Preprints
https://doi.org/10.5194/acp-2020-870
https://doi.org/10.5194/acp-2020-870

  21 Oct 2020

21 Oct 2020

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

Mesoscale simulations of tropical cyclone Enawo (March 2017) and its impact on TTL water vapor

Damien Héron1, Stephanie Evan1, Joris Pianezze1,2, Thibaut Dauhut3, Jerome Brioude1, Karen Rosenlof4, Vincent Noel5, Soline Bielli1, Christelle Barthe1, and Jean-Pierre Cammas1,6 Damien Héron et al.
  • 1Laboratoire de l’Atmosphère et des Cyclones, UMR8105 (Université de La Réunion, CNRS, Météo-France)
  • 2Mercator Ocean, Ramonville Saint-Agne, France
  • 3Max Planck Institute for Meteorology, Hamburg, Germany
  • 4Chemical Sciences Laboratory, Earth System Research Laboratory, NOAA, Boulder, 80305, CO, USA
  • 5Laboratoire d’Aérologie, CNRS/ UPS, Observatoire Midi -Pyrénées, 14 avenue Edouard Belin, Toulouse, France
  • 6Observatoire des Sciences de l’Univers de La Réunion, UMS3365 (CNRS, Université de La Réunion, Météo-France), Saint-Denis de la Réunion, France

Abstract. In early March 2017, tropical cyclone (TC) Enawo formed north of Réunion Island and moved westward toward Madagascar. Enawo evolved from a tropical depression on 2 March to an intense TC on 6 March. This study explores the water vapor transport into the tropical tropopause layer (TTL) throughout TC Enawo's development. High-resolution (2 km) mesoscale simulations using the Meso-NH model were performed to cover TC Enawo's lifecycle over the ocean for the period 2–7 March 2017. The simulated convective cloud field agrees with geostationary satellite infrared observations. Compared to the Global Precipitation Measurements (GPM) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite observations, the simulation seems to reproduce well both location and amplitude of the observed precipitation. Simulated and observed ice water content have similar ranges in the upper troposphere but simulated ice above the tropopause is overestimated by a factor 10. Balloon-borne measurements of water vapor, temperature and horizontal winds are also used to validate the Meso-NH simulations in the upper-troposphere and TTL regions. The simulations reveal that the maximum water vapor transport into the TTL occurred on 4 March, when deep (cold) convective clouds were observed. As a result, the lower stratospheric water vapor is increased by ~50 % when compared to pre-storm conditions. An increase of ~2 ppmv in water vapor mixing ratio was simulated in the lower stratosphere within a 700-km region surrounding Enawo's center. Our simulation of TC Enawo suggests that TCs over the Southwest Indian Ocean (0–30° S, 30–90° E) could produce a moistening of 0.4 ppmv. We extended our results to the global tropics (30° S–30° N) using the estimates from published work (Allison et al., 2018; Preston et al., 2019) and by calculating statistics on TC numbers and durations using the International Best Track Archive for Climate Stewardship (IBTrACS) dataset. We estimated a global impact of TC induced tropical lower stratospheric moistening of 0.3 to 0.5 ppmv. Our results suggest that TCs may play an important role in the moistening of the TTL/lower stratosphere via direct injection of ice particles and subsequent sublimation.

Damien Héron et al.

 
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Damien Héron et al.

Damien Héron et al.

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Short summary
Upward transport within tropical cyclones of water vapor from the low troposphere into the colder upper troposphere/lower stratosphere can result in the moistening of this region. Balloon observations and model simulations of tropical cyclone Enawo in the less-observed Southwest Indian Ocean (the third most tropical cyclone active region on Earth) are used to show how convective overshoots within Enawo penetrate the tropopause directly, injecting water/ice into the stratosphere.
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