scholarly journals Shape Dependence of Falling Snow Crystals’ Microphysical Properties Using an Updated Shape Classification

2020 ◽  
Vol 10 (3) ◽  
pp. 1163 ◽  
Author(s):  
Sandra Vázquez-Martín ◽  
Thomas Kuhn ◽  
Salomon Eliasson
Keyword(s):  
Shape Classification ◽  
Ice Crystal ◽  
Cross Sectional ◽  
Microphysical Properties ◽  
Shape Dependence ◽  
Snow Crystal ◽  
High Resolution Images ◽  
Snow Crystals ◽  
Natural Snow

We present ground-based in situ snow measurements in Kiruna, Sweden, using the ground-based in situ instrument Dual Ice Crystal Imager (D-ICI). D-ICI records dual high-resolution images from above and from the side of falling natural snow crystals and other hydrometeors with particle sizes ranging from 50 μ m to 4 mm. The images are from multiple snowfall seasons during the winters of 2014/2015 to 2018/2019, which span from the beginning of November to the middle of May. From our images, the microphysical properties of individual particles, such as particle size, cross-sectional area, area ratio, aspect ratio, and shape, can be determined. We present an updated classification scheme, which comprises a total of 135 unique shapes, including 34 new snow crystal shapes. This is useful for other studies that are using previous shape classification schemes, in particular the widely used Magono–Lee classification. To facilitate the study of the shape dependence of the microphysical properties, we further sort these individual particle shapes into 15 different shape groups. Relationships between the microphysical properties are determined for each of these shape groups.

scholarly journals Metamorphism of Air Bubbles in a Snow Crystal

1967 ◽  
Vol 6 (46) ◽  
pp. 561-564
Author(s):  
Norikazu Maeno ◽  
Daisuke Kuroiwa
Keyword(s):  
Activation Energy ◽  
Diffusion Processes ◽  
Atomic Diffusion ◽  
Mechanical Relaxation ◽  
Air Bubbles ◽  
A Value ◽  
Snow Crystal ◽  
Activation Energy For Diffusion ◽  
Snow Crystals ◽  
Natural Snow

RésuméObservations have been made of the modification produced by a temperature gradient in the shape of air bubbles in natural snow crystals, and also of the shrinkage of the bubbles with time. The rate of shrinkage is governed by a constant which is strongly temperature dependent with an activation energy of about 15.1 kcal./mole, a value sufficiently similar to the activation energy for diffusion of tritium, dielectric relaxation and mechanical relaxation to suggest that atomic diffusion processes may be responsible for all of these phenomena.

scholarly journals Mass of different snow crystal shapes derived from fall speed measurements

2021 ◽  
Author(s):  
Sandra Vázquez-Martín ◽  
Thomas Kuhn ◽  
Salomon Eliasson
Keyword(s):  
Particle Size ◽  
Climate Models ◽  
Cross Sectional Area ◽  
Particle Mass ◽  
Sectional Area ◽  
Cross Sectional ◽  
Microphysical Properties ◽  
Ice Particles ◽  
Fall Speed

Abstract. Meteorological forecast and climate models require good knowledge of the microphysical properties of hydrometeors and the atmospheric snow and ice crystals in clouds. For instance, their size, cross-sectional area, shape, mass, and fall speed. Especially shape is an important parameter in that it strongly affects the scattering properties of ice particles, and consequently their response to remote sensing techniques. The fall speed and mass of ice particles are other important parameters both for numerical forecast models and for the representation of snow and ice clouds in climate models. In the case of fall speed, it is responsible for the rate of removal of ice from these models. The particle mass is a key quantity that connects the cloud microphysical properties to radiative properties. Using an empirical relationship between the dimensionless Reynolds and Best numbers, fall speed and mass can be derived from each other if particle size and cross-sectional area are also known. In this work, ground-based in-situ measurements of snow particle microphysical properties are used to analyse mass as a function of shape and the other properties particle size, cross-sectional area, and fall speed. The measurements for this study were done in Kiruna, Sweden during snowfall seasons of 2014 to 2019 and using the ground-based in-situ instrument Dual Ice Crystal Imager (D-ICI), which takes high-resolution side- and top-view images of natural hydrometeors. From these images, particle size (maximum dimension), cross-sectional area, and fall speed of individual particles are determined. The particles are shape classified according to the scheme presented in our previous work, in which particles sort into 15 different shape groups depending on their shape and morphology. Particle masses of individual ice particles are estimated from measured particle size, cross-sectional area, and fall speed. The selected dataset covers sizes from about 0.1 mm to 3.2 mm, fall speeds from 0.1 m s−1 to 1.6 m s−1, and masses from close to 0.2 μg to 320 μg. In our previous work, the fall speed relationships between particle size and cross-sectional area were studied. In this work, the same dataset is used to determine the particle mass, and consequently, the mass relationships between particle size, cross-sectional area, and fall speed are studied for these 15 shape groups. Furthermore, the mass relationships presented in this study are compared with the previous studies.

scholarly journals Metamorphism of Air Bubbles in a Snow Crystal

1967 ◽  
Vol 6 (46) ◽  
pp. 561-564 ◽  
Author(s):  
Norikazu Maeno ◽  
Daisuke Kuroiwa
Keyword(s):  
Activation Energy ◽  
Diffusion Processes ◽  
Atomic Diffusion ◽  
Mechanical Relaxation ◽  
Air Bubbles ◽  
A Value ◽  
Snow Crystal ◽  
Activation Energy For Diffusion ◽  
Snow Crystals ◽  
Natural Snow

Résumé Observations have been made of the modification produced by a temperature gradient in the shape of air bubbles in natural snow crystals, and also of the shrinkage of the bubbles with time. The rate of shrinkage is governed by a constant which is strongly temperature dependent with an activation energy of about 15.1 kcal./mole, a value sufficiently similar to the activation energy for diffusion of tritium, dielectric relaxation and mechanical relaxation to suggest that atomic diffusion processes may be responsible for all of these phenomena.

scholarly journals Ice nucleation and cloud microphysical properties in tropical tropopause layer cirrus

2009 ◽  
Vol 9 (5) ◽  
pp. 20631-20675 ◽  
Author(s):  
E. J. Jensen ◽  
L. Pfister ◽  
T.-P. Bui ◽  
P. Lawson ◽  
D. Baumgardner
Keyword(s):  
Ice Nucleation ◽  
Nucleation Theory ◽  
Ice Crystal ◽  
Tropical Tropopause Layer ◽  
Microphysical Properties ◽  
Tropical Tropopause ◽  
Ice Nuclei ◽  
Ice Crystal Size ◽  
Homogeneous Freezing

Abstract. In past modeling studies, it has generally been assumed that the predominant mechanism for nucleation of ice in the uppermost troposphere is homogeneous freezing of aqueous aerosols. However, recent in situ and remote-sensing measurements of the properties of cirrus clouds at very low temperatures in the tropical tropopause layer (TTL) are broadly inconsistent with theoretial predictions based on the homogeneous freezing assumption. The nearly ubiquitous occurence of gravity waves in the TTL makes the predictions from homogeneous nucleation theory particularly difficult to reconcile with measurements. These measured properties include ice number concentrations, which are much lower than theory predicts; ice crystal size distributions, which are much broader than theory predicts; and cloud extinctions, which are much lower than theory predicts. Although other explanations are possible, one way to limit ice concentrations is to have on the order of 50 L−1 effective ice nuclei (IN) that could nucleate ice at relatively low supersaturations. We suggest that ammonium sulfate particles, which would be dry much of the time in the cold TTL, are a potential IN candidate for TTL cirrus. Possible implications of the observed cloud microphysical properties for ice sedimentation, dehydration, and cloud persistence are also discussed.

scholarly journals The origin of midlatitude ice clouds and the resulting influence on their microphysical properties

2015 ◽  
Vol 15 (23) ◽  
pp. 34243-34281 ◽  
Author(s):  
A. E. Luebke ◽  
A. Afchine ◽  
A. Costa ◽  
J. Meyer ◽  
C. Rolf ◽  
...  
Keyword(s):  
Bimodal Distribution ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiative Properties ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Microphysical Properties ◽  
Ice Crystal Size ◽  
Ice Water

Abstract. The radiative role of ice clouds in the atmosphere is known to be important, but uncertainties remain concerning the magnitude and net effects. However, through measurements of the microphysical properties of cirrus clouds, we can better characterize them, which can ultimately allow for their radiative properties to be more accurately ascertained. It has recently been proposed that there are two types of cirrus clouds – in situ and liquid origin. In this study, we present observational evidence to show that two distinct types of cirrus do exist. Airborne, in situ measurements of cloud ice water content (IWC), ice crystal concentration (Nice), and ice crystal size from the 2014 ML-CIRRUS campaign provide cloud samples that have been divided according to their origin type. The key features that set liquid origin cirrus apart from the in situ origin cirrus are a higher frequency of high IWC (> 100 ppmv), higher Nice values, and larger ice crystals. A vertical distribution of Nice shows that the in situ origin cirrus clouds exhibit a median value of around 0.1 cm−3, while the liquid origin concentrations are slightly, but notably higher. The median sizes of the crystals contributing the most mass are less than 200 μm for in situ origin cirrus, with some of the largest crystals reaching 550 μm in size. The liquid origin cirrus, on the other hand, were observed to have median diameters greater than 200 μm, and crystals that were up to 750 μm. An examination of these characteristics in relation to each other and their relationship to temperature provides strong evidence that these differences arise from the dynamics and conditions in which the ice crystals formed. Additionally, the existence of these two groups in cirrus cloud populations may explain why a bimodal distribution in the IWC-temperature relationship has been observed. We hypothesize that the low IWC mode is the result of in situ origin cirrus and the high IWC mode is the result of liquid origin cirrus.

scholarly journals The origin of midlatitude ice clouds and the resulting influence on their microphysical properties

2016 ◽  
Vol 16 (9) ◽  
pp. 5793-5809 ◽  
Author(s):  
Anna E. Luebke ◽  
Armin Afchine ◽  
Anja Costa ◽  
Jens-Uwe Grooß ◽  
Jessica Meyer ◽  
...  
Keyword(s):  
Bimodal Distribution ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiative Properties ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Microphysical Properties ◽  
Ice Crystal Size ◽  
Ice Water

Abstract. The radiative role of ice clouds in the atmosphere is known to be important, but uncertainties remain concerning the magnitude and net effects. However, through measurements of the microphysical properties of cirrus clouds, we can better characterize them, which can ultimately allow for their radiative properties to be more accurately ascertained. Recently, two types of cirrus clouds differing by formation mechanism and microphysical properties have been classified – in situ and liquid origin cirrus. In this study, we present observational evidence to show that two distinct types of cirrus do exist. Airborne, in situ measurements of cloud ice water content (IWC), ice crystal concentration (Nice), and ice crystal size from the 2014 ML-CIRRUS campaign provide cloud samples that have been divided according to their origin type. The key features that set liquid origin cirrus apart from the in situ origin cirrus are higher frequencies of high IWC ( > 100 ppmv), higher Nice values, and larger ice crystals. A vertical distribution of Nice shows that the in situ origin cirrus clouds exhibit a median value of around 0.1 cm−3, while the liquid origin concentrations are slightly, but notably higher. The median sizes of the crystals contributing the most mass are less than 200 µm for in situ origin cirrus, with some of the largest crystals reaching 550 µm in size. The liquid origin cirrus, on the other hand, were observed to have median diameters greater than 200 µm, and crystals that were up to 750 µm. An examination of these characteristics in relation to each other and their relationship to temperature provides strong evidence that these differences arise from the dynamics and conditions in which the ice crystals formed. Additionally, the existence of these two groups in cirrus cloud populations may explain why a bimodal distribution in the IWC-temperature relationship has been observed. We hypothesize that the low IWC mode is the result of in situ origin cirrus and the high IWC mode is the result of liquid origin cirrus.

scholarly journals Impact of surface and near-surface processes on ice crystal concentrations measured at mountain-top research stations

2018 ◽  
Vol 18 (12) ◽  
pp. 8909-8927 ◽  
Author(s):  
Alexander Beck ◽  
Jan Henneberger ◽  
Jacob P. Fugal ◽  
Robert O. David ◽  
Larissa Lacher ◽  
...  
Keyword(s):  
Ice Crystals ◽  
Surface Processes ◽  
Blowing Snow ◽  
Ice Crystal ◽  
Turbulent Layer ◽  
Near Surface ◽  
Microphysical Properties ◽  
Order Of Magnitude ◽  
The Impact

Abstract. In situ cloud observations at mountain-top research stations regularly measure ice crystal number concentrations (ICNCs) orders of magnitudes higher than expected from measurements of ice nucleating particle (INP) concentrations. Thus, several studies suggest that mountain-top in situ cloud microphysical measurements are influenced by surface processes, e.g., blowing snow, hoar frost or riming on snow-covered trees, rocks and the snow surface. This limits the relevance of such measurements for the study of microphysical properties and processes in free-floating clouds. This study assesses the impact of surface processes on in situ cloud observations at the Sonnblick Observatory in the Hohen Tauern region, Austria. Vertical profiles of ICNCs above a snow-covered surface were observed up to a height of 10 m. The ICNC decreases at least by a factor of 2 at 10 m if the ICNC at the surface is larger than 100 L−1. This decrease can be up to 1 order of magnitude during in-cloud conditions and reached its maximum of more than 2 orders of magnitudes when the station was not in cloud. For one case study, the ICNC for regular and irregular ice crystals showed a similar relative decrease with height. This suggests that either surface processes produce both irregular and regular ice crystals or other effects modify the ICNCs near the surface. Therefore, two near-surface processes are proposed to enrich ICNCs near the surface. Either sedimenting ice crystals are captured in a turbulent layer above the surface or the ICNC is enhanced in a convergence zone because the cloud is forced over a mountain. These two processes would also have an impact on ICNCs measured at mountain-top stations if the surrounding surface is not snow covered. Conclusively, this study strongly suggests that ICNCs measured at mountain-top stations are not representative of the properties of a cloud further away from the surface.

scholarly journals A Multisensor Approach Toward a Better Understanding of Snowfall Microphysics: The TOSCA Project

2011 ◽  
Vol 92 (5) ◽  
pp. 613-628 ◽  
Author(s):  
U. Löhnert ◽  
S. Kneifel ◽  
A. Battaglia ◽  
M. Hagen ◽  
L. Hirsch ◽  
...  
Keyword(s):  
Microwave Radiometer ◽  
Optimal Estimation ◽  
Supercooled Liquid ◽  
Environmental Research ◽  
Research Station ◽  
Vertical Column ◽  
Microphysical Properties ◽  
Snow Water ◽  
Snow Crystals

The Towards an Optimal estimation based Snow Characterization Algorithm (TOSCA) project addresses possible novel measurement synergies for deriving snowfall microphysical parameters from the ground by combining the unique information obtained from a suite of ground-based sensors: microwave radiometers (22–150 GHz), 24- and 36-GHz radar, lidar, and in situ optical disdrometer methods. During the winter of 2008/09, such instruments were deployed at the Environmental Research Station Schneefernerhaus (UFS; at 2650 m MSL) at the Zugspitze Mountain in Germany for deriving microphysical properties of snowfall. This contribution gives an overview of the measurements carried out and discusses the potential for the developments of synergetic retrieval algorithms for deriving snow water content within the vertical column. The identification of potentially valuable ground-based instrument synergy for the retrieval of snowfall parameters from the surface will also be of importance for the development of new space-borne observational techniques. Microwave radiometer measurements show that brightness temperature enhancements at 90 and 150 GHz are correlated with the radar-derived snow water path, which is supported by radiative transfer simulations. The synergy of these measurements toward an improved snow mass content, however, needs to be augmented by knowledge on water vapor, supercooled liquid water, particle size distribution, and shape, thus making clear the necessity of synergetic remote sensing and in situ measurements. The radiometric measurements also reveal the very frequent presence of supercooled water within snow clouds and its importance to microphysical diffusion and aggregation growth of snow crystals. Analysis of the disdrometer measurements shows a “secondary aggregation peak” around −12° to −15°C, a temperature range where the Wegener–Bergeron–Findeisen process is most effective and typically dendrite snow crystals forms dominate.

scholarly journals Ice nucleation and cloud microphysical properties in tropical tropopause layer cirrus

2010 ◽  
Vol 10 (3) ◽  
pp. 1369-1384 ◽  
Author(s):  
E. J. Jensen ◽  
L. Pfister ◽  
T.-P. Bui ◽  
P. Lawson ◽  
D. Baumgardner
Keyword(s):  
Ammonium Sulfate ◽  
Nucleation Theory ◽  
Ice Crystal ◽  
Tropical Tropopause Layer ◽  
Microphysical Properties ◽  
Tropical Tropopause ◽  
Ice Nuclei ◽  
Ice Crystal Size ◽  
Homogeneous Freezing

Abstract. In past modeling studies, it has generally been assumed that the predominant mechanism for nucleation of ice in the uppermost troposphere is homogeneous freezing of aqueous aerosols. However, recent in situ and remote-sensing measurements of the properties of cirrus clouds at very low temperatures in the tropical tropopause layer (TTL) are broadly inconsistent with theoretial predictions based on the homogeneous freezing assumption. The nearly ubiquitous occurence of gravity waves in the TTL makes the predictions from homogeneous nucleation theory particularly difficult to reconcile with measurements. These measured properties include ice number concentrations, which are much lower than theory predicts; ice crystal size distributions, which are much broader than theory predicts; and cloud extinctions, which are much lower than theory predicts. Although other explanations are possible, one way to limit ice concentrations is to have on the order of 50 L−1 effective ice nuclei (IN) that could nucleate ice at relatively low supersaturations. We suggest that ammonium sulfate particles, which would be dry much of the time in the cold TTL, are a potential IN candidate for TTL cirrus. However, this mechanism remains to be fully quantified for the size distribution of ammonium sulfate (possibly internally mixed with organics) actually present in the upper troposphere. Possible implications of the observed cloud microphysical properties for ice sedimentation, dehydration, and cloud persistence are also discussed.

Transmission Electron Microscopy Studies of Aluminum Oxidation

1985 ◽  
Vol 43 ◽  
pp. 268-269
Author(s):  
J.Y. Lee
Keyword(s):  
Nucleation And Growth ◽  
Ion Milling ◽  
Cross Sectional ◽  
Polycrystalline Aluminum ◽  
Axis Orientation ◽  
Temperature Oxidation ◽  
Aluminum Oxidation ◽  
Transmission Electron ◽  
High Resolution Images ◽  
Argon Ion

In the oxidation of metals and alloys, microstructural features at the atomic level play an important role in the nucleation and growth of the oxide, but little is known about the atomic mechanisms of high temperature oxidation. The present paper describes current progress on crystallographic aspects of aluminum oxidation. The 99.999% pure, polycrystalline aluminum was chemically polished and oxidized in 1 atm air at either 550°C or 600°C for times from 0.5 hr to 4 weeks. Cross-sectional specimens were prepared by forming a sandwich with epoxy, followed by mechanical polishing and then argon ion milling. High resolution images were recorded in a <110>oxide zone-axis orientation with a JE0L JEM 200CX microscope operated at 200 keV.

Sign in / Sign up

Export Citation Format

Share Document