CCN concentration and INP-relevant aerosol profiles in the Saharan Air Layer over Barbados from polarization lidar and airborne in situ measurements

Abstract

<p><strong>Abstract.</strong> The present study aims to validate lidar retrievals of cloud-relevant aerosol properties by using polarization lidar and coincident airborne in situ measurements in the Saharan Air Layer over the Barbados region. Vertical profiles of the number concentration of cloud condensation nuclei (CCN), large particles (diameter <i>d</i> > 500 nm), surface area, and ice nucleating particles (INP) are estimated from the lidar measurements and compared with CCN concentrations and the INP-relevant aerosol properties in situ measured with aircraft in the framework of the Saharan Aerosol Long-range Transport and Aerosol–Cloudinteraction Experiment (SALTRACE) in summer 2013. The CCN number concentrations derived from lidar observations were up to a factor of two higher than the ones measured in situ on board the research aircraft Falcon. However, a reasonable agreement was obtained when taking the lidar uncertainty into account. The number concentration of particles with dry radius > 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 cm<sup>3</sup> at 0.2 % water supersaturation and 25–65 INP per L at −25 °C. 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.</p>

Dust mass, cloud condensation nuclei, and ice-nucleating particle profiling with polarization lidar: updated POLIPHON conversion factors from global AERONET analysis

“…Here we assume that pure dust causes particle linear depolarization ratios of 0.3-0.35 around the globe, disregarding the dust source region. This is corroborated by numerous studies (see the reviews in Tesche et al, 2009;Ansmann, 2014, 2017) and also during recent field campaigns (Groß et al, 2015;Veselovskii et al, 2016;Haarig et al, 2017;Hofer et al, 2017). Details of the aerosol type separation procedure (including the separation of fine and coarse Table 1.…”

“…In addition, the impact of the selected conversion factors on the results is illuminated in the framework of an uncertainty analysis. The case presented here was already discussed in terms of optical properties by Hofer et al (2017). Figure 8 presents an overview of the aerosol conditions observed with lidar on 13 April 2015.…”

“…A sensitive impact of fine-mode-dominated fire smoke and urban haze on the conversion calculations is also unlikely as long as AE<0.3. Additional smoke contributions immediately lead to AE values clearly above 0.5 as our field campaign experience indicates (Tesche et al, 2009;Nisantzi et al, 2014;Hofer et al, 2017). In order to illustrate the variability in the POLIPHON conversion factors (summarized in Sect.…”

“…The derived total, fine-, and coarse-dust backscatter coefficients β d , β df , and β dc are then converted to respective dust extinction values σ d , σ df , and σ dc by means of appropriate dust extinction-to-backscatter ratios or lidar ratios S d , S df , and S dc . As shown in Table 2, the 532 nm dust lidar ratio S d may vary from about 30 to 60 sr for different mineral dust types (Müller et al, 2007;Tesche et al, 2011;Mamouri et al, 2013;Nisantzi et al, 2015;Groß et al, 2015;Veselovskii et al, 2016;Haarig et al, 2017;Hofer et al, 2017;Shin et al, 2018). However, for most dust regions, except the western Sahara, the typical dust lidar ratio is 40 sr at 532 nm.…”

“…), Tajikistan, in April 2015. The lidar observations were performed in the framework of the 18-month field campaign CADEX (Central Asian Dust Experiment) (Hofer et al, 2017). The full potential of the POLIPHON method (Table 1) is shown.…”