41. Consequence of that is ideal phase and group velocity matching for the two waves propagating along the crystal. 42. Usually the shorter Rossby waves have an eastward group velocity and the longer ones have a westward group velocity . 43. A common misconception occurs between phase velocity and group velocity ( analogous to centres of mass and gravity ). 44. Usually the shorter Rossby waves have an eastward group velocity and the longer ones have a westward group velocity. 45. The waves propagate on the ocean surface, and the wave energy is also transported horizontally with the group velocity . 46. The group velocity can also exceed c and is not the speed at which information is communicated in general. 47. The generated electromagnetic wave power has its group velocity directed oppositely to the direction of motion of the electrons. 48. The first superprism also modified group velocity rather than phase velocity in order to achieve the " superprism phenomena ". 49. The effect arises because wave parameters such as group velocity or vertical wavenumber depend on mean flow direction and strength. 50. Such a material allows an electromagnetic wave to convey energy ( have a group velocity ) against its phase velocity.
