A decreasing trend in the tropical (30°S ∼ 30°N) stratospheric water vapour (SWV) entry in recent four decades (from 1984 to 2020) is detected based on the Stratospheric Water and OzOne Satellite Homogenized (SWOOSH) measurements and the ERA5 reanalysis dataset using linear regression and Ensemble Empirical Mode Decomposition (EEMD) analysis. With the concurrent warming of the sea surface temperature (SST), the Indo-Pacific warm pool (IPWP) appears to be the most significant region among the tropical oceans based on correlation analysis. >43% of the decreasing tropical lower SWV trend is likely to be related to the IPWP SST warming. To validate this relationship, two groups of idealized runs are carried out with version 4 of the Whole Atmosphere Community Climate Model (WACCM4) and version 5 of the Community Atmosphere Model (CAM5). Both simulations agree with the observational-based linkage. The IPWP-SST-warming forced simulations show that the temperature in the tropical tropopause has decreased at the rate of around 0.318 K per decade in the coldest point region, as the tropical convection over the IPWP has become more vigorous and excited stronger equatorial waves to produce adiabatic cooling around tropopause. This cooling tropical tropopause leads to a dehydrating tropical lower stratosphere at the rate of 0.025 ppmv per decade, as expected by the freeze-drying mechanism. These results imply the substantial warming trend of IPWP is an important factor for the long-term trend of the tropical SWV entry under climate change, and a better representation of this relationship in the model is critical for the SWV projection under future climate scenarios.

中文翻译：

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印度太平洋暖池变暖引起的热带平流层水汽进入的长期变化

根据平流层水和OzOne卫星均一化（SWOOSH）测量和ERA5，近四十年（从1984年至2020年）热带（30°S ∼ 30°N）平流层水蒸气（SWV）进入量呈减少趋势使用线性回归和集成经验模式分解 (EEMD) 分析重新分析数据集。根据相关分析，随着海面温度（SST）同时变暖，印度太平洋暖池（IPWP）似乎是热带海洋中最重要的区域。 >43% 的热带低 SWV 下降趋势可能与 IPWP SST 变暖有关。为了验证这种关系，使用第四版整体大气社区气候模型 (WACCM4) 和第五版社区大气模型 (CAM5) 进行了两组理想化运行。两种模拟都符合基于观察的联系。 IPWP-SST增温强迫模拟表明，在最冷点区域，热带对流层顶的温度以每十年约0.318 K的速度下降，因为IPWP上空的热带对流变得更加活跃，并激发了更强的赤道波在对流层顶周围产生绝热冷却。正如冷冻干燥机制所预期的那样，热带对流层顶的冷却导致热带低平流层以每十年 0.025 ppmv 的速度脱水。这些结果表明IPWP的显着变暖趋势是气候变化下热带SWV进入的长期趋势的重要因素，在模型中更好地表达这种关系对于未来气候情景下的SWV预测至关重要。