1979—2008年夏季青藏高原东南部降水的低频振荡统计特征

Statistic Characteristics of Summer Precipitation Low-frequency Oscillation over the Southeast of the Tibetan Plateau from 1979 to 2008

利用青藏高原1979—2008年地面逐日降水资料及NCEP/NCAR逐日再分析资料,对高原东南部夏季降水的低频振荡特征进行统计分析,并讨论了该地区典型旱、涝年夏季降水的低频振荡特征以及低频环流的传播特征。结果表明：（1）青藏高原东南部作为高原夏季降水大值区,其低频振荡主要表现为10~20 d准双周振荡（QBWO）和30~60 d季节内振荡（ISO）,其中QBWO最显著;（2）该地区旱、涝年夏季降水的低频振荡存在差异。其中,旱年夏季降水以QBWO为主,而涝年夏季降水的ISO和QBWO均很重要,且QBWO的方差贡献在旱年更显著,而ISO的方差贡献在涝年相对更重要;（3）青藏高原高空100 h Pa散度的ISO和QBWO普遍以驻波为主,其次是从高原向东部传播,但也存在少数由东部向西传播进入高原的低频振荡,表明夏季青藏高原主要是低频振荡的源地,有时也受外来影响。

Based on the daily precipitation from 83 weather stations in the Tibetan Plateau and NCEP/NCAR reanalysis daily data with2 .5 ° × 2 .5 ° spatial resolution, the low - frequency oscillation characteristics of summer precipitation over the southeast of the TibetanPlateau from 1979 to 2008 were statistically analyzed. Furthermore, the characteristics of summer precipitation low - frequency oscillationand propagation of low - frequency circulation in typical flood and drought years were emphatically discussed. The results are asfollows ： （1 ） The precipitation in the Tibetan Plateau gradually decreased from southeast to northwest during 1979 -2 0 0 8 , and it wasmaximum in the southeast of the Tibetan Plateau. There were two main periods of low - frequency oscillation of summer precipitation inthe southeast of the Tibetan Plateau with 1 0 - 2 0 d Quasi - biweekly Oscillation （ QBWO） and 30 - 60 d Intra - seasonal Oscillation（ISO ） , and the QBWO of summer precipitation was most significant. （2 ） The low - frequency oscillation of summer precipitation inflood and drought years over the southeast of Tibetan Plateau was significantly different. The QBWO of summer precipitation was maintype in drought years, while ISO and QBWO were both significant in flood years. Furtherm ore, the variance contribution of QBWO ofsummer precipitation was more significant in drought years, while that of ISO was relatively more significant in flood years over thesoutheast of the Tibetan Plateau. （3 ） The standing wave was the main transmission mode of ISO and QBWO of divergence on 100 hPaover the southeast of the Tibetan Plateau, secondly it was the propagation from the southeastern Plateau to the eastern mainland. However,there were also a few oscillation waves propagating from the eastern mainland to the southeastern Plateau. In summary, the southeasternPlateau was main source of low - frequency oscillation in summer, but sometimes it was also affected by the external.