  The diamagnetic drift effects on the low-$n$ magnetohydrodynamic
instabilities at the high-mode (H-mode) pedestal are investigated in this paper
with the inclusion of bootstrap current for equilibrium and rotation effects
for stability, where $n$ is the toroidal mode number. The AEGIS (Adaptive
EiGenfunction Independent Solutions) code [L. J. Zheng, M. T. Kotschenreuther,
J. Comp. Phys. {\bf 211}, (2006)] is extended to include the diamagnetic drift
effects. This can be viewed as the lowest order approximation of the finite
Larmor radius effects in consideration of the pressure gradient steepness at
the pedestal. The H-mode discharges at Jointed European Torus (JET) is
reconstructed numerically using the VMEC code [P. Hirshman and J. C. Whitson,
Phys. Fluids {\bf 26}, 3553 (1983)], with bootstrap current taken into account.
Generally speaking, the diamagnetic drift effects are stabilizing. Our results
show that the effectiveness of diamagnetic stabilization depends sensitively on
the safe factor value ($q_s$) at the safety-factor reversal or plateau region.
The diamagnetic stabilization are weaker, when $q_s$ is larger than an integer;
while stronger, when $q_s$ is smaller or less larger than an integer. We also
find that the diamagnetic drift effects also depend sensitively on the rotation
direction. The diamagnetic stabilization in the co-rotation case is stronger
than in the counter rotation case with respect to the ion diamagnetic drift
direction.
