LESIA - Observatoire de Paris

  • Lundi 28 septembre 2015 à 11h00 (Salle de réunion du bâtiment 14)

    Testing CME models using force-free models of the coronal magnetic field : problems and progress

    Stuart Gilchrist (LESIA)

  • Jeudi 24 septembre 2015 à 16h00 (Salle de conférence du bâtiment 17)

    Pluto Revealed ! Latest Results from the New Horizons Mission

    Prof. Richard Binzel (MIT)

    After nearly two decades of struggling for approval, a NASA funded Pluto mission finally reached the launch pad in January 2006. Nine-and-a-half years later in July 2015, the piano-sized New Horizons spacecraft reached the Pluto system revealing an amazingly bizarre planetary world. Ice mountains as tall as the Alps and smooth plains of frozen carbon monoxide 500 km across are just some of the surprising features. Pluto appears to be a globally changing planet with seasonal cycles ranging from decades to millennia producing an evolving landscape of nitrogen ice glaciers and variable atmospheric pressure. Together with its largest satellite, Pluto and Charon form a “double planet” system orbiting a common center of gravity located outside of either body. Charon’s surface also appears relatively young and crater-free, implying some recent era geologic activity. Completing the system are four small moons found to be irregularly shaped with complex spin patterns in their own regularly spaced orbits. As New Horizons continues its voyage out of the solar system, a close encounter with at least one newly discovered Kuiper Belt object appears possible within the next four years.

  • Lundi 21 septembre 2015 à 11h00 (Salle de conférence du bâtiment 17)

    Data-constrained simulations and topology analysis of erupting sigmoids

    Antonia Savcheva (Harvard-Smithsonian Center for Astrophysics, USA)

    A long established goal of solar physics is to build physics-based flare and CME forecasting models. This study, building on the recent successes in non-linear forces free field (NLFFF) modeling and detailed numerical simulations, brings us closer to that goal. In the first part of the talk, I show that data-constrained NLFFF models built to reproduce the active region magnetic field in the pre-flare state can be rendered unstable and the sequence of unstable solutions produce quasi-separatrix layers (QSLs) that reproduce the observed flare ribbons. The results are fully consistant with the 3D extension of the standard flare/CME model. Three active regions are studied using SDO/AIA and HMI to constrain NLFFF models. Stable models that are well matched to pre-flare coronal loops are rendered unstable by the addition of axial magnetic flux. This results in a series of solutions in the magneto-frictional relaxation with the flux rope evolving to different heights. We present maps of the QSLs and current in cross sections through the flux ropes, which present the dynamical nature of the solutions. We compare the chromospheric maps of the squashing factor, Q, with flare ribbon positions at different times during the flare.

    In the second part of the talk, we go beyond the initial moments of the eruption to explore the CME from one of the regions that we have performed the topology analysis. We perform the first global data-constrained MHD simulation of a CME with the Space Weather Modeling Framework (SWMF). The initial condition for the simulation is the unstable model obtained with the flux rope insertion method of the active region CME on April 08, 2010. The boundary condition is a synoptic magnetogram from SOLIS, with a high resolution HMI piece around the active region. We discuss the newly developed capabilities built-in into SWMF for producing fully data-constrained models of CMEs. We show the initiation and propagation of the CME within 10Rsun. We compare simulated LASCO white light and SDO/AIA EUV images with the observations and demonstrate the power of using data to constrain the initial and boundary conditions ion such a simulation.

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