Quasi-biennial oscillations are found in the Sun’s interior rotation-rate residuals. They appear differently at different depths and latitudes, and evolve with time.
Instead of the center-annulus measurement geometry that time-distance helioseismology typically uses, a new one-sided center-arc measurement scheme is developed. This method shows advantage in measuring subsurface flows in in a close neighborhood of magnetic regions.
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 new website is developed to host HMI’s time-distance pipeline products, including far-side images, subsurface flows, evolution of near-surface zonal and meridional flows.
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.
The giant cellular flows, obtained through tracking HMI-observed Dopplergrams, are used to estimate kinetic helicity and Reynolds stress inside the Sun, as well as differential rotation and poleward drift near the bottom of the convection zone.
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.
Fourier Legendre decomposition is applied on HMI’s long-term Doppler-velocity observations to derive the Sun’s internal meridional circulation. In addition to the well-known center-to-limb effect, a non-axisymmetric component in the northern- and southern-hemisphere is identified as another systematic effect that complicates the derivation of the internal meridional circulation.
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.