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.
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.
The Sun’s near surface shear layer (NSSL) is characterized by using HMI ring-diagram results. It is found the NSSL is composed of three distinct layers: a deeper larger region with a small shear, a narrow middle layer with a strong shear, and a layer very close to the surface.
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 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.
In an MHD simulation of flux emergence, a δ-sunspot is formed spontaneously by a collision of areas with opposite polarities. Driven by convective flows and counter-streaming flows, sheared polarity inversion lines form and flux ropes are created above.
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.