Category Archives: Magnetic Field

168. Introducing the SPEAR Catalogue from HMI Data

Contributed by Aimee Norton. Posted on October 29, 2021

In order to make the properties of magnetic features observed by SDO/HMI more accessible, the Solar Photospheric Ephemeral and Active Region (SPEAR) catalogue has been created as an easy-to-read tabulated text file. Tilt angles from the SPEAR catalogue are shown as a histogram (top) and as a function of latitude (bottom) with colors indicating all regions (blue), regions with anti-Joy (red), and anti-Hale (purple) tilts. Over 40% of regions disobey the laws of Joy and Hale.

159. Magnetic Field Dependence of Bipolar Magnetic Region Tilts on the Sun: Indication of Tilt Quenching

Contributed by Bibhuti Kumar Jha. Posted on June 15, 2021

Magnetic-field dependence of active regions’ tilt angles are analyzed using the MDI and HMI observations for two solar cycles. The variation of the tilt angles with the maximum magnetic-field strength of the ARs indicates a nonlinear tilt quenching in the Babcock–Leighton process.

156. Fast and Accurate Emulation of the SDO/HMI Stokes Inversion with Uncertainty Quantification

Contributed by Richard Higgins. Posted on April 16, 2021

An emulation of the VFISV Stokes Inversion that trains a deep
network (U-Net) to map directly from IQUV polarized light to Milne-Eddington magnetic field parameters. The accuracy of this method suggests that it could serve as a warm-start for VFISV or as a pre-disambiguation stand-in.

151. Hemispheric Sign Preference of Magnetic Helicity Flux in Solar Cycle 24

Contributed by Sung-Hong Park. Posted on January 26, 2021

To study the physical processes causing the hemispheric sign preference (HSP) of helicity in the Sun, the authors surveyed active regions (ARs) observed during Solar Cycle 24 to estimate their magnetic helicity flux, and studied the HSP dependences of the magnetic helicity flux with respect to various properties of ARs.

150. Photospheric Oscillations in and around Active Region 11158, including the Polarity Inversion Line

Contributed by Aimee Norton. Posted on January 20, 2021

To search for signatures of Alfvénic waves in the solar photosphere, the authors analyze the oscillation amplitudes, phases and time-distance behavior between different observables in a sunspot umbra, its polarity inversion line, and surrounding area.

149. Activity Complexes and a Prominent Poleward Surge During Solar Cycle 24

Contributed by Zi-Fan Wang. Posted on December 15, 2020

A surface flux-transport dynamo model assimilation shows that the long-lasting active-region complexes, which appeared in the Sun’s southern hemisphere during Cycle 24, played a crucial role in the pole’s polarity reversal and the field strength at the cycle minimum.

147. Recurring Homologous Solar Eruptions in NOAA AR 11429

Contributed by Suman Dhakal. Posted on October 14, 2020

Through studying three homologous eruptive events in an active region, the authors conclude that shearing motions and magnetic flux cancellation play a dominant role leading to the recurrent eruptions, and are key processes forming the eruptive structures.