Variation of cylindrical velocity components with distance from the plane, |Z|, for FGKM stars with measured radial velocities (red dots). The top row shows 6548 stars towards the North Galactic Pole (b > 80°) and the bottom row shows 7578 stars towards the South Galactic Pole (b < −80°). Triangles show the mean values in bins of |Z| and the thick dashed lines show the ±2σ envelope around means, where σ is the standard deviation for each bin (i.e., velocity dispersion). The thick dot-dashed lines are models for the mean velocity (0 for v_R and v_Z, and given by Eq. (1) for v_ϕ). The thin dot-dashed lines show the ±2σ envelope, with σ (velocity dispersion) given by Eqs. (2), (5), and (6), for ϕ, R and Z panels, respectively. The thin dashed lines in the two left panels also show ±2σ envelopes, but with the velocity dispersion computed using Eq. (3) (see Sect. 3.2).