Changes within African mesoscale convective systems under the presence of Saharan Air Layer dust as examined by NPOL radar during NAMMA-06

In 2006, the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field campaign investigated the factors that control the fate of African Easterly waves (AEWs) and associated mesoscale convective systems (MCSs) as they transitioned from the continent to the tropical eastern Atlantic Ocean. The Saharan Air Layer (SAL) frequently accompanies AEWs, often introducing dry, dusty air into convective storm systems. Although the SAL tends to suppress convection by introducing hot, dry air into storms and increasing vertical wind shear, the dust associated with the SAL can also act as cloud condensation nuclei (CCN), thereby invigorating convection. This radar study examined the microphysical characteristics from nineteen case studies during the NAMMA field project at fifteen-minute intervals using the NASA Polarimetric (NPOL) radar. NPOL uses both horizontal and vertical propagating waves to provide physical characteristics of hydrometeors in addition to reflectivity. To determine the location of dust relative to the MCSs as viewed by NPOL, aerosol optical thickness (AOT) from the MODIS Aerosol Product was used. The high temporal resolution of changes in cloud microphysics where MCSs are in the presence of dust suggest that indirect aerosol effects can play an important role in the invigoration of convection.