Saharan dust and heterogeneous ice formation: Eleven years of cloud observations at a central European EARLINET site

Seifert, Patric; Ansmann, Albert; Mattis, Ina; Wandinger, Ulla; Tesche, Matthias; Engelmann, Ronny; Müller, Detlef; García‐Pando, Carlos Pérez; Haustein, Karsten

doi:10.1029/2009jd013222

Cited by 125 publications

(173 citation statements)

References 66 publications

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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: 97%

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: 97%

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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“…It can been assumed that all naturally occurring ice nucleators (IN) active at temperatures warmer than −10 • C are of biological origin (Christner et al, 2008). Although numerical simulations suggest a negligible role of biological IN on the global scale (Hoose et al, 2010a, b), a quarter of clouds observed over Central Europe with cloud top temperatures of −10 • C contained measurable amounts of ice (Seifert et al, 2010), so are probably influenced by biological IN.…”

Section: Motivationmentioning

confidence: 99%

Atmospheric ice nucleators active ≥ −12 °C can be quantified on PM<sub>10</sub> filters

Conen

Henne

Morris³

et al. 2012

Atmos. Meas. Tech.

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Abstract. Small number concentrations render it difficult to quantify ice nucleators (IN) in the atmosphere active at warm temperatures. A useful new method for IN measurement based around filter collections is proposed. It makes use of quartz filters used in 24 h PM 10 monitoring (720 m 3 air sample). Small subsamples (1.8 mm diameter) from the effective filter area and from the clean fringe (blank) are subjected to immersion freezing tests. We applied the method to eight filters from the High Alpine Research Station Jungfraujoch (3580 m above sea level) in the Swiss Alps. All filters carried IN active at −7 • C and below. Number concentrations of IN active at −8, −10, and −12 • C were on average 3.3, 10.7, and 17.2 m −3 , respectively. Several-fold larger numbers of IN active at ≥ −12 • C per unit mass of PM 10 were found in air masses influenced by Swiss and southern German atmospheric boundary layer air, compared to a Saharan dust event. In combination with data on PM 10 mass, the method may be used to re-construct time series of IN number concentrations.

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Saharan dust and heterogeneous ice formation: Eleven years of cloud observations at a central European EARLINET site

Cited by 125 publications

References 66 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

Atmospheric ice nucleators active ≥ −12 °C can be quantified on PM<sub>10</sub> filters

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Saharan dust and heterogeneous ice formation: Eleven years of cloud observations at a central European EARLINET site

Cited by 125 publications

References 66 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

Atmospheric ice nucleators active ≥ −12 °C can be quantified on PM&lt;sub&gt;10&lt;/sub&gt; filters

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Atmospheric ice nucleators active ≥ −12 °C can be quantified on PM<sub>10</sub> filters