scholarly journals Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer

2015 ◽  
Vol 15 (6) ◽  
pp. 8771-8799 ◽  
Author(s):  
T. Dinh ◽  
A. Podglajen ◽  
A. Hertzog ◽  
B. Legras ◽  
R. Plougonven
Keyword(s):  
Cooling Rate ◽  
Gravity Wave ◽  
High Frequency ◽  
Full Range ◽  
Temperature Fluctuations ◽  
Ice Nucleation ◽  
Microphysics Scheme ◽  
Tropical Tropopause ◽  
The Absolute ◽  
The Impact

Abstract. The impact of high-frequency fluctuations of temperature on homogeneous nucleation of ice crystals in the vicinity of the tropical tropopause is investigated using a bin microphysics scheme for air parcels. The imposed temperature fluctuations come from measurements during isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency, guaranteeing that gravity wave signals are well resolved. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentration (INC) as previously observed in the tropical upper troposphere. In particular, low INC may be obtained if the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work suggests that homogeneous ice nucleation is not necessarily inconsistent with observations of low INC.

scholarly journals Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer

2016 ◽  
Vol 16 (1) ◽  
pp. 35-46 ◽  
Author(s):  
T. Dinh ◽  
A. Podglajen ◽  
A. Hertzog ◽  
B. Legras ◽  
R. Plougonven
Keyword(s):  
Cooling Rate ◽  
Gravity Wave ◽  
High Frequency ◽  
Full Range ◽  
Temperature Fluctuations ◽  
Ice Nucleation ◽  
Microphysics Scheme ◽  
Tropical Tropopause ◽  
The Absolute ◽  
The Impact

Abstract. The impact of high-frequency fluctuations of temperature on homogeneous nucleation of ice crystals in the vicinity of the tropical tropopause is investigated using a bin microphysics scheme for air parcels. The imposed temperature fluctuations come from measurements during isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency, guaranteeing that gravity wave signals are well resolved.With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentration (INC) as previously observed in the tropical upper troposphere. In particular, a low INC may be obtained if the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work suggests that homogeneous ice nucleation is not necessarily inconsistent with observations of low INCs.

scholarly journals Analysis of isothermal and cooling rate dependent immersion freezing by a unifying stochastic ice nucleation model

2015 ◽  
Vol 15 (9) ◽  
pp. 13109-13166
Author(s):  
P. A. Alpert ◽  
D. A. Knopf
Keyword(s):  
Cooling Rate ◽  
Surface Area ◽  
Ice Nucleation ◽  
Rate Dependence ◽  
Nucleation Theory ◽  
Freezing Process ◽  
Nucleation Kinetics ◽  
Rate Dependent ◽  
Immersion Freezing ◽  
The Impact

Abstract. Immersion freezing is an important ice nucleation pathway involved in the formation of cirrus and mixed-phase clouds. Laboratory immersion freezing experiments are necessary to determine the range in temperature (T) and relative humidity (RH) at which ice nucleation occurs and to quantify the associated nucleation kinetics. Typically, isothermal (applying a constant temperature) and cooling rate dependent immersion freezing experiments are conducted. In these experiments it is usually assumed that the droplets containing ice nuclei (IN) all have the same IN surface area (ISA), however the validity of this assumption or the impact it may have on analysis and interpretation of the experimental data is rarely questioned. A stochastic immersion freezing model based on first principles of statistics is presented, which accounts for variable ISA per droplet and uses physically observable parameters including the total number of droplets (Ntot) and the heterogeneous ice nucleation rate coefficient, Jhet(T). This model is applied to address if (i) a time and ISA dependent stochastic immersion freezing process can explain laboratory immersion freezing data for different experimental methods and (ii) the assumption that all droplets contain identical ISA is a valid conjecture with subsequent consequences for analysis and interpretation of immersion freezing. The simple stochastic model can reproduce the observed time and surface area dependence in immersion freezing experiments for a variety of methods such as: droplets on a cold-stage exposed to air or surrounded by an oil matrix, wind and acoustically levitated droplets, droplets in a continuous flow diffusion chamber (CFDC), the Leipzig aerosol cloud interaction simulator (LACIS), and the aerosol interaction and dynamics in the atmosphere (AIDA) cloud chamber. Observed time dependent isothermal frozen fractions exhibiting non-exponential behavior with time can be readily explained by this model considering varying ISA. An apparent cooling rate dependence ofJhet is explained by assuming identical ISA in each droplet. When accounting for ISA variability, the cooling rate dependence of ice nucleation kinetics vanishes as expected from classical nucleation theory. The model simulations allow for a quantitative experimental uncertainty analysis for parameters Ntot, T, RH, and the ISA variability. In an idealized cloud parcel model applying variability in ISAs for each droplet, the model predicts enhanced immersion freezing temperatures and greater ice crystal production compared to a case when ISAs are uniform in each droplet. The implications of our results for experimental analysis and interpretation of the immersion freezing process are discussed.

Effect of Controlled Ice Nucleation on Primary Drying Stage and Protein Recovery in Vials Cooled in a Modified Freeze-Dryer

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Stéphanie Passot ◽  
Ioan Cristian Tréléa ◽  
Michèle Marin ◽  
Miquel Galan ◽  
G. John Morris ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Nucleating Agent ◽  
Ice Nucleation ◽  
Residual Water ◽  
Activity Recovery ◽  
Protective Medium ◽  
Ultrasound Technology ◽  
Controlled Nucleation ◽  
The Impact ◽  
Freeze Dryer

The freezing step influences lyophilization efficiency and protein stability. The main objective of this work was to investigate the impact on the primary drying stage of an ultrasound controlled ice nucleation technology, compared with usual freezing protocols. Lyophilization cycles involving different freezing protocols (applying a constant shelf cooling rate of 1°C/min or 0.2°C/min, putting vials on a precooled shelf, and controlling nucleation by ultrasounds or by addition of a nucleating agent) were performed in a prototype freeze-dryer. Three protective media including sucrose or maltodextrin and differing by their thermal properties and their ability to preserve a model protein (catalase) were used. The visual aspect of the lyophilized cake, residual water content, and enzymatic activity recovery of catalase were assessed after each lyophilization cycle and after 1 month of storage of the lyophilized product at 4°C and 25°C. The freezing protocols allowing increasing nucleation temperature (precooled shelf and controlled nucleation by using ultrasounds or a nucleating agent) induced a faster sublimation step and higher sublimation rate homogeneity. Whatever the composition of the protective medium, applying the ultrasound technology made it possible to decrease the sublimation time by 14%, compared with the freezing method involving a constant shelf cooling rate of 1°C/min. Concerning the enzyme activity recovery, the impact of the freezing protocol was observed only for the protective medium involving maltodextrin, a less effective protective agent than sucrose. Higher activity recovery results were obtained after storage when the ultrasound technology or the precooled shelf method was applied. Controlling ice nucleation during the freezing step of the lyophilization process improved the homogeneity of the sublimation rates, which will, in turn, reduce the intervial heterogeneity. The freeze-dryer prototype including the system of controlled nucleation by ultrasounds appears to be a promising tool in accelerating sublimation and improving intrabatch homogeneity.

scholarly journals Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

2013 ◽  
Vol 13 (19) ◽  
pp. 9801-9818 ◽  
Author(s):  
P. Spichtinger ◽  
M. Krämer
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Full Range ◽  
Ice Nucleation ◽  
Ice Formation ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Homogeneous Freezing

Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (< 1 cm s−1) and faster (> 1 cm s−1) large-scale updraughts, respectively. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed.

scholarly journals On the Susceptibility of Cold Tropical Cirrus to Ice Nuclei Abundance

2016 ◽  
Vol 73 (6) ◽  
pp. 2445-2464 ◽  
Author(s):  
Eric J. Jensen ◽  
Rei Ueyama ◽  
Leonhard Pfister ◽  
Thaopaul V. Bui ◽  
R. Paul Lawson ◽  
...  
Keyword(s):  
High Frequency ◽  
Regional Distribution ◽  
Ice Nucleation ◽  
Small Scale ◽  
Height Distribution ◽  
Microphysical Properties ◽  
Ice Nuclei ◽  
High Frequency Waves ◽  
The Impact

Abstract Numerical simulations of cirrus formation in the tropical tropopause layer (TTL) during boreal wintertime are used to evaluate the impact of heterogeneous ice nuclei (IN) abundance on cold cloud microphysical properties and occurrence frequencies. The cirrus model includes homogeneous and heterogeneous ice nucleation, deposition growth/sublimation, and sedimentation. Reanalysis temperature and wind fields with high-frequency waves superimposed are used to force the simulations. The model results are constrained by comparison with in situ and satellite observations of TTL cirrus and relative humidity. Temperature variability driven by high-frequency waves has a dominant influence on TTL cirrus microphysical properties and occurrence frequencies, and inclusion of these waves is required to produce agreement between the simulated and observed abundance of TTL cirrus. With homogeneous freezing only and small-scale gravity waves included in the temperature curtains, the model produces excessive ice concentrations compared with in situ observations. Inclusion of relatively numerous heterogeneous ice nuclei (NIN ≥ 100 L−1) in the simulations improves the agreement with observed ice concentrations. However, when IN contribute significantly to TTL cirrus ice nucleation, the occurrence frequency of large supersaturations with respect to ice is less than indicated by in situ measurements. The model results suggest that the sensitivity of TTL cirrus extinction and ice water content statistics to heterogeneous ice nuclei abundance is relatively weak. The simulated occurrence frequencies of TTL cirrus are quite insensitive to ice nuclei abundance, both in terms of cloud frequency height distribution and regional distribution throughout the tropics.

scholarly journals New investigations on homogeneous ice nucleation: the effects of water activity and water saturation formulations

2022 ◽  
Vol 22 (1) ◽  
pp. 65-91
Author(s):  
Manuel Baumgartner ◽  
Christian Rolf ◽  
Jens-Uwe Grooß ◽  
Julia Schneider ◽  
Tobias Schorr ◽  
...  
Keyword(s):  
Water Activity ◽  
Low Temperatures ◽  
Water Saturation ◽  
Aerosol Particles ◽  
Ice Nucleation ◽  
Ice Crystals ◽  
Microphysics Scheme ◽  
Cold Temperatures ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause

Abstract. Laboratory measurements at the AIDA cloud chamber and airborne in situ observations suggest that the homogeneous freezing thresholds at low temperatures are possibly higher than expected from the so-called “Koop line”. This finding is of importance, because the ice onset relative humidity affects the cirrus cloud coverage and, at the very low temperatures of the tropical tropopause layer, together with the number of ice crystals also the transport of water vapor into the stratosphere. Both the appearance of cirrus clouds and the amount of stratospheric water feed back to the radiative budget of the atmosphere. In order to explore the enhanced ice onset humidities, we re-examine the entire homogeneous ice nucleation process, ice onset, and nucleated crystal numbers, by means of a two-moment microphysics scheme embedded in the trajectory-based model (CLaMS-Ice) as follows: the well-understood and described theoretical framework of homogeneous ice nucleation includes certain formulations of the water activity of the freezing aerosol particles and the saturation vapor pressure of water with respect to liquid water. However, different formulations are available for both parameters. Here, we present extensive sensitivity simulations testing the influence of three different formulations for the water activity and four for the water saturation on homogeneous ice nucleation. We found that the number of nucleated ice crystals is almost independent of these formulations but is instead sensitive to the size distribution of the freezing aerosol particles. The ice onset humidities, also depending on the particle size, are however significantly affected by the choices of the water activity and water saturation, in particular at cold temperatures ≲205 K. From the CLaMS-Ice sensitivity simulations, we here provide combinations of water saturation and water activity formulations suitable to reproduce the new, enhanced freezing line.

scholarly journals New investigations on homogeneous ice nucleation: the effects of water activity and water saturation formulations

2021 ◽  
Author(s):  
Manuel Baumgartner ◽  
Christian Rolf ◽  
Jens-Uwe Grooß ◽  
Julia Schneider ◽  
Tobias Schorr ◽  
...  
Keyword(s):  
Water Activity ◽  
Low Temperatures ◽  
Water Saturation ◽  
Aerosol Particles ◽  
Ice Nucleation ◽  
Ice Crystals ◽  
Microphysics Scheme ◽  
Cold Temperatures ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause

Abstract. Laboratory measurements at the AIDA cloud chamber and airborne in-situ observations suggest that the homogeneous freezing thresholds at low temperatures are possibly higher than expected from the so-called “Koop-line”. This finding is of importance, because the ice onset relative humidity affects the cirrus cloud coverage and, at the very low temperatures of the tropical tropopause layer, together with the number of ice crystals also the transport of water vapor into the stratosphere. Both, the appearance of cirrus clouds and the amount of stratospheric water feed back to the radiative budget of the atmosphere. In order to explore the enhanced ice onset humidities, we re-examine the entire homogeneous ice nucleation process, ice onset and nucleated crystal numbers, by means of a two-moment microphysics scheme embedded in the trajectory based model (CLaMS-Ice) as follows: the well-understood and described theoretical framework of homogeneous ice nucleation yet includes certain formulations of the water activity of the freezing aerosol particles and the saturation vapor pressure of water with respect to liquid water. However, different formulations are available for both parameters. Here, we present extensive sensitivity simulations testing the influence of three different formulations for the water activity and four for the water saturation on homogeneous ice nucleation. We found that the number of nucleated ice crystals is almost independent of these formulations but is instead sensitive to the size distribution of the freezing aerosol particles. The ice onset humidities, also depending on the particle size, are however significantly affected by the choices of the water activity and water saturation, in particular at cold temperatures  205 K. From the CLaMS-Ice sensitivity simulations, we here provide combinations of water saturation and water activity formulations suitable to reproduce the new, enhanced freezing line.

scholarly journals Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

2012 ◽  
Vol 12 (10) ◽  
pp. 28109-28153 ◽  
Author(s):  
P. Spichtinger ◽  
M. Krämer
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Full Range ◽  
Ice Nucleation ◽  
Ice Formation ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Homogeneous Freezing

Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results of the scenarios are mixed for both heterogeneous/homogeneous and pure homogeneous ice formation occurring in very slow (<1 cm s−1) and faster (>1 cm s−1) large-scale updraughts. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed.

High-frequency gravity waves and homogeneous ice nucleation in tropical tropopause layer cirrus

2016 ◽  
Vol 43 (12) ◽  
pp. 6629-6635 ◽  
Author(s):  
Eric J. Jensen ◽  
Rei Ueyama ◽  
Leonhard Pfister ◽  
Theopaul V. Bui ◽  
M. Joan Alexander ◽  
...  
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Ice Nucleation ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause
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