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Doppler velocities studied simultaneously in the chromosphere and photosphere of an active region filament

Author(s): Kuckein, C. (1,2), Martinez Pillet, V. (1), Centeno, R. (3)

Institution(s): (1) Instituto de Astrofisica de Canarias, (2) Departamento de Astrofisica, Universidad de La Laguna, (3) High Altitude Observatory

Abstract:

We present line-of-sight velocities retrieved simultaneously at two different heights (chromosphere and photosphere) on two days in an active region (AR) filament. The velocities, as well as the magnetic field parameters, were inferred from full Stokes inversions of the photospheric Si I 10827A line and the chromospheric He I 10830A triplet. Various inversion methods with different number of components and different weights of the Stokes parameters were used. Moreover, the velocities were calibrated on an absolute scale. We found a ubiquitous chromospheric downflow in the faculae surrounding the AR filament with an average velocity of 1.6 km/s. However, in the filament region, upflows in the photosphere were detected, when the Stokes signals from the transverse fields are given more weight in the inversions. In the chromosphere, the filament is also moving upward as a whole with a mean speed of -0.24 km/s as deduced from the He I inversions. However, on the second day the chromospheric portion above an orphan penumbra shows localized upflow patches while the rest of the filament is dominated by the same downflows observed elsewhere in the plage region. Photospheric supersonic downflows are detected below the filament, close to the PIL, that last for tens of minutes. The observed velocities in this AR filament strongly suggest a scenario where the transverse fields are mostly dominated by upflows. The filament flux rope is seen to be emerging at all heights with a few exceptions in the chromosphere. No large scale downflow of transverse field lines is observed in the photosphere.




Hall Reconnection in Partially Ionized Plasmas in the Magnetic Reconnection Experiment

Author(s): Eric E. Lawrence, Hantao Ji, Masaaki Yamada, and Jongsoo Yoo

Institution(s): Princeton Plasma Physics Laboratory

Abstract:

In many space and astrophysical plasmas, such as the solar chromosphere and protoplanetary disks, the degree of ionization can be quite low; often 1\% or less. In addition, magnetic reconnection is thought to be a fundamental process in these plasmas. The presence of a large neutral atom population has at least two effects relevant to magnetic reconnection. First, electron-neutral collisions enhance resistive dissipation. Second, strong ion-neutral collisions increase effective ion inertia. This may increase the length scales on which fast Hall reconnection is predicted to occur. By using high gas fill pressures in the Magnetic Reconnection Experiment (MRX), we can study reconnection in partially or weakly ionized plasmas ($n_n/n_e = 1--200$). A newly constructed magnetic probe array allows us to make magnetic measurements of the reconnection region with high spatial resolution and large spatial extent. This will allow us to diagnose, for example, the structure of the Hall quadrupole field in these conditions. Langmuir and spectroscopic diagnostics will also provide insight into how neutrals affect ion outflows and therefore the overall reconnection process. These results will also be discussed in the context of ongoing theoretical work.




The formation of the Halpha line in the solar chromosphere

Author(s): Leenaarts, J. (1,2), Carlsson, M. (1,3), Rouppe van der Voort, L. (1)

Institution(s): (1) Institute for theoretical astrophysics, University of Oslo, Norway (2) Utrecht University, The Netherlands, (3) Center of mathematics for applications, University of Oslo, Norway

Abstract:

We use state-of-the-art radiation-MHD simulations and 3D non-LTE radiative transfer computations to investigate Halpha line formation in the solar chromosphere. We find that 3D radiative transfer is essential in modeling hydrogen lines due to the low photon destruction probability in Halpha. The Halpha opacity in the upper chromosphere is mainly sensitive to the mass density and only weakly sensitive to temperature. We find that the Halpha line-core intensity is correlated with the average formation height: the lower the intensity, the larger the average formation height. The line-core width is a measure of the gas temperature in the line-forming region. The fibril-like dark structures seen in Halpha line-core images computed from our model atmosphere are tracing magnetic field lines. These structures are caused by field-aligned ridges of enhanced chromospheric mass density that raise their average formation height, and therefore makes them appear dark against their deeper-formed surroundings.




Using non-LTE diagnostic tools: Multi3d

Author(s): Leenaarts, J. (1,2)

Institution(s): (1) Institute for theoretical astrophysics, University of Oslo, Norway (2) Utrecht University, The Netherlands, (3) Center of mathematics for applications, University of Oslo, Norway

Abstract:

I will give a tutorial session on the use of the 3D NLTE radiative transfer code Multi3d. The code uses MPI-parallelization and can handle large 3D input atmospheres such as those provided by radiation-MHD models. I'll show how to set up a run and discuss some of the commonly used input options and show how to analyze the results with IDL. I'll provide a web location where the code can be downloaded together with a manual, the IDL analysis package and a test problem. I'll show some results obtained by combining radiation-MHD models with radiative transfer computations done with Multi3d.




Spectropolarimetry in the Sodium 589.6nm D1 line: Evaluating the Resulting Chromospheric (?) Vector Field Maps.

Author(s): KD Leka, G. Barnes, R.G. Stockwell, E.L. Wagner, H. Uitenbroek, M. Derouich

Institution(s): NWRA, NSO

Abstract:

Pioneering work by T. R. Metcalf almost two decades ago pointed to the Na 589.6nm D1 line as a contender for providing chromospheric vector magnetic field measurements (using the Zeeman effect). We report here on a systematic examination of what can be expected from Sodium 589.6nm spectropolarimetry, with respects to polarization-signal amplitudes and retrieval, and the implementation of the inversion for this line based on the Jeffries, Lites & Skumanich Weak-Field Approximation algorithm. The analysis is performed using both synthetic data and observations from the Imaging Vector Magnetograph, for which a large dataset of Sodium 589.6nm vector spectropolarimetry exists. The synthetic data are based on a 3-D field extrapolated from photospheric vector magnetograms of two active regions, four distinct model atmospheres coupled with NLTE synthesis of the emergent NaI D1 Stokes polarization spectra, computed for a variety of viewing angles. In this manner, a broad representation of active-region features, field strengths and observing angles are tested using ``hare & hound'' approaches, including evaluating algorithm performance in the presence of noise and instrumental effects. We compare retrieval algorithms for the very weak (as expected) polarization signals, and evaluate the retrieved vector magnetic field at a range of inferred heights. Finally, we provide an example from the IVM and discuss the prospects for obtaining and interpreting chromospheric vector magnetic field maps. Support for this work comes from NASA NAG5-12466, NASA NNH09CE60C, AFOSR F49620-03-C-0019, NSF/NSWP ATM-0519107, NSF/SHINE ATM-0454610, and NSF CRG ATM-0551055.




Magnetic Helicity in Emerging Active Regions: A Statistical Study

Author(s): Yang Liu, and HMI Team

Institution(s): Stanford University

Abstract:

Magnetic helicity in emerging active regions in early phase of solar cycle 24 is studied using HMI vector magnetic field data. Magnetic helicity in the active-region corona is computed from the helicity flux across the photosphere, which is derived using the measured vector magnetic field on the photosphere and the velocity field derived from time-series vector magnetic field data using the algorithm DAVE4VM (Schuck 2008). The so-called ``hemisphere rule'' of magnetic helicity is examined. Relationship between solar transient and magnetic helicity in active regions is also explored here.




SDO/AIA Observations of Various Coronal EUV Waves Associated with Flares/CMEs and Their Coronal Seismology Implications

Author(s): Wei Liu, Leon Ofman, Markus J. Aschwanden, Nariaki Nitta, Junwei Zhao, Alan M. Title

Institution(s): (1) Stanford-Lockheed Institute for Space Research; (2) Catholic University of America and NASA Goddard Space Flight Center; (3),(4),(6) Lockheed Martin Solar and Astrophysics Laboratory; (5) W. W. Hansen Experimental Physics Laboratory, Stanford University.

Abstract:

MHD waves can be used as diagnostic tools of coronal seismology to decipher otherwise elusive critical physical parameters of the solar corona, such as the magnetic field strength and plasma density. They are analogous to acoustic waves used in helioseismology, but with complexities arising from the magnetic field and nonlinearity. Recent high cadence, high resolution, full-disk imaging observations from SDO/AIA have opened a new chapter in understanding these waves. Various types of EUV waves associated with flares/CMEs have been discovered or observed in unprecedented detail. In this presentation, we will review such new AIA observations, focusing on the following topics and their interrelationships: (1) quasi-periodic fast waves traveling along coronal funnels within CME bubbles at speeds up to 2000 km/s, associated with flare pulsations at similar frequencies; (2) quasi-periodic wave trains within broad, diffuse pulses of global EUV waves (so-called EIT waves) running ahead of CME fronts; (3) interactions of global EUV waves with local coronal structures on their paths, such as flux-rope coronal cavities and their embedded filaments (kink oscillations) and coronal holes/active regions (deflections). We will discuss the implications of these observations on coronal seismology, on their roles in transporting energy through different parts of the solar atmosphere, and on understanding their associated eruptive flares/CMEs.




SDO/AIA Observations of Sustained Coronal Condensation and Mass Drainage in Prominences as Return Flows of the Chromosphere-Corona Mass Cycle

Author(s): Wei Liu, Thomas Berger, B. C. Low

Institution(s): (1) Stanford-Lockheed Institute for Space Research; (2) Lockheed Martin Solar and Astrophysics Laboratory; (3) High Altitude Observatory

Abstract:

It has recently been proposed that prominences are manifestations of a magneto-thermal convection process that involves ever-present dynamic descents of cool material threads and upflows of hot bubbles (Berger et al. 2011 Nature). On global scales, prominences may play an important role as the return flows of the chromosphere-corona mass cycle, in which hot mass is originally transported upward through spicules. A critical step in this cycle is the condensation of million-degree coronal plasma into T<10,000 K prominence material by radiative cooling instability. However, direct observation of coronal condensation has been difficult in the past, a situation recently changed with the launch of the Hinode/SOT and SDO/AIA. We present here the first example observed with SDO/AIA, in which hours of gradual cooling through multiple EUV channels (from 2 MK to 80,000 K) in large-scale loops leads to eventual condensation at magnetic dips, forming a moderate-size prominence of 10^14 gram. The prominence mass is not static but maintained by a continual supply through condensation at a high rate of 10^10 gram/s against a comparable drainage through numerous vertical threads at less than free-fall speeds. Most of the total condensation of 10^15 gram, comparable to a CME mass and an order of magnitude more than the instantaneous mass of the prominence itself, is drained in merely one day. These new observations show that a macroscopically quiescent prominence is microscopically dynamic, involving the passage of a significant mass that bears important implications for the chromosphere-corona mass cycle. This interpretation is further supported by the recent theoretical development on spontaneous formation of current sheets and cool condensations (Low, Berger, Casini, & Liu, this meeting).




The Hydromagnetic Nature of Quiescent Prominences

Author(s): B.C. Low^1, T. Berger^2, R. Casini^1, W. Liu^{2,3}

Institution(s): 1 HAO/NCAR; 2 LMSAL; 3 Stanford University

Abstract:

High-resolution observations of quiescent prominences with Hinode and SDO have revealed within their interiors the ever-¬present descent at less than free-fall speeds of cool, vertical dense filaments interspersed among upward, narrow streams at comparable speeds of heated, low-density plasma. We address the physical nature of this dynamical state. Despite the high magnetic Reynolds numbers characterizing this hydromagnetic environment, magnetic reconnection takes place via spontaneous formation and dissipation of current sheets by the coupled effects of highly-anisotropic thermal conduction, gravity, optically-thin radiation, heating, and high electrical conductivity. In this interesting new version of the theory of Parker (1994, Spontaneous current sheets in magnetic fields, Cambridge U Press), pervasive reconnections produce a perennial local descent of dense condensations under gravity along newly reconnected magnetic field lines and a concurrent turbulent rise of buoyant pockets of heated magnetized plasma through the large-scale magnetic structure. This mechanism may explain the massive downward drainage through a quiescent prominence observed recently (Liu et al. 2012 ApJ 745, L21) and, in the broader context, relate the quiescent prominence to the surrounding chromosphere/corona as a novel, large-scale, magneto-thermal convective phenomenon (Berger et al. 2011, Nature 472, 197).




Braided Solar Magnetic Field Structures Observed with SDO

Author(s): Lundstedt, H. (1), Persson, T. (2)

Institution(s): Swedish Institute of Space Physics, Lund, Sweden (1), Center for Mathematical Sciences, Lund University, Lund, Sweden (2)

Abstract:

Stretching, twisting and folding of the magnetic field due to chaotic plasma motions below solar surface can not only drive a large-scale dynamo but also produce braided structures as seen on and above solar surface. Multifractal studies of the photospheric magnetic field, measured with HMI, suggest braided structures of many different sizes. Braided magnetic structures contain magnetic energy. In this presentation we discuss whether or not the release of it, can explain Ellerman bombs and nano-flares. A series of AIA images of a filament in wavelengths 304 , 211 and 171 were analyzed. In an earlier helioseismic study of the AR 486 in 2003, we showed a good correlation between strong vorticity below solar surface, strong magnetic fields on surface and strong X-ray flares in the corona. Current study is therefore also considered to be extended to more intense solar flares.





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Last Updated on Tuesday, 24 January 2012 13:45