Emily Tinney - November 10

Weather and Climate Systems

Occurrence, Sources, and Transport Characteristics of Observed Water Vapor Extrema in the Lower Stratosphere

Emily Tinney

Wednesday, November 10

03:00 PM

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Stratospheric water vapor has been shown to have a substantial impact on the radiation budget and surface climate, with per molecule impacts of water vapor maximized near the tropopause. The stratosphere is primarily moistened through stratosphere-troposphere exchange processes such as the Brewer-Dobson circulation, Rossby wave breaking events, isentropic cross-tropopause ascent, and deep convection. Efforts to understand the distribution, transport, and sources of stratospheric water vapor have increased in recent years, with many studies utilizing long-term satellite observations. While much work has focused on stratospheric entry water vapor concentrations in the deep tropics, increasing attention has been given to stratospheric water vapor extrema from tropopause-overshooting convection. The Microwave Limb Sounder (MLS) aboard the Aura satellite has been measuring upper tropospheric and lower stratospheric water vapor at individual pressure levels since 2005. Previous work with MLS to examine stratospheric water vapor has typically focused on pressures <100 hPa to ensure the observations are truly stratospheric. However, this leads to the exclusion of (at least part of) the lowermost stratosphere in the midlatitudes and polar regions where tropopause pressures are frequently >200 hPa. Our current understanding of near-tropopause stratospheric water vapor extrema is therefore likely an underestimation, which is particularly problematic as this region is where the radiative forcing of water vapor is maximized. Additionally, this could lead to an underestimation of the contribution of convection to stratospheric water vapor, as extratropical tropopause-overshooting convection (especially over North America) has a substantial seasonal impact on concentrations within ~3 km of the tropopause. We therefore expand on previous work by examining 16 years (2005–2020) of MLS water vapor extrema in both the lowermost and overworld stratosphere, providing additional context to these observations through analysis of common transport pathways and potential convective sources associated with water vapor extrema from the Global Precipitation Measurement (GPM) mission. Analysis is performed on a seasonal basis, and long-term changes in high water vapor occurrence and transport are also evaluated.