They are alternating bands of faster and slower rotation.So far there is no generally accepted theoretical explanation for them, even though a close relation to the solar cycle is evident, as they have a period of eleven years, as was known since they were first observed in 1980.
Analysis of these overlapping modes constitutes the discipline of global helioseismology.
Solar oscillation modes are essentially divided up into three categories, based on the restoring force that drives them: acoustic, gravity, and surface-gravity wave modes.
(l=20, m=16 and n=14.) Note that the increase in the speed of sound as waves approach the center of the sun causes a corresponding increase in the acoustic wavelength.
Helioseismology is the study of the propagation of wave oscillations, particularly acoustic pressure waves, in the Sun.
The data from time-series of solar spectra show all the oscillations overlapping.
Thousands of modes have been detected (with the true number perhaps being in the millions).Unlike seismic waves on Earth, solar waves have practically no shear component (s-waves).Solar pressure waves are believed to be generated by the turbulence in the convection zone near the surface of the sun.In other words, the turbulence "rings" the sun like a bell.The acoustic waves are transmitted to the outer photosphere of the sun, which is where the light generated through absorption of radiant energy from nuclear fusion at the centre of the sun, leaves the surface.The science can be compared to asteroseismology, which studies the propagation of sound waves in stars.