Frequency Shifts of the Solar Fundamental Mode
  The observed frequency shifts of the high-degree solar fundamental mode are explained using a simple geometrical optics approximation. The predicted fractional frequency shift is proportional to the mean squared velocity of the convection flow at the surface of the Sun and inversely proportional to the group velocity of the mode squared. The data converge to the predicted behavior at very high degrees. The inferred root mean squared convection velocity is 1.3 km/s. 
Andrei Gruzinov