Evolution of the ice phase in tropical altocumulus: SAMUM lidar observations over Cape Verde

Ansmann, Albert; Tesche, Matthias; Seifert, Patric; Althausen, Dietrich; Engelmann, Ronny; Fruntke, Julia; Wandinger, Ulla; Mattis, Ina; Müller, Detlef

doi:10.1029/2008jd011659

Cited by 173 publications

(264 citation statements)

References 81 publications

(134 reference statements)

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“…Atmospheric observations indicate that heterogeneous ice nucleation in mixed-phase clouds can already occur at temperatures higher than −20 • C (Ansmann et al, 2009;Seifert et al, 2010;Kanitz et al, 2011). In contrast, laboratory studies showed that the majority of non-biological substances found in atmospheric ice crystal residues, i.e., natural mineral dust (e.g., Twohy and Poellot, 2005;Pratt et al, 2009;Kamphus et al, 2010), are only ice active at lower temperatures (e.g., Hoose and Möhler, 2012;Murray et al, 2012).…”

Section: Introductionmentioning

confidence: 96%

Immersion freezing of ice nucleation active protein complexes

et al. 2013

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Utilising the Leipzig Aerosol Cloud Interaction Simulator (LACIS), the immersion freezing behaviour of droplet ensembles containing monodisperse particles, generated from a Snomax™ solution/suspension, was investigated. Thereto ice fractions were measured in the temperature range between −5 °C to −38 °C. Snomax™ is an industrial product applied for artificial snow production and contains Pseudomonas syringae} bacteria which have long been used as model organism for atmospheric relevant ice nucleation active (INA) bacteria. The ice nucleation activity of such bacteria is controlled by INA protein complexes in their outer membrane.

In our experiments, ice fractions increased steeply in the temperature range from about −6 °C to about −10 °C and then levelled off at ice fractions smaller than one. The plateau implies that not all examined droplets contained an INA protein complex. Assuming the INA protein complexes to be Poisson distributed over the investigated droplet populations, we developed the CHESS model (stoCHastic modEl of similar and poiSSon distributed ice nuclei) which allows for the calculation of ice fractions as function of temperature and time for a given nucleation rate. Matching calculated and measured ice fractions, we determined and parameterised the nucleation rate of INA protein complexes exhibiting class III ice nucleation behaviour. Utilising the CHESS model, together with the determined nucleation rate, we compared predictions from the model to experimental data from the literature and found good agreement.

We found that (a) the heterogeneous ice nucleation rate expression quantifying the ice nucleation behaviour of the INA protein complex is capable of describing the ice nucleation behaviour observed in various experiments for both, Snomax™ and P. syringae bacteria, (b) the ice nucleation rate, and its temperature dependence, seem to be very similar regardless of whether the INA protein complexes inducing ice nucleation are attached to the outer membrane of intact bacteria or membrane fragments, (c) the temperature range in which heterogeneous droplet freezing occurs, and the fraction of droplets being able to freeze, both depend on the actual number of INA protein complexes present in the droplet ensemble, and (d) possible artifacts suspected to occur in connection with the drop freezing method, i.e., the method frequently used by biologist for quantifying ice nucleation behaviour, are of minor importance, at least for substances such as P. syringae, which induce freezing at comparably high temperatures. The last statement implies that for single ice nucleation entities such as INA protein complexes, it is the number of entities present in the droplet population, and the entities' nucleation rate, which control the freezing behaviour of the droplet population. Quantities such as ice active surface site density are not suitable in this context.

The results obtained in this study allow a different perspective on the quantification of the immersi...

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Section: Introductionmentioning

confidence: 96%

Immersion freezing of ice nucleation active protein complexes

et al. 2013

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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: 97%

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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“…However, a number of field and modelling studies have indicated that in mixed-phase clouds water saturation is a prerequisite for the formation of ice, suggesting that deposition mode nucleation or condensation below water saturation may be of limited importance for such clouds (Field et al, 2012;Twohy et al, 2010;Ansmann et al, 2009;de Boer et al, 2011;Westbrook and Illingworth, 2011). Consequently both immersion and contact modes are expected to dominate ice formation in mixed-phase clouds (Hoose et al, 2010b).…”

Section: O'sullivan Et Al: Ice Nucleation By Fertile Soil Dustsmentioning

confidence: 99%

Ice nucleation by fertile soil dusts: relative importance of mineral and biogenic components

et al. 2014

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Abstract. Agricultural dust emissions have been estimated to contribute around 20 % to the global dust burden. In contrast to dusts from arid source regions, the ice-nucleating abilities of which have been relatively well studied, soil dusts from fertile sources often contain a substantial fraction of organic matter. Using an experimental methodology which is sensitive to a wide range of ice nucleation efficiencies, we have characterised the immersion mode ice-nucleating activities of dusts (d < 11 µm) extracted from fertile soils collected at four locations around England. By controlling droplet sizes, which ranged in volume from 10 −12 to 10 −6 L (concentration = 0.02 to 0.1 wt % dust), we have been able to determine the ice nucleation behaviour of soil dust particles at temperatures ranging from 267 K (−6 • C) down to the homogeneous limit of freezing at about 237 K (−36 • C). At temperatures above 258 K (−15 • C) we find that the ice-nucleating activity of soil dusts is diminished by heat treatment or digestion with hydrogen peroxide, suggesting that a major fraction of the ice nuclei stems from biogenic components in the soil. However, below 258 K, we find that the ice active site densities tend towards those expected from the mineral components in the soils, suggesting that the inorganic fraction of soil dusts, in particular the K-feldspar fraction, becomes increasingly important in the initiation of the ice phase at lower temperatures. We conclude that dusts from agricultural activities could contribute significantly to atmospheric IN concentrations, if such dusts exhibit similar activities to those observed in the current laboratory study.

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Evolution of the ice phase in tropical altocumulus: SAMUM lidar observations over Cape Verde

Cited by 173 publications

References 81 publications

Immersion freezing of ice nucleation active protein complexes

Immersion freezing of ice nucleation active protein complexes

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

Ice nucleation by fertile soil dusts: relative importance of mineral and biogenic components

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