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There are 123 abstracts


PSF Correction for AIA Using Lunar Limb Data

Author(s): Craig DeForest and Bala Poduval

Institution(s): Southwest Research Institute

Abstract:

PSF correction is important for myriad inferences that can be made from EUV imagery, including heating distribution and impulsivity; DEM; and wave amplitude measurements. Using lunar limb and solar flare data, we have prepared model PSF functions to describe the scattering performance of the six EUV channels of AIA. We have not attempted to model the core of the PSF (focus), only its wings (stray light) of each channel. We find that, typically, about half of the scattered light is in the diffuse component of the PSF model, although there is significant variation across the channels. The diffraction component of the PSF was determined by direct inspection of the diffraction pattern from flaring images, with some a priori knowledge of the physics and nature of the diffraction grid (following the methods of Gburek on TRACE and more recently, Cheung on AIA); and the diffuse component was determined by iteratively fitting imaging performance around the lunar limb in eclipse images, with the assumption that the Moon is dark in the EUV. We present the PSFs and summary data, along with a preliminary comparision with the diffraction-only models developed at SAO, and describe where to get both the quantitative PSF models and their inverses (for direct deconvolution) in FITS format.




Topological tools for the analysis of active region filament stability

Author(s): Edward E. DeLuca (1), A. Savcheva (1,2), A. van Ballegooijen (1), E. Pariat (3), G. Aulanier (3), Y. Su (1)

Institution(s): (1) CfA, (2) Boston University, (3) Observatoire de Paris

Abstract:

The combination of accurate NLFFF models and high resolution MHD simulations allows us to study the changes in stability of an active region filament before a CME. Our analysis strongly supports the following sequence of events leading up to the CME: first there is a build up of magnetic flux in the filament through flux cancellation beneath a developing flux rope; as the flux rope develops a hyperbolic flux tube (HFT) forms beneath the flux rope; reconnection across the HFT raises the flux rope while adding addition flux to it; the eruption is triggered when the flux rope becomes torus-unstable. The work applies topological analysis tools that have been developed over the past decade and points the way for future work on the critical problem of CME initiation in solar active regions. We will discuss the uses of this approach, current limitations and future prospects.




The impact of the chromosphere on magnetic fields: field extrapolations

Author(s): DeRosa, Marc L.

Institution(s): Lochkeed Martin Solar and Astrophysics Laboratory, Palo Alto, CA USA

Abstract:

Because knowledge of the coronal magnetic field is the key to gaining an understanding of the dynamics of the coronal plasma, efforts to measure or infer coronal magnetic fields have received much attention. In particular, many techniques for extrapolating the coronal magnetic field from photospheric boundary data have been developed, especially as magnetic field data at increasingly higher resolution in space and time as well as vector magnetogram inversions have become more readily available. However, it has become apparent that some extrapolation methods encounter difficulties, as the resulting extrapolations often do not provide reliable estimates of important coronal properties such as free energy and relative helicity. In this talk, we review some of the various difficulties associated with magnetic field extrapolations based on photospheric magnetograms, and discuss likely causes and solutions. We will particularly elucidate the impact of the chromospheric layer on such extrapolations, which is likely impacting the reliability of the extrapolation process as it lies between the region sampled by the boundary data [the photosphere] and the region of interest [the corona].




NASA SDO - Solar & Space Weather Education via Social Media

Author(s): Romeo Durscher, Martha Wawro

Institution(s): Stanford University, Adnet Systems, Inc;

Abstract:

NASA has embraced social media as a valuable tool to communicate the activities of the agency in fulfillment of its mission. Team SDO continues to be on the forefront of using social media in a very engaging and interactive way and share mission information, solar images and space weather updates via a variety of social media platforms and outlets. We will present the impact SDO's social media strategy has made, including follower, friends and fan statistics from Twitter, Facebook, YouTube, Google+ and other outlets. We will discuss the various social media outlets and the techniques we use for reaching and engaging our audience. Effectiveness is measured through the use of various automatically-gathered statistics and level of public engagement. Of key importance to effective social media use is having access to scientists who can quickly respond to questions and express their answers in meaningful ways to the public. Our presentation will highlight the importance of scientist involvement and suggest ways for encouraging more scientists to support these efforts. We will present some of the social media plans for 2012 and discuss how we can continue to educate, inform, engage and inspire.




Electric Fields and Poynting Fluxes from Vector Magnetograms

Author(s): G. H. Fisher, B. T. Welsch, W. P. Abbett

Institution(s): University of California, Berkeley

Abstract:

The availability of vector-magnetogram sequences with sufficient accuracy and cadence to estimate the temporal derivative of the magnetic field allows us to use Faraday’s law to find an approximate solution for the electric field in the photosphere, using a Poloidal–Toroidal Decomposition (PTD) of the magnetic field and its partial time derivative. Without additional information, however, the electric field found from this technique is under-determined – Faraday’s law provides no information about the electric field that can be derived from the gradient of a scalar potential. Here, we show how additional information in the form of line-of-sight Doppler-flow measurements, and motions transverse to the line-of-sight determined with ad-hoc methods such as local correlation tracking, can be combined with the PTD solutions to provide much more accurate solutions for the solar electric field, and therefore the Poynting flux of electromagnetic energy in the solar photosphere. Reliable, accurate maps of the Poynting flux are essential for quantitative studies of the buildup of magnetic energy before flares and coronal mass ejections.




On the Magnetic-Field Diagnostics Potential of SDO/HMI

Author(s): B.Fleck (1), K. Hayashi (2), R. Rezaei (3), N. Vitas (4), R. Centeno (5), M. Cheung (6), S. Couvidat (2), C. Fischer (1), O. Steiner (3), T. Straus (7), B. Viticchie (1)

Institution(s): (1) ESA, (2) Stanford Univ, (3) KIS, (4) SRON, (5) HAO, (6) LMSAL, (7) INAF/OAC

Abstract:

The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) is designed to study oscillations and the magnetic field in the solar photosphere. It observes the full solar disk in the Fe I absorption line at 6173 Å. We use the output of three high-resolution 3D, time-dependent, radiative magneto-hydrodynamics simulations (two based on the MURaM code, one on the CO5BOLD code) to calculate Stokes profiles Fi(λ,x,y; i=I, V, Q, U) for the Fe I 6173 Å line for snapshots of a sunspot, a plage area and an enhanced network region. Stokes filtergrams are constructed for the 6 nominal HMI wavelengths by multiplying the Stokes profiles with a representative set of HMI filter response functions. The magnetic field vector B(x,y) and line-of-sight Doppler velocities V(x,y) are determined from these filtergrams using a simplified version of the HMI magnetic field processing pipeline. Finally, the reconstructed magnetic field B(x,y) and line-of-sight velocity V(x,y) are compared to the actual magnetic field B0(x,y,z) and vertical velocity V0(x,y,z) in the simulations.




State of the art single fluid MHD numerical modeling of the coupled solar atmosphere

Author(s): Boris Gudiksen

Institution(s): Instute for theoretical astrophysics, University of Oslo

Abstract:

Modeling the solar atmosphere has for a long time been known to be a very complex problem. The wealth of observational features identified in solar observations have multiplied with increasing spatial, temporal and spectral resolution. To explain the high quality of space and ground based observations, models must be very sophisticated and be able to treat a number of physical regimes, where the dominating terms in the equations change drastically. Numerical simulations are now able to explain some, but certainly not all of the observed features. The numerical complexity of solving the equations governing the physics of the solar atmosphere is very high, and a number of different numerical techniques must be used in order to create a coherent picture of the connected solar atmosphere. We are now at a level where simulations have to include a much larger range in vertical extend than has been previously done. The wealth of numerical problems arising when doing so has lead to a number of numerical codes that are specialized to deal with a specific problem, and which now are being augmented to handle a larger range of problems. Hopefully with time we will have a number of numerical codes that are sophisticated enough to deal reliably with the whole solar atmosphere. I will give a review of some the codes that have been able to produce results from a fully connected solar model.




Post-Flare Half-Loops: What are They?

Author(s): Guidoni, Silvina E. (1), McKenzie, David E. (1), Longcope, Dana W. (1)

Institution(s): Montana State University - Bozeman

Abstract:

The M1.4 flare of Jan 28, 2011 has a remarkable resemblance to the famous Tsuneta flare of 1992. It was observed with Hinode/XRT, SDO/AIA, and STEREO (A)/EUVI, giving us higher resolution, greater temperature coverage, and stereoscopic views of this iconic structure. The high temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the post-flare arcade. They also show that loops that are successively connected to this tower develop a density increase in one of their legs that can reach 4 times the density value of the other leg, giving the appearance of “half loops”. These jumps in density last for an extended period of time. On the other hand, XRT filter ratios suggest that temperature is approximately uniform along the entire loop. XRT filter-ratio density maps corroborate that the brighter legs have higher density than the rest of the loop. The tower is a localized density increase at even higher densities than the brighter side of the loop. This may correspond to a shock at the top of the loops. We use STEREO images to show that the half loop brightening is not a line-of-sight projection effect of the type suggested by Forbes & Acton.




Overview of simulations and observations of the coupling between solar regions

Author(s): Viggo Hansteen

Institution(s): Institute of Theoretical Astro., Univ. of Oslo

Abstract:

We will discuss simulations and observations of the outer solar atmosphere, in particular the chromosphere, transition region and corona, as a coupled system. Focus will be on how the atmosphere is energized, how mass and energy is transferred between various regions, and what the mechanisms are that couple the various regions. Current simulations are described with an eye towards the physics included, and a discussion of what is missing, e.g. the topology of magnetic fields studied, large physical scales, non-equilibrium ionization and generalized Ohm's law. The impact of the physical assumptions is assessed. Specific synthetic observables from the IRIS instrument are presented and their diagnostic value is discussed.




Photosphere-Corona Connection in Active-Region Plage

Author(s): H. Hara

Institution(s): National Astronomical Observatory of Japan

Abstract:

We discuss the relationships between the temperature of coronal loops and photospheric magnetic properties at their footpoints in an active-region plage from observations by Hinode. The motion of photospheric magnetic fields is tracked by the correlation tracking of SOT FG Stokes-V maps to estimate the photospheric horizontal velocity. We find that the horizontal velocity is anti-correlated with the filling factor of photospheric magnetic fields estimated from the SOT SP data. It is confirmed from high-resolution observations by Hinode that the footpoints of hot (warm) coronal loops in X-ray (EUV) observations are rooted at low (high) magnetic filing factor regions within the plage. The distribution of energy flux to the corona in the plage is calculated from observations according to a model in Katsukawa & Tsuneta (2005). The distribution appears to explain the footpoint position of hot and warm loops.





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Last Updated on Tuesday, 24 January 2012 13:45