[en] Two extrapolation models of the solar coronal magnetic field are compared using magnetogram data from the Solar Dynamics Observatory /Helioseismic and Magnetic Imager instrument. The two models, a horizontal current–current sheet–source surface (HCCSSS) model and a potential field–source surface (PFSS) model, differ in their treatment of coronal currents. Each model has its own critical variable, respectively, the radius of a cusp surface and a source surface, and it is found that adjusting these heights over the period studied allows for a better fit between the models and the solar open flux at 1 au as calculated from the Interplanetary Magnetic Field (IMF). The HCCSSS model provides the better fit for the overall period from 2010 November to 2015 May as well as for two subsets of the period: the minimum/rising part of the solar cycle and the recently identified peak in the IMF from mid-2014 to mid-2015 just after solar maximum. It is found that an HCCSSS cusp surface height of 1.7 R _⊙ provides the best fit to the IMF for the overall period, while 1.7 and 1.9 R _⊙ give the best fits for the two subsets. The corresponding values for the PFSS source surface height are 2.1, 2.2, and 2.0 R _⊙ respectively. This means that the HCCSSS cusp surface rises as the solar cycle progresses while the PFSS source surface falls.

[en] Spectra of the cellular photospheric flows are determined from full-disk Doppler velocity observations acquired by the Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory spacecraft. Three different analysis methods are used to separately determine spectral coefficients representing the poloidal flows, the toroidal flows, and the radial flows. The amplitudes of these spectral coefficients are constrained by simulated data analyzed with the same procedures as the HMI data. We find that the total velocity spectrum rises smoothly to a peak at a wavenumber of about 120 (wavelength of about 35 Mm), which is typical of supergranules. The spectrum levels off out to wavenumbers of about 400, and then rises again to a peak at a wavenumber of about 3500 (wavelength of about 1200 km), which is typical of granules. The velocity spectrum is dominated by the poloidal flow component (horizontal flows with divergence but no curl) at wavenumbers above 30. The toroidal flow component (horizontal flows with curl but no divergence) dominates at wavenumbers less than 30. The radial flow velocity is only about 3% of the total flow velocity at the lowest wavenumbers, but increases in strength to become about 50% at wavenumbers near 4000. The spectrum compares well with the spectrum of giant cell flows at the lowest wavenumbers and with the spectrum of granulation from a 3D radiative-hydrodynamic simulation at the highest wavenumbers

[en] Solar active region (AR) 12192 of 2014 October hosts the largest sunspot group in 24 years. It is the most prolific flaring site of Cycle 24 so far, but surprisingly produced no coronal mass ejection (CME) from the core region during its disk passage. Here, we study the magnetic conditions that prevented eruption and the consequences that ensued. We find AR 12192 to be “big but mild”; its core region exhibits weaker non-potentiality, stronger overlying field, and smaller flare-related field changes compared to two other major flare-CME-productive ARs (11429 and 11158). These differences are present in the intensive-type indices (e.g., means) but generally not the extensive ones (e.g., totals). AR 12192's large amount of magnetic free energy does not translate into CME productivity. The unexpected behavior suggests that AR eruptiveness is limited by some relative measure of magnetic non-potentiality over the restriction of background field, and that confined flares may leave weaker photospheric and coronal imprints compared to their eruptive counterparts

[en] In this work, we derive magnetic toroids from surface magnetograms by employing a novel optimization method, based on the trust region reflective algorithm. The toroids obtained in this way are combinations of Fourier modes (amplitudes and phases) with low longitudinal wavenumbers. The optimization also estimates the latitudinal width of the toroids. We validate the method using synthetic data, generated as random numbers along a specified toroid. We compute the shapes and latitudinal widths of the toroids via magnetograms, generally requiring several m's to minimize residuals. A threshold field strength is chosen to include all active regions in the magnetograms for toroid derivation, while avoiding non-contributing weaker fields. Higher thresholds yield narrower toroids, with an m = 1 dominant pattern. We determine the spatiotemporal evolution of toroids by optimally weighting the amplitudes and phases of each Fourier mode for a sequence of five Carrington Rotations (CRs) to achieve the best amplitude and phases for the middle CR in the sequence. Taking more than five causes “smearing” or degradation of the toroid structure. While this method applies no matter the depth at which the toroids actually reside inside the Sun, by comparing their global shape and width with analogous patterns derived from magnetohydrodynamic (MHD) tachocline shallow water model simulations, we infer that their origin is at/near the convection zone base. By analyzing the “Halloween” storms as an example, we describe features of toroids that may have caused the series of space weather events in 2003 October–November. Calculations of toroids for several sunspot cycles will enable us to find similarities/differences in toroids for different major space weather events.