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Modeling magnetic reconnection in partially ionized chromospheric plasmas

Author(s): Murphy, Nicholas A. (1), Raymond, John C. (1), and Zweibel, Ellen G. (2)

Institution(s): (1) Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA, (2) University of Wisconsin, Madison, WI, USA

Abstract:

Simulations of magnetic reconnection generally assume that the plasma is fully ionized. However, the ionization fraction in the solar chromosphere ranges from 0.005 to 0.5 so we must consider partial ionization effects such as ambipolar diffusion. In this poster we report on the initial stages of development for a new plasma simulation code to model partially ionized chromospheric reconnection. We will model ions and neutrals separately and include time-dependent ionization. By including elements with both high and low first ionization potentials, we will determine the amount of elemental fractionation that should be expected during chromospheric reconnection. These simulations will provide insight into observations of Type II spicules and chromospheric reconnection events by IRIS, SDO/AIA, and Hinode/SOT.




Equilibrium and Stability of Solar-Relevant Magnetized Arc Discharges

Author(s): C. E. Myers, M. Yamada, E. E. Lawrence, H. Ji, R. M. Kulsrud, J. Yoo, and T. D. Tharp

Institution(s): Princeton Plasma Physics Laboratory

Abstract:

The equilibrium and stability properties of solar-relevant partial-toroidal arc discharges are studied in the laboratory. These discharges, which have an arched magnetic flux rope topology, are formed between two electrodes in the Magnetic Reconnection Experiment (MRX). Using internal magnetic probes and a fast framing camera, the discharge equilibria are found to expand and contract in response to radially-directed J×B forces. This behavior is similar to that of arched structures found in the solar corona. With regard to stability, the ideal external kink mode is studied in detail. It is found that the flux rope boundary conditions at each electrode play an important role in the kink stability of the discharges. In particular, changing the boundary conditions at the anode changes both the observed mode structure and the measured stabilization criteria.




Modeling waves, flows, and instabilities produced by impulsive events in coronal active regions

Author(s): Ofman, L. (1,2), Liu, W. (3), Wang, T.J. (1), Davila, J.M. (2), Thompson, B.J. (2)

Institution(s): (1) Catholic University of America, Washington, DC, (2) NASA GSFC, Greenbelt, MD, (3) Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA

Abstract:

Recent high-resolution observations by SDO/AIA combined with spectral data from Hinode provide insights into the properties of MHD waves, flows, and instabilities in coronal active region plasma and their connection with impulsive energy release. Shear flow driven instabilities, such as the Kelvin-Helmholtz (KH) instability were only recently detected in detail in the corona. I will present recent results of 3D MHD models of slow and fast magnetosonic waves in active regions excited by jets and quasi-periodic flows driven by micro-flares at loops’ footpoints. I will discuss models of super-fast magnetosonic waves detected recently by SDO/AIA. I will also discuss models of global (EIT) waves, and KH instabilities driven by CMEs. The relations between waves, flows, instabilities, and impulsive events such as flares and CMEs are becoming apparent thanks to the combination of observational data analysis and the 3D MHD modeling. Understanding these relations is useful for coronal seismology and for tracing the flow of energy from the transition region to the corona.




Propagating waves along spicules

Author(s): (1) Okamoto, Joten (2) De Pontieu, Bart

Institution(s): (1) NAOJ, (2) LMSAL

Abstract:

We investigated the detailed and statistical properties of Alfvenic waves along spicules in the polar coronal hole using very high cadence observations of the Solar Optical Telescope onboard Hinode. We developed a technique for the automated detection of spicules and high-frequency waves in a time series of images. We detected 89 spicules, and obtained several observational results (i.e., we found a mix of upward propagating (59%), downward propagating (21%), as well as standing waves (20%)). We speculate that upward propagating waves are produced near the solar surface (below the spicule) and downward propagating waves are caused by reflection of (initially) upward propagating waves off the transition region at the spicule top. The mix of upward and downward propagating waves implies that exploiting these waves to perform seismology of the spicular environment requires careful analysis and may be problematic.




Non-equilibrium ionization in 3D numerical models

Author(s): Kosovare Olluri, Boris Gudiksen, Viggoh Hansteen

Institution(s): Institute of theoretical Atrophsics, University of Oslo

Abstract:

The dynamic timescales in the chromosphere and transition region have been observed to be much smaller then the ionization equilibration timescales of many ions found in the region. Due to the fast changes in the properties of the atmosphere, long ionization- and recombination times may lead to ions being found far from their equilibrium temperatures. Spectroscopic investigations therefore needs to be interpreted with the help of numerical modeling in order to produce reliable results. By solving the rate equations within a realistic MHD simulation of the solar atmosphere, we are able to follow the ionization balance, and study the non equilibrium effects of the emitting gas. Due top lack of computation power, this has previously been done in simple 1D, but because of the many free parameters in these models, their conclusions are not free of uncertainties. The resent development in computing technology and atmospheric modeling makes it possible to study the full 3D effect of non equilibrium ionization. With the solar atmosphere model Bifrost, we have a 3D platform for calculating and following the ionization degree of important atoms of high abundances in the solar atmosphere. We will present our implementation, and a study of the carbon IV 1549 Å , Iron XII 195 Å, Oxygen IV 1399 Å and 1401 Å lines in 2D.




Non-equilibrium ionization in 3D numerical models

Author(s): Kosovare Olluri, Boris Gudiksen, Viggo Hansteen

Institution(s): Institute of theoretical Astrophysics, University of Oslo

Abstract:

The dynamic timescales in the chromosphere and transition region have been observed to be much smaller then the ionization equilibration timescales of many ions found in the region. Due to the fast changes in the properties of the atmosphere, long ionization- and recombination times may lead to ions being found far from their equilibrium temperatures. Spectroscopic investigations therefore needs to be interpreted with the help of numerical modeling in order to produce reliable results. By solving the rate equations within a realistic MHD simulation of the solar atmosphere, we are able to follow the ionization balance, and study the non equilibrium effects of the emitting gas. Due top lack of computation power, this has previously been done in simple 1D, but because of the many free parameters in these models, their conclusions are not free of uncertainties. The resent development in computing technology and atmospheric modeling makes it possible to study the full 3D effect of non equilibrium ionization. With the solar atmosphere model Bifrost, we have a 3D platform for calculating and following the ionization degree of important atoms of high abundances in the solar atmosphere. We will present our implementation, and a study of the carbon IV 1549 Å , Iron XII 195 Å, Oxygen IV 1399 Å and 1401 Å lines in 2D.




What can we learn from propagating Alfvenic waves?

Author(s): D. J. Pascoe, I. De Moortel, A. W. Hood, and A. N. Wright

Institution(s): University of St Andrews

Abstract:

Observations have revealed ubiquitous transverse velocity perturbation waves propagating in the solar corona. We perform 3D numerical simulations of footpoint-driven transverse waves propagating in a low beta plasma. When density structuring is present, mode coupling in inhomogeneous regions leads to the coupling of the kink mode to the Alfvén mode. The frequency-dependent decay of the propagating kink wave is observed as energy is transferred to the local Alfvén mode. Modest changes in density are capable of efficiently converting energy from the driving footpoint motion to localised Alfvén modes. Thus, realistic transverse footpoint motions will deposit energy to (azimuthal) Alfvén modes in the corona. Mode coupling is investigated in detail for propagating kink modes as an explanation for the observed wave damping and as a possible seismological tool. The observed strong damping of the Doppler shift oscillations indicates the presence of wide inhomogeneous layers at the edges of the loops. Our simulations (backed up by analytical calculations) show that in this regime, the traditional exp(-z/L) damping rate no longer applies. Hence, care has to be taken when seismologically inferring damping lengths from the observed oscillations. In addition, taking into account line-of-sight integration of multiple loops supporting transverse oscillations, we show that the energy budget present in the 3D coronal volume could be substantially higher than the energy budget derived from the observed Doppler shift oscillations.




Coronal loops with constant cross-section reproduced in 3D MHD models

Author(s): Peter, Hardi (1) and Bingert, Sven (1)

Institution(s): (1) Max-Planck-Institut fuer Sonnenphysik, Katlenburg-Lindau, Germany

Abstract:

EUV and X-ray images of the solar corona show loops with a more or less constant cross-section. Because the magnetic field is expanding with height, one would expect the coronal loops to expand with height. Suggestions on special magnetic structures have been made to understand the constant cross section of the loops, e.g. introducing helicity. However no convincing picture could be presented yet. We present results from a 3D MHD box model of a solar active region, which is heated through braiding of magnetic field lines and subsequent Ohmic dissipation. From the MHD model we synthesize emission as it would be observed with AIA/SDO. These synthetic images clearly show EUV loops with constant cross-section and thus can reproduce the observed structures. The analysis of the densities and temperatures in relation to the magnetic structure in the 3D model box shows that the constant cross section is a result of the temperature and density variation in the loop structure perpendicular to the magnetic field. These results underline that one has to account for the three-dimensional nature of the corona even when investigating a seemingly one-dimensional structure such as a coronal loop.




Circumfacular regions and magnetic canopies as seen in Ca II 8542 \AA

Author(s): Anna Pietarila, Jack Harvey

Institution(s): National Solar Observatory

Abstract:

Active regions appear bright in Ca II 8542 \AA\ line core intensity while the surrounding areas are darker than the active region or the quiet Sun. These areas are referred to as circumfacular regions. We use SOLIS VSM Ca II 8542 \AA\ data (photospheric and chromospheric full disk magnetograms as well as high spectral resolution Stokes $I$ and $V$ profiles) to study the relationship between photospheric and chromospheric LOS magnetic fields and detailed properties (e.g., line bisectors, Stokes $V$ asymmetries) of the spectral profiles. There is a connection between magnetic canopies, circumfacular regions and Ca II 8542 \AA\ bisector spans which may explain the observed solar cycle variation of the Sun-as-a-star Ca II 8542 \AA\ bisectors.




Fast DEMs for EIS and AIA

Author(s): Joseph Plowman(1), Charles Kankelborg(1), Petrus Martens(1), Miriam Ritchie(2), Jason Scott(1), Rahul Sharma(3)

Institution(s): (1) Montana State University, Bozeman, MT, USA, (2) University of St Andrews, Scotland, UK, (3) Mohanlal Sukhadia University, Rajasthan, India

Abstract:

We present a method for constructing Differential Emission Measures (DEMs) using data from solar imagers such as EIS and AIA. In its basic form, the method is very fast (approximately one minute per full disk AIA image), although the DEMs obtained can contain regions of moderately negative emission measure (EM). We demonstrate an extension of the method which removes regions of negative EM while closely matching the data. The fidelity of the method is analyzed, its results are compared to those of the PINTofALE MCMC DEM algorithm, and it is applied to a coronal loop observed on April 19, 2011.





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Last Updated on Tuesday, 24 January 2012 13:45