Preprints
https://doi.org/10.5194/acp-2021-543
https://doi.org/10.5194/acp-2021-543

  19 Jul 2021

19 Jul 2021

Review status: this preprint is currently under review for the journal ACP.

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

Abhinna K. Behera1,2, Emmanuel D. Riviere1, Sergey M. Khaykin3, Virginie Marecal4, Melanie Ghysels1, Jérémie Burgalat1, and Gerhard Held5 Abhinna K. Behera et al.
  • 1GSMA, UMR CNRS 7331, UFR Sciences Exactes et Naturelles, 51687 Reims CEDEX 2, France
  • 2Now at: Univ. Lille, CNRS, UMR 8518, Laboratoire d’Optique Atmosphérique (LOA), 59000, Lille, France
  • 3LATMOS/IPSL, UVSQ Université Paris-Saclay, UPMC University Paris 06, CNRS, Guyancourt, France
  • 4Centre National de Recherches Météorologiques, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 5Instituto de Pesquisas Meteorológicas (IPMet)/ Universidade Estadual Paulista (UNESP), Bauru, S.P., 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 km2 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.

Abhinna K. Behera et al.

Status: open (until 30 Aug 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-543', Anonymous Referee #1, 26 Jul 2021 reply
  • RC2: 'Comment on acp-2021-543', Anonymous Referee #2, 27 Jul 2021 reply

Abhinna K. Behera et al.

Abhinna K. Behera et al.

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Short summary
Overshooting deep convection and its contribution to the tropical stratospheric water budget is debatable. Although its local-scale investigations are often reported, large-scale or global-scale impacts are still not addressed directly in any literature. This work paves the way for an approach of upscaling overshoot at a large scale. We perform several cloud-resolving simulations of an observational case of overshoots and quantify multiple features that can lead to a forcing scheme of overshoot.
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