By using barotropic model equations, this article analyzed the characteristics of Rossby waves, the propagation features of wave energy and the influence of dynamic and thermal effects of the Tibetan Plateau on Rossby waves,and the focus is on discussing the plateau's topographic gradient effects on atmospheric Rossby waves. Then based on the WRF3.2 and the NCEP/NCAR FNL reanalysis data, we devised comparative tests of changing the plateau's topographic gradient and simulated a process of persistent heavy rain that happened in May 2010 in South China. The results are shown as follows. The Tibetan Plateau's topography is conducive to the formation of atmospheric Rossby waves. while the plateau's terrain, its friction and heating effects can all make the atmospheric Rossby waves develop into the planetary waves; The effects of plateau's north and south slopes on the Rossby wave' phase velocity is opposite,and when the slope reached a certain value can the quasi-steady normal fluctuations be generated; Simultaneously, due to the plateau's topographic gradient, descending motion appears at the west side of the plateau while ascending motion appears at the east side, and the vertical movement increased with the amplification of topographic gradients. The plateau's topographic gradient also obviously amplified the precipitation in South China, and the rainfall area increased with the amplification of topographic gradients and gradually moved from south to north and from west to east, which is conducive to the occurrence and development of convective activities in the downstream areas of the Tibetan Plateau;Moreover, for the plateau's dynamic and thermal effects, the Rossby wave' propagation shows upstream effects of energy dispersion, so the plateau can then affect the weather in downstream areas. Moreover, the wave group velocity increased with the degree of topographic slope.
This study uses NCEP/NCAR daily reanalysis data,NOAA outgoing long-wave radiation(OLR) data,the real-time multivariate MJO(RMM) index from the Australian Bureau of Meteorology and Tibetan Plateau vortex(TPV)data from the Chengdu Institute of Plateau Meteorology to discuss modulation of the Madden-Julian Oscillation(MJO)on the Tibetan Plateau Vortex(TPV).Wavelet and composite analysis are used.Results show that the MJO plays an important role in the occurrence of the TPV that the number of TPVs generated within an active period of the MJO is three times as much as that during an inactive period.In addition,during the active period,the number of the TPVs generated in phases 1 and 2 is larger than that in phases 3 and 7.After compositing phases 1 and 7 separately,all meteorological elements in phase 1 are apparently conducive to the generation of the TPV,whereas those in phase 7 are somewhat constrained.With its eastward propagation process,the MJO convection centre spreads eastward,and the vertical circulation within the tropical atmosphere changes.Due to the interaction between the mid-latitude and low-latitude atmosphere,changes occur in the baroclinic characteristics of the atmosphere,the available potential energy and eddy available potential energy of the atmosphere,and the circulation structures of the atmosphere over the Tibetan Plateau(TP) and surrounding areas.This results in significantly different water vapour transportation and latent heat distribution.Advantageous and disadvantageous conditions therefore alternate,leading to a significant difference among the numbers of plateau vortex in different phases.
