  In this work, we revisit the linear gyro-kinetic theory of geodesic acoustic
modes (GAMs) and derive a general dispersion relation for an arbitrary
equilibrium distribution function of ions. A bi-Maxwellian distribution of ions
is then used to study the effects of ion temperature anisotropy on GAM
frequency and growth rate. We find that ion temperature anisotropy yields
sensible modifications to both the GAM frequency and growth rate as both tend
to increase with anisotropy and these results are strongly affected by the
electron to ion temperature ratio.
