Modeling the TTL at continental scale for a wet season: An evaluation of the BRAMS mesoscale model using TRO-Pico campaign, and measurements from airborne and spaceborne sensors

Abhinna K. Behera (1) , Emmanuel D. Rivière (1) , Virginie Marecal (2) , Jean-François Rysman (3) , Chantal Claud (3) , Geneviève Sèze (3) , Nadir Amarouche (4) , Melanie Ghysels (1) , Sergey Khaykin (5) , Jean-Pierre Pommereau (6) , Gerhard Held (7) , Jeremie Burgalat (1) , Georges Durry (1)

1 GSMA - Groupe de spectrométrie moléculaire et atmosphérique
2 CNRM - Centre national de recherches météorologiques
3 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
4 DTI - Division technique INSU/SDU
5 TROPO - LATMOS
6 STRATO - LATMOS
7 IPMet - Instituto de Pesquisas Meteorológicas

In order to better understand the water vapor (WV) intrusion into the tropical stratosphere, a mesoscale simulation of the tropical tropopause layer (TTL) using the BRAMS (Brazilian version of RAMS) model is evaluated for a wet season. This simulation with a horizontal grid-point resolution of 20 km × 20 km cannot resolve the stratospheric overshooting convection (SOC). Its ability to reproduce other key parameters playing a role in the stratospheric WV abundance is investigated using the balloon-borne TRO-Pico campaign measurements, the upper-air soundings over Brazil, and the satellite observations by Aura MLS (Microwave Limb Sounder), MHS (Microwave Humidity Sounder) and GOES-12. The BRAMS exhibits a good ability in simulating temperature, cold-point, WV variability around the tropopause. However, the simulation is typically observed to be warmer by ∼2.0°C and wetter by ∼0.4 ppmv at the hygropause, which can be partly affiliated with the grid-boundary nudging of the model by ECMWF operational analyses. The modeled cloud tops show a good correlation (maximum cross-correlation of ∼0.7) with GOES-12. Furthermore, the overshooting cells detected by MHS are observed at the locations, where 75% of the modeled cloud tops are higher than 11 km. Finally, the modeled inertia-gravity wave periodicity and wavelength are comparable with those deduced from the radio sounding measurements during TRO-Pico campaign. The good behavior of BRAMS confirms the SOC contribution in the WV abundance and variability is of lesser importance than the large-scale processes. This simulation can be used as a reference run for upscaling the impact of SOC at a continental scale for future studies.

Mots clés: Mesoscale Modeling; BRAMS; Inertia-gravity waves; Stratospheric overshooting convection; Tropical tropopause layer; Water vapor budget

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]

Abhinna K. Behera, Emmanuel D. Rivière, Virginie Marecal, Jean-François Rysman, Chantal Claud, et al.. Modeling the TTL at continental scale for a wet season: An evaluation of the BRAMS mesoscale model using TRO-Pico campaign, and measurements from airborne and spaceborne sensors. Journal of Geophysical Research: Atmospheres, 2018, 123 (5), pp.2491-2508. ⟨10.1002/2017JD027969⟩. ⟨insu-01709004⟩