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Submitted Abstracts

There are 146 abstracts


Tomographic reconstructions of large scale coronal structures

Author(s): C. Guennou, F. Auchère, D. Seaton, A. Canou, N. Barbey, K. Bocchialini

Institution(s): Institut d'Astrophysique Spatiale/CNRS

Abstract:

Classical plasma diagnostic techniques suffer from the line of sight (LOS) integration problem, which can confuse structures to the point that measurements crucial to the understanding of coronal physics are difficult to interpret. Tomography provides one way of understanding the LOS content, giving important insights on the morphology and physical properties of the coronal structures. Large scale, long-lived, arch-like structures are observed in the field of view of EUV telescopes at mid-latitudes, most notably in the 174 nm passband. In the present work, we use tomographic inversions of the solar corona the 3D morphology of these structures. We focus on a 28 days period of data from July/August 2012 during which some of these features were observed up to 1.7 Rsol by the SWAP/PROBA2 telescope. Additional multi-wavelength observations in the 6 bands of AIA/SDO are used to derive the corresponding 3-D maps of electron density and temperature. The results are then compared with global magnetic field extrapolations. We conclude by proposing an interpretation of the morphology of these structures as seen in EUV images.




Spatiotemporal scaling of the photospheric magnetic field in the active region AR11158

Author(s): Guerra, Jordan (1,2); Pulkkinen, Antti (1,2); Uritsky, Vadim (1,2); Yashiro, Seiji; Davila, Joe (2)

Institution(s): (1) Catholic University of America, Washington DC. (2) NASA GSFC, Greenbelt, MD.

Abstract:

Spectral analysis of the multiscale photospheric magnetic field in solar active regions requires high spatial and temporal resolution of the data in order to resolve small and rapidly varying magnetic structures. The Helioseismic and Magnetic Imager (HMI) on board the SDO spacecraft provides high quality imaging data which can be used to extract detailed spectral information on solar dynamics. In this talk, we analyze an extensive set of line-of-sight SDO HMI magnetograms corresponding to the active region NOAA AR 11158, between Feb. 10 and 19, 2011. During this time period, a major X-class flare (Feb. 15) and a few M-class flares were observed. We study the spatial and temporal behavior of the magnetograms by measuring the power-law exponents of the magnetic field power spectra as a function of the Fourier wavenumber and frequency, correspondingly. Our results show that the joint time evolution of these scaling indices are an informative measure of solar magnetic complexity providing a new insight into the turbulent state of the photospheric magnetic field. The behavior of the magnetic spectral indices is compared with the dynamics of the coronal emission from the same active region as observed at two AIA wavelengths (094 Å and 193 Å) in the search of new precursors of flaring activity.




Temperature and Electron Density Diagnostics of a Candle-Flame Shaped Flare. Asymmetric Reconnection Evidence

Author(s): Silvina E. Guidoni (1), David E. McKenzie (2), Dana W. Longcope (2), Joseph E. Plowman (2), Keiji Yoshimura (2)

Institution(s): (1) NASA Goddard Space Flight Center, (2) Montana State University - Bozeman

Abstract:

Candle-flame shaped flares are archetypical structures that represent indirect evidence of magnetic reconnection. For long-lived events, most of their observed features can be explained with the classic magnetic reconnection model of solar flares, the CSHKP model. A flare resembling 1992 Tsuneta's famous candle-flame flare occurred on January 28 2011; we present its temperature and electron density diagnostics. This flare was observed with Hinode/XRT, SDO/AIA, and STEREO (A)/EUVI, resulting in high resolution, broad temperature coverage, and stereoscopic views of this iconic structure. Our XRT filter-ratio temperature and density maps corroborate the general reconnection scenario. 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, a feature that has been observed in other long duration events. This tower is a localized density increase, as shown by our XRT electron density maps. Despite the extensive work on the standard reconnection scenario, there is no complete agreement among models regarding the nature of this tower-like structure. The XRT maps also reveal that reconnected loops that are successively connected at their tops to this tower develop a density increase in one of their legs that can reach over 2 times the density value of the other leg, giving the appearance of ``half-loops''. Their density is nevertheless still lower than at the tower. These jumps in density last longer than several acoustic transit times along 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 and Acton (1996). This would indicate that asymmetric reconnection took place between loops originally belonging to systems with different magnetic field strengths, densities, and temperatures. We hypothesize that the heat generated by reconnection's slow shocks is then transferred to each leg of the loop at different rates. Therefore, the increase in electron density due to chromospheric evaporation is different in each leg. Thermal pressure balance between the legs is prevented by shocked plasma at the top of the loops. We also present preliminary results comparing a new fast DEM method that uses SDO/AIA data with the XRT filter ratio method. Both methods complement each other, they agree at the overlap between their instruments' temperature response functions ($3-12$ MK) while the SDO/AIA method works well at lower temperatures and the XRT one at higher temperatures.




Weak convective flows on large scales in the solar interior

Author(s): Shravan Hanasoge

Institution(s): Princeton University

Abstract:

Seismic analyses of observations taken by HMI reveal convective velocities that are almost two orders in magnitude smaller than current theoretical and computational predictions. The associated Reynolds' stresses would be too small to explain the observed large-scale flow systems of meridional circulation and differential rotation in the convection envelope of the Sun, throwing into question models of dynamo action.




Diary of a Wimpy Cycle

Author(s): Hathaway, David H. (1), Upton, Lisa (2) (3)

Institution(s): (1) NASA Marshall, Huntsville, AL, (2) Univ. Alabama, Huntsville, AL, (3) Vanderbilt University, Nashville, TN

Abstract:

The cause of the low and extended minimum in solar activity between Sunspot Cycles 23 and 24 was the small size of Sunspot Cycle 24 itself – small cycles start late and leave behind low minima. Cycle 24 is small because the polar fields produced during Cycle 23 were substantially weaker than those produced during the previous cycles and those (weak) polar fields are the seeds for the activity of the following cycle. Here we discuss the observed characteristics of Cycle 24 and contrast them to the characteristics of previous cycles. We present observations and Magnetic Flux Transport simulations with data assimilated from SOHO/MDI and SDO/HMI that help to explain these differences and point the way to predictions of future activity levels.




A data-driven MHD simulation of solar active regions with HMI data.

Author(s): Keiji Hayashi(1) and HMI vector magnetic field team

Institution(s): (1) Stanford University

Abstract:

We will show our preliminary results of the MHD simulation of the active regions using the HMI vector magnetic field data. In this simulation, the initial value of the magnetic field is the nonlinear force-free field (NLFFF), and the plasma flow on the bottom boundary is given by DAVE4VM that, in this case, uses the HMI vector data. In this way, all data given as initial and boundary values are deducted from HMI vector magnetic field measurements. Then, the evolution of the MHD variables is traced by means of time-dependent MHD model. Our MHD model uses computational strategies, such as TVD, MUSCL, FVM, and the projected normal characteristic method. Results from test runs suggest that the results depend on the initial density that can be given somewhat arbitrarily. This is somewhat expected but challenging. We are refining model and settings, and we will show the latest results and status of our model.




What can the stars tell us about the Sun?

Author(s): Hekker, Saskia

Institution(s): Astronomical Institute Anton Pannekoek, Amsterdam, The Netherlands

Abstract:

The Sun is our best studied star, but it is only one star. To study the context of the Sun in terms of stellar evolution, but also in parameter space such as metallicity, rotation, magnetic fields or mass we need information about other stars. The CoRoT and Kepler satellites provide excellent data for asteroseismology on a wide variety of stars. With these observations it will be possible to find out whether our Sun is just an ordinary star or a very special one. We may also learn about the past of the Sun and predict how the Sun will evolve.




Polar Coronal Hole Areas from 1996 through Present

Author(s): S.A. Hess Webber, N. Karna, W.D. Pesnell

Institution(s): GMU, GSFC

Abstract:

The evolutionary analysis of the polar coronal hole (PCH) areas from the beginning of solar cycle 23 through the cycle 24 minimum has introduced several new scientific results regarding changes in the magnetic field configuration during the past solar cycle. Observations show that the PCH sizes peak at discrete times in the two hemispheres, suggesting that the two poles reach solar minimum (magnetic maximum) up to three years apart. The northern polar hole has also decreased significantly in size since 2010, while the southern hole has remained stable. This indicates that the northern hemisphere has already reached solar maximum even though the southern hemisphere has yet to peak.




Asymmetries in Flare Production during Solar Cycle 24

Author(s): Rachel Hock

Institution(s): US Air Force Research Laboratory, Space Vehicle Directorate

Abstract:

The EVE flare catalog was created to study all of solar flares observed by SDO larger than C1.0 and to produce a complete picture of the EUV variability of flares. In the process of developing the catalog, I discovered that flares can be placed into one of five EVE flare categories. The EUV irradiance signature of these categories is unique and closely related to the magnetic structure of the flare region. Preliminary analysis of the EVE flare catalog from the first eighteen months of the SDO mission show strong asymmetries both in the total number of flares and EVE flare categories between the northern and southern hemispheres. Over 60% of flares larger than C1.0 occurred in the northern hemisphere. Furthermore, arcade or two-ribbon flares occurred frequently than expected in the northern hemisphere while more localized eruptive flares (flares associated with EUV surges) occurred in the southern hemisphere while This work will expand that preliminary analysis by examining the full SDO mission and including other features of the flares such as the McIntosh classification of the active region and associated radio bursts. By examining asymmetries in flare production for almost three years, I will be able to address whether the hemispheric differences in flares are a result of the southern hemisphere is simply “lagging behind” the northern hemisphere or whether each hemisphere is undergoing a unique cycle.




Solar global convection with the Reduced Speed of Sound Technique

Author(s): Hideyuki, Hotta. (1) Matthias, Rempel (2) Takaaki, Yokoyama (3)

Institution(s): (1), (3) University of Tokyo, Tokyo, Japan (2) High Altitude Observatory, CO, USA

Abstract:

We achieve high-resolution numerical calculations of the solar global convection with the reduced speed of sound technique (RSST). Compared with the anelastic approximation, the RSST has two advantages: 1. Good scaling in parallel computing. 2. Accessibility to the real solar surface. Thus, our calculation can have the resolution of 720x1280x3072 and the top boundary can be at r=0.99Rsun at maximum. In addition we adopt OPAL repository, since the ionization effect is not negligible in near-surface region. Our calculation can capture supergranulation scale (10Mm) convection pattern. In the presentation, the detail of our achievement will be shown.





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Last Updated on Tuesday, 29 March 2011 09:36