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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 31, issue 1
Ann. Geophys., 31, 107-125, 2013
https://doi.org/10.5194/angeo-31-107-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 31, 107-125, 2013
https://doi.org/10.5194/angeo-31-107-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 24 Jan 2013

Regular paper | 24 Jan 2013

A numerical study of orographic forcing on TC Dina (2002) in South West Indian Ocean

S. Jolivet1,2, F. Chane-Ming1, D. Barbary1, and F. Roux3 S. Jolivet et al.
  • 1Laboratoire de l'Atmosphère et des Cyclones, UMR 8105 CNRS – Météo-France – Université de la Réunion, 15 avenue René Cassin, CS 92003, 97744 Saint Denis Cedex 9, Ile de la Réunion, France
  • 2Singapore-Delft Water Alliance, National University of Singapore, 1 Engineering Drive 2, Blk E1, #08-25, 117576 Singapore, Singapore
  • 3Laboratoire d'Aérologie, UMR 5560 CNRS – Université Paul Sabatier, 14 avenue Edouard Belin, 31400 Toulouse, France

Abstract. Using the French non-hydrostatic mesoscale numerical model Méso-NH, intense tropical cyclone (TC) Dina (2002) is simulated to investigate the forcing caused by the steep orography of Réunion island (20.8° S, 55.5° E) in the southwest Indian Ocean. The model initialised by a bogus vortex derived from Doppler radar observations reproduces quite well the dynamical characteristics of TC Dina approaching the island and provides some clues on the orographic influence on the structure and the evolution of the TC.

The presence of the island is observed to stabilise the cyclonic circulation by damping the natural elliptical eyewall rotation and forcing the flow circulation. Initially, the cyclonic flow is blocked upwind of the orography which induces a convergence associated with upward vertical velocities, intense precipitation and maximum horizontal winds along the upwind slopes of the island. A mountain wave, generated over the highest terrains, is associated with downward motions on the lee side. When the strongest winds reach the island, the flow changes its behaviour from passing around to over the island. Non-dimensional flow parameters in agreement with recent theories are calculated to explain TC track.

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