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Paul J Demott - One of the best experts on this subject based on the ideXlab platform.
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ship based measurements of Ice Nuclei concentrations over thearctic atlantic pacific and southern ocean
Atmospheric Chemistry and Physics, 2020Co-Authors: Paul J Demott, Andre Welti, Keith E Bigg, Xianda Gong, Markus Hartmann, Mike Harvey, S Henning, Paul Herenz, Thomas C HillAbstract:Abstract. Ambient concentrations of Ice-forming particles measured during ship expeditions are collected and summarized with the aim of establishing a spatial distribution and variability of Ice Nuclei in oceanic regions. The presented data from literature and previously unpublished data from over 23 months of ship-based measurements stretch from the Arctic to the Southern Ocean and include a circumnavigation of Antarctica. In comparison to continental observations, ship-based measurements of ambient Ice Nuclei show one to two order of magnitude lower mean concentrations. To quantify the geographical variability in oceanic areas, the concentration range of potential Ice Nuclei in different climate zones is analysed by meridionally dividing the expedition tracks into: tropical, temperate and polar climate zones. We find that concentrations of Ice Nuclei in these meridional zones follow temperature spectra with similar slope, but vary in absolute concentration. Typically, the frequency with which specific concentrations of Ice Nuclei are observed at a certain temperature follows a log-normal distribution. A consequence of the log-normal distribution is that the mean concentration is higher than the most frequently measured concentration. Finally, the potential contribution of ship exhaust to the measured Ice Nuclei concentration on board of research-vessels is analysed as function of temperature. We find a sharp onset of the influence at approximately −36 °C, but none at warmer temperatures that could bias ship-based measurements.
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laboratory measurements of Ice Nuclei concentrations from ocean water spray
19th International Conference on Nucleation and Atmospheric Aerosols ICNAA 2013, 2013Co-Authors: Paul J Demott, R C Sullivan, Matthew J Ruppel, Thomas C Hill, Ryan H Mason, Andrew P Ault, Kimberly A Prather, Douglas B Collins, Allan K Bertram, T H BertramAbstract:Preliminary studies of sea spray-produced particles as Ice Nuclei (IN) are presented. Ice Nuclei were found within aerosols produced by realistic wave generation and sea spray production. These IN were less efficient than those typically found in the free troposphere, with number concentrations more or less in accord with previous measurements over remote ocean regions. Nevertheless, sea spray IN could play a role in affecting cloud properties in remote marine regions, and differences in ocean biology could also influence IN efficiency from sea spray generation.
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hunting the snark identifying the organic Ice Nuclei in soils
Nucleation and Atmospheric Aerosols, 2013Co-Authors: C J T Hill, Paul J Demott, Yutaka Tobo, Janine Frohlichnowoisky, William L Stump, Gary D FrancAbstract:The contribution of soil organic matter as a potential source of atmospheric Ice Nuclei (IN) has long been postulated. Rather surprisingly, considering the abundance of IN active at warm temperatures in many soils, it remains unresolved. This research aimed to identify sources of high-temperature, organic IN in a range of Wyoming and Colorado soils. Methods used included physical, chemical and enzymatic tests combined with quantitative PCR to estimate the number of Ice nucleation active bacteria. All soils contained 106 to >107 IN active at −10°C. Reductions in IN after heating or digestion with hydrogen peroxide suggested that IN active >−15°C were effectively all organic. Ice Nuclei active >−7°C appear to be primarily a mixture of biological macromolecules. At colder temperatures there was a large pool of organic IN that were quite resistant to most physico-chemical challenges.
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Biological Ice Nuclei and the impact of rain on Ice Nuclei populations
2013Co-Authors: A J Prenni, Paul J Demott, Thomas C Hill, Yutaka Tobo, Gary D Franc, E. Garcia, J. A. Huffman, Christina S. Mccluskey, Jessica E. Prenni, Christopher PöhlkerAbstract:With 18% of total US landmass devoted to croplands, farmland is a potentially major source of biogenic particles to the atmosphere. We investigated two farms as potential sources of biological Ice Nuclei (IN). We found that each of these farms contained abundant INA bacteria on the vegetation; however, airborne ina gene concentrations were typically below detectable limits, demonstrating a disconnect between local vegetative sources and the air above them. The question remains, then, as to how biological IN are released into the atmosphere. In a second study, we investigated how precipitation impacted the concentration and composition of IN. Results from these measurements show that ground level IN concentrations were enhanced during rain events, and that some portion of these IN were biological. In this paper, we present results from both of these studies, and discuss modified measurement techniques aimed at characterizing the often very low number concentrations of biological IN.
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Observations of Ice Nuclei associated with biomass burning
2013Co-Authors: Christina S. Mccluskey, A J Prenni, Paul J Demott, Christian M Carrico, Amy P Sullivan, G R Mcmeeking, Gary D Franc, Ezra J. T. Levin, Shunsuke Nakao, Thomas C HillAbstract:Laboratory and field studies have identified biomass burning as a potentially important contributor to the global atmospheric heterogeneous Ice Nuclei (IN) reservoir. However, IN production from biomass burning is poorly characterized and dependent upon changes in aerosol properties associated with differences in fuel type, combustion efficiency, and/or plume aging. Measurements from four prescribed burns, two wildfires and laboratory studies support biomass burning as a potential source of IN to the atmosphere, and have provided insight regarding the characteristics of IN emitted from biomass burning sources.
A J Prenni - One of the best experts on this subject based on the ideXlab platform.
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Biological Ice Nuclei and the impact of rain on Ice Nuclei populations
2013Co-Authors: A J Prenni, Paul J Demott, Thomas C Hill, Yutaka Tobo, Gary D Franc, E. Garcia, J. A. Huffman, Christina S. Mccluskey, Jessica E. Prenni, Christopher PöhlkerAbstract:With 18% of total US landmass devoted to croplands, farmland is a potentially major source of biogenic particles to the atmosphere. We investigated two farms as potential sources of biological Ice Nuclei (IN). We found that each of these farms contained abundant INA bacteria on the vegetation; however, airborne ina gene concentrations were typically below detectable limits, demonstrating a disconnect between local vegetative sources and the air above them. The question remains, then, as to how biological IN are released into the atmosphere. In a second study, we investigated how precipitation impacted the concentration and composition of IN. Results from these measurements show that ground level IN concentrations were enhanced during rain events, and that some portion of these IN were biological. In this paper, we present results from both of these studies, and discuss modified measurement techniques aimed at characterizing the often very low number concentrations of biological IN.
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Observations of Ice Nuclei associated with biomass burning
2013Co-Authors: Christina S. Mccluskey, A J Prenni, Paul J Demott, Christian M Carrico, Amy P Sullivan, G R Mcmeeking, Gary D Franc, Ezra J. T. Levin, Shunsuke Nakao, Thomas C HillAbstract:Laboratory and field studies have identified biomass burning as a potentially important contributor to the global atmospheric heterogeneous Ice Nuclei (IN) reservoir. However, IN production from biomass burning is poorly characterized and dependent upon changes in aerosol properties associated with differences in fuel type, combustion efficiency, and/or plume aging. Measurements from four prescribed burns, two wildfires and laboratory studies support biomass burning as a potential source of IN to the atmosphere, and have provided insight regarding the characteristics of IN emitted from biomass burning sources.
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Ice initiation by aerosol particles measured and predicted Ice Nuclei concentrations versus measured Ice crystal concentrations in an orographic wave cloud
Journal of the Atmospheric Sciences, 2010Co-Authors: Trude Eidhammer, A J Prenni, Markus D Petters, Cynthia H Twohy, D C Rogers, Jeffrey L Stith, Paul J Demott, Andrew J. Heymsfield, Zhien WangAbstract:The initiation of Ice in an isolated orographic wave cloud was compared with expectations based on Ice nucleating aerosol concentrations and with predictions from new Ice nucleation parameterizations applied in a cloud parcel model. Measurements of Ice crystal number concentrations were found to be in good agreement both with measured number concentrations of Ice Nuclei feeding the clouds and with Ice Nuclei number concentrations determined from the residual Nuclei of cloud particles collected by a counterflow virtual impactor. Using lognormal distributions fitted to measured aerosol size distributions and measured aerosol chemical compositions, Ice Nuclei and Ice crystal concentrations in the wave cloud were reasonably well predicted in a 1D parcel model framework. Two different empirical parameterizations were used in the parcel model: a parameterization based on aerosol chemical type and surface area and a parameterization that links Ice Nuclei number concentrations to the number concentrations of particles with diameters larger than 0.5 μm. This study shows that aerosol size distribution and composition measurements can be used to constrain Ice initiation by primary nucleation in models. The data and model results also suggest the likelihood that the dust particle mode of the aerosol size distribution controls the number concentrations of the heterogeneous Ice Nuclei, at least for the lower temperatures examined in this case.
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predicting global atmospheric Ice Nuclei distributions and their impacts on climate
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Paul J Demott, M. S. Richardson, Trude Eidhammer, A J Prenni, Markus D Petters, Cynthia H Twohy, Sonia M Kreidenweis, D C RogersAbstract: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 ∼103 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.
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Predicting global atmospheric Ice Nuclei distributions and their impacts on climate
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Paul J Demott, M. S. Richardson, Trude Eidhammer, A J Prenni, Markus D Petters, Cynthia H Twohy, Sonia M Kreidenweis, X Liu, D C RogersAbstract: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 degrees 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 microm in diameter. This new relationship reduces unexplained variability in Ice Nuclei concentrations at a given temperature from approximately 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 approximately 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.
Markus D Petters - One of the best experts on this subject based on the ideXlab platform.
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high relative humidity as a trigger for widespread release of Ice Nuclei
Aerosol Science and Technology, 2014Co-Authors: T. P. Wright, J. D. Hader, G R Mcmeeking, Markus D PettersAbstract:This supplement is divided into five major sections. Sections 1 and 2 expound on the experimental methods for Ice Nuclei particles (INP) measurements and fluorescent measurements, respectively. Section 3 describes the measurement site and meteorological conditions. Section 4 presents extended results including data from the second case study and details about particle size distribution results from the ambient air measurements. Section 5 provides modelling results.
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Contribution of pollen to atmospheric Ice Nuclei concentrations
Atmospheric Chemistry and Physics, 2014Co-Authors: J. D. Hader, T. P. Wright, Markus D PettersAbstract:Abstract. Recent studies have suggested that the Ice-nucleating ability of some types of pollen is derived from non-proteinaceous macromolecules. These macromolecules may become dispersed by the rupturing of the pollen grain during wetting and drying cycles in the atmosphere. If true, this mechanism might prove to be a significant source of Ice Nuclei (IN) concentrations when pollen is present. Here we test this hypothesis by measuring ambient IN concentrations from the beginning to the end of the 2013 pollen season in Raleigh, North Carolina, USA. Air samples were collected using a swirling aerosol collector twIce per week and the solutions were analysed for Ice Nuclei activity using a droplet freezing assay. Rainwater samples were collected at times when pollen grain number concentrations were near their maximum value and analysed with the drop-freezing assay to compare the potentially enhanced IN concentrations measured near the ground with IN concentrations found aloft. Ambient Ice Nuclei spectra, defined as the number of Ice Nuclei per volume of air as a function of temperature, are inferred from the aerosol collector solutions. No general trend was observed between ambient pollen grain counts and observed IN concentrations, suggesting that Ice Nuclei multiplication via pollen grain rupturing and subsequent release of macromolecules was not prevalent for the pollen types and meteorological conditions typically encountered in the southeastern US. A serendipitously sampled collection after a downpour provided evidence for a rain-induced IN burst with an observed IN concentration of approximately 30 per litre, a 30-fold increase over background concentrations at −20 °C. The onset temperature of freezing for these particles was approximately −12 °C, suggesting that the Ice-nucleating particles were biological in origin.
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Contribution of pollen to atmospheric Ice Nuclei concentrations
Atmospheric Chemistry and Physics Discussions, 2013Co-Authors: J. D. Hader, T. P. Wright, Markus D PettersAbstract:Abstract. Recent studies have suggested that the Ice nucleating ability of some types of pollen is derived from non-proteinaceous macromolecules. These macromolecules may become dispersed by the rupturing of the pollen sac during wetting and drying cycles in the atmosphere. If true, this mechanism might prove to be a significant source of Ice Nuclei (IN) concentrations when pollen are present. Here we test this hypothesis by measuring ambient IN concentrations from the beginning to the end of the 2013 pollen season in Raleigh, North Carolina, USA. Air samples were collected using a swirling aerosol collector twIce per week and the solutions were analysed for Ice Nuclei activity using a droplet freezing assay. Rainwater samples were collected at the peak of the pollen season and analysed with the drop freezing assay to compare the potentially enhanced IN concentrations measured near the ground with IN concentrations found aloft. Ambient Ice Nuclei spectra, defined as the number of Ice Nuclei per volume of air as a function of temperature, are inferred from the aerosol collector solutions. No general trend was observed between ambient pollen counts and observed IN concentrations, suggesting that Ice Nuclei multiplication via pollen sac rupturing and subsequent release of macromolecules was not prevalent for the pollen types and meteorological conditions typically encountered in the Southeastern US. A serendipitously sampled collection after a downpour provided evidence for a rain-induced IN burst with an observed IN concentration of approximately 30 per litre, a 30-fold increase over background concentrations at −20 °C. The onset temperature of freezing for these particles was approximately −12 °C, suggesting that the Ice nucleating particles were biological in origin. The magnitude of the IN burst was significantly larger than previously observed, providing additional evidence to merit further investigation of a self-regulated feedback cycle between the atmosphere and biosphere via the release of cloud forming particles in rain forest environments.
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minimal cooling rate dependence of Ice Nuclei activity in the immersion mode
Journal of Geophysical Research, 2013Co-Authors: T. P. Wright, J. D. Hader, Markus D Petters, Travis Morton, Amara L HolderAbstract:[1] We present new measurements of the time dependence of the Ice-nucleating ability of a wide range of materials including the minerals montmorillonite and kaolinite, the biological proxy Ice Nuclei Icemax, and flame soot generated from the incomplete combustion of ethylene gas. We also present time dependence for ambient Ice Nuclei collected from rainwater samples. Our data show that the time dependence for all materials studied here is weak, suggesting that the modified singular approximation is valid over the range of times and temperatures encountered for mixed phase clouds.
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resurgence in Ice Nuclei measurement research
Bulletin of the American Meteorological Society, 2011Co-Authors: Paul J Demott, Ulrich Bundke, Markus D Petters, Gabor Vali, Zev Levin, O Mohler, O Stetzer, Masataka Murakami, Thomas Leisner, H KleinAbstract:Understanding cloud and precipitation responses to variations in atmospheric aerosols remains an important research topic for improving the prediction of climate. Knowledge is most uncertain, and the potential impact on climate is largest with regard to how aerosols impact Ice formation in clouds. In this paper, we show that research on atmospheric Ice nucleation, including the development of new measurement systems, is occurring at a renewed and historically unparalleled level. A historical perspective is provided on the methods and challenges of measuring Ice Nuclei, and the various factors that led to a lull in research efforts during a nearly 20-yr period centered about 30 yr ago. Workshops played a major role in defining critical needs for improving measurements at that time and helped to guide renewed efforts. Workshops were recently revived for evaluating present research progress. We argue that encouraging progress has been made in the consistency of measurements using the present generation of ic...
Sonia M Kreidenweis - One of the best experts on this subject based on the ideXlab platform.
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predicting global atmospheric Ice Nuclei distributions and their impacts on climate
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Paul J Demott, M. S. Richardson, Trude Eidhammer, A J Prenni, Markus D Petters, Cynthia H Twohy, Sonia M Kreidenweis, D C RogersAbstract: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 ∼103 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.
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Predicting global atmospheric Ice Nuclei distributions and their impacts on climate
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Paul J Demott, M. S. Richardson, Trude Eidhammer, A J Prenni, Markus D Petters, Cynthia H Twohy, Sonia M Kreidenweis, X Liu, D C RogersAbstract: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 degrees 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 microm in diameter. This new relationship reduces unexplained variability in Ice Nuclei concentrations at a given temperature from approximately 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 approximately 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.
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relative roles of biogenic emissions and saharan dust as Ice Nuclei in the amazon basin
Nature Geoscience, 2009Co-Authors: A J Prenni, Markus D Petters, Sonia M Kreidenweis, Colette L Heald, S T Martin, Paulo Artaxo, R M Garland, A G Wollny, Ulrich PoschlAbstract:Some aerosol particles—known as Ice Nuclei—initiate Ice formation in clouds, thereby influencing precipitation, cloud dynamics and incoming and outgoing solar radiation. Measurements of the concentration and elemental composition of Ice Nuclei in the Amazon basin indicate that local bioparticles and Saharan dust could explain the presence of almost all Ice Nuclei during the wet season.
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Ice Nuclei emissions from biomass burning
Journal of Geophysical Research, 2009Co-Authors: Markus D Petters, A J Prenni, Paul J Demott, Sonia M Kreidenweis, Matthew T Parsons, Christian M Carrico, Amy P Sullivan, G R McmeekingAbstract:[1] Biomass burning is a significant source of carbonaceous aerosol in many regions of the world. When present, biomass burning particles may affect the microphysical properties of clouds through their ability to function as cloud condensation Nuclei or Ice Nuclei. We report on measurements of the Ice nucleation ability of biomass burning particles performed on laboratory-generated aerosols at the second Fire Lab at Missoula Experiment. During the experiment we generated smoke through controlled burns of 21 biomass fuels from the United States and Asia. Using a Colorado State University continuous flow diffusion chamber, we measured the condensation/immersion freezing potential at temperatures relevant to cold cumulus clouds (−30°C). Smokes from 9 of the 21 fuels acted as Ice Nuclei at fractions of 1:10,000 to 1:100 particles in at least one burn of each fuel; emissions from the remaining fuels were below the Ice Nuclei detection limit for all burns of each fuel. Using a bottom-up emission model, we estimate that smokes that emit Ice Nuclei fractions exceeding 1:10,000 particles can perturb Ice Nuclei concentrations on a regional scale.
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african dust aerosols as atmospheric Ice Nuclei
Geophysical Research Letters, 2003Co-Authors: Paul J Demott, Sarah D Brooks, A J Prenni, Michael R. Poellot, Kenneth Sassen, David C Rogers, Darrel Baumgardner, Sonia M KreidenweisAbstract:[1] Measurements of the Ice nucleating ability of aerosol particles in air masses over Florida having sources from North Africa support the potential importance of dust aerosols for indirectly affecting cloud properties and climate. The concentrations of Ice Nuclei within dust layers at particle sizes below 1 μm exceeded 1 cm−3; the highest ever reported with our devIce at temperatures warmer than homogeneous freezing conditions. These measurements add to previous direct and indirect evidence of the Ice nucleation efficiency of desert dust aerosols, but also confirm their contribution to Ice Nuclei populations at great distances from source regions.
D C Rogers - One of the best experts on this subject based on the ideXlab platform.
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Ice initiation by aerosol particles measured and predicted Ice Nuclei concentrations versus measured Ice crystal concentrations in an orographic wave cloud
Journal of the Atmospheric Sciences, 2010Co-Authors: Trude Eidhammer, A J Prenni, Markus D Petters, Cynthia H Twohy, D C Rogers, Jeffrey L Stith, Paul J Demott, Andrew J. Heymsfield, Zhien WangAbstract:The initiation of Ice in an isolated orographic wave cloud was compared with expectations based on Ice nucleating aerosol concentrations and with predictions from new Ice nucleation parameterizations applied in a cloud parcel model. Measurements of Ice crystal number concentrations were found to be in good agreement both with measured number concentrations of Ice Nuclei feeding the clouds and with Ice Nuclei number concentrations determined from the residual Nuclei of cloud particles collected by a counterflow virtual impactor. Using lognormal distributions fitted to measured aerosol size distributions and measured aerosol chemical compositions, Ice Nuclei and Ice crystal concentrations in the wave cloud were reasonably well predicted in a 1D parcel model framework. Two different empirical parameterizations were used in the parcel model: a parameterization based on aerosol chemical type and surface area and a parameterization that links Ice Nuclei number concentrations to the number concentrations of particles with diameters larger than 0.5 μm. This study shows that aerosol size distribution and composition measurements can be used to constrain Ice initiation by primary nucleation in models. The data and model results also suggest the likelihood that the dust particle mode of the aerosol size distribution controls the number concentrations of the heterogeneous Ice Nuclei, at least for the lower temperatures examined in this case.
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predicting global atmospheric Ice Nuclei distributions and their impacts on climate
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Paul J Demott, M. S. Richardson, Trude Eidhammer, A J Prenni, Markus D Petters, Cynthia H Twohy, Sonia M Kreidenweis, D C RogersAbstract: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 ∼103 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.
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Predicting global atmospheric Ice Nuclei distributions and their impacts on climate
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Paul J Demott, M. S. Richardson, Trude Eidhammer, A J Prenni, Markus D Petters, Cynthia H Twohy, Sonia M Kreidenweis, X Liu, D C RogersAbstract: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 degrees 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 microm in diameter. This new relationship reduces unexplained variability in Ice Nuclei concentrations at a given temperature from approximately 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 approximately 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.
