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Communication incl. Poster: BibTeX citation key:  Bouniola
Bouniol, D., Delanoe, J., Duroure, C., Protat, A., Giraud, V. & Penide, G. 2009. Microphysical characterisation of West African MCS anvils. Work presented at Third International AMMA Conference, July 20—24, at Ouagadougou, Burkina Faso.
Added by: Devic 2009-09-10 15:42:59    Last Edited by: roussot 2009-10-18 17:28:07
Categories: Weather to Climatic modelling and forecasting
Creators: Bouniol, Delanoe, Duroure, Giraud, Penide, Protat
Publisher: African Monsoon Multidisciplinary Analyses (Ouagadougou, Burkina Faso)
Collection: Third International AMMA Conference

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Deep convection is the ultimate source of tropical upper tropospheric extended clouds, i. e. tropical anvils. The anvil lifetime, typically 6-12 hours, exceeds the duration of deep convection by many hours. Far from the active centre of the convective core, the anvil structure becomes optically thinner but still has significant radiative and chemical impacts. The microphysics of crystals in this type of clouds is an important parameter impacting radiation budget, the amount of water stored in ice phase (that may lead to precipitation) within the troposphere and chemical concentrations for both soluble species and species that adsorb onto ice.
During the AMMA field campaign a Special Observing Period was dedicated to the microphysical characterisation of the MCS anvils using aircraft instrumentation (cloud radar, lidar and a suite of microphysical in-situ measurements). The measurements are combined in order to diagnose the most representative density law for ice hydrometeors within the different regions of the sampled anvils. A confirmation of this diagnostic is proposed by using the analysis of the roughness parameter (that links area and the perimeter of the particles). A density between graupel and aggregates (depending of the anvil region) appears to be most representative, with a predominant growth through the riming process. The particle size distribution is investigated and a normalisation process is applied. The shape of the normalised particle size distribution has also been studied, and is found to be reasonably invariant, which implies that it can be represented by a single mathematical shape for all ice clouds, which is consistent with earlier studies.
Microphysical and radiative parameters are derived from this data set in the different regions of the anvils. Expected behavior is found with an increase in the ice water content, the effective radius and reflectivity-weighted fall velocity, and a decrease of the total concentration as a function of temperature. These values are compared with statistical relationships that are often found in models (mesoscale or general circulation models).
Last Edited by: roussot