In the
cruise at a constant IAS, your EAS is more or less constant too, but with
increasing altitude the TAS will increase.
If you encounter a disturbance that causes a wing to drop then static lateral
stability has two parts that constitute the recovery.
Firstly the "roll damping". At altitude
there is less roll damping, because the higher TAS means there will be a
smaller change in angle of attack, so for a given disturbance the wing will
drop through a greater angle before roll damping stops the roll.
Secondly the "dihedral effect" because they specify
a swept wing aircraft. With more bank on the
sideslip will be greater, so the dihedral effect will roll the wings level,
faster because that is based on the EAS.
So static lateral stability will be increased.
Because of the reduced roll damping, the increased roll rate to level the wings
level, means that it will overshoot the neutral
position because of the inertia, and now the reverse has occurred with the
opposite wing being low, and the cycle is repeated. This means it will take
longer to settle down, in some cases you could even have neutral or negative
dynamic lateral stability.