Microphysical characterisation of West African MCS anvils

Deep convection in the Tropics is the source of Large tropospheric extended clouds usually called anvils These anvils may produce precipitation (stratiform region of deep convective storms), and also cirrus shields persisting from several hours to several days Anvils impact the radiation budget, they induce a storage term in the whole water budget which is still relatively poorly quantified. and dynamical feedbacks may be induced in the upper troposphere The AMMA field campaign which was held over West Africa during the 2006 wet season provided a unique opportunity to document the microphysics of these anvils from unprecedented an borne observations Airborne in situ measurements of ice crystals and observations born a 95 GHz Doppler radar are used to characterize the microphysical properties of tropical anvils. The dataset is binned into stratiform and cirriform regions Some data in the stratiform regions were likely obtained close enough to convective cotes that the particles may have grown primarily within those cores The data obtained over the continent and over the ocean arc also characterized separately Particle habit and growth processes ale inferred from an examination of the collected particle images. from quantitative comparisons of 95 GHz reflectivities calculated from the in Aim microphysical observations with the measured racial reflectivities, and from a statistical analysis of the two-dimensional particle images. The predominant precipitation particles above the 0 degrees C isotherm in the stratiform anvil region ale rimed aggregates These rimed aggregates seem to get less dense and of smaller diameter when moving rearward of the system towards the cirri form region The retrieved density laws (assumed to be power laws) he close to the relationship for rimed particles of Locatelli and Hobbs Particle size distributions in tropical anvils are also studied. The exponential shape seems to be a good approximation for these panicle size distributions overall The decrease in concentration with diameter is also found to be faster for cirriform melons than for stratiform regions Normalising these particle size distributions produces a relatively invariant shape (in agreement with earlier studies). with however an increased variability for the smallest and hugest values of the normalised diameter The characterisation of the bulk microphysical properties using these in sun microphysical observations shows that the ice water content. the effective radius and the reflectivity-weighted fall velocity generally increase with an temperature. in agreement with earlier studies These parameters are found to be systematically smaller on average in cirriform regions than in strati form regions. and this is true at all temperatures These values are then compared with statistical relationships used in cloud-resolving models and general circulation models, since a realistic representation of microphysics in models is very important to understand not only the processes at work, but the dynamical feedbacks and effects on climate Large differences are found, the current parametrizations being unable to reproduce the lame values of the considered microphysical parameters Copyright (C) 2010 Royal Meteorological Society