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.
A sunquake event was excited by an M9.3 flare; however, the source of the sunquake waves was wave-mechanically extrapolated to about 1 megameter beneath the photosphere.
Apparent 3-min waves observed inside sunspot umbrae are modeled as excited about 1000 to 2000 km beneath sunspots’ surface.
Newly developed time-distance helioseismic imaging method, which includes more multiskip acoustic waves, is proved to be more reliable in mapping the Sun’s far-side active regions.
Subsurface meridional flows from ring-diagram analysis showed a clear hemispheric asymmetry in last 18 years. Interestingly, this flow asymmetry leads the magnetic flux and sunspot number asymmetry by 3.1 – 3.6 years.
What excites the sunspot umbral oscillations? Through analyzing two sunspots observed by FeI line, the authors found that the 3-minute umbral oscillations are likely excited by internal small-scale magnetoconvection associated with umbral dots.
A number of sunquake events were detected in the photosphere after the X9.3 flare of 6 September 2017. This analysis reported the first detection of the chromspheric response to the sunquake events using CaII and Hα observations made by the Swedish 1-meter Solar Telescope.
Power-spectrum analysis is applied on the time-distance measured travel-time shifts in the Sun’s north-south direction along the equatorial area, and the existence of Rossby waves is confirmed.
The Sun’s oblateness shows a variation with solar cycles, in phase with the solar activity level in Cycle 23 but in anti-phase with the activity level in Cycle 24. Such a trend of in-phase during odd cycles and anti-phase during even cycles is confirmed after examining past observations.
To minimize cross-talk effect from vertical flows and sound-speed perturbations, a new inversion code is developed to invert for flows and sound-speed perturbations simultaneously from time-distance travel-time measurements. The code is validated using numerical simulation data.