Filter Results

113 results

- The solar magnetic helicity has opposite signs not only in the two hemispheres, but also at large and small length scales. The latter can be detected by computing magnetic helicity spectra, but this must be done separately in each hemisphere. Here we utilize a two-scale method from mean-field dynamo theory that allows us to compute magnetic helicity spectra as a function of two different wavenumbers: one corresponding to rapidly varying scale and one corresponding to a slowly varying one. We generalize this method to spherical harmonics and compute in that way global magnetic helicity spectra for that part of the field that shows a global dipolar symmetry. We present results from simple one-dimensional model calculations, three-dimensional dynamo simulations, and the two-dimensional magnetic field from synaptic vector magnetograms.Data Types:
- Video

- Solar eruptions manifesting as solar flares and coronal mass ejections (CMEs) are the explosive liberations of magnetic energy contained in the solar corona. However, the onset mechanism of solar eruptions is not yet clearly explained, although many different models have been proposed so far. In particular, what triggers solar eruptions is an important question for improving the predictability of solar eruptions. Here, we propose a new scheme of prediction of solar eruptions based on the critical condition of eruptive instability in the solar corona, which was recently proposed by Ishiguro and Kusano (2017). Their analysis indicated that a new parameter kappa, which is given by the magnetic twist, provides a critical condition to destabilize the sheared magnetic field. We build a new predictive scheme of solar eruptions using the analysis of magnetic twist and demonstrate how the structure of magnetic twist in solar active regions correlates with the activities of solar eruptions based on the space-born data of several active regions.Data Types:
- Video

- Inversions for solar meridional flows from frequency dependent travel times are presented. Born approximation kernels for meridional flows and tests on model flows are also presented.Data Types:
- Video

- Helicities as well as the turbulent energies are key players of the dynamo process. From viewpoint of turbulent transport, helicities mainly suppress the effective transports. In the presence of inhomogeneous large-scale flow, the turbulent cross helicity (cross-correlation between the velocity and magnetic-field fluctuations) enters the turbulent electromotive force and its suppression/generation effect tends to be balanced with the turbulent magnetic diffusivity. At the same time, the turbulent cross helicity coupled with the mean magnetic strain affects the momentum transport. In addition to these effects of helicities, in strong compressible magnetohydrodynamic (MHD) turbulence, the density variance contributes to the turbulent electromotive force as the coupling coefficient of the obliqueness of the mean magnetic field to the density gradient. This means that the density variance as well as the helicities alters the turbulent transport. This density-variance effect is expected to enhance the intensity of turbulence across the slow MHD shock, which may contribute to the realization of a localized fast magnetic reconnection.Data Types:
- Video

- We investigated statistical characteristics of magnetic helicity injected per unit time through the active region photosphere using vector magnetic field data from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The photospheric helicity injection rate of a given active region was calculated from the formula of the gauge-invariant relative helicity flux derived by Berger and Field (1984), applying the optical flow technique Differential Affine Velocity Estimator for Vector Magnetogram (DAVE4VM) to co-registered pairs of vector magnetograms sampled 12 minutes apart. We determined helicity injection rates for a total of 30,628 SHARP vector magnetogram pairs sampling 866 unique active regions from 2012 September to 2016 December. Using this large data set, we studied long-term, large-scale characteristics of helicity injection rates in the active region photosphere. We will present how helicity injection rates are distributed with respect to Heliographic latitude, Carrington longitude, solar cycle epoch and Hale magnetic class. It will be also discussed how helicity injection rate is related to other magnetic parameters and flare productivity of active regions.Data Types:
- Video

- The solar magnetic helicity has opposite signs not only in the two hemispheres, but also at large and small length scales. The latter can be detected by computing magnetic helicity spectra, but this must be done separately in each hemisphere. Here we utilize a two-scale method from mean-field dynamo theory that allows us to compute magnetic helicity spectra as a function of two different wavenumbers: one corresponding to rapidly varying scale and one corresponding to a slowly varying one. We generalize this method to spherical harmonics and compute in that way global magnetic helicity spectra for that part of the field that shows a global dipolar symmetry. We present results from simple one-dimensional model calculations, three-dimensional dynamo simulations, and the two-dimensional magnetic field from synaptic vector magnetograms.Data Types:
- Video

- This is a copy of presentation given at the Committee on Solar and Space Physics October 24, 2017 - October 25, 2017, Irvine, CaliforniaData Types:
- Video

- LARS is an Absolute Reference Spectrograph. It performs fiber-coupled solar observations with the high-resolution Echelle Spectrograph of the Vacuum Tower Telescope (VTT) at the Observatorio del Teide on Tenerife. The scientific instrument is operated by the Kiepenheuer Institute for Solar Physics, Freiburg. The spectral observation is supported by a Laser Frequency Comb which serves as an absolute ruler for the wavelength calibration of the solar spectrum. This novel technique of spectroscopic observations allows the determination of absolute velocities in the solar atmosphere with the best accuracy (m s-1).Data Types:
- Video

- This talk is about the current and past work on estimating the meridional flow and solar rotation with a global helioseismic approach using mode eigenfunction perturbations. We discuss in detail crucial points in measuring the meridional flow by this approach and overview and relate the results to findings from other approaches like the time distance analysis.Data Types:
- Video

- In current approaches to time-distance helioseismology, the line-of-sight projection effect on the traveltimes is not fully taken into account. Furthermore, filtering of full-disc data induces leakage due to the projection onto the CCD, which has so far not been accounted for. We develop a theoretical approach to consider these effects when computing sensitivity functions. As the formulas obtained do not seem to give results for spherical Born approximation sensitivity functions in a reasonable computation time, we develop tests to estimate the strength of the effects.Data Types:
- Video

3