Direct evidence that twisted flux tube emergence creates solar active regions

The magnetic nature of the formation of solar active regions lies at the heart of understanding solar activity and, in particular, solar eruptions. A widespread model, used in many theoretical studies, simulations and the interpretation of observations, is that the basic structure of an active region is created by the emergence of a large tube of pre-twisted magnetic field. Despite plausible reasons and the availability of various proxies suggesting the accuracy of this model, there has not yet been a methodology that can clearly and directly identify the emergence of large pre-twisted magnetic flux tubes. Here, we present a clear signature of the emergence of pre-twisted magnetic flux tubes by investigating a robust topological quantity, called magnetic winding, in solar observations. This quantity detects the emerging magnetic topology despite the significant deformation experienced by the emerging magnetic field. Magnetic winding complements existing measures, such as magnetic helicity, by providing distinct information about field line topology, thus allowing for the direct identification of emerging twisted magnetic flux tubes

Deciphering the Pre–solar-storm Features of the 2017 September Storm From Global and Local Dynamics

We investigate whether global toroid patterns and the local magnetic field topology of solar active region (AR) 12673 together can hindcast the occurrence of the biggest X-flares of solar cycle (SC)-24. Magnetic toroid patterns (narrow latitude belts warped in longitude, in which ARs are tightly bound) derived from the surface distributions of ARs, prior and during AR 12673 emergence, reveal that the portions of the south toroid containing AR 12673 was not tipped away from its north-toroid counterpart at that longitude, unlike the 2003 Halloween storms scenario. During the minimum phase there were too few emergences to determine multimode longitudinal toroid patterns. A new emergence within AR 12673 produced a complex nonpotential structure, which led to the rapid buildup of helicity and winding that triggered the biggest X-flare of SC-24, suggesting that this minimum-phase storm can be anticipated several hours before its occurrence. However, global patterns and local dynamics for a peak-phase storm, such as that from AR 11263, behaved like the 2003 Halloween storms, producing the third biggest X-flare of SC-24. AR 11263 was present at the longitude where the north and south toroids tipped away from each other. While global toroid patterns indicate that prestorm features can be forecast with a lead time of a few months, their application to observational data can be complicated by complex interactions with turbulent flows. Complex nonpotential field structure development hours before the storm are necessary for short-term prediction. We infer that minimum-phase storms cannot be forecast accurately more than a few hours ahead, while flare-prone ARs in the peak phase may be anticipated much earlier, possibly months ahead from global toroid patterns

Magnetic Winding as an Indicator of Flare Activity in Solar Active Regions

Magnetic helicity is a measure of the entanglement of magnetic field lines used to characterize the complexity of solar active region (AR) magnetic fields. Previous attempts to use helicity-based indicators to predict solar eruptive/flaring events have shown promise but not been universally successful. Here we investigate the use of a quantity associated with the magnetic helicity, the magnetic winding, as a means to predict flaring activity. This quantity represents the fundamental entanglement of magnetic field lines and is independent of the magnetic field strength. We use vector magnetogram data derived from the Helioseismic Magnetic Imager (HMI) to calculate the evolution and distribution of the magnetic winding flux associated with five different ARs, three of them with little flaring activity/nonflaring (AR 11318, AR 12119, AR 12285) and two highly active with X-class flares (AR 11158, AR 12673). We decompose these quantities into "current-carrying" and "potential" parts. It is shown that the ARs that show flaring/eruptive activity have significant contributions to the winding input from the current-carrying part of the field. A significant and rapid input of current-carrying winding is found to be a precursor of flaring/eruptive activity, and, in conjunction with the helicity, sharp inputs of both quantities are found to precede individual flaring events by several hours. This suggests that the emergence/submergence of topologically complex current-carrying field is an important element for the ignition of AR flaring

ARTop: an open-source tool for measuring Active Region Topology at the solar photosphere

No abstract available

Inference of the topology of geomagnetic field multipole interactions

The geomagnetic field is generated by a dynamo process in the Earth’s core and is characterized by a predominant dipole component that has been steadily decreasing in the last few centuries. The physical drivers behind the fluctuations of the geomagnetic dipole field remain poorly understood. One of the possible explanations rely on the interaction between the dipole mode and other multipole terms of the geomagnetic field. To test this hypothesis, we used two millennial scale models based on spherical harmonic fitting of paleomagnetic data, which allowed to reconstruct the geomagnetic field of the past. By performing causality and information statistical analysis, we found significant interactions between the dipole and smaller scale harmonics (quadrupole and octupole) of the geomagnetic field. In particular, both data sets agree that the spherical harmonic $$Y_2^2$$ acts as a source term, whereas the axial dipole term $$Y_1^0$$ consists of the term with least information loss. The results suggest a possible control of core–mantle boundary inhomogeneities on the interaction between the components of the geomagnetic field. Our results also show a net information flux from larger to smaller scales, which is compatible with a direct turbulent cascade view of the geodynamo

Information flow between MJO-related waves: a network approach on the wave space

The complex network approach has proved to be a valuable tool for climate and atmospheric sciences in recent years. Here, we show an application of causality ideas in complex networks to infer properties of equatorial wave interactions associated with the Madden–Julian Oscillation (MJO), the dominant component of the atmospheric system on intraseasonal timescales in the equatorial region. We use the normal mode function approach to obtain the time series of baroclinic Kelvin and Rossby mode energies, since both of these wave modes are known to play an important role in the MJO dynamics. The partial directed coherence method reveals the structure of the interaction among those modes and shows that the Kelvin mode is the main driver of the MJO system, transferring energy to the Rossby modes. Investigation on the Kelvin mode information source might help evaluating the state-of-the-art of MJO theories

Deciphering pre-solar-storm features of September-2017 storm from global and local dynamics

We investigate whether global toroid patterns and the local magnetic field topology of solar active region (AR) 12673 together can hindcast the occurrence of the biggest X-flares of solar cycle (SC)-24. Magnetic toroid patterns (narrow latitude belts warped in longitude, in which ARs are tightly bound) derived from the surface distributions of ARs, prior and during AR 12673 emergence, reveal that the portions of the south toroid containing AR 12673 was not tipped away from its north-toroid counterpart at that longitude, unlike the 2003 Halloween storms scenario. During the minimum phase there were too few emergences to determine multimode longitudinal toroid patterns. A new emergence within AR 12673 produced a complex nonpotential structure, which led to the rapid buildup of helicity and winding that triggered the biggest X-flare of SC-24, suggesting that this minimum-phase storm can be anticipated several hours before its occurrence. However, global patterns and local dynamics for a peak-phase storm, such as that from AR 11263, behaved like the 2003 Halloween storms, producing the third biggest X-flare of SC-24. AR 11263 was present at the longitude where the north and south toroids tipped away from each other. While global toroid patterns indicate that prestorm features can be forecast with a lead time of a few months, their application to observational data can be complicated by complex interactions with turbulent flows. Complex nonpotential field structure development hours before the storm are necessary for short-term prediction. We infer that minimum-phase storms cannot be forecast accurately more than a few hours ahead, while flare-prone ARs in the peak phase may be anticipated much earlier, possibly months ahead from global toroid patterns