10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Airborne Investigation of the Vertical Layering and Transport Processes of Aerosol Particles in the Marine Boundary Layer and the Free Troposphere over the Atlantic Ocean
BIRGIT WEHNER, Silvia Henning, Felix Lauermann, Janine Lueckerath, Greg Roberts, Kai-Erik Szodry, Holger Siebert, Leibniz-Institute for Tropospheric Research
Abstract Number: 1242 Working Group: Aerosol Transport and Transformation
Abstract Persistent low-level stratocumulus (Sc) clouds are widespread over the globe and cover on average about 20% of the Earth's surface and play an important role due to their influence on the planetary albedo. The Sc-topped boundary layer (STBL) is usually separated from the free troposphere (FT) by a thin layer characterized by strong gradients in thermodynamic and dynamic properties called entrainment interfacial layer (EIL). Closely connected to the stratification of the cloudy marine boundary layer is the spatial distribution of aerosol particles. Aerosol particles strongly interact with clouds, serving on the one hand side as cloud condensation nuclei (CCN). On the other hand, clouds are known as aerosol sources, due to new particle formation in their outflow or entrainment regions. These processes may have significant influences on both, particle and droplet number concentrations in the STBL. Furthermore, long-range transport of aerosol plays a significant role for the local balance. Due to the different sources and sinks of aerosol particles, the spatial aerosol distribution in marine areas is often characterized by complex layering closely linked to the boundary layer structure.
One main focus of this study is to improve the knowledge of sources and exchange processes of aerosol particles in the marine boundary layer. Therefore the measurement campaign “Azores stratoCumulus measurements Of Radiation, turbulEnce and aeroSols“ (ACORES) was conducted in order to have a detailed study of the stratification and layering of the marine boundary layer in terms of clouds and aerosol. ACORES took place in July 2017 on the Azores, an archipelago in the northeastern Atlantic Ocean located about 1200 km west of Portugal (39° N, 28° W). While being a remote place and having negligible influences of local anthropogenic sources, the Azores are considered being representative for the undisturbed North-East Atlantic, making it an ideal location for this study.
During the ACORES experiment airborne measurements were performed using the helicopter-borne ACTOS and SMART-HELIOS payloads which sampled almost from sea level up to 2200 m in the vicinity of Graciosa. The measurements were completed by continuous ground-based observations at sea level and in the free troposphere being the topic of a separate presentation.
For the period between July 3rd and July 22nd 2017, datasets from 17 research flights with ACTOS and SMART-HELIOS are available. The helicopter-borne payload ACTOS measured meteorological parameters with high temporal resolution, such as 3D-wind vector, temperature, and absolute humidity, but also aerosol particle number size distribution and total number concentrations of aerosol particles Np and CCN. A new pyrano- and pyrgeometer combination provides up- and downward radiation observations in the terrestrial and solar band. Furthermore, cloud droplet number concentrations, liquid water content and droplet size distributions are available.
A typical measurement flight comprises of a vertical profile up to 2000 m or higher at the begin of the flight, horizontal legs at various height levels in order to obtain robust statistics of quantities such as number size distributions and series of vertical profiles around a layer of interest, so called dolphin-flight patterns.
Number size distributions at different height levels are similar in shape: most of them consist of two modes being the typical structure for marine aerosol. However, the ratio between number concentrations of these modes varied mainly due to air mass origin. The vertical transport of aerosol particles between marine boundary layer and free troposphere will be investigated in more detail and will be subject of this presentation.
Vertical flights through the EIL show frequently enhanced particle number concentrations above the cloud layer indicating new particle formation. This process and the potential vertical transport of these newly formed particles will be investigated in this contribution.