Quantifying the sources of increasing stratospheric water vapour concentrations
<p>According to satellite measurements from multiple instruments, water vapour (<span class="inline-formula">H<sub>2</sub>O</span>) concentrations, in most regions of the stratosphere, have been increasing at a statistically significant rate of <span class=...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-05-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/5199/2025/acp-25-5199-2025.pdf |
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| Summary: | <p>According to satellite measurements from multiple instruments, water vapour (<span class="inline-formula">H<sub>2</sub>O</span>) concentrations, in most regions of the stratosphere, have been increasing at a statistically significant rate of <span class="inline-formula">∼1</span> <span class="inline-formula">%</span>–5 <span class="inline-formula">%</span> per decade since the early 2000s. Previous studies have estimated stratospheric <span class="inline-formula">H<sub>2</sub>O</span> trends, but none have simultaneously quantified the contributions from all main sources (temperature variations in the tropical tropopause region, changes in the Brewer–Dobson circulation, and changes in methane (<span class="inline-formula">CH<sub>4</sub></span>) concentrations and oxidation) at all latitudes. Atmospheric Chemistry Experiment–Fourier Transform Spectrometer (ACE-FTS) measurements are used to estimate altitude-/latitude-dependent stratospheric <span class="inline-formula">H<sub>2</sub>O</span> trends from 2004–2021 due to these sources. Results indicate that rising temperatures in the tropical tropopause region play a significant role in the increases, accounting for <span class="inline-formula">∼1</span> <span class="inline-formula">%</span>–4 <span class="inline-formula">%</span> per decade in the tropical lower mid-stratosphere and in the mid-latitudes below <span class="inline-formula">∼20</span> <span class="inline-formula">km</span>. By regressing to ACE-FTS <span class="inline-formula">N<sub>2</sub>O</span> concentrations, it is found that, in the lower mid-stratosphere, general circulation changes have led to both significant <span class="inline-formula">H<sub>2</sub>O</span> increases and significant <span class="inline-formula">H<sub>2</sub>O</span> decreases on the order of 1 <span class="inline-formula">%</span>–2 <span class="inline-formula">%</span> per decade depending on the altitude/latitude region. Making use of measured and modelled <span class="inline-formula">CH<sub>4</sub></span> concentrations, the increase in <span class="inline-formula">H<sub>2</sub>O</span> due to <span class="inline-formula">CH<sub>4</sub></span> oxidation is calculated to be <span class="inline-formula">∼1</span> <span class="inline-formula">%</span>–2 <span class="inline-formula">%</span> per decade above <span class="inline-formula">∼30</span> <span class="inline-formula">km</span> in the Northern Hemisphere and throughout the stratosphere in the Southern Hemisphere. After accounting for these sources, there are still regions of the mid-latitude lower mid-stratosphere that exhibit significant residual <span class="inline-formula">H<sub>2</sub>O</span> trends increasing at 1 <span class="inline-formula">%</span>–2 <span class="inline-formula">%</span> per decade. Results indicate that these unaccounted-for increases could potentially be explained by increases in upper-tropospheric molecular hydrogen.</p> |
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| ISSN: | 1680-7316 1680-7324 |