Non-potential field formation in the X-shaped quadrupole magnetic field configuration

Some types of solar flares are observed in X-shaped quadrupolar field configuration. To understand the magnetic energy storage in such a region, we studied non-potential field formation in an X-shaped quadrupolar field region formed in the active region NOAA 11967, which produced three X-shaped M-class flares on February 2, 2014. Nonlinear force-free field modeling was applied to a time series of vector magnetic field maps from the Solar Optical Telescope on board Hinode and Helioseismic and Magnetic Imager on board Solar Dynamics Observatory. Our analysis of the temporal three-dimensional magnetic field evolution shows that the sufficient free energy had already been stored more than 10 hours before the occurrence of the first M-class flare and that the storage was observed in a localized region. In this localized region, quasi-separatrix layers (QSLs) started to develop gradually from 9 hours before the first M-class flare. One of the flare ribbons that appeared in the first M-class flare was co-spatial with the location of the QSLs, suggesting that the formation of the QSLs is important in the process of energy release. These QSLs do not appear in the potential field calculation, indicating that they were created by the non-potential field. The formation of the QSLs was associated with the transverse photospheric motion of the pre-emerged flux and the emergence of a new flux. This observation indicates that the occurrence of the flares requires the formation of QSLs in the non-potential field in which free magnetic energy is stored in advance.Comment: Accepted for publication in Ap

Magnetohydrodynamic Simulations for Studying Solar Flare Trigger Mechanism

In order to understand the flare trigger mechanism, we conducted three-dimensional magnetohydrodynamic simulations using a coronal magnetic field model derived from data observed by the Hinode satellite. Several types of magnetic bipoles were imposed into the photospheric boundary of the Non-linear Force-Free Field (NLFFF) model of Active Region NOAA 10930 on 2006 December 13 to investigate what kind of magnetic disturbance may trigger the flare. As a result, we confirm that certain small bipole fields, which emerge into the highly sheared global magnetic field of an active region, can effectively trigger a flare. These bipole fields can be classified into two groups based on their orientation relative to the polarity inversion line: the so called opposite polarity (OP) and reversed shear (RS) structures as it was suggested by Kusano et al. (2012). We also investigated the structure of the footpoints of reconnected field lines. By comparing the distribution of reconstructed field lines and the observed flare ribbons, the trigger structure of the flare can be inferred. Our simulation suggests that the data-constrained simulation taking into account both the large-scale magnetic structure and the small-scale magnetic disturbance such as emerging fluxes is a good way to find out a flare productive active region for space weather prediction.Comment: 28 pages, 10 figure

Vitamin K, SXR, and GGCX

Vitamin K was discovered in 1929 as a substance essential for blood coagulation and had been clinically utilized before the precise mechanism of action became aware in 1970s. The function as a cofactor of γ-glutamyl carboxylase (GGCX) was the mechanism firstly discovered with the identification of several substrate proteins including blood coagulation factors and osteocalcin. Recently, we and others have shown that vitamin K has other modes of function, such as ligand of nuclear receptor SXR (steroid and xenobiotic receptor) and its murine ortholog PXR (pregnane X receptor) and modulator of protein kinase A (PKA) activity. Besides its importance in blood coagulation, involvement of vitamin K has been shown in two major aging-related diseases, osteoporosis and osteoarthritis. Based on clinical and epidemiological studies, vitamin K is shown to have protective roles for both of them. Interestingly, clinical studies concerning single nucleotide polymorphisms (SNPs) of GGCX and γ-carboxylated status of osteocalcin suggested relationship between GGCX activity and bone-protective effect, while recent findings from basic research indicated that vitamin K functions mediated by SXR/PXR as well as GGCX are important in the bone metabolism. We also suggested that cartilage-protective effect is mediated by SXR/PXR signaling by animal experiments using Pxr knockout mice