In-situ ice particle measurements in the UT/LS and in mesoscale convective system outflows during the West-African Monsoon

During the SCOUT-AMMA campaign in Ouagadougou, Burkina Faso, in 2006, measurements in the tropical UT/LS and in the vicinity of Mesoscale Convective Systems (MCS) were performed onboard the Russian high altitude research aircraft M55 “Geophysica” at altitudes up to 20 km. A combination of a Cloud Imaging Probe (CIP) and a Forward Scattering Spectrometer Probe (FSSP-100) was utilized to perform in-situ measurements of ice crystal size distributions over a broad size range. While the FSSP-100 here covers ice particle sizes ranging from 2 to 47µm, also single particle information along with particle shapes are provided by the CIP. The CIP delivers 2-dimensional shadow cast images of particles with sizes roughly between 25 and 1600µm. Among various other instruments (e.g. for NO, ozone, CO, CO2, water vapour) a four channel condensation particle counter (i.e., the COPAS -COndensation PArticle counting System) also was operated on “Geophysica”. It is capable of detecting (albeit not sizing) aerosol particles with sizes of 6 nm up to 1μm in diameter.

In focus of most flights were the MCS outflow regions. Air masses of recent as well as aged outflow have been probed. These have been identified by tracer measurements such as NO or CO2. Ice particles with sizes >1000µm have been observed in young outflow, whereas particle sizes and number concentrations decrease in aged outflow. A comparison of the cloud particle measurements in outflows of different ages and their correlation with various gas phase constituents will be presented. Also the activation of aerosol to cloud particles inside and outside of the MCS outflow will be compared. Vertical profiles of cloud particle data as size distributions were obtained during ascent through a MCS. This observation shows a decrease of effective radius with altitude in the upper troposphere, which is in agreement with data obtained during the SCOUT-O3 (2005) campaign in Darwin, Australia. These profile measurements are compared to size distribution profiles obtained during CEPEX and SCOUT-O3.