Étude des conditions de cyclogenèse tropicale sur le sud-ouest de l'océan Indien

Abstract : Mature tropical cyclones around the world form through similar atmospheric and oceanic processes. Whereas the necessary conditions for tropical cyclogenesis to occur are identical over all tropical basins, the specific environments within which pre-existing disturbances evolve into warm-core cyclonic circulations can be fairly different. This is partly due to the influence of large-scale climatic cycles (e.g., ENSO, IOD, etc.) and synoptic-scale propagating modes (e.g., equatorial waves, MJO, etc.). While many studies have examined the specific situations of the tropical basins in the northern hemisphere, storm formation is much less known in the southern hemisphere. This thesis presents an analysis of cyclogenetic evolution of named storms (tropical storms and cyclones) in the Southwestern Indian Ocean (10% of global cyclone activity) during 12 cyclonic seasons from December to March, from 1999-2000 to 2010-2011, based on ECMWF ERA-Interim reanalyses, METEOSAT satellite images and IBTrACS cyclone data, in connection with ENSO, MJO and equatorial waves (Equatorial Rossby, Mixed Rossby- Gravity and Kelvin waves). First, an objective method is used to detect tropical storms (also identified in the IBTrACS database) in the ERA-Interim reanalyses. The overall characteristics of cyclonic perturbations (warm/cold cores, baroclinicity and upper-level forcing) that evolve into tropical storms and cyclones in the SWIO are also discussed. Then, an objective determination of relevant predictors and their associated weight is presented, followed by the determination of their combination in a linear form to derive an environmental cyclogenesis tracker adapted to the SWIO cyclonic season. The various dynamical and thermodynamical environmental parameters that compose the tracker’s formula are analyzed spectrally in space and time. The influence of the different wave modes on cyclogenesis is discussed through their impact on the environmental values that play a significant role in cyclogenesis. Finally, numerical simulations of tropical cyclone Alenga (Nov/Dec 2011) are carried out to study the small-scale processes involved in the storm’s formation and development within an MJO active phase.
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Cherina Meetoo. Étude des conditions de cyclogenèse tropicale sur le sud-ouest de l'océan Indien. Physique Atmosphérique et Océanique [physics.ao-ph]. Universite Toulouse III Paul Sabatier, 2014. Français. ⟨tel-01128104⟩

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