales of the waves are much smaller than those of the photospheric footpoint motions. As a result, the turbulence in the corona proceeds very rapidly and is able to dissipate the injected energy very quickly, leading to small misalignment angles consistent with coronal observations. We find that most of the wave energy is dissipated in the lower atmosphere, consistent with observations of chromospheric and coronal heating rates in active regions. Therefore, this new dynamic braiding model appears to be consistent with a variety of observational constraints. We conclude there is a close relationship between the braiding of coronal field lines and wave heating processes.




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

Author(s): Tom Van Doorsselaere

Institution(s): KULeuven

Abstract:

In this presentation, I aim to provide elements for the subsequent discussion. I will give an overview of the strengths and achievements of atmospheric seismology. I will also focus on the inherent limitations that are connected with this technique. Finally, I will highlight a few areas that have not been studied yet, but have a large potential for gaining additional information via atmospheric seismology.




2D Inversions

Author(s): Michiel van Noort

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

Abstract:

A new approach to inversion of high-resolution spectro-polarimetric solar image data is presented that explicitly takes the effects of telescope diffraction and other optical abberations in the observed data into account. The 2-dimensional solution can reliably reproduce the atmospheres from simulated data cubes and significantly improves the accuracy of profiles fitted to Hinode-SP data, compared to an equivalent 1-dimensional solution, without needing a more complex atmospheric model.




Think Scientifically: The Solar Dynamics Observatory's Elementary Science Literacy Program

Author(s): Van Norden, Wendy, Wawro, Martha

Institution(s): ADNET Systems Inc.

Abstract:

The pressure to focus on math and reading at the elementary level has increased in recent years. As a result, science education has taken a back seat in elementary classrooms. The Think Scientifically book series provides a way for science to easily integrate with existing math and reading curriculum. This story-based science literature program integrates a classic storybook format with solid solar science, to make an educational product that meets state literacy standards. Each story is accompanied by hands-on labs and activities that teachers can easily conduct in their classrooms with minimal training and materials, as well as math and language arts extensions and assessment questions. These books are being distributed through teacher workshops and conferences.




Multi-instrument study of chromospheric jets

Author(s): Kamalam Vanninathan, Maria Madjarska, Gerry Doyle

Institution(s): Armagh Observatory

Abstract:

The contribution to coronal heating by jets of various kinds like spicules, mottles, surges etc. originating in the solar chromosphere is an issue which is being currently largely explored. We analyse multi-instrument data taken in the plage area of active regions during dedicated observing runs with ROSA, IBIS at Sac Peak, USA, SOT, EIS/XRT/Hinode and AIA/SDO. The high-resolution and high-cadence data allow us to track chromospheric jets through the solar atmosphere and thus helps us to understand the dynamics and plasma properties of these features. The study is a forward step towards the exploration of the forthcoming state-of-art IRIS observations.




Determining the Typical Nanoflare Cadence in Active Regions: Comparing SDO/AIA Observations with Modeled Active Region Light Curves

Author(s): Viall, Nicholeen M. (1), and Klimchuk, James A. (1)

Institution(s): 1. NASA Goddard Space Flight Center, Greenbelt, MD

Abstract:

Coronal plasma in active regions is typically measured to be at temperatures near ~1-3 MK. Is the majority of the coronal plasma in hydrostatic equilibrium, maintained at these temperatures through a form of quasi-steady heating, or is this simply a measure of the average temperature of widely varying, impulsively heated coronal plasma which is continually undergoing heating and cooling cycles? Addressing this question is complicated by the fact that the corona is optically thin: many thousands of strands which are heated completely independently are contributing to the total emission along a given line of sight. There is a large body of work focused on the heating of coronal loops, which are impulsively heated, however it is the diffuse emission between loops which often comprises the majority of active region emission. Therefore, a different and necessary approach to analyzing active region heating is to analyze all of the emission in an active region, and account for emission along the line of sight from all of the contributing strands. We investigate light curves systematically in an entire active region using SDO/AIA observations. We also model the active region corona as a line-of-sight integration of many thousands of completely independently heated strands. The emission from these flux tubes may be time dependent, quasi-steady, or a mix of both, depending on the cadence of heat release on each strand. We examine a full range of heat cadences from effectively steady (heat pulse repeat time << plasma cooling time) to fully impulsive (heat pulse repeat time >> plasma cooling time) and model the resulting emission when superposing strands undergoing these differing heat cycles. We demonstrate that despite the superposition of randomly heated strands, different distributions of heat cadences produce distinct signatures in light curves observed with multi-wavelength and high time cadence data, such as those from the AIA telescopes on SDO. Using these model predictions in conjunction with SDO/AIA observations, we evaluate the typical cadence of heat release in different active regions and patterns therein, which is a crucial constraint on coronal heating mechanisms.





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Last Updated on Tuesday, 24 January 2012 13:45