热带大气低频振荡对高原低涡的调制作用

THE MODULATION OF MADDEN-JULIAN OSCILLATION ON TIBETAN PLATEAU VORTEX

利用NCEP/NCAR逐日再分析资料、NOAA向外长波辐射(OLR)资料、澳大利亚气象局实时MJO指数(RMM)以及中国气象局成都高原研究所高原低涡年鉴统计数据,运用小波分析、合成分析等方法初步研究了热带大气低频振荡(MJO)对高原低涡的调制作用。结果表明,MJO对高原低涡具有显著的调制作用,MJO活跃期生成的高原低涡数约为MJO不活跃期的3倍。MJO活跃期中,第1和第2位相高原低涡频数分布较多,第3和第7位相较少。分别对第1位相和第7位相进行合成,发现各气象要素在第1位相的合成场中呈现出明显有利于高原低涡生成的因素,而在第7位相的合成场中则呈现出一定的抑制作用。MJO在向东传播的过程中,MJO对流中心东移,热带地区大气垂直环流结构随之改变。由于中低纬大气环流的相互作用,中低纬间的大气斜压性、大气有效位能以及涡动有效位能分布状况也随之改变,这使得青藏高原及周边大气环流结构发生变化,水汽输送因此产生明显差异,高原的潜热分布随之发生变化,有利于和不利于高原低涡生成的条件交替出现,从而造成不同位相高原低涡频数显著差异。

The NCEP/NCAR daily reanalysis data and the NOAA outgoing long-wave radiation （OLR） data and the Real-time Multivariate MJO （RMM） index from the Australian Bureau of Meteorology and plateau vortex data from Chengdu Institute of Plateau Meteorology are used to discuss the modulation of MJO on Tibetan Plateau vortex. Wavelet. Composite analysis is also used. The results show that the MJO plays an important role in Tibetan Plateau vortex, and the number of plateau vortex generated in the active period of MJO is three times more than that in the inactive period. During the active period, this number is larger during phase 1 and phase 2 than during phase 3 and phase 7. With the composite of phase 1 and phase 7 respectively, we discovered that the synthetic fields of all meteorological elements in phase 1 contain factors apparently conducive to the generation of the Plateau vortex, but they somewhat constrain it in phase 7. During its eastward propagation, MJO＇s convection center also spreads eastward and the tropical atmosphere changes its vertical circulation. Due to the interaction between mid-latitude atmosphere and low-latitude atmosphere, the baroclinic characteristic of the atmosphere and the available potential energy and eddy available potential energy of the atmosphere, along with the circulation structures of the atmosphere in Qinghai-Tibet Plateau and the surroundings, also change, resulting in a significant difference between water vapor transport and the distribution of the latent heat. Advantageous and disadvantageous conditions are alternating, leading to a significant difference in the number of plateau vortex in different phases.