Climatology, sources, and transport characteristics of observed water vapor extrema in the lower stratosphere
<p>Stratospheric water vapor (H<span class="inline-formula"><sub>2</sub></span>O) is a substantial component of the global radiation budget and therefore important to variability in the climate system. Efforts to understand the distribution, transport, and sou...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2023-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/14375/2023/acp-23-14375-2023.pdf |
| Summary: | <p>Stratospheric water vapor (H<span class="inline-formula"><sub>2</sub></span>O) is a substantial component of the global radiation budget and therefore important to variability in the climate system. 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. Previous work to examine stratospheric H<span class="inline-formula"><sub>2</sub></span>O extrema has typically focused on the stratospheric overworld (pressures <span class="inline-formula">≤</span> 100 hPa) to ensure the observations used are truly stratospheric. However, this leads to the broad exclusion of the lowermost stratosphere, which can extend over depths of more than 5 km below the 100 hPa level in the midlatitudes and polar regions and has been shown to be the largest contributing layer to the stratospheric H<span class="inline-formula"><sub>2</sub></span>O feedback. Moreover, focusing on the overworld only can lead to a large underestimation of stratospheric H<span class="inline-formula"><sub>2</sub></span>O extrema occurrence. Therefore, we expand on previous work by examining 16 years of Microwave Limb Sounder (MLS) observations of water vapor extrema (<span class="inline-formula">≥</span> 8 ppmv) in both the stratospheric overworld and the lowermost stratosphere to create a new lower-stratosphere climatology. The resulting frequency of H<span class="inline-formula"><sub>2</sub></span>O extrema increases by more than 300 % globally compared to extrema frequencies within stratospheric overworld observations only, though the percentage increase varies substantially by region and season. Additional context is provided for this climatology through a backward isentropic trajectory analysis to identify potential sources of the extrema. We show that, in general, tropopause-overshooting convection presents itself as a likely source of H<span class="inline-formula"><sub>2</sub></span>O extrema in much of the world, while meridional isentropic transport of air from the tropical upper troposphere to the extratropical lower stratosphere is also possible.</p> |
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| ISSN: | 1680-7316 1680-7324 |