Processes influencing lower stratospheric water vapour in monsoon anticyclones: insights from Lagrangian modelling

Abstract. We investigate the influence of different chemical and physical processes on water vapour distribution in lower stratosphere (LS), particular Asian North American monsoon anticyclones (AMA NAMA, respectively). Specifically, we use chemistry transport model CLaMS to analyse effects large-scale temperatures, methane oxidation, ice microphysics, small-scale atmospheric mixing experiments. All these hydrate LS and, particularly, AMA. While microphysics has largest global moistening impact, it is which dominates specific signature AMA In particular, parameterization strongly contributes this region improves simulation intra-seasonal variability, resulting a better agreement with Aura Microwave Limb Sounder (MLS) observations. Although none our experiments reproduces spatial pattern NAMA as seen MLS observations, they all exhibit realistic annual cycle are mainly controlled by temperatures. further sensitivity results domain-filling trajectory set-up, here-called Lagrangian filling (LTF). Compared observations multiyear reference using full-blown version CLaMS, find that LTF schemes result drier weaker signal over regions, likely related specification boundary condition. Overall, emphasize importance subgrid-scale multiple pathways from troposphere representing