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By combining LAMOST DR4 and Gaia DR2 common red clump stars with age andproper motion, we analyze the amplitude evolution of the stellar warpindependently of any assumption with a simple model. The greatest height of thewarp disk increases with Galactocentric distance in different populations andit is dependent on the age: the younger stellar populations exhibit strongerwarp features than the old ones, accompanied with the warp amplitude $\gamma({\rm age})$ decreasing with age and its first derivative $\dot{\gamma} ({\rmage})$ is different from zero. The azimuth of line of nodes $\phi _w$ is stableat $-$5 degree without clear time evolution, which perfectly confirms some ofprevious works. All these self-consistent evidences support that our Galacticwarp should most likely be a long lived, but non-steady structure and not atransient one, which is supporting the warp is originated from gas infall ontothe disk or other hypotheses that suppose that the warp mainly affects to thegas, and consequently younger populations tracing the gas are stronger than theolder ones. In other words, the Galactic warp is induced by thenon-gravitational interaction over the disk models.

the astrophysical journal

Mapping the Galactic disk with the LAMOST and Gaia Red clump sample. VI:  An evidence for the long lived non-steady warp of non-gravitational scenarios