The RAVE survey , combined with proper motions and distance estimates , can be used to study in detail stellar kinematics in the extended solar neighbourhood ( solar suburb ) .
Using 72 , 365 red clump stars , we examine the mean velocity components in 3D between 6 < R < 10 \mathrm { kpc } and -2 < Z < 2 \mathrm { kpc } , concentrating on North-South differences .
Simple parametric fits to the ( R,\ > Z ) trends for V _ { \phi } and the velocity dispersions are presented .
We confirm the recently discovered gradient in mean Galactocentric radial velocity , V _ { R } , finding that the gradient is marked below the plane ( \delta \langle V _ { R } \rangle / \delta R = -8 \mathrm { kms } ^ { -1 } / \mathrm { kpc } for Z < 0 , vanishing to zero above the plane ) , with a Z gradient thus also present .
The vertical velocity , V _ { Z } , also shows clear , large-amplitude ( |V _ { Z } | = 17 \mathrm { kms } ^ { -1 } ) structure , with indications of a rarefaction-compression pattern , suggestive of wave-like behaviour .
We perform a rigorous error analysis , tracing sources of both systematic and random errors .
We confirm the North-South differences in V _ { R } and V _ { Z } along the line-of-sight , with the V _ { R } estimated independent of the proper motions .
The complex three-dimensional structure of velocity space presents challenges for future modelling of the Galactic disk , with the Galactic bar , spiral arms and excitation of wave-like structures all probably playing a role .