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On the cross-tropopause transport of water by tropical convective overshoots: a mesoscale modelling study constrained by in-situ observations during TRO-Pico field campaign in Brazil

Abstract : Deep convection overshooting the lowermost stratosphere is well known for its role in the local stratospheric water vapour (WV) budget. While it is seldom the case, local enhancements of WV associated with stratospheric overshoots are often published. Nevertheless, one debatable topic prevails on the global impact of this event with respect to the temperature-driven dehydration of air parcels entering the stratosphere. As a first step, it is crucial to quantify their role at a local scale before assessing their impact at a large-scale in a meteorological model. It would lead to a forcing scheme for overshoots in the global models. This paper reports on the local enhancements of WV linked to stratospheric overshoots, observed during the TRO-Pico campaign conducted in March 2012 in Bauru, Brazil, using the BRAMS (Brazilian version of RAMS) mesoscale model. Since numerical simulation depends on the choice of several preferred parameters, each having its uncertainties, we vary the microphysics or the vertical resolution while simulating the overshoots. Thus, we produce a set of simulations illustrating the possible variations in representing the stratospheric overshoots. To resolve better the stratospheric hydration, we opt for simulations with the 800-m-horizontal-grid-point presentation. Next, we validate these simulations against the Bauru S-band radar echo tops and the TRO-Pico balloon-borne observations of WV and particles. Two of the three simulations' setups yield results compatible with the TRO-Pico observations. From these two simulations, we determine approximately 333 t to 2000 t of WV mass prevailing in the stratosphere due to an overshooting plume depending on the simulation setup. About 70% of the ice mass remains between the 380 K to 385 K isentropic levels. The overshooting top comprises pristine ice and snow, while aggregates only play a role just above the tropopause. Interestingly, the horizontal cross-section of the overshooting top is about 450 km 2 at 380 K isentrope, which is similar to the horizontal-grid-point resolution of a simulation that cannot compute overshoots explicitly. These results could establish a forcing scheme of overshooting hydration or dehydration in a large-scale simulation.
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Contributor : Catherine Cardon <>
Submitted on : Sunday, July 25, 2021 - 11:06:20 AM
Last modification on : Tuesday, July 27, 2021 - 3:38:43 AM

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Abhinna Behera, Emmanuel Rivière, Sergey Khaykin, Virginie Marécal, Mélanie Ghysels, et al.. On the cross-tropopause transport of water by tropical convective overshoots: a mesoscale modelling study constrained by in-situ observations during TRO-Pico field campaign in Brazil. Atmospheric Chemistry and Physics Discussions, European Geosciences Union, 2021, pp.(Under Review). ⟨10.5194/acp-2021-543⟩. ⟨insu-03298933⟩

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