准双周振荡（QBWO）是夏季南海—西北太平洋地区季节内变率的一个典型模态，其对东亚—西北太平洋天气和气候有重要影响。因而，研究夏季南海—西北太平洋地区QBWO强度变异及其机理具有重要意义。1990s末太平洋年代际振荡（PDO）发生位相转变，其对天气和气候的影响得到关注，但其能否影响夏季南海—西北太平洋大气和海洋QBWO强度的年际和年代际变率尚不清楚。项目申请人初步研究表明，此次PDO位相转变有利于8～11月热带西北太平洋大气QBWO强度年代际减弱，据此本项目拟开展以下两个方面研究：首先，1990s末PDO位相转变对8～11月热带西北太平洋大气和海洋QBWO强度年代际变率的影响及其机理；其次，1990s末PDO位相转变对8～11月南海—西北太平洋大气和海洋QBWO强度与赤道中太平洋海表温度的年际关系的影响及其机理。期望通过本项目的开展加深对南海—西北太平洋地区QBWO强度变异机理的认识。

Quasi-biweekly oscillation (QBWO) is a typical mode of intraseasonal variability in the South China Sea-western North Pacific (SCS-WNP) during summer. It has important influence on the weather and climate in the East Asia-WNP. Therefore, it is important to study mechanisms of variations of QBWO intensity in the SCS-WNP during summer. The Pacific Decadal Oscillation (PDO) experienced a phase transition around the late 1990s. Previous studies have paid attention to its influence on the weather and climate. However, whether it can influence interannual and decadal variability of atmospheric and oceanic QBWO intensity in the SCS-WNP during summer remains unknown. The applicant’s preliminary study shows that the phase transition of the PDO around the late 1990s favors weakened atmospheric QBWO intensity in the tropical WNP during August to November. Based on this, the following two aspects are planned to be studied: first, influence of the phase transition of the PDO around the late 1990s on decadal variability of atmospheric and oceanic QBWO intensity in the tropical WNP during August to November and its mechanism; second, influence of the phase transition of the PDO around the late 1990s on interannual relationship between atmospheric and oceanic QBWO intensity in the SCS-WNP during August to November and sea surface temperature in the equatorial central Pacific and its mechanism. By carrying out the program, it is expected to deepen the understanding about mechanisms of variation of QBWO intensity in the SCS-WNP.