Tag Archives: solar cycles

223. Helioseismic evidence that the solar dynamo originates near the tachocline

Contributed by Krishnendu Mandal. Posted on February 26, 2026

Helioseismic analysis of solar torsional oscillations reveals dynamo-wave–like signatures that originate near the tachocline and propagate through the convection zone, linking internal zonal flows to the surface magnetic cycle. Additional evidence from frequency-splitting coefficients and rotational shear variations shows strong solar-cycle correlations, supporting the tachocline as a primary site of solar dynamo action.

221. The Tilted Structure of Equatorial Rossby Waves Beneath the Solar Surface

Contributed by Oana Vesa. Posted on February 13, 2026

Equatorial Rossby waves at different depths are studied, and it is found that the Rossby waves are tilted retrograde with depth rather than being a columnar structure. The tilt remains relatively stable through the solar cycle without being consistently modulated by magnetic activity.

219. SOHO/MDI and SDO/HMI Sunspot Area Measurement

Contributed by Peter Meadows. Posted on October 14, 2025

A robust, calibrated method for measuring sunspot areas from SOHO/MDI and SDO/HMI full-disk images enables a consistent, observer-independent, long-term catalogue of daily sunspot areas, revealing detailed patterns of sunspot group area evolution and solar cycle variability.

214. Characterizing the Observational Properties of the Sun’s High-latitude m=1 Inertial Mode

Contributed by Boyang Ding. Posted on July 25, 2025

High-latitude m=1 inertial modes were analyzed and characterized using the time-distance helioseismic subsurface flows. It was found that the mode’s power exhibits an anti-correlation with solar activity. Magnetic flux transported from low to high latitudes influences both the mode’s power and lifetime, enhancing its power and shortening its lifetime upon arrival.

206. Magnetic power spectra of the Sun and cycle dependence of magnetic network

Contributed by Yukun Luo. Posted on January 7, 2025

Magnetic power spectra were calculated using MDI and HMI data for two solar cycles. It is found that the sizes of the magnetic networks do not show a cycle dependence, but the power-law indices estimated from the active region and network sizes show an anti-correlation with the sunspot numbers.

186. Solar-Cycle Variation of quiet-Sun Magnetism and Surface Gravity Oscillation Mode

Contributed by Andreas Korpi-Lagg. Posted on October 17, 2022

Twelve years of HMI Dopplergram and magnetogram data have been used to uncover the solar cycle dependence of the magnetically quietest regions on the Sun and to reveal an enigmatic behavior of the surface-gravity wave energy contained in those regions.

170. Solar Toroidal Field Evolution Spanning Four Sunspot Cycles Seen By WSO, SOHO/MDI, and SDO/HMI

Contributed by Allison L. Liu. Posted on November 19, 2021

The Sun’s toroidal field is derived using 45 years of Wilcox Solar Observatory data, 16 years of Michelson Doppler Imager data, and 11 years of Helioseismic and Magnetic Imager data. The duration of each cycle in both hemispheres is also estimated.

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.