Measurements of the concentration and composition of nuclei for cirrus formation

DeMott, Paul J.; Cziczo, D. J.; Prenni, A. J.; Murphy, D. M.; Kreidenweis, Sonia M.; Thomson, D. S.; Borys, Randolph D.; Rogers, D. C.

doi:10.1073/pnas.2532677100

Cited by 556 publications

(531 citation statements)

References 36 publications

(43 reference statements)

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“…The apparent relation of ice nuclei number concentrations to the number concentrations of certain subsets of the atmospheric aerosol has been recognized for more than 40 years (20,(22)(23)(24). All of these studies noted either linear or power law relations between ice nuclei and aerosol number concentrations within restricted size ranges, generally those particles larger than 0.3-μm diameter.…”

Section: Discussionmentioning

confidence: 99%

Predicting global atmospheric ice nuclei distributions and their impacts on climate

DeMott

Prenni²,

Liu³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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1,101

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Knowledge of cloud and precipitation formation processes remains incomplete, yet global precipitation is predominantly produced by clouds containing the ice phase. Ice first forms in clouds warmer than −36°C on particles termed ice nuclei. We combine observations from field studies over a 14-year period, from a variety of locations around the globe, to show that the concentrations of ice nuclei active in mixed-phase cloud conditions can be related to temperature and the number concentrations of particles larger than 0.5 μm in diameter. This new relationship reduces unexplained variability in ice nuclei concentrations at a given temperature from ∼10 3 to less than a factor of 10, with the remaining variability apparently due to variations in aerosol chemical composition or other factors. When implemented in a global climate model, the new parameterization strongly alters cloud liquid and ice water distributions compared to the simple, temperature-only parameterizations currently widely used. The revised treatment indicates a global net cloud radiative forcing increase of ∼1 W m −2 for each order of magnitude increase in ice nuclei concentrations, demonstrating the strong sensitivity of climate simulations to assumptions regarding the initiation of cloud glaciation.aerosol indirect effects | climate forcing | ice nucleation T he formation of ice in clouds is of vital importance to life on Earth, as ice formation is one of the key processes initiating precipitation. In addition, since ice nucleation is tied to the action of specific aerosol particles, natural and human impacts on ice nucleation in the atmosphere can lead to alteration of the energy and hydrological cycles (1). Ice nucleation in clouds occurs via two primary pathways: homogeneous freezing of liquid particles below about −36°C and heterogeneous ice nucleation, triggered by "ice nuclei" that possess surface properties favorable to lowering the energy barrier to crystallization. Once ice is formed, some circumstances may favor generation of ice from preexisting ice particles, or secondary ice formation (2). Heterogeneous ice nucleation remains an enigmatic topic involving multiple mechanistic processes (3) that sometimes defy ready investigation or description. Despite the lack of a complete understanding of heterogeneous ice formation processes, a variety of techniques have been developed and used to detect the presence of and quantify the number concentrations of atmospheric ice nuclei as a function of temperature (4). These measurements show that, although generally representing only 1 in 10 5 of ambient particles in the free troposphere (5), ice nuclei (IN) can nevertheless exert an influence on cold cloud microphysical processes that is disproportionate to their low number concentrations. For example, the concentrations of IN needed to explain observed precipitation rates range from as small as 10 −3 per standard liter at −10°C (6) to more typical estimates of a few IN per standard liter at −20°C (7).The sensitivity of precipitation initiation fro...

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Section: Discussionmentioning

confidence: 99%

Predicting global atmospheric ice nuclei distributions and their impacts on climate

DeMott

Prenni²,

Liu³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

1,101

1,218

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“…), cloud internal dynamics (Marsham and Dobbie, 2005;Fusina and Spichtinger, 2010) and background aerosols that are either liquid and freeze homogeneously (Hoyle et al, 2005;Spichtinger and Gierens, 2009a) or contain a solid and may act as heterogeneous ice nuclei (DeMott et al, 2010). Ice in the upper troposphere is known to nucleate via both pathways, homogeneous freezing of aqueous solution droplets (Koop et al, 2000) or heterogeneous nucleation on solid aerosol particles (DeMott et al, 2003). Both mechanisms, and especially homogeneous freezing, require regions with very low temperatures and high supersaturation with respect to ice.…”

Section: A Cirisan Et Al: Balloon-borne Match Measurementsmentioning

confidence: 99%

“…Here we adopted the canonical value of 10 L −1 by DeMott et al (2003). Table 4 lists two heterogeneous scenarios in comparison with other scenarios, while Table C1 shows additional calculations for various IN concentrations (see Appendix C).…”

Section: Heterogeneous Nucleation Of Icementioning

confidence: 99%

Balloon-borne match measurements of midlatitude cirrus clouds

et al. 2014

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Abstract.Observations of high supersaturations with respect to ice inside cirrus clouds with high ice water content (> 0.01 g kg −1 ) and high crystal number densities (> 1 cm −3 ) are challenging our understanding of cloud microphysics and of climate feedback processes in the upper troposphere. However, single measurements of a cloudy air mass provide only a snapshot from which the persistence of ice supersaturation cannot be judged. We introduce here the "cirrus match technique" to obtain information about the evolution of clouds and their saturation ratio. The aim of these coordinated balloon soundings is to analyze the same air mass twice. To this end the standard radiosonde equipment is complemented by a frost point hygrometer, "SnowWhite", and a particle backscatter detector, "COBALD" (Compact Optical Backscatter AerosoL Detector). Extensive trajectory calculations based on regional weather model COSMO (Consortium for Small-Scale Modeling) forecasts are performed for flight planning, and COSMO analyses are used as a basis for comprehensive microphysical box modeling (with grid scale of 2 and 7 km, respectively). Here we present the results of matching a cirrus cloud to within 2-15 km, realized on 8 June 2010 over Payerne, Switzerland, and a location 120 km downstream close to Zurich. A thick cirrus cloud was detected over both measurement sites. We show that in order to quantitatively reproduce the measured particle backscatter ratios, the smallscale temperature fluctuations not resolved by COSMO must be superimposed on the trajectories. The stochastic nature of the fluctuations is captured by ensemble calculations. Possibilities for further improvements in the agreement with the measured backscatter data are investigated by assuming a very slow mass accommodation of water on ice, the presence of heterogeneous ice nuclei, or a wide span of (spheroidal) particle shapes. However, the resulting improvements from these microphysical refinements are moderate and comparable in magnitude with changes caused by assuming different regimes of temperature fluctuations for clear-sky or cloudysky conditions, highlighting the importance of proper treatment of subscale fluctuations. The model yields good agreement with the measured backscatter over both sites and reproduces the measured saturation ratios with respect to ice over Payerne. Conversely, the 30 % in-cloud supersaturation measured in a massive 4 km thick cloud layer over Zurich cannot be reproduced, irrespective of the choice of meteorological or microphysical model parameters. The measured supersaturation can only be explained by either resorting to an unknown physical process, which prevents the ice particles from consuming the excess humidity, or -much more likely -by a measurement error, such as a contamination of the sensor housing of the SnowWhite hygrometer by a precipitation drop from a mixed-phase cloud just below the cirrus layer or from some very slight rain in the boundary layer. This uncertainty calls for in-flight checks or calibrations of hygrom...

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“…It has also recently been observed that atmospheric particles with high organic content are not as efficient at ice nucleation (DeMott et al, 2003;Cziczo et al, 2004). The effects that organic compounds have on the ability of particles to nucleate ice has only recently begun to be studied in the laboratory.…”

Section: Introductionmentioning

confidence: 99%

“…The Koop et al (2000) model is also potentially applicable even if aerosols are not in equilibrium with atmospheric water vapor, as long as the aerosol organic content can be determined and related to aerosol water activity. However, field measurements have indicated that mixed organic/sulfate aerosol might be less efficient at ice nucleation (DeMott et al, 2003;Cziczo et al, 2004). One possible explanation for this observation is that the presence of organic compounds modifies the water uptake properties of the aerosol, and serves to sever the equilibrium between aerosol water content and atmospheric water vapor.…”

Section: Introductionmentioning

confidence: 99%

Ice nucleation in sulfuric acid/organic aerosols: implications for cirrus cloud formation

et al. 2006

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Abstract.Using an aerosol flow tube apparatus, we have studied the effects of aliphatic aldehydes (C 3 to C 10 ) and ketones (C 3 and C 9 ) on ice nucleation in sulfuric acid aerosols. Mixed aerosols were prepared by combining an organic vapor flow with a flow of sulfuric acid aerosols over a small mixing time (∼60 s) at room temperature. No acid-catalyzed reactions were observed under these conditions, and physical uptake was responsible for the organic content of the sulfuric acid aerosols. In these experiments, aerosol organic content, determined by a Mie scattering analysis, was found to vary with the partial pressure of organic, the flow tube temperature, and the identity of the organic compound. The physical properties of the organic compounds (primarily the solubility and melting point) were found to play a dominant role in determining the inferred mode of nucleation (homogenous or heterogeneous) and the specific freezing temperatures observed. Overall, very soluble, low-melting organics, such as acetone and propanal, caused a decrease in aerosol ice nucleation temperatures when compared with aqueous sulfuric acid aerosol. In contrast, sulfuric acid particles exposed to organic compounds of eight carbons and greater, of much lower solubility and higher melting temperatures, nucleate ice at temperatures above aqueous sulfuric acid aerosols. Organic compounds of intermediate carbon chain length, C 4 -C 7 , (of intermediate solubility and melting temperatures) nucleated ice at the same temperature as aqueous sulfuric acid aerosols. Interpretations and implications of these results for cirrus cloud formation are discussed.

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Measurements of the concentration and composition of nuclei for cirrus formation

Cited by 556 publications

References 36 publications

Predicting global atmospheric ice nuclei distributions and their impacts on climate

Predicting global atmospheric ice nuclei distributions and their impacts on climate

Balloon-borne match measurements of midlatitude cirrus clouds

Ice nucleation in sulfuric acid/organic aerosols: implications for cirrus cloud formation

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