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There are 146 abstracts


Dynamical Processes At Vertical Current Sheets Behind Erupting Flux Ropes

Author(s): Rui Liu

Institution(s): University of Science and Technology of China

Abstract:

We report in this presentation two solar eruptive events, in both of which a vertical current sheet (VCS) is detected in the wake of the erupting flux rope in the SDO/AIA 131~{\AA} passband. Plasma blobs are observed to move along the VCS bidirectionally. In the 2011 March 14 event, the VCS is observed after a nonthermal hard X-ray (HXR) burst which is due to a loop-loop interaction leading up to the ejection of the flux rope, while in the 2012 July 19 event, the VCS is observed following the impulsive acceleration of the erupting flux rope but prior to the onset of a nonthermal HXR/microwave burst. The initial, slow acceleration of the erupting structure is associated with the slow elevation of a thermal looptop HXR source and the subsequent, impulsive acceleration is associated with the downward motion of the looptop source, the latter of which therefore reflects a catastrophic release of magnetic free energy in corona. However, the poor temporal correlation between VCSs and nonthermal HXR/microwave bursts suggest that neither the VCS nor the magnetic islands (i.e., the blobs) in the tearing mode is the primary accelerator for nonthermal electrons emitting HXRs/microwaves. In the 2012 July 19 event, we find that the blobs moving downward within the VCS into the cusp region and the flare loops retracting from the cusp region make a continuous process, with the former apparently initiating the latter. This provides a 3D perspective on reconnections at the VCS and implies a transportation of magnetic twist to the lower atmosphere via Alfv\'{e}n waves. We also identify a dark void which moves within the VCS toward the flare arcade, which suggests that dark voids observed in supra-arcade downflows are also magnetic islands formed within the VCS in the high corona and move with the downward reconnection outflow.




Bi-directional Ejections and Loop Contractions in an Eruptive M7.7 Solar Flare: Evidence of Particle Acceleration and Heating in Magnetic Reconnection Outflows

Author(s): Wei Liu, Qingrong Chen, Vahe Petrosian

Institution(s): (1) Lockheed Martin Solar and Astrophysics Laboratory; (2) Hansen Experimental Physics Laboratory, Stanford University; (3) Department of Physics, Stanford University

Abstract:

Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We report analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI. Bi-directional ejections in forms of plasmoids and contracting cusp-shaped loops originate between an erupting flux rope and underlying flare loops at speeds of typically 200-300 km/s up to 1050 km/s. These ejections are associated with spatially separated double coronal X-ray sources with centroid separation decreasing with energy. The highest temperature is located near the nonthermal X-ray loop-top source well below the original heights of contracting cusps near the inferred reconnection site. These observations suggest that the primary loci of particle acceleration and plasma heating are in the reconnection outflow regions, rather than the reconnection site itself. This supports particle acceleration by turbulence, shocks, and/or collapsing traps associated with reconnection outflows, not by a DC electric field within the reconnection region. In addition, there is an initial ascent of the X-ray and EUV loop-top source prior to its recently recognized descent. The impulsive phase onset is delayed by 10 minutes from the start of the descent, but coincides with the rapid speed increases of the upward plasmoids, the individual loop shrinkages, and the overall loop-top descent, suggestive of an intimate relation of the energy release rate and reconnection outflow speed.




The Coronal Pulse Identification and Tracking Algorithm (CorPITA)

Author(s): Long, David M. (1), Bloomfield, D. Shaun (2), Feeney-Barry, R. (2), Gallagher, Peter T. (2), Pérez-Suárez, David (2,3)

Institution(s): (1) Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK. (2) School of Physics, Trinity College Dublin, Dublin 2, Ireland, (3) Finnish Meteorological Institute, POB 503, 00101 Helsinki, Finland

Abstract:

The Coronal Pulse Identification and Tracking Algorithm (CorPITA) is an automated technique for detecting and analysing "EIT Waves" in data from the Solar Dynamics Observatory (SDO) spacecraft. CorPITA will operate as part of the Heliophysics Event Knowledgebase (HEK), providing unbiased, near-real-time identification of coronal pulses. When triggered by the start of a solar flare, the algorithm uses an intensity profile technique radiating from the source of the flare to examine the entire solar disk. If a pulse is identified, the kinematics and morphological variation of the pulse are determined for all directions along the solar surface. Here, CorPITA is applied to a test data-set encompassing a series of solar flares of different classes from 13-20 February 2011. This allows the effectiveness of the algorithm in dealing with the varied morphology of different eruptions to be characterised. The automated nature of this approach will enable an unbiased examination of "EIT Waves" and their relationship to coronal mass ejections.




Measuring the magnetic field strength of the quiet solar corona using "EIT waves"

Author(s): Long, David M. (1), Williams, David R. (1), Régnier, Stéphane (2), Harra, Louise K. (1)

Institution(s): (1) Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK. (2) Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire, PR1 2HE, UK

Abstract:

Variations in the propagation of globally-propagating disturbances (commonly called "EIT waves") through the low solar corona offer a unique opportunity to probe the plasma parameters of the solar atmosphere. Here, high-cadence observations of two "EIT wave" events taken using SDO/AIA are combined with spectroscopic measurements from Hinode/EIS and used to examine the variability of the quiet coronal magnetic field strength. The combination of pulse kinematics from AIA and plasma density from EIS is used to show that the magnetic field strength is in the range ~2-6G in the quiet corona. The magnetic field estimates are then used to determine the height of the pulse, allowing a direct comparison with theoretical values obtained from SDO/HMI magnetic field using PFSS and local-domain extrapolations. While local-scale extrapolations predict heights inconsistent with prior measurements, the agreement between observations and the PFSS model indicates that "EIT waves" are a global phenomenon influenced by global-scale magnetic field.




EUV Coronal Holes as a Proxy for Open Magnetic Field Regions

Author(s): Lowder, Chris; Qiu, Jiong; Leamon, Robert

Institution(s): Montana State University, Bozeman, MT

Abstract:

Coronal holes are regions marked by a decreased intensity in the extreme ultraviolet and x-ray wavelengths. Associated with regions of open magnetic field, plasma is allowed to escape along open magnetic field lines resulting in a rarefied plasma below. This study seeks to quantify the relationship between boundaries of coronal holes and open magnetic field. Using a combination of STEREO and SDO data in EUV wavelengths, we can provide a full solar surface map of coronal hole boundaries. These boundaries in conjunction with charts of radial magnetic field can be used to calculate open magnetic fluxes. Direct comparison is made with potential magnetic extrapolations as well as a non-potential, magneto-frictional model. There is strong agreement both in the geometry of regions as well as associated magnetic fluxes. These data provide a unique opportunity to study the far side dynamics of coronal holes and open magnetic field evolution.




Coronal and Solar Wind Ion heating by dispersive Alfven waves -- 2.5D hybrid simulations

Author(s): Maneva, Y. (1,2), Ofman, L. (1,2) and Vinas, A. (2)

Institution(s): (1) Catholic University of America, Washington DC, USA; (2) NASA Goddard Space Flight Center, MD, USA

Abstract:

We perform 2.5D hybrid simulations to model the preferential heating and differential acceleration of minor ions as observed by remote sensing in coronal holes and measured in situ in the fast solar wind at various heliospheric distances. We consider a low-beta plasma consisting of fluid electrons, particle-in-cell protons and He++ ions and different spectra of parallel propagating Alfven-cyclotron waves as initial energy source for the ion heating and acceleration. For fixed low wave-numbers the generated wave spectrum generally shifts towards higher frequencies in multi-species plasma. This effect is further enhanced when differential streaming is present due to the expected preferential acceleration of heavy ions in coronal holes. We use the results from the cold plasma linear theory to initialize the nonlinear 2.5D hybrid simulations and compare the resulting ion heating, temperature anisotropies and differential streaming when the initial wave spectra belongs to the alpha-cyclotron and the proton-cyclotron dispersion branches, with and without initial relative drifts, and study the nonlinear 2D effects, extending our previous 1D hybrid studies. Finally, we investigate the effect of a gradual solar wind expansion, consider its influence on the wave-particle interactions and discuss its implications for non-adiabatic perpendicular cooling for both ion species.




Approach to Integrate Global-Sun Models of Magnetic Flux Emergence and Transport for Space Weather Studies

Author(s): Nagi Nicolas Mansour, NASA, Moffett Field, CA; and A. Wray, P. Mehrotra, C. Henney, N. arge, C. Manchester, H. Godinez, J. Koller, A. Kosovichev, P. Scherrer, J. Zhao, R. Stein, T. Duvall, and Y. Fan

Institution(s): NASA Ames Research Center

Abstract:

The Sun lies at the center of space weather and is the source of its variability. The primary input to coronal and solar wind models is the activity of the magnetic field in the solar photosphere. Recent advancements in solar observations and numerical simulations provide a basis for developing physics-based models for the dynamics of the magnetic field from the deep convection zone of the Sun to the corona with the goal of providing robust near real-time boundary conditions at the base of space weather forecast models. The goal is to develop new strategic capabilities that enable characterization and prediction of the magnetic field structure and flow dynamics of the Sun by assimilating data from helioseismology and magnetic field observations into physics-based realistic magnetohydrodynamics (MHD) simulations. The integration of first-principle modeling of solar magnetism and flow dynamics with real-time observational data via advanced data assimilation methods is a new, transformative step in space weather research and prediction. This approach will substantially enhance an existing model of magnetic flux distribution and transport developed by the Air Force Research Lab. The development plan is to use the Space Weather Modeling Framework (SWMF) to develop Coupled Models for Emerging flux Simulations (CMES) that couples three existing models: (1) an MHD formulation with the anelastic approximation to simulate the deep convection zone (FSAM code), (2) an MHD formulation with full compressible Navier-Stokes equations and a detailed description of radiative transfer and thermodynamics to simulate near-surface convection and the photosphere (Stagger code), and (3) an MHD formulation with full, compressible Navier-Stokes equations and an approximate description of radiative transfer and heating to simulate the corona (Module in BATS-R-US). CMES will enable simulations of the emergence of magnetic structures from the deep convection zone to the corona. Finally, a plan will be summarized on the development of a Flux Emergence Prediction Tool (FEPT) in which helioseismology-derived data and vector magnetic maps are assimilated into CMES that couples the dynamics of magnetic flux from the deep interior to the corona.




Modeling small-scale flux emergence from the Convection Zone into the Corona

Author(s): Juan Martinez-Sykora

Institution(s): Lockheed Martin Solar & Astrophysics Lab

Abstract:

High resolution telescopes reveal small-scale flux in the photosphere and roughly 20% of these events seem to reach and impact the chromosphere. As a result of such flux emergence, reconnection with the ambient field or other processes that do not necessarily involve reconnection but nevertheless impact the chromosphere and lower corona may occur. I am going to present recent simulations that show small-scale flux emergence in a computational domain that captures the upper-convection zone, photosphere, chromosphere and lower corona. As we will see, small scale activity is strongly dependent on the physics that dominate in the various layers of the atmosphere, such as thermo-dynamics, radiative transfer in the photosphere and thermal conduction along field lines in the corona (we use for that Bifrost). In addition, small scale activity is also dependent on the ambient field which changes rapidly with height both in strength and topology through the different layers of the solar atmosphere. Some of these small-scale events erupts into the atmosphere destabilizes the pre-existing magnetic field and drives it to new configurations.




Understanding Solar Eruptive Events

Author(s): Mason, James P. (1); Hock, Rachel A. (2); Woods, Thomas N. (1); Thompson, Barbara J. (3); Webb, David F. (4); Caspi, Amir (1)

Institution(s): (1) LASP / University of Colorado, Boulder; (2) Kirtland AFB; (3) NASA GSFC; (4) Boston College

Abstract:

Coronal dimming is studied using data from the EUV Variability Experiment (EVE) and the Atmospheric Imaging Assembly (AIA), both onboard the Solar Dynamics Observatory (SDO). Dimming can be caused by a number of physical processes, including mass loss (e.g. coronal mass ejections), obscuration of bright features (e.g. flaring loops) by dark features (e.g. filament eruptions), global scale waves, and changes of temperature in the emitting plasma. Each of these processes have unique spectral signatures, which EVE and AIA are well suited to observe. We are building a method for isolating the signature indicative of mass loss, which is thought to be correlated with the kinetics of coronal mass ejections. Our analysis of the M9 flare on August 4, 2011 are shown as an example of all four of these physical processes and their spectral signatures.




Chromospheric Waves and Oscillations in Sunspots

Author(s): R. A. Maurya and J. Chae

Institution(s): Astronomy Program, Seoul National University, Seoul 151-747, Korea

Abstract:

We studied the chromospheric oscillations in and around a sunspot of the active region NOAA 11242 using high spectral and spatial resolution observations in the spectral lines H$\alpha$ and Ca II 8542\AA~obtained from the Fast Imaging Solar Spectrograph (FISS) of 1.6 meter New Solar Telescope (NST) at Big Bear Solar Observatory. A suitable bisector method is applied to the spectral observations, to construct the chromospheric Doppler Velocity maps. Time series analysis of Doppler maps, in both the spectral bands, revealed enhanced high frequency oscillations inside the umbra of the sunspot. The frequency of oscillations gradually decreases from the umbra to outward. We have found clear evidence of two boundaries for the peak power frequency transformation, one of which occurs close to the umbral and penumbral boundary, and the other near the penumbral and super-penumbral boundary of the sunspot. The oscillation power is found to be associated with magnetic field strength and inclination, although they showed different relationships in different frequency bands.





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Last Updated on Tuesday, 29 March 2011 09:36