Tropical cold point tropopause temperature (CPT) anomalies determine lower stratospheric water vapor (LSWV) variations, leading to a high correlation between variations in tropical average CPT and changes in tropical average LSWV. However, this high correlation is only found in winter and spring. This work revisits the factors controlling LSWV variations using observations and simulations over the past ~40 years. It is found that the first and second empirical orthogonal function (EOF) modes of tropical CPT variations together explain the tropical average LSWV changes much better than the tropical average CPT variations. The high correlation between the first and second EOF modes of tropical CPT variations and tropical average LSWV changes holds in all four seasons. A further analysis shows that the first and second EOF modes of tropical CPT variations are related to canonical El Niño–Southern Oscillation (ENSO) activity and sea surface temperature (SST) variations in the central Pacific Ocean, respectively. ENSO Modoki is also an important factor that affects LSWV variations by influencing the vertical velocity at the tropopause. The quasi-biennial oscillation (QBO) affects the CPT, and is the third process modulating the LSWV changes. The simulations also support the results.

热带冷点对流层顶温度（CPT）异常决定了平流层较低的水汽（LSWV）变化，从而导致热带平均CPT变化与热带平均LSWV变化之间存在高度相关性。但是，仅在冬季和春季才发现这种高度相关性。这项工作通过过去40年来的观察和模拟，重新研究了控制LSWV变化的因素。发现热带CPT变化的第一和第二经验正交函数（EOF）模式共同解释了热带平均LSWV变化比热带平均CPT变化要好得多。热带CPT变化的第一和第二EOF模式与热带平均LSWV变化之间的高度相关性在所有四个季节中均成立。进一步的分析表明，热带CPT变化的第一和第二EOF模式分别与太平洋中部的典型厄尔尼诺-南方涛动（ENSO）活动和海面温度（SST）变化有关。ENSO Modoki还是通过影响对流层顶的垂直速度影响LSWV变化的重要因素。准每两年一次的振荡（QBO）影响CPT，并且是调制LSWV变化的第三个过程。仿真也支持结果。准每两年一次的振荡（QBO）影响CPT，并且是调制LSWV变化的第三个过程。仿真也支持结果。准每两年一次的振荡（QBO）影响CPT，并且是调制LSWV变化的第三个过程。仿真也支持结果。