Seasonal variability of heterogeneous ice formation in stratiform clouds over the Amazon Basin

Seifert, Patric; Kunz, Clara; Baars, Holger; Ansmann, Albert; Bühl, Johannes; Senf, Fabian; Engelmann, Ronny; Althausen, Dietrich; Artaxo, Paulo

doi:10.1002/2015gl064068

Cited by 29 publications

(49 citation statements)

References 41 publications

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“…3.1, we ignore a marine contribution of σ m to the particle extinction coefficient in the free troposphere, and therefore a marine contribution to the CCN and INP reservoirs (n CCN , n INP ) in the free troposphere. This is corroborated by our lidar observation at Punta Arenas, Chile, Cape Town, South Africa, aboard the R/V Polarstern, and many Polly lidar sites around the globe (Kanitz et al, 2013;Seifert et al, 2015;Baars et al, 2012Baars et al, , 2016. We conclude from these lidar observations that the marine extinction coefficient σ m is < 1-2 Mm −1 for free-tropospheric heights < 3-5 km, and of the order of 0.01-0.2 Mm −1 for heights > 5 km.…”

Section: Estimation Of N Inp From N 250drysupporting

confidence: 84%

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

Mamouri¹,

Ansmann²

2016

Atmos. Chem. Phys.

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142

184

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Abstract. We investigate the potential of polarization lidar to provide vertical profiles of aerosol parameters from which cloud condensation nucleus (CCN) and ice nucleating particle (INP) number concentrations can be estimated. We show that height profiles of particle number concentrations n 50,dry considering dry aerosol particles with radius > 50 nm (reservoir of CCN in the case of marine and continental non-desert aerosols), n 100,dry (particles with dry radius > 100 nm, reservoir of desert dust CCN), and of n 250,dry (particles with dry radius > 250 nm, reservoir of favorable INP), as well as profiles of the particle surface area concentration s dry (used in INP parameterizations) can be retrieved from lidar-derived aerosol extinction coefficients σ with relative uncertainties of a factor of 1.5-2 in the case of n 50,dry and n 100,dry and of about 25-50 % in the case of n 250,dry and s dry . Of key importance is the potential of polarization lidar to distinguish and separate the optical properties of desert aerosols from non-desert aerosol such as continental and marine particles. We investigate the relationship between σ , measured at ambient atmospheric conditions, and n 50,dry for marine and continental aerosols, n 100,dry for desert dust particles, and n 250,dry and s dry for three aerosol types (desert, non-desert continental, marine) and for the main lidar wavelengths of 355, 532, and 1064 nm. Our study is based on multiyear Aerosol Robotic Network (AERONET) photometer observations of aerosol optical thickness and column-integrated particle size distribution at Leipzig, Germany, and Limassol, Cyprus, which cover all realistic aerosol mixtures. We further include AERONET data from field campaigns in Morocco, Cabo Verde, and Barbados, which provide pure dust and pure marine aerosol scenarios. By means of a simple CCN parameterization (with n 50,dry or n 100,dry as input) and available INP parameterization schemes (with n 250,dry and s dry as input) we finally compute profiles of the CCN-relevant particle number concentration n CCN and the INP number concentration n INP . We apply the method to a lidar observation of a heavy dust outbreak crossing Cyprus and a case dominated by continental aerosol pollution.

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Section: Estimation Of N Inp From N 250drysupporting

confidence: 84%

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

Mamouri¹,

Ansmann²

2016

Atmos. Chem. Phys.

Self Cite

142

184

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“…Ångström exponents were 1.0-1.5, and the observed lidar ratios at 355 and 532 nm were 50-80 sr . Seifert et al (2015) studied the relationship between aerosol properties, temperature, and the efficiency of heterogeneous ice formation in thin stratiform clouds using the data set obtained in Brazil. It was found that the fraction of ice-containing clouds was enhanced by a factor of 1.5 to 2 in the dry compared to the wet season.…”

Section: Southern Hemispherementioning

confidence: 99%

An overview of the first decade of Polly<sup>NET</sup>: an emerging network of automated Raman-polarization lidars for continuous aerosol profiling

et al. 2016

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Abstract.A global vertically resolved aerosol data set covering more than 10 years of observations at more than 20 measurement sites distributed from 63 • N to 52 • S and 72 • W to 124 • E has been achieved within the Raman and polarization lidar network Polly NET . This network consists of portable, remote-controlled multiwavelength-polarization-Raman lidars (Polly) for automated and continuous 24/7 observations of clouds and aerosols. Polly NET is an independent, voluntary, and scientific network. All Polly lidars feature a standardized instrument design with different capabilities ranging from single wavelength to multiwavelength systems, and now apply unified calibration, quality control, and data analysis. The observations are processed in near-real time without manual intervention, and are presented online at polly.tropos.de. The paper gives an overview of the observations on four continents and two research vessels obtained with eight Polly systems. The specific aerosol types at these locations (mineral dust, smoke, dust-smoke and other dusty mixtures, urban haze, and volcanic ash) are identified by their Ångström exponent, lidar ratio, and depolarization ratio. The vertical aerosol distribution at the Polly NET locations is discussed on the basis of more than 55 000 automatically retrieved 30 min particle backscatter coefficient profiles at 532 nm as this operating wavelength is available for all Polly lidar systems. A seasonal analysis of measurements at selected sites revealed typical and extraordinary aerosol conditions as well as seasonal differences. These studies show the potential of Polly NET to support the establishment of a global aerosol climatology that covers the entire troposphere.

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“…Lidars are used since the 1970s to monitor clouds and their evolution, although primarily cirrus and mixed-phase clouds (Platt, 1973(Platt, , 1977Sassen, 1991). Our group also contributed to these observations over the last 25 years (Ansmann et al, 1993(Ansmann et al, , 2005Ansmann et al, 2009;Seifert et al, 2007Seifert et al, , 2010Seifert et al, , 2015Kanitz et al, 2011). Observations are rare in the case of liquid-water clouds because lidars are not appropriate for clouds with typical optical depths of 10 and more.…”

Section: Introductionmentioning

confidence: 99%

Strong aerosol–cloud interaction in altocumulus during updraft periods: lidar observations over central Europe

et al. 2015

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Abstract. For the first time, a liquid-water cloud study of the aerosol-cloud-dynamics relationship, solely based on lidar, was conducted. Twenty-nine cases of pure liquid-water altocumulus layers were observed with a novel dual-field-ofview Raman lidar over the polluted central European site of Leipzig, Germany, between September 2010 and September 2012. By means of the novel Raman lidar technique, cloud properties such as the droplet effective radius and cloud droplet number concentration (CDNC) in the lower part of altocumulus layers are obtained. The conventional aerosol Raman lidar technique provides the aerosol extinction coefficient (used as aerosol proxy) below cloud base. A collocated Doppler lidar measures the vertical velocity at cloud base and thus updraft and downdraft occurrence. Here, we present the key results of our statistical analysis of the 2010-2012 observations. Besides a clear aerosol effect on cloud droplet number concentration in the lower part of the altocumulus layers during updraft periods, turbulent mixing and entrainment of dry air is assumed to be the main reason for the found weak correlation between aerosol proxy and CDNC higher up in the cloud. The corresponding aerosol-cloud interaction parameter based on changes in cloud droplet number concentration with aerosol loading was found to be close to 0.8 at 30-70 m above cloud base during updraft periods and below 0.4 when ignoring vertical-wind information in the analysis. Our findings are extensively compared with literature values and agree well with airborne observations.

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Seasonal variability of heterogeneous ice formation in stratiform clouds over the Amazon Basin

Cited by 29 publications

References 41 publications

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

An overview of the first decade of Polly<sup>NET</sup>: an emerging network of automated Raman-polarization lidars for continuous aerosol profiling

Strong aerosol–cloud interaction in altocumulus during updraft periods: lidar observations over central Europe

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Seasonal variability of heterogeneous ice formation in stratiform clouds over the Amazon Basin

Cited by 29 publications

References 41 publications

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

An overview of the first decade of Polly&lt;sup&gt;NET&lt;/sup&gt;: an emerging network of automated Raman-polarization lidars for continuous aerosol profiling

Strong aerosol–cloud interaction in altocumulus during updraft periods: lidar observations over central Europe

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An overview of the first decade of Polly<sup>NET</sup>: an emerging network of automated Raman-polarization lidars for continuous aerosol profiling