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Mise en place de simulateurs d'instruments de télédétection dans un modèle méso-échelle (BRAMS): Application à l'étude d'un système convectif observé pendant la campagne AMMA.

Abstract : This thesis presents the study of a mesoscale convective system (MCS), observed in Niamey (West Africa) during the AMMA campaign (African Monsoon Multidisciplinary Analysis) in 2006, using a mesoscale numerical model (BRAMS). The objective is to document the life cycle of these complex cloud systems and to characterize the predominant microphysical processes using synthetic observations. For this, several simulators of remote sensing instruments were coupled from the model outputs to create a set of data that is comparable to the observations performed during the campaign (on ground, airborne, and satellite): a 95 GHz radar (equivalent reflectivity and Doppler velocity), a 532 nm lidar (attenuated backscattering coefficient) and an infrared radiometer (brightness temperatures at 8.7, 10.6, and 12 µm). Direct and statistical comparisons have highlighted the importance of using a two-moment bulk microphysical scheme to represent this kind of cloud systems. The mesoscale characterization of this MCS was performed using an original method to discriminate the convective, stratiform and cirriform parts with brightness temperatures and radar reflectivity. Statistical analysis of brightness temperature fields has shown that the model BRAMS is realistic concerning the representation of the MCS life cycle. In the frame of a small-scale analysis, comparisons between radar reflectivities and Doppler velocities (observed and simulated) have shown that riming was overestimated by the model even in the stratiform part of the MCS. The study of the various exchanges between hydrometeor classes has highlighted the fact that rimed aggregates, often observed, were not properly represented by the model. An adjustment of the parameterization of two hydrometeor classes (aggregate and graupel) is necessary. The shape parameter of the gamma function used to represent the size distribution of these hydrometeors as well as the mass-diameter power-law coefficients must be modified to better represent the range of densities observed in situ. However, variability in size distributions calculated from the 7 classes of hydrometeors in this anvil part is consistent with in situ observed size distributions.
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https://tel.archives-ouvertes.fr/tel-00532834
Contributor : Guillaume Penide <>
Submitted on : Thursday, November 4, 2010 - 3:06:27 PM
Last modification on : Friday, April 5, 2019 - 8:07:51 PM
Document(s) archivé(s) le : Saturday, February 5, 2011 - 3:01:42 AM

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  • HAL Id : tel-00532834, version 1

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Guillaume Penide. Mise en place de simulateurs d'instruments de télédétection dans un modèle méso-échelle (BRAMS): Application à l'étude d'un système convectif observé pendant la campagne AMMA.. Planète et Univers [physics]. Université Blaise Pascal - Clermont-Ferrand II, 2010. Français. ⟨tel-00532834⟩

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