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| Home > Publications database > Sensitivities of modelled water vapour in the lower stratosphere: temperature uncertainty, effects of horizontal transport and small-scale mixing |
| Journal Article | FZJ-2018-00024 |
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2017
EGU
Katlenburg-Lindau
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Please use a persistent id in citations: http://hdl.handle.net/2128/16343 doi:10.5194/acp-2017-1072
Abstract: Water vapour (H2O) in the upper troposphere and lower stratosphere (UTLS) is a key player for global radiation. A realistic representation of H2O is critical for climate model predictions of future climate change. Here, we investigate the effects of current uncertainties in tropopause temperature, horizontal transport and small-scale mixing on simulated H2O in the lower stratosphere (LS).To assess the sensitivities of simulated H2O, we use the Chemical Lagrangian Model of the Stratosphere (CLaMS). First, we examine CLaMS driven by two different reanalysis, ERA-Interim and Japanese 55-year (JRA-55) reanalysis, to investigate the robustness with respect to the meteorological dataset. Second, we carry out CLaMS simulations with transport barriers along latitude circles (at the equator, 15° N/S and 35° N/S) to assess the effects of horizontal transport. Third, we vary the strength of parametrized small-scale mixing in CLaMS.Our results show significant differences (about 0.5 ppmv) in simulated stratospheric H2O due to uncertainties in the tropical tropopause temperatures between current reanalysis datasets. The JRA-55 based simulation is significantly moister when compared to ERA-Interim, due to a warmer tropical tropopause in JRA-55 reanalysis. The transport barrier experiments demonstrate that the Northern Hemisphere (NH) subtropics have a strong moistening effect on global stratospheric H2O. Interhemispheric exchange shows only a very weak effect on stratospheric H2O. Small-scale mixing mainly increases troposphere–stratosphere exchange, causing an enhancement of stratospheric H2O, particularly along the subtropical jets and in the Asian monsoon region.The sensitivity studies presented here provide new insights into the leading processes that control stratospheric H2O, important for assessing and improving climate model projections.
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