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Education
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In 1908, American astronomer George E. Hale discovered the presence of the magnetic field in sunspots, and in 1917, a systematic observations of sunspot magnetic fields begun at Mount Wilson Observatory (MWO). In early 1950s, the first photoelectric magnetograph was developed by H. W. Babcock, and soon after, a number of magnetographs was developed in several countries around the globe. In mid-1960s, regular observations of full disk longitudinal magnetograms started at MWO, and in early 1970s, the full disk magnetograph observations begun at the National Solar Observatory at Kitt Peak. This dataset continues using Vector SpectroMagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) platform. Since 2010, the full disk magnetogams are observed by Helioseismic and Magnetic Imager (HMI) on board of Solar Dynamics Observatory (SDO). In this talk, I briefly review history and methods of observations of magnetic fields on the Sun, and discuss major discoveries in long-term studies of the photospheric magnetic fields.
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Document
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The European Solar Telescope offers unique and novel opportunities for solving some of the long-standing problems related to solar flares, such as the slow evolution of the stored energy preceding the flare, the rapid deposition in the chromosphere during the flare impulsive phase, and the response of the chromosphere as the atmosphere responds. The focus of EST on the solar chromosphere - where flare radiation is intense and flare-related magnetic changes likely to be significant, will lead to unique insights. This talk overviews some of the science topics identified by Working Group 6 on Solar Flares and Eruptive Events.
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The Swedish 1-m Solar Telescope has been operating on La Palma since 2002. Before that, the Swedish solar observatory hosted other solar telescopes for almost 20 years. From this experience we will formulate a number of conclusions that we believe are relevant for the EST. These points will touch upon telescope and instrument design, telescope operations, and the science that could or should be made with EST. Finally we will try to answer the question “When is the seeing good?”
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  • Video
How do sunspots form? How is this large amount of magnetic flux gath- ered? Why do certain pores become sunspots? Why some large pores never develop penumbra? How is penumbra formed? What is the role of light bridges during sunspot formation? What is hidden in the dark umbrae? How do sunspots decay? What is the role of the moat flow? We will review our current understanding on sunspot formation, evolu- tion and decay addressing these and other questions.
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  • Video
Collision-less large-Reynolds-number astrophysical plasmas are prone to turbulence. In this context, it is necessary to consider the impact of turbulence during believed magnetic reconnection events in solar and stellar flares or in planetary magnetospheres. Magnetic reconnection is a multi-scale process and turbulence can be the key to bridge the gap between the magnetic energy release at large scales due to magnetic diffusion at small scales through the Richardson's picture of direct and inverse energy cascade. Moreover, diffusion of magnetic field by turbulence at small scales might lead to fast reconnection. Such an interaction between turbulence and fast magnetic reconnection in weakly dissipative plasmas is considered through the plasmoid instability. The turbulent transport coefficients are characterize by a turbulent mean-field model and are identified as a turbulent diffusion, crosshelicity and a residual helicity. These turbulent coefficients are found to lead to fast reconnection for a single 'X'-point current sheet as well as in the case of multiple 'X'-points, as present in plasmoid unstable current sheets. For the plasmoid instability, the turbulent coefficients are also found to be responsible for fast reconnection. In addition, the dynamics between diffusion and sustainment of magnetic field, related to the turbulent diffusion and residual helicity effects, are shown to be important for fast magnetic reconnection in presence of strong guide-magnetic field perpendicular to the reconnection plane. For residual helicity intensities stronger than turbulent diffusive ones, a time delay in reaching fast reconnection regime is observed. Finally, this turbulence dynamics obtained during the fast magnetic reconnection phase of the plasmoid instability is used to relate energetic electrons often found near astrophysical current sheets and magnetic reconnection. We obtain that fast energetic particles are accelerated by turbulence during fast reconnection processes if residual helicity intensities are weaker than the strength of the diffusion of magnetic field by turbulence.
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  • Video
The Large Angle Spectrometric Coronagraph (LASCO), onboard the Solar and Heliospheric Observatory (SOHO) provided us observations extending for the two Solar Cycles 23 and 24 (31 July 1996 - 31 March 2014) that allow one to compare some properties (speed, acceleration, polar angle, angular width, and mass) of Coronal Mass Ejection (CMEs). The Coordinated Data Analysis Workshops (CDAW) Data Center datasets uses manual identification for the detection of the CMEs, while the Computer Aided CME Tracking software (CACTus) datasets uses an automatic detection algorithm. Some important results found in this analysis, for both dataset, are that there are more CMEs during the maximum of Solar Cycle 24 than during the maximum of Solar Cycle 23, although the photospheric level and magnetic activity of the Sun during Cycle 24 was weaker than during Cycle 23. Peaks of CMEs observed by CACTus are of the same order of magnitude with respect to the two cycles, but the distribution of CMEs observed by CACTus exhibits a long lasting peak during the Solar Cycle 24. The discrepancy between the CACTus and CDAW results may be due to an observer bias giving origin to different definition of CMEs in CDAW catalog. In order to investigate on the correlation between Flares and CMEs, during the Solar Cycles 23 and 24 we used the Geostationary Operational Environmental Satellite (GOES) datasets that contain observations of 19811 flares of C-, M-, and X-class and found 11441 flares temporally correlated with CMEs for CDAW and 9120 for CACTus. We also found some characteristics of the mean CMEs velocity and acceleration of the CMEs associated with flares and the CMEs not associated with flares. The most important results of this statistical analysis is a log-log relationship between the flux of the flares integrated from the start to end in the 0.1 – 0.8 nm range and the CME mass, valid not only when we consider the energy released by the flare during the whole events, but also considering the flux emitted at the peak of the corresponding flares and the mass ejected by the CMEs.
Data Types:
  • Video
The Large Angle Spectrometric Coronagraph (LASCO), onboard the Solar and Heliospheric Observatory (SOHO) provided us observations extending for the two Solar Cycles 23 and 24 (31 July 1996 - 31 March 2014) that allow one to compare some properties (speed, acceleration, polar angle, angular width, and mass) of Coronal Mass Ejection (CMEs). The Coordinated Data Analysis Workshops (CDAW) Data Center datasets uses manual identification for the detection of the CMEs, while the Computer Aided CME Tracking software (CACTus) datasets uses an automatic detection algorithm. Some important results found in this analysis, for both dataset, are that there are more CMEs during the maximum of Solar Cycle 24 than during the maximum of Solar Cycle 23, although the photospheric level and magnetic activity of the Sun during Cycle 24 was weaker than during Cycle 23. Peaks of CMEs observed by CACTus are of the same order of magnitude with respect to the two cycles, but the distribution of CMEs observed by CACTus exhibits a long lasting peak during the Solar Cycle 24. The discrepancy between the CACTus and CDAW results may be due to an observer bias giving origin to different definition of CMEs in CDAW catalog. In order to investigate on the correlation between Flares and CMEs, during the Solar Cycles 23 and 24 we used the Geostationary Operational Environmental Satellite (GOES) datasets that contain observations of 19811 flares of C-, M-, and X-class and found 11441 flares temporally correlated with CMEs for CDAW and 9120 for CACTus. We also found some characteristics of the mean CMEs velocity and acceleration of the CMEs associated with flares and the CMEs not associated with flares. The most important results of this statistical analysis is a log-log relationship between the flux of the flares integrated from the start to end in the 0.1 – 0.8 nm range and the CME mass, valid not only when we consider the energy released by the flare during the whole events, but also considering the flux emitted at the peak of the corresponding flares and the mass ejected by the CMEs.
Data Types:
  • Video