Characterization of long-range transported Saharan dust by means of ground-based Raman and depolarization lidar measurements at Barbados

Abstract:

In June and July 2013 the Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE) took place at Barbados to investigate long-range transported dust after its transport over the Atlantic Ocean. Ground-based lidar measurements were performed to characterize the optical properties of long-range transported dust, and to investigate possible changes of the optical properties during transport. Measurements of the particle linear depolarization ratio (PLDR) at 355 nm and 532 nm and of the vibrational Raman signals at 387 nm and 607 nm were conducted with the small portable lidar system POLIS of the Meteorological Institute (MIM) of the Ludwig-Maximilians-Universität München in cooperation with the Institute of Atmospheric Physics (IPA) of the German Aerospace Centre (DLR). The measurements were performed in a routine manner every day for 3 hours starting at sunrise and another 3 hours starting at sunset (combined Raman and PLDR). During heavy dust events or during the formation of tropical storm Chantal measurements were performed continuously up to 48 hours.

During SALTRACE the vertical aerosol distribution was dominated by a three layer structure. The boundary layer was dominated by marine air masses in most of the cases. Above the boundary layer a mixing layer with very variable structure was found up to heights of 1.5 km to 2 km. This layer was often affected by cumulus clouds. The Saharan dust layer was observed in a height range of about 2 km to about 3.5 km. In some cases the upper boundary was even 5 km.

In our presentation we will give an overview over the general measurement situation and the POLIS measurements. We will present first results of the PLDR and the lidar ratio of long-range transported dust, as well as of the marine dominated air masses in the boundary layer. Furthermore we will compare our findings with results found for fresh Saharan dust and dust at the beginning of the long-range transport investigated during the Saharan Mineral Dust Experiment (SAMUM).