Low-degree modes
  The quest of the knowledge of the structure and dynamics of the solar interior has been possible thanks to the study of the resonant acoustic (p) modes that are trapped in the solar interior.   Since the solar rotation lifts the azimuthal degeneracy of the resonant modes, their eigenfrequencies are split into their m-components; where l is the angular degree, n the radial order, and, m the azimuthal order. This separation --usually called rotational splitting (or just splitting)-- depends on the rotation rate in the region sampled by the mode. In the same way, the precise frequency of a mode depends on the physical properties of the cavity where the mode propagates. Using inversion techniques the rotation rate, the sound speed or the density profile at different locations inside the Sun can be inferred from a suitable lineal combination of the measured modes. But, during the last year, a particular effort has been done in the extraction of physical information directly from the combination of frequencies: the large and the small frequency separations. 
R.A. Garcia