Fig. 4

The behavior of the dimensionless velocities in the single-valuedness area. The dependence of the dimensionless velocity components β _x , β _y from the dimensionless components p _x , p _y of wave momentum in the single-valuedness area {|p _x |, |p _y |} ≤ π/2 presented. As it can be seen, this area is a subset of the area: {|p _x |, |p _y |} ≤ 2π/3. a The normal mode for β _x component (corresponds to the lower sign in the left formula of definitions (7)). b The abnormal mode for β _x component (corresponds to the upper sign in the left formula of definitions (7)). c The normal mode for β _y component (corresponds to the lower sign in the right formula of definitions (7)). d The abnormal mode for β _y component (corresponds to the upper sign in the right formula of definitions (7))