  The GAM group velocity is estimated from the ratio of the radial free energy
flux to the total free energy applying gyrokinetic and two-fluid theory. This
method is much more robust than approaches that calculate the group velocity
directly and can be generalized to include additional physics, e.g. magnetic
geometry. The results are verified with the gyrokinetic code GYRO [J. Candy and
R. E. Waltz, J. Comp. Phys. 186, pp. 545-581 (2003)], the two-fluid code NLET
[K. Hallatschek and A. Zeiler, Physics of Plasmas 7, pp. 2554-2564 (2000)], and
analytical calculations. GAM propagation must be kept in mind when discussing
the windows of GAM activity observed experimentally and the match between
linear theory and experimental GAM frequencies.
