Documentation of the dynamical, microphysical, and radiative properties of the stratiform part of West-African squall lines sampled with the airborne cloud radar RASTA during AMMA

Two Special Observing Periods of the AMMA (African Monsoon Multidisciplinary Analyses) field campaign (SOP2a3 in the Niamey area, and SOP3a2 in the Dakar area) were dedicated to the investigation of the dynamical, microphysical, and radiative properties of the stratiform part of the West-African mesoscale convective systems, the understanding of the modulation of the monsoon cycle by these stratiform parts, and the investigation of the differences in cloud properties at the land-ocean transition and between the Niger and Senegal areas. 7 and 4 useful flights for these objectives have been carried out around Niger and Senegal, respectively, during AMMA. An original variational method has been first developed in order to retrieve the three-dimensional wind from the 3 downward-looking antennas of the cloud radar and the two-dimensional wind from the 2 upward-looking antennas of the cloud radar. Then, the RadOn (Radar-Only) method, initially developed for the retrieval of the microphysical and radiative properties of ice clouds from a vertically-pointing ground-based Doppler cloud radar has been adapted to the airborne cloud radar case. This method uses the Doppler velocity and radar reflectivity to retrieve the two parameters of the normalized ice particle size distribution, thereby allowing the retrieval of the main microphysical and radiative parameters characterizing ice clouds : ice water content, terminal fall speed of the ice crystals, visible extinction (and therefore optical depth by integration in the vertical), and effective radius. From this unique set of observations the first documentation of the ice cloud properties within the anvil part of West-African squall lines has been carried out, which will be described and analyzed during the conference, the differences in cloud properties between oceanic and continental mesoscale convective systems.

Type of presentation : oral