Processes influencing lower stratospheric water vapour in monsoon anticyclones: insights from Lagrangian modelling
<p>We investigate the influence of different chemical and physical processes on the water vapour distribution in the lower stratosphere (LS), in particular in the Asian and North American monsoon anticyclones (AMA and NAMA, respectively). Specifically, we use the chemistry transport model CLaM...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/9585/2021/acp-21-9585-2021.pdf |
| Summary: | <p>We investigate the influence of different chemical and physical processes on the water vapour distribution in the lower stratosphere (LS), in particular in
the Asian and North American monsoon anticyclones (AMA and NAMA, respectively). Specifically, we use the chemistry transport model CLaMS to
analyse the effects of large-scale temperatures, methane oxidation, ice microphysics, and small-scale atmospheric mixing processes in different model
experiments. All these processes hydrate the LS and, particularly, the
AMA. While ice microphysics has the largest global moistening impact, it is
small-scale mixing which dominates the specific signature in the AMA in the
model experiments. In particular, the small-scale mixing parameterization
strongly contributes to the water vapour transport to this region and improves
the simulation of the intra-seasonal variability, resulting in a better
agreement with the Aura Microwave Limb Sounder (MLS) observations. Although none of our experiments reproduces the spatial pattern of the NAMA as seen in MLS observations, they all exhibit a realistic annual cycle and intra-seasonal variability, which are mainly
controlled by large-scale temperatures. We further analyse the sensitivity of
these results to the domain-filling trajectory set-up, here-called Lagrangian
trajectory filling (LTF). Compared with MLS observations and with a multiyear reference simulation using the full-blown chemistry transport model version of
CLaMS, we find that the LTF schemes result in a drier global LS and in a
weaker water vapour signal over the monsoon regions, which is likely related
to the specification of the lower boundary condition. Overall, our results
emphasize the importance of subgrid-scale mixing and multiple transport
pathways from the troposphere in representing water vapour in the AMA.</p> |
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| ISSN: | 1680-7316 1680-7324 |