The solar electromagnetic and corpuscular emissions are strongly modulated by the evolution of the magnetic structure of the solar atmosphere, which is imprinted in the solar surface. The evolution of the magnetic structure leads to gradual changes in the solar activity (space climate) as well as violent events (space weather) that affect the whole Heliosphere. In particular, the solar output affects the ionized and neutral components of the Earth’s atmosphere that have a direct impact on human activities from agriculture to high-technological systems. The solar magnetism is driven by the energy transport from the inner layers to the solar atmosphere. Although systematic observations have revealed several features related to the evolution of solar activity, there is not a complete explanation of the physical processes that lead to solar activity cyclic variability and its long-term changes. Here we present a brief description of the development of a magnetograph and visible-light imager instrument to study the solar dynamo processes through observations of the solar surface magnetic field distribution. The instrument will provide measurements of the vector magnetic field and the line-of-sight velocity in the solar photosphere. As the magnetic field anchored at the solar surface produces most of the structures and energetic events in the upper solar atmosphere and significantly influences the Heliosphere, the development of this instrument plays an essential role in reaching the scientific goals of The Atmospheric and Space Science Coordination (CEA) at the Brazilian National Institute for Space Research (INPE). In particular, the INPE’s Space Weather program will benefit most from the development of this technology. Additionally, we expect that this project will be the starting point to establish a robust research program on Solar System Research at INPE. The proposed instrument has been designed to operate on the ground, but with a conceptual design flexible enough to be adapted to work on a balloon and space-based platforms. In this way, our main aim is acquiring know-how progressively to build state-of-art solar vector magnetograph and visible-light imagers for space-based platforms to contribute to the efforts of the solar-terrestrial physics community to address the main unanswered questions on how our nearby Star works.

G. Hornig, M.H. Page

What if there were a way to identify **where** the magnetic helicity is concentrated within a three- dimensional magnetic field? At first sight this question appears meaningless, since magnetic helicity is an integral over the whole volume of the magnetic field. But, in fact, it is possible to decompose this total helicity as an integral over individual "field line helicities" for each magnetic field line in the domain. All of these are ideal-invariant, topological quantities, and they allow us to quantify in a meaningful way how magnetic helicity is distributed within the domain. In this talk, I will show how this idea can be practically applied to typical extrapolations of the Sun's coronal magnetic field that are used in solar physics.

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.

Jack Harvey

SOLIS stands for Synoptic Optical Long-term Investigations of the Sun. Daily fulldisk magnetic fields measurements of the Sun are being done for several decades at NSO Kittpeak. The SOLIS/VSM instrument replaced earlier instruments at Kitt Peak. The current SOLIS/VSM instrument has capability to make full Stokes polarimetry in photospheric lines, however, for chromosphere only longitudinal polarimetry exists. With the recent progress in non-LTE inversions of the chromospheric spectra it was decided that a full Stokes polarimeter needs to be developed. Based on similar design to photospheric modulator we have developed a separate modulator for chromospheric full Stokes measurements using Ca II 854.2 nm line. We will present design and performance of the new modulator and possibly sample observations.

Integral field units (IFUs) represent the most important instrumental development for solar telescopes in recent times. They aim at obtaining the simultaneous spectral/spectropolarimetric information in all points in a 2D field of view at the best achievable spatial resolution. Present IFU developments are based on three different approaches: image slicers, microlenses, and optical fibres. The first two options have been addressed under the EST framework and very promising results have been obtained up to now. Fibre-based IFUs are being developed for one of the first-light instruments of DKIST. In this talk, the three alternatives will be presented and described, putting especial emphasis on the alternatives developed as prototypes of the future EST instruments. A microlens-based IFU has been developed by MPS and tested at the SST. In parallel, a slicer-based IFU has also been developed by IAC and tested at GREGOR. The latter has been offered to all observers at this telescope to gain experience about its performance, stability and data reduction and analysis. These prototypes are fundamental for the final definition of the EST spectrograph(s) and crucial for the science that will be addressable with EST. IFUs will facilitate, v.g., the study of the fast evolution of small-scale solar structures, high-frequency waves, fast acceleration and heating of the plasma, reconnection events, etc. The present status of these instrument developments will be presented, as well as the future steps for their improvement and their final expected performance if/when installed at EST.

Markus Roth, Frank Hill, Michael Thompson

Synoptic observations of the Sun are very important to understand the long term behavior of the solar activity cycle. Our current understanding solar magnetic cycle is rather in its infancy, as can be inferred from our very poor prediction for the strength of solar cycle 24, based on various dynamo models. Solar magnetism is at the heart of all solar activity and therefore it is important to understand what parameters govern the magnetic cycle in the Sun. An important parameter that is realized more recently is the internal dynamics, i.e., profile of solar internal rotation and nature of large scale meridional flows. Therefore, it is important to study the solar interior by making use of helioseismology. Ground based helioseismology networks such as GONG are now quite few decades old and its possible failure poses risk to the continuity of solar oscillation data. Hence, a next generation of synoptic network SPRING is being proposed and is currently under design study. We will present science requirements and the details of the SPRING network.

S. Brun

The aim of the present study is to characterize the effect of the rotation rate in building magnetic field via dynamo action in solar-like stars. We use the code ASH to model the convective dynamo for solar-like stars at various rotation rates and hence Rossby numbers. We find that stable magnetic configuration without cycling evolution; with steady low latitude magnetic field wreaths are found for slowly rotating cases with large Rossby number. For models rotating faster with a low Rossby number, the convective dynamo shows a cycling activity, leading to systematic pole inversion. We also note that a topology change of the stellar magnetic field occurs going from a dipolar-like to a quadrupolar-like structure when the system magnetic energy drops during the cyclic activity, in good agreement with our star the Sun.

A review of solar flares

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The unusually large NOAA active region (AR) 2192, observed in October and November 2014, was outstanding in its productivity of major flares (GOES class M5 and larger). However, none of the X-flares was associated to a coronal mass ejection. The AR showed a predominantly north-south oriented magnetic system of arcade fields, which served as a strong, also lateral, confinement for the flares at the core of the active region. The large initial separation of the flare ribbons, together with an almost absent growth in ribbon separation suggests a confined reconnection site high up in the corona. Based on a detailed analysis of the confined X1.6 flare of Oct 22, we show how exceptional the flaring of this AR was. We find evidence for repeated energy release, presumably due to magnetic reconnection in a narrow flaring volume, closely associated to the location of hard X-ray sources. We demonstrate that a considerable portion of the magnetic energy released during the X-flare was consumed by the non-thermal flare energy.  

P. Heinzel, M. Švanda, J. Jurčák, D. del Moro, and F. Berrilli

Several mechanisms may heat the solar chromosphere: acoustic waves, magnetoacoustic waves (slow, fast, and Alfven waves), and small-scale magnetic reconnections. Based on observations in the Ca II 854.2 nm line, the contribution of acoustic waves to the heating of quiet and plage regions in the chromosphere is discussed. The point is to compare the energy released by radiative losses with the energy deposited by acoustic waves. Radiative losses are computed using a grid of semi-empirical chromospheric models. The deposited acoustic flux is calculated using power spectra of Doppler oscillations measured in the Ca II line core. The comparison shows that the spatial correlation of maps of radiative losses and acoustic flux is 72 %. The deposited acoustic flux covers only 15 % of radiative losses in quiet chromosphere but 23 % in network and 54 % in plage areas. This estimate is a lower limit of the real acoustic energy flux.

In this talk, I review the availability and use of ground-based observations for the study of the solar sources of space weather. High-cadence full-disk imaging in the H-alpha spectral line provides us with a valuable means to identify solar flares, erupting filaments which may be associated with Earth-directed coronal mass ejections and Moreton waves indicating shock waves propagating through the solar corona. We present the automatic real-time detection of solar flares and filaments, which was developed and implemented at the Kanzelhöhe Observatory H-alpha observing system (in the frame work of ESA’s SSA space weather segment, http:// http://swe.ssa.esa.int). Specific problems related to ground-based observations and the potential of observing networks for space weather research will be discussed