Observation of Dust Aging Processes During Transport from Africa into the Caribbean – A Lagrangian Case Study

Thursday, 18 December 2014: 2:50 PM
Bernadett Weinzierl1,2, Daniel N Sauer2, Adrian Walser2, Maximilian Dollner2, Oliver Reitebuch1, Silke Gross1, Fernando Chouza1, Albert Ansmann3, Carlos Toledano4, Volker Freudenthaler2, Konrad Kandler5, Andreas Schäfler1, Robert Baumann1, Ina Tegen3 and Bernd Heinold3, (1)German Aerospace Center (DLR), Institute of Atmospheric Physics, Oberpfaffenhofen, Germany, (2)Ludwig-Maximilians-Universität, Meteorological Institute, München, Germany, (3)Leibniz Institute for Tropospheric Research, Leipzig, Germany, (4)Universidad de Valladolid, Grupo de Optica Atmosferica, Valladolid, Spain, (5)Technische Universität Darmstadt, Institut für Angewandte Geowissenschaften, Darmstadt, Germany
Aerosol particles are regularly transported over long distances impacting air quality, health, weather and climate thousands of kilometers downwind of the source. During transport, particle properties are modified thereby changing the associated impact on the radiation budget. Although mineral dust is of key importance for the climate system many questions such as the change of the dust size distribution during long-range transport, the role of wet and dry removal mechanisms, and the complex interaction between mineral dust and clouds remain open.

In June/July 2013, the Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE: http://www.pa.op.dlr.de/saltrace) was conducted to study the transport and transformation of Saharan mineral dust. Besides ground-based lidar and in-situ instruments deployed on Cape Verde, Barbados and Puerto Rico, the DLR research aircraft Falcon was equipped with an extended aerosol in-situ instrumentation, a nadir-looking 2-µm wind lidar and instruments for standard meteorological parameters.

During SALTRACE, five large dust outbreaks were studied by ground-based, airborne and satellite measurements between Senegal, Cape Verde, the Caribbean, and Florida. Highlights included the Lagrangian sampling of a dust plume in the Cape Verde area on 17 June which was again measured with the same instrumentation on 21 and 22 June 2013 near Barbados. Between Cape Verde and Barbados, the aerosol optical thickness (500 nm) decreased from 0.54 to 0.26 and the stratification of the dust layers changed significantly from a rather homogenous structure near Africa to a 3-layer structure with embedded cumulus clouds in the Caribbean. In the upper part of the dust layers in the Caribbean, the aerosol properties were similar to the observations near Africa. In contrast, much more variability in the dust properties was observed between 0.7 and 2.5 km altitude probably due to interaction of the mineral dust with clouds.

In our presentation, we show vertical profiles of dust size distributions, CCN and dust optical properties. Based on the Lagrangian measurements, we discuss the effects of dust aging processes during long-range transport. Special attention will be given on changes in fine and coarse mode size distribution and aerosol mixing state.