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Article Dans Une Revue Atmospheric Chemistry and Physics Année : 2023

A simple model to assess the impact of gravity waves on ice-crystal populations in the tropical tropopause layer

Résumé

The role of gravity waves on microphysics of tropical cirrus clouds and air-parcel dehydration was studied using the combination of Lagrangian observations of temperature fluctuations and a 1.5D model. High-frequency measurements during isopycnal balloon flights were used to resolve the gravity-wave signals with periods ranging from a few days to 10 min. The detailed microphysical simulations with homogeneous freezing, sedimentation, and a crude horizontal mixing represent the slow ascent of air parcels in the tropical tropopause layer (TTL). A reference simulation describes the slow ascent of air parcels in the tropical tropopause layer, with nucleation occurring only below the cold-point tropopause with a small ice-crystal density. The inclusion of the gravity waves drastically modifies the vertical profile of low ice concentration and weak dehydration found during the ascent alone, with the increased ice-crystal number and size distribution agreeing better with observations. Numerous events of nucleation occur below and above the cold-point tropopause, efficiently restoring the relative humidity over ice to equilibrium with respect to the background temperature, as well as increasing the cloud fraction in the vicinity of the cold-point tropopause. The corresponding decrease in water vapor is estimated at 2 ppmv around the cold-point tropopause.
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insu-04195511 , version 1 (04-09-2023)

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Milena Corcos, Albert Hertzog, Riwal Plougonven, Aurélien Podglajen. A simple model to assess the impact of gravity waves on ice-crystal populations in the tropical tropopause layer. Atmospheric Chemistry and Physics, 2023, 23, pp.6923-6939. ⟨10.5194/acp-23-6923-2023⟩. ⟨insu-04195511⟩
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