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There are 146 abstracts


CHIANTI 7.1: a new database release for SDO data analysis

Author(s): Young, P.R. (1), Landi, E. (2), Del Zanna, G. (3), Dere, K.P.(1), Mason, H.E. (3

Institution(s): (1) George Mason University, VA, USA, (2) University of Michigan, MI, USA, (3) University of Cambridge, Cambridge, UK

Abstract:

Version 7.1 of the CHIANTI atomic database was released in October 2012 and contains a number of improvements to better model data returned by the AIA and EVE instruments on board SDO. Specifically the models for the important iron ions Fe VIII to Fe XIV have been greatly expanded, yielding many thousands of new transitions in the 50-170 angstrom range that enable the irradiance spectra obtained by EVE to be modeled more accurately. A lack of available atomic data meant that the AIA 94 angstrom channel was not well modeled at low temperatures in earlier versions of CHIANTI. New data for Fe VIII, Fe X and Fe XIV added to CHIANTI 7.1 give important contributions to the channel and greatly improve comparisons with theory.




Studies of the dynamics and energetics of cool plasma ejections into the corona

Author(s): Zacharias, Pia (1), Bingert, Sven (2), Peter, Hardi (2)

Institution(s): (1) ISSI, Bern, Switzerland, (2) MPS, Katlenburg-Lindau, Germany

Abstract:

The corona is highly dynamic and shows transient events on various scales in space and time. Most of these features are related to changes in the magnetic field structure or impulsive heating caused by the conversion of magnetic to thermal energy. We are applying three-dimensional magnetohydrodynamic models in order to investigate the structure and dynamics in the upper solar atmosphere above a small active region. Emission line spectra are synthesized from the model and compared to spectra and images observed by current space-based instruments, such as the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory. We investigate mass and energy flows between the solar chromosphere and corona and discuss possible scenarios for a mass cycle between the lower and upper solar atmosphere. In particular, we have studied the processes that lead to the formation and ejection of a confined plasma ejection into the solar corona. A description of the nature of this particular feature will be presented which is found to be a hydrodynamic phenomenon triggered by a heating event above the chromosphere. A detailed analysis of 1D coronal loop models has been performed to understand how the plasma responds to a heating pulse. The results confirm the formation mechanism of the blob observed in the 3D model. This raises the question if other small-scale ejection features seen on the Sun could also be based on hydrodynamic processes instead of being plasmoid-type phenomena as it is usually assumed.




Evidences on the Existence of Magnetic Flux Rope Before and During a Solar Eruption

Author(s): Jie Zhang, Xin Cheng, Kai Liu

Institution(s): George Mason University

Abstract:

We report the observational evidences from the advanced SDO observations that magnetic flux ropes exist before and during solar eruptions. The solar eruption is defined as coronal mass ejection, whether or not associated with a solar flare. Magnetic flux ropes are directly observed as hot EUV channels as seen in the hot AIA 131 (10 MK) and/or AIA 94 (6.4 MK) passbands, but are absent in cool AIA passbands. The fact that flux ropes are only seen in hot temperatures explains their evasion of detection from previous EUV observations, such as SOHO/EIT, TRACE and STEREO/EUVI. The hot channel usually appears as a writhed sigmoidal shape and slowly rises prior to the onset of the impulsive acceleration as well as the onset of the flare. The hot channel transforms into a CME-like semi-circular shape in a continuous way, indicating its trapping or organization by a coherent magnetic structure. The dynamic and thermal properties of flux ropes will also be presented. We further discuss the critical role of flux ropes in CME initiation and subsequent acceleration, in light of contrasting the standard eruptive flare models.




Solar-cycle variation of helicity characters

Author(s): Zhang M. (1), Zhao J.W. (2), Miesch M. (3)

Institution(s): (1) National Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012, China; (2) W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA; (3) High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307, USA

Abstract:

We present results of our recent study on the solar-cycle variation of magnetic helicity, current helicity and kinematic helicity. We first show that hemispheric helicity sign rule is observed on the photosphere and shows solar-cycle variation. Strong and weak magnetic fields show opposite current helicity signs in some active regions and this property also has a solar-cycle variation. Then we use a convective Babcock-Leighton dynamo model to show that these observed solar-cycle variations are also evident in the model, with the usual hemispheric helicity sign rule better preserved in magnetic helicity density than that of current helicity. And finally we show that both in the dynamo model and by helioseismology observation no solar-cycle variation of kinematic helicity is present. These results, from SP/Hinode and HMI/SDO observations, give constraints on the mechanism of helicity production. These results can also be used to constrain dynamo models.




Recent Local Helioseismology Results from SDO/HMI

Author(s): Junwei Zhao, R.S.Bogart, A.G.Kosovichev, T.L.Duvall,Jr., Thomas Hartlep

Institution(s): HEPL, Stanford University

Abstract:

Since the launch of Solar Dynamics Observatory, the Helioseismic and Magnetic Imager has accumulated 2.5 years of continuous observations. Using time-distance helioseismology, we have obtained new results on both global and local scales. By analyzing the first two years' observations, we were able to detect the equator-ward meridional flow at a depth of around 70 Mm, and detect the existence of a second meridional circulation below about 120 Mm. This new profile of interior meridional flow will pose challenges to the current dynamo models. At the shallower depth, we studied the temporal evolution of zonal flows, as well as the residual meridional flow, which was obtained by subtracting an averaged meridional flow profile. We found that both quantities showed strong hemispherical asymmetries. On local scales, we studied subsurface flows inside active regions and supergranules, as well as the potential links between solar flares and these subsurface dynamics.




Highlights of significant space weather events in 2012

Author(s): Yihua Zheng and NASA/GSFC SWRC team

Institution(s): NASA/GSFC

Abstract:

As solar maximum is expected in 2013, solar activities have been on the rise in 2012 in comparison to 2010 and 2011. In this presentation, we will provide an overview of space weather events in 2012 and highlight a few significant ones in terms of SEP (Solar Energetic Particles) radiation storms (due to solar energetic particles) and geomagnetic storms. In particular,  the 7 March 2012 event and the 12 July 2012 resulting in both SEP enhancement and a major geomagnetic storm, the first GLE event in 17 May 2012, and the remarkable 23 July 2012 event will be discussed in detail.  Characteristics and comparisons of SEP events near Earth, at STEREO A and STEREO B locations will be given. Challenges in forecasting space weather events will also be discussed. 





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Last Updated on Tuesday, 29 March 2011 09:36