Effect of topographic perturbation on the precipitation distribution in Tibetan Plateau

A method for spatial spectral analysis under the constraint of spectrum power conservation and a presentation for relative terrain height(topographic perturbation with respect to mean topographic trend)are proposed,in order to analyze the effect of topographic forcing on precipitation distribution in Tibetan Plateau.The results show that below the relative maximal precipitation height,the ordinary ‘classical coherent relationship' between topographic height and the precipitation profile (i.e.,the distributing profile of precipitation is similar to the undulating profile of topography,and the ridges and peaks of precipitation correspond well to those of terrain)are very complex and the terrain-rainfall pattern in Tibetan Plateau can not correctly describe.It is further found that the so-called lock-phase relationship between terrain and precipitation to be presented in a spectral space can essentially measure the coherent degree and the profile agreement between terrains and precipitation. This paper reveals that the two different phase-locked patterns can depict well the topography-precipitation relationship in Tibetan Plateau.One is the resonance-pattern that the ridges and peaks of precipitation are well correspondent to that of terrain. Another one is the shift-pattern,in which the precipitation increases or decreases with the terrain decreases or increases,respectively.