Context. Magnetic clouds are transient magnetic structures expulsed from the Sun that travel toward the external heliosphere carrying a significant amount of magnetic flux and helicity. Aims. To improve our understanding of magnetic clouds in relation to their solar source regions, we need a reliable method to compute magnetic flux and helicity in both regions. Here we evaluate the sensitivity of the results using different models, methods and magnetic cloud boundaries applied to the same magnetic cloud data. Methods. The magnetic cloud was observed by the spacecraft Wind on October [18][19][20] 1995. We analyze this cloud considering four different theoretical configurations (two force free and two non-force free) that have been previously proposed to model cloud fields. These four models are applied using two methods to determine the orientation of the cloud axis: minimum variance and simultaneous fitting. Finally, we present a new method to obtain the axial and azimuthal magnetic fluxes and helicity directly from the observed magnetic field when rotated to the cloud frame. Results. The results from the fitted models have biases that we analyze. The new method determines the centre and the rear boundary of the flux rope when the front boundary is known. It also gives two independent measurements in the front and back parts for the fluxes and helicity; they are free of model and boundary biases. We deduce that the leading flux of the magnetic cloud had reconnected with the overtaken solar wind magnetic field and estimate the fluxes and helicity present in the full cloud before this reconnection.

Bipolar active regions (ARs) are thought to be formed by twisted flux tubes, as the presence of such twist is theoretically required for a cohesive rise through the whole convective zone. We use longitudinal magnetograms to demonstrate that a clear signature of a global magnetic twist is present, particularly, during the emergence phase when the AR is forming in a much weaker pre-existing magnetic field environment. The twist is characterised by the presence of elongated polarities, called "magnetic tongues", which originate from the azimuthal magnetic field component. The tongues first extend in size before retracting when the maximum magnetic flux is reached. This implies an apparent rotation of the magnetic bipole. Using a simple half-torus model of an emerging twisted flux tube having a uniform twist profile, we derive how the direction of the polarity inversion line and the elongation of the tongues depend on the global twist in the flux rope. Using a sample of 40 ARs, we verify that the helicity sign, determined from the magnetic polarity distribution pattern, is consistent with the sign derived from the photospheric helicity flux computed from magnetogram time series, as well as from other proxies such as sheared coronal loops, sigmoids, Electronic supplementary material The online version of this article (46 M.L. Luoni et al.flare ribbons and/or the associated magnetic cloud observed in situ at 1 AU. The evolution of the tongues observed in emerging ARs is also closely similar to the evolution found in recent MHD numerical simulations. We also found that the elongation of the tongue formed by the leading magnetic polarity is significantly larger than that of the following polarity. This newly discovered asymmetry is consistent with an asymmetric -loop emergence, trailing the solar rotation, which was proposed earlier to explain other asymmetries in bipolar ARs.

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Solar observations in the infrared domain can bring important clues on the response of the low solar atmosphere to primary energy released during flares. At present the infrared continuum has been detected at 30 THz (10 µm) in only a few flares. SOL2012-03-13 , which is one of these flares, has been presented and discussed in Kaufmann et al. (2013). No firm conclusions were drawn on the origin of the mid-infrared radiation. In this work we present a detailed multi-frequency analysis of the SOL2012-03-13 event, including observations at radio millimeter and sub-millimeter wavelengths, in hard X-rays (HXR), gamma-rays (GR), Hα, and white-light. HXR/GR spectral analysis shows that SOL2012-03-13 is a GR line flare and allows estimating the numbers of and energy contents in electrons, protons and α particles produced during the flare. The energy spectrum of the electrons producing the HXR/GR continuum is consistent with a broken power-law with an energy break at ∼ 800 keV. It is shown that the high-energy part (above ∼ 800 keV) of this distribution is responsible for the high-frequency radio emission (> 20 GHz) time-independent models of the quiet and flare atmospheres, we find that most (∼80%) of the observed 30 THz radiation can be attributed to thermal freefree emission of an optically-thin source. Using the F2 flare atmospheric model (Machado et al., 1980) this thin source is found to be at temperatures T ∼ 8000 K and is located well above the minimum temperature region. We argue that the chromospheric heating, which results in 80 % of the 30 THz excess radiation, can be due to energy deposition by non-thermal flare accelerated electrons, protons and α particles. The remaining 20% of the 30 THz excess emission is found to be radiated from an optically-thick atmospheric layer at T ∼ 5000 K, below the temperature minimum region, where direct heating by non-thermal particles is insufficient to account for the observed infrared radiation.

Several late-type stars present activity cycles similar to that of the Sun.However, these cycles have been mostly studied in F to K stars. Due to their small intrinsic brightness, M dwarfs are not usually the targets of long-term observational studies of stellar activity, and their long-term variability is generally not known. In this work, we study the long-term activity of two M dwarf stars: Gl 229 A (M1/2) and Gl 752 A (M2.5). We employ medium resolution echelle spectra obtained at the 2.15 m telescope at the Argentinian observatory CASLEO between the years 2000 and 2010 and photometric observations obtained from the ASAS database. We analyzed Ca II K line-core fluxes and the mean V magnitude with the Lomb-Scargle periodogram, and we obtain possible activity cycles of ∼4 yr and ∼7 yr for Gl 229 A and Gl 752 A respectively.