Abstract
Abstract. The present study aims to evaluate lidar retrievals of cloud-relevant aerosol properties by using polarization lidar and coincident airborne in situ measurements in the Saharan Air Layer (SAL) over the Barbados region. Vertical profiles of the number concentration of cloud condensation nuclei (CCN), large particles (diameter d>500 nm), surface area, mass, and ice-nucleating particle (INP) concentration are derived from the lidar measurements and compared with CCN concentrations and the INP-relevant aerosol properties measured in situ with aircraft. The measurements were performed in the framework of the Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE) in summer 2013. The CCN number concentrations derived from lidar observations were up to a factor of 2 higher than the ones measured in situ aboard the research aircraft Falcon. Possible reasons for the difference are discussed. The number concentration of particles with a dry radius of more than 250 nm and the surface-area concentration obtained from the lidar observations and used as input for the INP parameterizations agreed well (<30 %–50 % deviation) with the aircraft measurements. In a pronounced lofted dust layer during summer (10 July 2013), the lidar retrieval yielded 100–300 CCN per cubic centimeter at 0.2 % water supersaturation and 10–200 INPs per liter at −25 ∘C. Excellent agreement was also obtained in the comparison of mass concentration profiles. During the SALTRACE winter campaign (March 2014), the dust layer from Africa was mixed with smoke particles which dominated the CCN number concentration. This example highlights the unique lidar potential to separate smoke and dust contributions to the CCN reservoir and thus to identify the sensitive role of smoke in trade wind cumuli developments over the tropical Atlantic during the winter season.
Highlights
Climate predictions are highly uncertain (IPCC, 2013)
Methods have been developed to retrieve cloud condensation nuclei (CCN)- and ice-nucleating particle (INP)-relevant particle microphysical properties from particle extinction coefficients measured with lidar (Mamouri and Ansmann, 2016; Sawamura et al, 2017; Lv et al, 2018)
We present a detailed comparison of groundbased lidar retrievals to airborne in situ observations of CCN number concentration and INP-relevant aerosol properties
Summary
Climate predictions are highly uncertain (IPCC, 2013). One of the reasons is our poor knowledge of the impact of atmospheric aerosol on cloud processes. We present a detailed comparison of groundbased lidar retrievals to airborne in situ observations of CCN number concentration and INP-relevant aerosol properties. Using observations of transported dust over the remote Atlantic 5000 km west of the source regions in Africa, we demonstrate the capability of the lidar retrievals to predict the aerosol properties relevant to aerosol–cloud interaction. A dust–smoke mixture and a pure marine case from the SALTRACE-2 (winter campaign) are presented in addition to contrast the almost pure dust conditions prevailing during the summer half-year This comparison highlights the strong impact of smoke particles on the CCN levels over the remote tropical Atlantic during the winter half-year (biomassburning season). The three Saharan dust cases (used in our comparison study) are described with respect to dust layering, the meteorological context, and air mass transport A summary and concluding remarks are given in the last section
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