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There are 146 abstracts


Collective Solar Behavior

Author(s): ALAN TITLE, KAREL SCHRIJVER, MARC DEROSA

Institution(s): LOCKHEED MARTIN ATC

Abstract:

The Atmospheric Imaging Assembly (AIA) on the Solar Dynamic Observatory (SDO) together with the Helioseismic and Magnetic Imager (HMI) and the Extreme Ultraviolet Variability Experiment (EVE) allow observations of the entire Sun from 6000 K to 20,000,000 K with arcsecond resolution and a 12 second cadence (AIA), obtain doppler and continuum images at a 45 second cadence and Line of Sight and vector magnetograms (HMI) every few minutes, and integrated solar spectra from 1 to 100 nm on a 2 second cadence (EVE) 24/7.  Because of the enhanced thermal and temporal coverage and the high dynamic range available with AIA, it has been able to discovery associated behavior associated with extreme solar events that are apparently driven by the rapid expansion of magnetic structures.  The extent of the events are recognized by using co-temporal STEREO data.  The rapidly expanding magnetic structures, speeds between 500 and 2000 km/s, can apparently trigger filament eruptions, CME’s, and other flares.  These “triggered” events are sometimes larger that the initial disturbance.  The remote triggering makes flare prediction based upon ONLY local energy build up models less valuable, but suggests that with proper coverage prediction of solar events with potential for Earth impact may be made more reliable.  Movies of sample events discovered in AIA together with STEREO data will be shown.




Characterizing the Magnetic Topology of Solar Eruptions

Author(s): Titov, Viacheslav S., Mikic, Zoran (1), Torok, Tibor (1), Linker, Jon A. (1), Lionello, Roberto (1), Riley, Pete (1)

Institution(s): (1) Predictive Science, Inc., California, USA

Abstract:

Numerical MHD simulations of solar eruptions have made it possible to model the evolution of magnetic configurations with considerable realism. However, a comprehensive understanding of these complex configurations requires the development of sophisticated techniques to analyze the three-dimensional magnetic field structure. We describe the current state of the art in this kind of analysis, with detailed illustrations from on-going projects at Predictive Science. Separatrix surfaces and quasi-separatrix layers form a structural skeleton of magnetic configurations by dividing them into multiple components with a simple topology. We discuss the principles and capabilities of our techniques for analyzing the structural skeletons in erupting configurations. In particular, we show how these techniques allow one: (1) to identify erupting and non-erupting strands of the flux ropes; (2) to determine the global topological flux cells in which such flux ropes reside, and how they interact in successive eruptions; (3) to calculate evolving magnetic fluxes for each component of these configurations; (4) to relate certain structural features to observational features, such as H-alpha flare ribbons, extreme-ultraviolet dimmings, and X-ray sigmoids in solar eruptions. The ability to compare our results with observations enables us to verify the accuracy of the MHD models and to understand how the coronal magnetic field opens during eruptions.




Helioseismic Detection of the Pre-emerging Magnetic Flux in the Shallow Convection Zone

Author(s): S. Toriumi, S. Ilonidis, T. Sekii, and T. Yokoyama

Institution(s): University of Tokyo, Stanford University, National Astronomical Observatory of Japan

Abstract:

We detect the rising magnetic flux in the shallower convection zone of the Sun by observing acoustic power reduction, and evaluate its rising speed. Here we aim to reveal the rising speed of the magnetic flux in the shallow convection zone, before the active region are created. We apply six different Fourier filters to the Doppler data of NOAA AR 10488 taken by SOHO/MDI, to detect the reduction of acoustic power at six different depths from −15 to −2 Mm. The filtered powers show reductions before the start of flux appearance at the visible surface. The start times of these reductions show a rising trend, first at several km/s in a depth range of 15–10 Mm, then ∼1.5 km/s at 10–5 Mm, and finally at ∼0.5 km/s at 5–2 Mm. If we assume that the power reduction is actually caused by the rising magnetic flux, the rising rate of the order of 1 km/s is well in accordance with previous observations and numerical simulations. Moreover, the gradual deceleration supports our simulations and theoretical model that the rising flux slows down in the uppermost convection zone, just before its further emergence into the solar atmosphere.




M6.6 Flare in NOAA AR 11158: Formation of the Flare-triggering Region

Author(s): S. Toriumi, Y. Iida, Y. Bamba, K. Kusano, and S. Inoue

Institution(s): University of Tokyo, Nagoya University, Kyung Hee University

Abstract:

In this study, we investigate the formation process of the magnetic field structure in NOAA AR 11158 from its birth to the M6.6 flare, which occurred at 17:28 UT on 2011 February 13. AR 11158, which consisted of two major emerging fluxes, showed prominent activities including one X-class and some M-class flares. Here we report that the magnetic configuration that triggered the M6.6 flare is consistent with the Reversed-Shear (RS) type structure, one scenario suggested by Kusano et al. (2012). We used CaH images and spectropolarization data obtained by Hinode/SOT, 3D magnetograms by SDO/HMI to study the formation process of this flare-triggering region. We found that this region was initially built through the continuous accumulation of small-scale emerging bipoles. In CaH images, the emerging bipole collided with the pre-existing field and, through magnetic reconnection, they created a new loop arching over the both polarities, which had an RS configuration. The M-flare occurred a few hours later above this region.




Ring-Diagram Analysis of Active Regions using HMI and AIA data

Author(s): Tripathy, S.C (1), Jain, K. (1), Howe, R. (2), Bogart, R. (3), Basu, S. (4), Hill, F. (1)

Institution(s): (1) National Solar Observatory, Tucson, USA (2) University of Birmingham, Birmingham, UK, (3) Stanford University, CA, USA, (4) Yale University, CT, USA

Abstract:

With the launch of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, high-resolution observations of the Sun are available in Doppler velocity and continuum intensity. In addition, data is also available from the Atmospheric Imaging Assembly in 160 and 170 nm bands, which are useful for helioseismic studies. Here we use the ring-diagram technique and analyze six active regions, simple and complex, observed simultaneously in different wavelengths, and focus on the characteristics of high-degree modes e.g. frequencies and asymmetry parameters. We further investigate the dependence of sub-surface flows on the choice of the observables to comprehend the effect of the observing heights, which may be important in multi-wavelength local helioseismic studies.




Heating frequency in active region cores as observed in AIA Fe XVIII images

Author(s): Ugarte-Urra, I (1), Warren H.P. (2)

Institution(s): (1) George Mason University, (2) Naval Research Laboratory

Abstract:

We present a study of the frequency and duration of brightenings in the core of solar active regions as observed in the Fe XVIII line component of AIA/SDO 94 A filter images. The Fe XVIII emission was isolated by removing the "warm" emission contribution using as proxy the emission from the AIA 193 and 171 channels. We examined the evolution of loop in cores of several active regions that span a wide range of total magnetic field strengths and at various stages of evolution. Using a newly developed event detector algorithm we find that the typical frequency of occurrence of brightness enhancements is in the order of tens of minutes. We then use those values to evaluate different scenarios of heating frequency using 1D hydrodynamical models of loops.




Rescaling MDI Magnetic Data to Match HMI

Author(s): Upton , Lisa A. (1), Hathaway , David H. (2)

Institution(s): Vanderbilt, Nashville, TN (1), UAH, Huntsville, AL (1), and NASA/MSFC (2)

Abstract:

Comparison of Helioseismic and Magnetic Imager (HMI) and Michelson Doppler Investigation (MDI) magnetograms reveals a systematic difference in the field strengths as a function of center-to-limb distance and magnetic field strength itself (Liu et al., 2012). While MDI data exhibits an annual variation at polar latitudes, HMI does not. The more capable HMI uses 6 samples across the spectral line, rather than 2 to obtain the magnetic field. Therefore, HMI data is expected to more accurately represent the Sun and the MDI magnetic data should be rescaled to match HMI. Here, the HMI magnetograms have been resampled at the MDI resolution of 1024x1024. The magnetograms were then co-aligned by cross-correlating blocks of pixels from each image to identify and correct differences in orientation and magnification. The ratio of HMI magnetic field to MDI magnetic field was obtained for each pixel. This was repeated for ~650 cotemporal HMI-MDI magnetogram. The ratios were then averaged and plotted as a function of center-to-limb distance and magnetic field strength. Here, we present a function f(|B|, cos




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

Author(s): Wendy Van Norden, Martha Wawro

Institution(s): ADNET Systems Inc/NASA GSFC

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.




Helicity Injection by the Shearing Motion of Fluxes in Relation to Flares and Coronal Mass Ejections

Author(s): Vemareddy, P. (1), Ambastha, A. (1), Maurya, R.A. (2), Chae, J. (2)

Institution(s): (1) Physical Research laboratory, (2) Seoul National University

Abstract:

An investigation of helicity injection by photospheric shear motions is carried out for two active regions (ARs), NOAA 11158 and 11166, using line-of-sight magnetic field observations obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We derived the horizontal velocities in the ARs from the differential affine velocity estimator (DAVE) technique. Persistent strong shear motions at maximum velocities in the range of 0.6–0.9 km s^{−1} along the magnetic polarity inversion line and outward flows from the peripheral regions of the sunspots were observed in the two ARs. The helicities injected in NOAA 11158 and 11166 during their six-day evolution period were estimated as 14.16x10^{42} Mx^2 and 9.5×10^{42} Mx^2, respectively. The estimated injection rates decreased up to 13% by increasing the time interval between the magnetograms from 12 minutes to 36 minutes, and increased up to 9% by decreasing the DAVE window size from 21×18 to 9×6 pixel2, resulting in 10% variation in the accumulated helicity. In both ARs, the flare-prone regions (R2) had inhomogeneous helicity flux distribution with mixed helicities of both signs and coronal mass ejection (CME) prone regions had almost homogeneous distribution of helicity flux dominated by a single sign. The temporal profiles of helicity injection showed impulsive variations during some flares/CMEs due to negative helicity injection into the dominant region of positive helicity flux. A quantitative analysis reveals a marginally significant association of helicity flux with CMEs but not flares in AR 11158, while for the AR 11166, we find a marginally significant association of helicity flux with flares but not CMEs, providing evidence of the role of helicity injection at localized sites of the events. These short-term variations of helicity flux are further discussed in view of possible flare-related effects. This study suggests that flux motions and spatial distribution of helicity injection are important to understanding the complex nature of the magnetic flux system of the AR, and how it can lead to conditions favorable for eruptive events.




Understanding Coronal Heating by Comparing SDO/AIA Observations with Modeled Light Curves

Author(s): Nicholeen M. Viall & James A. Klimchuk

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

Abstract:

An important signature of nanoflare heated coronal plasma is the sudden appearance of the plasma at hot temperatures, followed by a comparatively slow cooling and draining phase. This is due to the impulsive nature of nanoflare heating and the heat conduction and mass exchange between the corona and chromosphere. Identifying such nanoflare signatures is complicated by the fact that the solar corona is optically thin: many thousands of flux tubes which are heated completely independently are contributing to the total emission along a given line of sight. One approach has been to analyze isolated features such as coronal loops; however the diffuse emission between and around isolated features contribute as much, if not more to the EUV coronal emission, and therefore is crucial to the understanding of coronal heating. In this study we move beyond isolated features and analyze all of the emission in an entire active region and quiet Sun area. We investigate SDO/AIA light curves, systematically identifying nanoflare signatures. We compare the observations with a model of the corona as a line-of-sight integration of many thousands of completely independently heated flux tubes. We consider that the emission from these flux tubes may be due exclusively to impulsive nanoflare bursts, quasi-steady heating, or a mix of both, depending on the cadence of heat release. We demonstrate that despite the superposition of randomly heated flux tubes, different distributions of nanoflare cadences produce distinct signatures in light curves observed with multi-wavelength and high time cadence data, such as those from SDO/AIA. We find that much of the solar corona is heated through impulsive nanoflares.





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Last Updated on Tuesday, 29 March 2011 09:36