210 Ice Crystal Properties in the Outflow of Mesoscale Convective Systems over West Africa

Wednesday, 11 July 2018
Regency A/B/C (Hyatt Regency Vancouver)
Yvonne Boose, DLR, Wessling, Germany; and J. Kleine, V. Hahn, S. Kaufmann, D. Sauer, H. Schlager, V. Catoire, and C. Voigt

Mesoscale convective systems (MCSs) contribute more than 50 % of the annual precipitation in southern West Africa (SWA). However, in-situ cloud observations in West Africa are scarce and the high uncertainties in cloud properties limit the quality of weather forecast and climate models in this region.

We present airborne data from the DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) campaign, which took place in June and July 2016 and involved ground-based and aircraft-based measurements in five countries in SWA. The DLR Falcon conducted 12 research flights, two of which were targeting the outflow of MCSs at an altitude of 10 to 12 km. Cloud particle microphysical properties were measured with a 2D-S optical array probe, recording the particle number density, size distribution and shape of particles between 10 and 1280 µm in diameter, and a CAS-DPOL (Cloud and Aerosol Spectrometer, with an additional detector for backscatter and depolarization) for particles between 0.5 and 50 µm. Number concentration and size distribution of aerosol particles larger than 10 nm were recorded with a set of condensation particle counters and optical particle counters.

First results show that one of the MCS outflows, measured on 13 July 2016 at an altitude of 11-12 km, consists of large ice crystals of various shapes. The second MCS outflow, which was probed on 11 July 2016 at an altitude of 10 km and 12 km, seems to be generally dryer and influenced by a dust layer. The observed ice crystals are smaller than in the first MCS outflow. To explain these differences, the source region of the deep convection is investigated using Hysplit back trajectories in combination with carbon monoxide measured onboard the Falcon as a tracer for anthropogenically influenced boundary layer air. Microphysical and optical properties of the in-situ cloud measurements can be compared to satellite observations to study the radiative impact of these high convective clouds.

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