scholarly journals The Melting Layer: A Laboratory Investigation of Ice Particle Melt and Evaporation near 0°C

2005 ◽  
Vol 44 (2) ◽  
pp. 206-220 ◽  
Author(s):  
R. G. Oraltay ◽  
J. Hallett
Keyword(s):  
Particle Production ◽  
Reverse Flow ◽  
Water Layer ◽  
Melting Process ◽  
Capillary Forces ◽  
Ambient Conditions ◽  
Melting Layer ◽  
Ice Particles ◽  
Initial Melting ◽  
Snow Crystals

Abstract Melting, freezing, and evaporation of individual and aggregates of snow crystals are simulated in the laboratory under controlled temperature, relative humidity, and air velocity. Crystals of selected habit are grown on a vertical filament and subsequently melted or evaporated in reverse flow, with the velocity adjusted for appropriate fall speed to reproduce conditions of the melting layer. Nonequilibrium conditions are simulated for larger melting ice particles surrounded by smaller drops at a temperature up to +5°C or growth of an ice crystal surrounded by freezing ice particles down to −5°C. Initial melting of well-defined faceted crystals, as individuals or in combination, occurs as a water layer >10 μm thick. For larger (>100 μm) crystals the water becomes sequestered by capillary forces as individual drops separated by water-free ice regions, often having quasiperiodic locations along needles, columns, or arms from evaporating dendrites. Drops are also located at intersections of aggregate crystals and dendrite branches, being responsible for the maximum of the radar scatter. The drops have a finite water–ice contact angle of 37°–80°, depending on ambient conditions. Capillary forces move water from high-curvature to low-curvature regions as melting continues. Toward the end of the melting process, the ice separating the drops becomes sufficiently thin to fracture under aerodynamic forces, and mixed-phase particles are shed. Otherwise ice-free drops are shed. The melting region and the mechanism for lowering the melting layer with an increasing precipitation rate are associated with smaller ice particle production capable of being lofted in weaker updrafts.

scholarly journals Experimental Study on Freeze-Thaw Cycle Duration of Saturated Tuff

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Man Huang ◽  
Bin Tang ◽  
Jianliang Jiang ◽  
Renqiu Guan ◽  
Huajun Wang
Keyword(s):  
Phase Transition ◽  
Power Function ◽  
Melting Process ◽  
Freezing Process ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle ◽  
Initial Melting ◽  
Time Required ◽  
Ice Water

The freeze-thaw duration is one of the important factors affecting the change of rock properties. However, this factor has not formed a unified standard in the freeze-thaw cycle test. This study uses saturated tuff samples taken from eastern Zhejiang, China, as research objects to explore the change law of the time required for the rock to reach a full freeze-thaw cycle. Measured results show that the total duration of the freeze-thaw cycle presents an increasing power function with the increase in the number of freeze-thaw cycles. The freezing process is divided into three phases: initial freezing, water-ice phase transition, and deep freezing. The melting process is also divided into three phases: initial melting, ice-water phase transition, and deep melting. The time required for the ice-water phase change stage of the melting process does not change with the increase in the number of freeze-thaw cycles, while the other stages increase as a power function. The proportion of duration of each stage in the freezing process does not change with the increase in the number of cycles. By contrast, the duration proportion of the initial melting phase in the melting process decreases, and the deep melting phase increases. Experimental results of the freeze-thaw cycles of tuff demonstrate that the freeze-thaw duration of the freeze-thaw cycles within 40 times can be set to 9 h. The freezing and melting processes are 6 and 3 h, respectively.

Packing Characteristics and Its Effect on Heat Transfer Characteristics in Melting of Granular Packed Bed Subject to Horizonal Forced Convection

2002 ◽  
Author(s):  
Y. L. Hao ◽  
Y.-X. Tao
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Melting Process ◽  
Packed Bed ◽  
Time Interval ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Ice Particles ◽  
Different Types ◽  
Series Of Experiments

A series of experiments are conducted to investigate the characteristics and its effect on the melting and heat of a packed bed consisting of melting ice particles to horizontal forced convection. The volumes and situations of the melting ganular packed beds are by the visualization observations and measurements digital camcorders within the range of Re = 71 ~ 2291, Gr/Re2 = 1.48×10−5 ~ 17.32, and Ste = 0.0444 ~ 0.385, respectively. The mass of ice particles is measured at the time interval during the melting process. Two types of pattern can be found under the different conditions. The different types of heat transfer characteristics emerge in type of packing pattern. The correlations for each type of pattern are obtained based on the experimental results.

scholarly journals The IMPROVE-1 Storm of 1–2 February 2001. Part II: Cloud Structures and the Growth of Precipitation

2005 ◽  
Vol 62 (10) ◽  
pp. 3456-3473 ◽  
Author(s):  
Amanda G. Evans ◽  
John D. Locatelli ◽  
Mark T. Stoelinga ◽  
Peter V. Hobbs
Keyword(s):  
Liquid Water ◽  
Lower Layer ◽  
Leading Edge ◽  
Particle Growth ◽  
Cloud Particle ◽  
Cyclonic Storm ◽  
Melting Layer ◽  
Ice Particles ◽  
Research Aircraft ◽  
Particle Imaging

Abstract On 1–2 February 2001, a strong cyclonic storm system developed over the northeastern Pacific Ocean and moved onto the Washington coast. This storm was one of several that were documented during the first field phase of the Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE). In the 1–2 February case, soundings and wind profiler measurements showed that a wide cold-frontal rainband was coincident with the leading edge of an upper-level cold front in a classical warm occlusion. Ground-based radar observations revealed the presence of subbands within the wide cold-frontal rainband and two layers of precipitation generating cells within this rainband: one at 5–7 km MSL and the other at 9–10 km MSL. The lower layer of generating cells produced fallstreaks that were traced from the cells down to the radar bright band at 2 km MSL. Observations suggest a connection between the subbands and the lower layer of generating cells. A research aircraft, equipped for cloud microphysical measurements, passed through at least two generating cells in the 5–7-km region. These cells were in their formative stage, with elevated liquid water contents and low ice particle concentrations. The microphysical structure of the wide cold-frontal rainband was elucidated by particle imagery from a Cloud Particle Imaging (CPI) probe aboard the research aircraft. These images provide detailed information on crystal habits and degrees of riming throughout the depth of the rainband. The crystal habits are used to deduce the temperature and saturation conditions under which the crystals grew and, along with in situ measurements of particle size spectra, they are used to estimate particle terminal fall velocities, precipitation rates, radar reflectivities, and vertical air motions. The radar reflectivity derived in this way generally compared well with direct measurement. Both the derived and directly measured parameters are used to determine the primary particle growth processes in the wide cold-frontal rainband. Above the melting layer, vapor deposition was the dominant growth process in the rainband; growth of ice particles by riming was small. Significant aggregation of ice particles occurred in the region just above the melting layer. A doubling in the air-relative vertical precipitation mass flux occurred between the region where sheath ice crystals formed (−3° ≤ T ≤ −8°C) and the surface. Substantial amounts of liquid water were found within the melting layer where growth occurred by the accretion of cloud droplets and also by condensation. Growth by the collision and coalescence of raindrops was not significant below the melting layer.

scholarly journals Examining Polarimetric Radar Observations of Bulk Microphysical Structures and Their Relation to Vortex Kinematics in Hurricane Arthur (2014)

2017 ◽  
Vol 145 (11) ◽  
pp. 4521-4541 ◽  
Author(s):  
Anthony C. Didlake ◽  
Matthew R. Kumjian
Keyword(s):  
Tropical Cyclone ◽  
Lower Layer ◽  
Polarimetric Radar ◽  
Arthur Prior ◽  
Radar Observations ◽  
Melting Layer ◽  
Ice Particles ◽  
Planar Crystal ◽  
Differential Reflectivity ◽  
Left Quadrant

Dual-polarization radar observations were taken of Hurricane Arthur prior to and during landfall, providing needed insight into the microphysics of tropical cyclone precipitation. A total of 30 h of data were composited and analyzed by annuli capturing storm features (eyewall, inner rainbands, and outer rainbands) and by azimuth relative to the deep-layer environmental wind shear vector. Polarimetric radar variables displayed distinct signatures indicating a transition from convective to stratiform precipitation in the downshear-right to downshear-left quadrants, which is an organization consistent with the expected kinematic asymmetry of a sheared tropical cyclone. In the downshear-right quadrant, vertical profiles of differential reflectivity ZDR and copolar correlation coefficient ρHV were more vertically stretched within and above the melting layer at all annuli, which is attributed to convective processes. An analysis of specific differential phase KDP indicated that nonspherical ice particles had an increased presence in two layers: just above the melting level and near 8-km altitude. Here, convective updrafts generated ice particles in the lower layer, which were likely columnar crystals, and increased the available moisture in the upper layer, leading to increased planar crystal growth. A sharp transition in hydrometeor population occurred downwind in the downshear-left quadrant where ZDR and ρHV profiles were more peaked within the melting layer. Above the melting layer, these signatures indicated reduced ice column counts and shape diversity owing to aggregation in a predominantly stratiform regime. The rainband quadrants exhibited a sharper transition compared to the eyewall quadrants owing to weaker winds and longer distances that decreased azimuthal mixing of ice hydrometeors.

scholarly journals Relationship between temperature and apparent shape of pristine ice crystals derived from polarimetric cloud radar observations during the ACCEPT campaign

2016 ◽  
Vol 9 (8) ◽  
pp. 3739-3754 ◽  
Author(s):  
Alexander Myagkov ◽  
Patric Seifert ◽  
Ulla Wandinger ◽  
Johannes Bühl ◽  
Ronny Engelmann
Keyword(s):  
Free Fall ◽  
Crystal Shape ◽  
Ice Crystal ◽  
Ambient Conditions ◽  
Axis Ratio ◽  
Microwave Scattering ◽  
Cloud Radar ◽  
Ice Particles ◽  
Rapid Changes ◽  
Good Agreement

Abstract. This paper presents first quantitative estimations of apparent ice particle shape at the top of liquid-topped clouds. Analyzed ice particles were formed under mixed-phase conditions in the presence of supercooled water and in the temperature range from −20 to −3 °C. The estimation is based on polarizability ratios of ice particles measured by a Ka-band cloud radar MIRA-35 with hybrid polarimetric configuration. Polarizability ratio is a function of the geometrical axis ratio and the dielectric properties of the observed hydrometeors. For this study, 22 cases observed during the ACCEPT (Analysis of the Composition of Clouds with Extended Polarization Techniques) field campaign were used. Polarizability ratios retrieved for cloud layers with the cloud-top temperatures of  ∼ −5,  ∼ −8,  ∼ −15, and  ∼ −20 °C were 1.6, 0.9, 0.6, and 0.9, respectively. Such values correspond to prolate, quasi-isotropic, oblate, and quasi-isotropic particles, respectively. Data from a free-fall chamber were used for the comparison. A good agreement of detected apparent shapes with well-known shape–temperature dependencies observed in laboratories was found. Polarizability ratios used for the analysis were estimated for areas located close to the cloud top, where aggregation and riming processes do not strongly affect ice particles. We concluded that, in microwave scattering models, ice particles detected in these areas can be assumed to have pristine shapes. It was also found that even slight variations of ambient conditions at the cloud top with temperatures warmer than  ∼ −5 °C can lead to rapid changes of ice crystal shape.

scholarly journals Aircraft measurements of microphysical properties of subvisible cirrus in the tropical tropopause layer

2007 ◽  
Vol 7 (3) ◽  
pp. 6255-6292 ◽  
Author(s):  
R. P. Lawson ◽  
B. Pilson ◽  
B. Baker ◽  
Q. Mo ◽  
E. Jensen ◽  
...  
Keyword(s):  
Water Vapor ◽  
Costa Rica ◽  
High Water ◽  
Radiation Budget ◽  
Ambient Conditions ◽  
Cloud Particle ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Ice Particles ◽  
Validation Experiment

Abstract. Subvisible cirrus (SVC) clouds are often observed within the tropical tropopause layer (TTL) and have been shown to have a significant impact on the earth radiation budget. The Costa Rica Aura Validation Experiment (CR-AVE) sponsored by the National Aeronautics and Space Administration (NASA) took place near San Jose, Costa Rica from 14 January–15 February 2006. The NASA WB-57F sampled SVC in the TTL from −75°C to −90°C with an improved set of cloud particle probes. The first digital images of ice particles in the TTL are compared with replicator images of ice particles collected in 1973 by a WB-57F in the TTL. The newer measurements reveal larger particles, on the order of 100 μm compared with <50 μm from the earlier measurements, and also different particle shapes. The 1973 particles were mainly columnar and trigonal, whereas the newer measurements are quasi-spherical and hexagonal plates. The WB-57F also measured very high water vapor contents with some instruments, up to 4 ppmv, and aerosols with mixed organics and sulfates. It is unknown whether these ambient conditions were present in the 1973 studies, and whether such conditions have an influence on particle shape and the development of the large particles. A companion paper (Jensen et al., 2007) presents crystal growth calculations that suggest that the high water vapor measurements are required to grow ice particles to the observed sizes of 100 μm and larger.

scholarly journals Ice formation and development in aged, wintertime cumulus over the UK: observations and modelling

2012 ◽  
Vol 12 (11) ◽  
pp. 4963-4985 ◽  
Author(s):  
I. Crawford ◽  
K. N. Bower ◽  
T. W. Choularton ◽  
C. Dearden ◽  
J. Crosier ◽  
...  
Keyword(s):  
Particle Production ◽  
Ice Crystals ◽  
Dust Particles ◽  
Ice Formation ◽  
Crystal Formation ◽  
Surface Acting ◽  
Model Simulations ◽  
Ice Nuclei ◽  
Ice Particles ◽  
High Concentrations

Abstract. In situ high resolution aircraft measurements of cloud microphysical properties were made in coordination with ground based remote sensing observations of a line of small cumulus clouds, using Radar and Lidar, as part of the Aerosol Properties, PRocesses And InfluenceS on the Earth's climate (APPRAISE) project. A narrow but extensive line (~100 km long) of shallow convective clouds over the southern UK was studied. Cloud top temperatures were observed to be higher than −8 °C, but the clouds were seen to consist of supercooled droplets and varying concentrations of ice particles. No ice particles were observed to be falling into the cloud tops from above. Current parameterisations of ice nuclei (IN) numbers predict too few particles will be active as ice nuclei to account for ice particle concentrations at the observed, near cloud top, temperatures (−7.5 °C). The role of mineral dust particles, consistent with concentrations observed near the surface, acting as high temperature IN is considered important in this case. It was found that very high concentrations of ice particles (up to 100 L−1) could be produced by secondary ice particle production providing the observed small amount of primary ice (about 0.01 L−1) was present to initiate it. This emphasises the need to understand primary ice formation in slightly supercooled clouds. It is shown using simple calculations that the Hallett-Mossop process (HM) is the likely source of the secondary ice. Model simulations of the case study were performed with the Aerosol Cloud and Precipitation Interactions Model (ACPIM). These parcel model investigations confirmed the HM process to be a very important mechanism for producing the observed high ice concentrations. A key step in generating the high concentrations was the process of collision and coalescence of rain drops, which once formed fell rapidly through the cloud, collecting ice particles which caused them to freeze and form instant large riming particles. The broadening of the droplet size-distribution by collision-coalescence was, therefore, a vital step in this process as this was required to generate the large number of ice crystals observed in the time available. Simulations were also performed with the WRF (Weather, Research and Forecasting) model. The results showed that while HM does act to increase the mass and number concentration of ice particles in these model simulations it was not found to be critical for the formation of precipitation. However, the WRF simulations produced a cloud top that was too cold and this, combined with the assumption of continual replenishing of ice nuclei removed by ice crystal formation, resulted in too many ice crystals forming by primary nucleation compared to the observations and parcel modelling.

Nanolithograhpy Using Tip-Sample Material Transport Process

2005 ◽  
Vol 11 (S03) ◽  
pp. 10-13
Author(s):  
M. I. N. da Silva ◽  
B. R. A. Neves
Keyword(s):  
Water Layer ◽  
Sample Surface ◽  
Scanning Probe ◽  
Nanometer Scale ◽  
Direct Write ◽  
Water Effect ◽  
Ambient Conditions ◽  
Material Transport ◽  
Scanning Probe Lithography ◽  
Flat Substrate

Scanning Probe Microscopy (SPM) [1] has been an important tool to organize matter on the nanometer scale. It has been proved to be a powerful tool not only for imaging but also for nanofabrication. SPM-based nanofabrication comprises manipulation of atoms or molecules and SPM-based nanolithography. SPM-based nanolithography, referred to as scanning probe lithography (SPL) holds good promise for fabrication of nanometer-scale patterns as an emerging generic lithography technique that employs SPM to directly pattern nanometer-scale features under appropriate conditions. The water meniscus formation between the tip and the flat substrate, due to the water layer present on any surface of a material at ambient conditions, has been studied experimentally and theoretically [2-6] using SPM techniques. The water effect in the imaging process is well understood [2, 4, 6-8]. Dip pen nanolithogaphy (DPN) [9] is one example of a technique that uses the water effect to transfer material from the tip onto sample surface in direct-write fashion with nanoscopic resolution.

Theoretical and Experimental Investigation of the Melting Process of Ice Particles

2016 ◽  
Vol 30 (4) ◽  
pp. 946-954 ◽  
Author(s):  
Tobias Hauk ◽  
Elmar Bonaccurso ◽  
Philippe Villedieu ◽  
Pierre Trontin
Keyword(s):  
Experimental Investigation ◽  
Melting Process ◽  
Ice Particles
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