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T. L. Thompson – One of the best experts on this subject based on the ideXlab platform.

  • Ice Supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration
    Atmospheric Chemistry and Physics, 2005
    Co-Authors: E. J. Jensen, J. B. Smith, L. Pfister, J. V. Pittman, E. M. Weinstock, D. S. Sayres, R. L. Herman, R. F. Troy, K. Rosenlof, T. L. Thompson
    Abstract:

    Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate Supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a Supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of aqueous aerosol freezing. The high Supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had Supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values are at least 20% too low, (2) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing, and (3) if surface freezing dominates, organic coatings may increase the surface energy of the ice embryo/vapor interface resulting in suppressed ice nucleation. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere. The TTL cirrus simulations show that even if very large Supersaturations are required for ice nucleation, these large Supersaturations should occur very rarely.

  • Ice Supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration
    Atmospheric Chemistry and Physics Discussions, 2004
    Co-Authors: E. Jensen, J. B. Smith, L. Pfister, E. M. Weinstock, D. S. Sayres, R. L. Herman, R. F. Troy, J. V. Pitman, K. Troy, T. L. Thompson
    Abstract:

    Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate Supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a Supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of sulfate aerosol freezing. The high Supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had Supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values at least 20% too low, (2) most of the available aerosols had a composition that makes them much more resistant to ice nucleation than aerosols used in laboratory experiments, and (3) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if these decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere.

S Yoda – One of the best experts on this subject based on the ideXlab platform.

  • Systematic analysis of Supersaturation and lysozyme crystal quality.
    Acta crystallographica. Section D Biological crystallography, 2001
    Co-Authors: I Yoshizaki, T. Sato, N Igarashi, M Natsuisaka, N Tanaka, H. Komatsu, S Yoda
    Abstract:

    A systematic study of the correlation between Supersaturation and protein crystal quality was carried out employing atomic force microscopy (AFM) and X-ray crystallography with synchrotron radiation (SR). The surface morphology and growth rates of hen egg-white (HEW) lysozyme crystals soaked in various supersaturated solutions were first investigated by AFM. The results showed that the formation of two-dimensional islands increased as a function of Supersaturation. The growth rate (molecule intake speed) also increased as a function of Supersaturation. In order to examine the correlation between the surface morphology, growth rate and the crystal quality, X-ray diffraction experiments were performed. It was confirmed that crystals grown at lower Supersaturations diffracted better with higher signal-to-noise ratios, including better agreement between symmetry-related reflections. The results strongly suggested that the molecular misorientation at high Supersaturation affected the crystal quality.

  • Systematic analysis of Supersaturation and lysozyme crystal quality.
    Acta crystallographica. Section D Biological crystallography, 2001
    Co-Authors: I Yoshizaki, T. Sato, N Igarashi, M Natsuisaka, N Tanaka, H. Komatsu, S Yoda
    Abstract:

    A systematic study of the correlation between Supersaturation and protein crystal quality was carried out employing atomic force microscopy (AFM) and X-ray crystallography with synchrotron radiation (SR). The surface morphology and growth rates of hen egg-white (HEW) lysozyme crystals soaked in various supersaturated solutions were first investigated by AFM. The results showed that the formation of two-dimensional islands increased as a function of Supersaturation. The growth rate (molecule intake speed) also increased as a function of Supersaturation. In order to examine the correlation between the surface morphology, growth rate and the crystal quality, X-ray diffraction experiments were performed. It was confirmed that crystals grown at lower Supersaturations diffracted better with higher signal-to-noise ratios, including better agreement between symmetry-related reflections. The results strongly suggested that the molecular misorientation at high Supersaturation affected the crystal quality.

I Yoshizaki – One of the best experts on this subject based on the ideXlab platform.

  • Systematic analysis of Supersaturation and lysozyme crystal quality.
    Acta crystallographica. Section D Biological crystallography, 2001
    Co-Authors: I Yoshizaki, T. Sato, N Igarashi, M Natsuisaka, N Tanaka, H. Komatsu, S Yoda
    Abstract:

    A systematic study of the correlation between Supersaturation and protein crystal quality was carried out employing atomic force microscopy (AFM) and X-ray crystallography with synchrotron radiation (SR). The surface morphology and growth rates of hen egg-white (HEW) lysozyme crystals soaked in various supersaturated solutions were first investigated by AFM. The results showed that the formation of two-dimensional islands increased as a function of Supersaturation. The growth rate (molecule intake speed) also increased as a function of Supersaturation. In order to examine the correlation between the surface morphology, growth rate and the crystal quality, X-ray diffraction experiments were performed. It was confirmed that crystals grown at lower Supersaturations diffracted better with higher signal-to-noise ratios, including better agreement between symmetry-related reflections. The results strongly suggested that the molecular misorientation at high Supersaturation affected the crystal quality.

  • Systematic analysis of Supersaturation and lysozyme crystal quality.
    Acta crystallographica. Section D Biological crystallography, 2001
    Co-Authors: I Yoshizaki, T. Sato, N Igarashi, M Natsuisaka, N Tanaka, H. Komatsu, S Yoda
    Abstract:

    A systematic study of the correlation between Supersaturation and protein crystal quality was carried out employing atomic force microscopy (AFM) and X-ray crystallography with synchrotron radiation (SR). The surface morphology and growth rates of hen egg-white (HEW) lysozyme crystals soaked in various supersaturated solutions were first investigated by AFM. The results showed that the formation of two-dimensional islands increased as a function of Supersaturation. The growth rate (molecule intake speed) also increased as a function of Supersaturation. In order to examine the correlation between the surface morphology, growth rate and the crystal quality, X-ray diffraction experiments were performed. It was confirmed that crystals grown at lower Supersaturations diffracted better with higher signal-to-noise ratios, including better agreement between symmetry-related reflections. The results strongly suggested that the molecular misorientation at high Supersaturation affected the crystal quality.

R. F. Troy – One of the best experts on this subject based on the ideXlab platform.

  • Ice Supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration
    Atmospheric Chemistry and Physics, 2005
    Co-Authors: E. J. Jensen, J. B. Smith, L. Pfister, J. V. Pittman, E. M. Weinstock, D. S. Sayres, R. L. Herman, R. F. Troy, K. Rosenlof, T. L. Thompson
    Abstract:

    Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate Supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a Supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of aqueous aerosol freezing. The high Supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had Supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values are at least 20% too low, (2) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing, and (3) if surface freezing dominates, organic coatings may increase the surface energy of the ice embryo/vapor interface resulting in suppressed ice nucleation. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere. The TTL cirrus simulations show that even if very large Supersaturations are required for ice nucleation, these large Supersaturations should occur very rarely.

  • Ice Supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration
    Atmospheric Chemistry and Physics Discussions, 2004
    Co-Authors: E. Jensen, J. B. Smith, L. Pfister, E. M. Weinstock, D. S. Sayres, R. L. Herman, R. F. Troy, J. V. Pitman, K. Troy, T. L. Thompson
    Abstract:

    Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate Supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a Supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of sulfate aerosol freezing. The high Supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had Supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values at least 20% too low, (2) most of the available aerosols had a composition that makes them much more resistant to ice nucleation than aerosols used in laboratory experiments, and (3) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if these decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere.

R. L. Herman – One of the best experts on this subject based on the ideXlab platform.

  • Ice Supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration
    Atmospheric Chemistry and Physics, 2005
    Co-Authors: E. J. Jensen, J. B. Smith, L. Pfister, J. V. Pittman, E. M. Weinstock, D. S. Sayres, R. L. Herman, R. F. Troy, K. Rosenlof, T. L. Thompson
    Abstract:

    Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate Supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a Supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of aqueous aerosol freezing. The high Supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had Supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values are at least 20% too low, (2) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing, and (3) if surface freezing dominates, organic coatings may increase the surface energy of the ice embryo/vapor interface resulting in suppressed ice nucleation. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere. The TTL cirrus simulations show that even if very large Supersaturations are required for ice nucleation, these large Supersaturations should occur very rarely.

  • Ice Supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration
    Atmospheric Chemistry and Physics Discussions, 2004
    Co-Authors: E. Jensen, J. B. Smith, L. Pfister, E. M. Weinstock, D. S. Sayres, R. L. Herman, R. F. Troy, J. V. Pitman, K. Troy, T. L. Thompson
    Abstract:

    Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate Supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a Supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of sulfate aerosol freezing. The high Supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had Supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values at least 20% too low, (2) most of the available aerosols had a composition that makes them much more resistant to ice nucleation than aerosols used in laboratory experiments, and (3) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if these decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere.