Conveners
Local flux concentration: theoretical results and local helioseismology
- Serge Koutchmy (Institut d'Astrophysique de Paris CNRS & UPMC)
Local flux concentration: theoretical results and local helioseismology
- Gustavo Guerrero (Universidade Federal de Minas Gerais)
Local flux concentration: theoretical results and local helioseismology
- Dhrubaditya Mitra (NORDITA)
Local flux concentration: theoretical results and local helioseismology
- Robert Cameron (MPS)
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Junwei Zhao (Stanford University)11/03/2015, 09:00Through cross-correlating oscillation signals at different locations, we are able to reconstruct how waves propagate away from a virtual wave source inside a sunspot in the photospheric level. Before helioseismic waves are visible from the source inside the sunspot, a surprisingly fast-moving wave is detected propagating along the sunspot's radial direction from the inside to the...Go to contribution page
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Paul Cally (Monash University)11/03/2015, 09:40Magnetic field dominates wave behaviour in sunspots. The direction of the magnetic field has profound effects on mode conversion, "travel times" (as inferred from local helioseismology), and on wave polarization. These in turn affect what we see when observing spots from different orientations. I will discuss recent work at Monash on both travel time dependence on field direction, and...Go to contribution page
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Aaron Birch (Max Planck Institute for Solar System Research)11/03/2015, 10:40We have carried out a study of about one hundred emerging sunspot regions observed by the HMI instrument. For each active region, we measure flows by applying helioseismic holography to time series of Doppler images and also by applying local correlation tracking to intensity images. We show that these two methods give very similar results in non-magnetic regions. We find that the active...Go to contribution page
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Neal Hurlburt (Lockheed Martin Solar & Astrophysics Laboratory)11/03/2015, 11:20Flows in the vicinity of sunspots are investigated, focusing on the statistical behavior of radial and rotational motions. We identify datasets for study using the sunspot records captured in the Heliophysics Events Knowledgebase (HEK) using the sunspot detection method developed under the EGSO and SDO/FFT projects.Go to contribution page
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Illa Rivero Losada11/03/2015, 11:50In a strongly stratified turbulent layer, a uniform horizontal magnetic field can become unstable to spontaneously form local flux concentrations due to a negative contribution of turbulence to the large-scale (mean-field) magnetic pressure. This mechanism, called the negative effective magnetic pressure instability (NEMPI), is of interest in connection with dynamo scenarios where...Go to contribution page
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Jörn Warnecke (Max-Planck-Institut für Sonnesystemforschung)11/03/2015, 12:10Abstract: This work presents an extensive study of the previously discovered formation of bipolar flux concentrations in a two-layer model. We relate the formation process to the negative effective magnetic pressure instability (NEMPI), which is a possible mechanism to explain the origin of sunspots. In our simulations we use a Cartesian domain of isothermal stratified gas which...Go to contribution page
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Petri Käpylä (University of Helsinki)11/03/2015, 12:30We present preliminary results from high resolution magneto-convection simulations where we find the formation of flux concentrations from an initially uniform magnetic field. We compute the effective magnetic pressure but find that the concentrations appear also in places where it is positive. The structures appear in roughly ten convective turnover times and live close to a turbulent...Go to contribution page
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Alexander Kosovichev (New Jersey Institute of Technology)12/03/2015, 09:00I will present results of helioseismology analysis of subsurface flows and sound-speed structures of the largest emerging active regions observed by Solar Dynamics Observatory.Go to contribution page
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Nishant Singh (Nordita)12/03/2015, 09:30We show that in the presence of a magnetic field that is varying harmonically in space, the fundamental or f-mode in a stratified layer is altered in such a way that it fans out in the diagnostic k-omega diagram, with mode power also within the fan. In our simulations, the surface is defined by a temperature and density jump in a piecewise isothermal layer. Unlike our previous work...Go to contribution page
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Aneta Wisniewska (Kiepenheuer-Institut fuer Sonnenphysik)12/03/2015, 09:50We present our preliminary results from multi-height observations taken for active regions with the HELLRIDE (HELioseismology Large Regions Interferometric Device) Instrument at the Vacuum Tower Telescope (VTT). The goal of our work is to study the differences between propagation of solar acoustic waves in the case of the quiet Sun atmosphere and the atmosphere above the active regions.Go to contribution page
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Dhrubaditya Mitra12/03/2015, 10:40We show, from direct numerical simulations of stratified MHD, that bipolar structures can emerge from from dynamo simulations. The emerged structures show intriguing dynamical behaviour. The emergence may be attributed to the Negative Effective Magnetic Pressure Instability (NEMPI).Go to contribution page
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Sarah Jabbari (PhD student)12/03/2015, 11:10We study a system of a highly stratified turbulent plasma. In such a system, when the magnetic Reynolds number is large enough and there is a background field of suitable strength, a new effect will play role in concentrating magnetic fields such that it leads to the formation of magnetic spots and bipolar regions. This effect is due to the fact that the turbulent pressure is suppressed...Go to contribution page
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Igor Rogachevskii (Ben-Gurion University of the Negev)12/03/2015, 11:30A review of different theories of sunspots formation is presented. Comparisons with numerical simulations is made.Go to contribution page
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Robert Cameron12/03/2015, 12:00