Understanding Long-term Variations in Stratospheric Water Vapor

该项目旨在了解在观测和未来气候变化模式模拟中看到的热带平流层水蒸气的变化。对未来气候的模拟一致显示，由于温室气体增加，热带平流层水汽呈增加趋势，但1980年代以来的卫星资料显示年际和年代际变化，但趋势不大。此外，逐月平流层水汽与100hPa升温速率在观测资料中呈负相关，在未来气候模拟中呈正相关。如果水汽和升温速率的变化与布鲁尔-多布森环流的变化有关，则预计会出现负相关，因为较强的BD环流与较强的热带加热（即较强的非绝热上升流）和较冷的热带平流层温度有关。但未来的气候模拟显示，水蒸汽和低压环流的强度都在增加。此外，预计地表温度的升高会使平流层水汽增加，但在观测记录中，地表温度升高，而热带平流层水汽没有升高。本项目采用一套模式，包括区域填充轨迹模式、全大气群落气候模式（WACCM）和一维辐射传输模式，以了解造成观测和模拟水汽变化的潜在过程。由于平流层水汽的气候效应，以及平流层臭氧与水汽之间的关系，这项工作具有更广泛的影响。此外，PI将通过新媒体渠道向普通受众进行宣传，从而努力增加公众对本研究所涉及的现象的理解。该项目还支持和培训一名研究生，从而为该研究领域的科学劳动力的发展提供支持。

This project seeks to understand changes in tropical stratospheric water vapor seen in observations and in model simulations of future climate change. Simulations of future climate consistently show an increasing trend in tropical stratospheric water vapor due to greenhouse gas increases, but satellite data since the 1980s show interannual and decadal variability but little trend. In addition, comparison of monthly stratospheric water vapor and 100hPa heating rate are negatively correlated in observational data, but positively correlated in future climate simulations. Negative correlations are expected if changes in water vapor and heating rates are linked to variations in the Brewer-Dobson circulation, as a stronger BD circulation is associated with stronger tropical heating (i.e. stronger diabatic upwelling) and colder tropical stratospheric temperatures. But future climate simulations show increases in both water vapor and the strength of the BD circulation. Moreover, increases in surface temperature are expected to produce increases in stratospheric water vapor, but surface temperatures rose over the observed record while tropical stratospheric water vapor did not. This project uses a suite of models including a domain-filling trajectory model, the Whole Atmosphere Community Climate Model (WACCM), and a one-dimensional radiative transfer model, to understand the underlying processes responsible for the changes in observed and simulated water vapor changes.The work has broader impacts due to the climatic effects of stratospheric water vapor, and the relationship between stratospheric ozone and water vapor. In addition, the PI will conduct outreach to general audiences through new-media outlets, thereby working to increase public understanding of the phenomena addressed in this research. The project also supports and trains a graduate student, thereby providing for the development of the scientific workforce in this research area.