Equatorial Rossby waves are detected using the HMI’s time-distance subsurface flow fields. It is also found that the power of the Rossby waves show a positive correlation with the sunspot number, while the frequency of the waves shows an anti-correlation with the sunspot number.
Spectral analysis of the spatial structure of solar subphotospheric convection is carried out for subsurface flow maps. It is found that the horizontal flow scales increase rapidly with depth, from supergranulation to giant-cell values. The total power of the convective flows is found to be anticorrelated with the sunspot number variation over the solar activity cycle in shallow subsurface layers and positively correlated at larger depths.
Forward modeling is applied to numerous global hydrodynamic solar models, and helioseismic measurements on the meridional circulation are made using the forward modeling results. Comparison against the observational measurements shows significant differences, indicating our insufficient knowledge on either the global hydrodynamic modeling or the helioseismic inversions.
Analysis on high-spectral resolution data shows that oscillations in the higher atmosphere lead those in the lower atmosphere by an order of 1 s when their frequencies are below about 3.0 mHz, and lags behind by about 1 s when their frequencies are above 3.0 mHz. These phase shifts in the evanescent waves pose great challenges to the interpretation of some local helioseismic measurements that involve data acquired at different atmospheric heights.
High-frequency inertial waves were detected inside the Sun, propagating retrograde relative to the solar rotation with a phase speed faster than equatorial Rossby waves. How these waves are generated is discussed but remains unclear.
A new method, which is to characterize the multiscale convective spectrum of the Sun using high-resolution line-of-sight Dopplergram images from HMI, is developed, enabling the authors to estimate the spectrum to the finest observable scales.
A neural network has been developed and applied on helioseismic far-side images, and substantially improved the number of far-side active region detections with higher true positive rate.
Helioseismic wavefields are simulated using different meridional-circulation models. Time-distance helioseismic measurements applied on the simulated data indicate that it may be difficult to distinguish between single- or double-cell meridional circulation profiles.
Why do some flares cause sunquakes and others do not? A survey of 60 strong flares in Solar Cycle 24 supports a hypothesis that the coupling of downward photospheric oscillations and the impacts from flares may play a role in causing sunquakes.
A new method to derive the helioseismic sensitivity kernels for the Sun’s large-scale internal flows is developed. The new method is based on the idea of placing a small-volume flow perturbation inside the Sun’s model, simulating the wavefield in the photosphere, and then measuring the phase shifts caused by this internal perturbation.