Comparison of tropical convective systems life cycle characteristics from geostationary and TRMM observations for the West African and South American regions

Abstract : In the tropics most of the rainfall comes in the form of individual storm events embedded in the synoptic circulations (e.g., monsoons). Understanding the rainfall and its variability hence requires to document these highly contributing tropical convective systems (MCS). Our knowledge of the MCS life cycle, from a physical point of view mainly arises from individual observational campaigns heavily based on ground radar observations. While this large body of observations enabled the creation of conceptual models of MCS life cycle, it nevertheless does not reach any statistically significant integrated perspective yet. To overcome this limitation, a composite technique, that will serve as a Day-1 algorithm for the Megha-Tropiques mission, is considered in this study. this method is based on a collocation in space and time of the level-2 rainfall estimates (BRAIN) derived from the TMI radiometer onboard TRMM with the cloud systems determined by a new tracking algorithm called TOOCAN. This tracking method is based on a 3-dimensional segmentation (image+time) of the geostationary IR imagery in order to detect and track objectively and automatically MCSs and is much more effective than traditional single threshold/overlap method to identify MCSs. A comparison of the MCSs life cycle is then performed for the 2010-2012 summer seasons over the West African, and South American regions. On the whole region of study, the results show that the temporal evolution of the cold cloud shield associated to MCSs describes a symmetry between the growth and the decay phases. It is also shown that the parameters of the conceptual model of MCSs are strongly correlated, reducing thereby the problem to a single degree of freedom. At the system scale, over both land and oceanic regions, rainfall is described by an increase at the beginning (the first third) of the life cycle and then smoothly decreases as the system shrinks and dissipates. The evolutions of the precipitating properties associated to MCSs indicate that the life cycle of these systems can be described by three phases: initiation, mature and dissipation. This pattern is robust across the entire monsoonal region and the scale factors of this idealized model indicate complex regional specificities.
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Submitted on : Friday, March 1, 2013 - 7:05:03 PM
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  • HAL Id : hal-00796190, version 1

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Thomas Fiolleau, R. Roca, Nicolas Viltard, F. C. Angelis. Comparison of tropical convective systems life cycle characteristics from geostationary and TRMM observations for the West African and South American regions. 6th Workshop of the International Precipitation Working Group (IPWG6), Oct 2012, São José dos Campos, Brazil. ⟨hal-00796190⟩

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