Growth Of Ice Particles Research Articles

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

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.

Numerical Simulation of Supercooling Process and Frazil Ice Evolution

A mathematical model to simulate the supercooling process and frazil ice evolution is developed from previous models. It incorporates improvements for the physical process of initial seeding, ice particle growth, secondary nucleation, flocculation/breakup, and gravitational removal. A variable Nusselt number related to the flow turbulence is used. It has been found that two calibrated parameters, initial seeding, and a parameter that limits the secondary nucleation are correlated to the turbulence intensity, which is useful for the practical application of the model developed in this paper. Furthermore sensitivity analysis is carried out for these two parameters. The simulations results show good agreements with experimental data.

Coupling of acoustic waves to clouds in the jovian troposphere

Seismology is the best tool for investigating the interior structure of stars and giant planets. This paper deals with a photometric study of jovian global oscillations. The propagation of acoustic waves in the jovian troposphere is revisited in order to estimate their effects on the planetary albedo. According to the standard model of the jovian cloud structure there are three major ice cloud layers (e.g., [Atreya et al., 1999. A comparison of the atmospheres of Jupiter and Saturn: Deep atmospheric composition, cloud structure, vertical mixing, and origin. Planet Space Sci. 47, 1243–1262]). We consider only the highest layers, composed of ammonia ice, in the region where acoustic waves are trapped in Jupiter's atmosphere. For a vertical wave propagating in a plane parallel atmosphere with an ammonia ice cloud layer, we calculate first the relative variations of the reflected solar flux due to the smooth oscillations at about the ppm level. We then determine the phase transitions induced by the seismic waves in the clouds. These phase changes, linked to ice particle growth, are limited by kinetics. A Mie model [Mishchenko et al., 2002. Scattering, Absorption, and Emission of Light by Small Particles. Cambridge Univ. Press, Cambridge, pp. 158–190] coupled with a simple radiation transfer model allows us to estimate that the albedo fluctuations of the cloud perturbed by a seismic wave reach relative variations of 70 ppm for a 3-mHz wave. This albedo fluctuation is amplified by a factor of ∼70 relative to the previously published estimates that exclude the effect of the wave on cloud properties. Our computed amplifications imply that jovian oscillations can be detected with very precise photometry, as proposed by the microsatellite JOVIS project, which is dedicated to photometric seismology [Mosser et al., 2004. JOVIS: A microsatellite dedicated to the seismic analysis of Jupiter. In: Combes, F., Barret, D., Contini, T., Meynadier, F., Pagani, L. (Eds.), SF2A-2004, Semaine de l'Astrophysique Francaise, Les Ulis. In: EdP-Sciences Conference Series, pp. 257–258].

On the occurrence and formation of multiple layers of polar mesosphere summer echoes

Polar Mesosphere Summer Echoes (PMSE) have been studied at Andenes (69°N, 16°E), Norway, using VHF radar observations from 1994–1997 and since 1999. One remarkable feature of all PMSE is the fact that the radar echoes often occur in the form of two or more distinct layers that can persist for periods of up to several hours. Until now, the layering mechanism leading to these multiple structures is not well understood. Here we are studying the occurrence and the mean altitude distribution of these multiple layer events. To discuss the processes that are potentially responsible for the creation of these multiple structures, we apply a microphysical model of the generation and growth of mesospheric ice particles under the influence of temperature and wind variations caused by a long period gravity wave. Finally, this model approach is tested with gravity wave characteristics derived from MF and VHF radar wind measurements during the PMSE observations.

Homogeneous Ice Nucleation in Subtropical and Tropical Convection and Its Influence on Cirrus Anvil Microphysics

Abstract This study uses a unique set of microphysical measurements obtained in a vigorous, convective updraft core at temperatures between −33° and −36°C, together with a microphysical model, to investigate the role of homogeneous ice nucleation in deep tropical convection and how it influences the microphysical properties of the associated cirrus anvils. The core and anvil formed along a sea-breeze front during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL–FACE). The updraft core contained two distinct regions as traversed horizontally: the upwind portion of the core contained droplets of diameter 10–20 μm in concentrations of around 100 cm−3 with updraft speeds of 5–10 m s−1; the downwind portion of the core was glaciated with high concentrations of small ice particles and stronger updrafts of 10–20 m s−1. Throughout the core, rimed particles up to 0.6-cm diameter were observed. The anvil contained high concentrations of both small particles and large aggregates. Thermodynamic analysis suggests that the air sampled in the updraft core was mixed with air from higher altitudes that descended along the upwind edge of the cloud in an evaporatively driven downdraft, introducing free-tropospheric cloud condensation nuclei into the updraft below the aircraft sampling height. Farther downwind in the glaciated portion of the core, the entrained air contained high concentrations of ice particles that inhibit droplet formation and homogeneous nucleation. Calculations of droplet and ice particle growth and homogeneous ice nucleation are used to investigate the influence of large ice particles lofted in updrafts from lower levels in this and previously studied tropical ice clouds on the homogeneous nucleation process. The preexisting large ice particles act to suppress homogeneous nucleation through competition via diffusional and accretional growth, mainly when the updrafts are < 5 m s−1. In deep convective updrafts > 5–10 m s−1, the anvil is the depository for the small, radiatively important ice particles (homogeneously nucleated) and the large ice particles from below (heterogeneously or secondarily produced, or recycled).

Tropical Rain Characteristics and Microphysics in a Three-Dimensional Cloud Model

Abstract The rain characteristics of convective clouds have been investigated numerically. Five different microphysical model settings have been used to study the roles of various mechanisms influencing rain formation: maritime ice (full microphysics, low cloud nuclei), maritime frozen (neglecting ice nuclei, enhancing drop freezing), maritime warm (only warm rain), continental ice (high cloud nuclei), and continental warm. Rain patterns and accumulation, drop growth modes, cell organization, heating rate profiles, and the alignment of rain cells in rainbands all differ greatly with different microphysics. Rainfall amounts were highest with maritime ice. With ice, a single, large rain cell was formed by absorbing small cells from the front and sides of the main cell. Forward in the cell, frozen drop formation dominated. Graupel-based hail fell from the storm center. A unique rain accumulation process produced heavy rain in a sloped updraft. Graupel fell from above, producing a high hail water content near the freezing level by collecting many supercooled drops from merging cells. The apparent heating source peaked at two different levels: one by drop condensation growth at about 3 km, and the other by depositional growth at about 5 km. With maritime ice, a 60-km rain ring appeared and persisted. In the cases of the rainband model, lines of rain cells moved intermittently through the formation of cells at the cloud's leading edge in maritime ice. The results of these investigations, with and without ice, indicates the importance of diffusive and riming growth of ice particles and the associated release of latent heat in the development of convection and rain.

Preventing agglomeration and growth of ice particles in water with suitable additives

The present paper reviews the technologies on preventing the agglomeration and the growth of ice particles in water with a very small amount of suitable additives. This summarizes studies on the effects of anti-agglomeration of ice particles and suppression of ice growth by using anti-freeze protein and its substitutes or some kinds of surfactants, and on their applications to ice slurry making systems, and to the coupling technology with surfactant drag reduction of ice slurries. These anti-agglomeration additives are found to well disperse ice particles in water at a very low concentration without a serious depression of the equilibrium freezing temperature. This is concluded to improve the ability of ice slurries as a secondary refrigerant.

Theoretical model of the Bergeron–Findeisen mechanism of ice crystal growth in clouds

Abstract A numerical study of growth rate of ice particles in an array of water droplets (Bergeron–Findeisen mechanism) has used the method of electrostatic image charges to determine the vapour field in which a particle grows. Analysis of growth rate in various conditions of relevance to clouds has shown that it is proportional to liquid water content and to ice particle size, while it is inversely proportional to cloud droplet size. The results show that growth rate is enhanced by several percent relative to the usual treatment in which vapour is assumed to diffuse from infinity towards a growing ice particle. The study was performed for ice particles between 25 and 150 μm radii, water droplet sizes between 6 and 20 μm diameter and a wide range of liquid water contents. A study was also made to determine the effect of reducing the vapour source at infinity so that the droplets alone provided the vapour for particle growth. A parameterisation of ice particle growth rate is given as a function of liquid water content and ice particle and droplet sizes. These studies are of importance to considerations in thunderstorm electrification processes, where the mechanism of charge transfer between ice particles and graupel could take place.

Suppression of Ice Particle Growth and the Possibility of Energy Saving Latent Heat Transportation by Using Surfactant Additives

Latent heat transportation by ice/water slurry is an effective technology to establish the energy saving air conditioning system. Modak et al. (2002) reported a new surfactant system in which the good agglomeration control of ice particles was available, and effective turbulent drag reduction was simultaneously attained. However, this system needed the addition of a considerable amount of sodium chloride. In this paper, the combined use of zwitterionic surfactant with a suitable brine with no corrosive characteristic is proposed to prepare ice/water slurry. It is certified that newly prepared ice/water slurry shows a good dispersion condition of ice particles and the flowability of the slurry is much improved if it is compared with the previous ice/water slurries. The ice/water slurry thus obtained is promising for the use of the high efficiency heat transportation technology by utilizing surfactant drag reduction and latent heat transportation.

The Anatomy of a Continental Tropical Convective Storm

Abstract This study provides a very clear picture of the microphysics and flow field in a convective storm in the Rondonia region of Brazil through a synthesis of observations from two unique radars, measurements of the surface drop size distribution (DSD), and particle types and sizes from an aircraft penetration. The primary findings are 1) the growth of rain by the collision–coalescence–breakup (CCB) process to equilibrium drop size distributions entirely below the 0°C level; 2) the subsequent growth of larger ice particles (graupel and hail) at subfreezing temperatures; 3) the paucity of lightning activity during the former process, and the increased lightning frequency during the latter; 4) the occurrence of strong downdrafts and a downburst during the latter phase of the storm resulting from cooling by melting and evaporation; 5) the occurrence of turbulence along the main streamlines of the storm; and 6) the confirmation of the large drops reached during the CCB growth by polarimetric radar observa...

A Parameterization of cirrus cloud formation: Homogeneous freezing including effects of aerosol size

In a previous study, we have derived an approximate, physically based parameterization of cirrus cloud formation by homogeneous freezing, applying to a wide class of supercooled aerosols in the upper troposphere and tropopause region. In this study, the parameterization scheme is extended to include the effects of aerosol size on the freezing process in adiabatically rising air parcels. Aerosol size effects become important when the timescale of the freezing event is fast compared to the timescale of depositional growth of the pristine ice particles. The generalized parameterization scheme is validated with parcel model simulations and can directly be applied in models that do not explicitly resolve the ice nucleation process, such as cloud‐resolving models, weather forecast models, and climate models. The relationship between aerosol and ice crystal number concentrations in cirrus clouds formed by homogeneous freezing is discussed. This relationship is much weaker than in liquid water clouds. It is shown that even freezing of enhanced levels of sulfate aerosol originating from strong volcanic eruptions is unlikely to exert a sensible influence on cirrus formation.

Transient eddies in the southern hemisphere of Mars

Mars Global Surveyor is providing the first observations of transient eddies in the southern hemisphere of Mars. We derive basic properties of the traveling eddies that appear in midwinter (Ls = 134°–148°) through analysis of radio occultation measurements at 67°–70°S latitude. The dominant mode has a period of ∼2 solar days and a zonal wavenumber s = 3. Strong zonal variations in eddy amplitude signal the presence of a possible “storm zone” at 150°–330°E longitude. Within this longitude band the eddies achieve peak amplitudes at the 300‐Pa pressure level of ∼7 K in temperature and 10–15 m s−1 in meridional wind speed. The minimum temperature associated with the eddies is ∼2 K colder than saturation of CO2, close to the threshold where nucleation and growth of new ice particles can occur. A simulation by a Mars general circulation model produces traveling eddies that closely resemble the observations.

A parameterization of cirrus cloud formation: Homogeneous freezing of supercooled aerosols

The nucleation and initial growth of ice crystals in cirrus clouds at low (<235 K) temperatures prevailing in the upper troposphere and in the tropopause region is theoretically considered. The analysis explains the dependence of the number density of ice crystals on the vertical velocity and temperature seen in numerical simulations of cirrus formation when the timescale of depositional growth of the pristine ice particles is fast compared to the timescale of the freezing event. In such cases, applicable in many situations, the number of crystals formed via homogeneous freezing of aqueous solution droplets is rather insensitive to details of the aerosol size distribution, but increases rapidly with updraft velocity and decreases with temperature. The derived parameterization is validated with parcel model simulations, and its applicability for use in climate models is discussed. The potential role of aerosol size and heterogeneous freezing processes in altering the predicted cirrus properties is briefly addressed.

PMCs and the water frost point in the Arctic summer mesosphere

In August, 1997 the Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) obtained vertical profiles of OH number density and polar mesospheric cloud (PMC) brightness by scanning the limb up to 71° N while the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) obtained co‐located vertical profiles of temperature. MAHRSI OH densities are converted to water vapor using a one‐dimensional model that assumes photochemical equilibrium. By combining water vapor profiles with CRISTA temperatures we map the frost point both vertically and horizontally in the Arctic summer mesosphere. Our data show that supersaturation can exist between 80‐87 km suggesting that growth of ice particles is limited to these altitudes. Additionally, we find that not only is supersaturation an insufficient condition for a PMC but also that PMCs can exist in apparently unsaturated air.

Physical properties of the organic aerosols and clouds on Titan

Titan's haze is optically thick in the visible, with an optical depth at 0.5 μm of about three. The haze varies with latitude in a seasonal cycle and has a detached upper layer. Microphysical models, photochemical models, and laboratory simulations all imply that the production rate of the haze is in the range of 0.5– 2×10 −14 g cm −2 s −1 . Given the rate of sedimentation, the total mass loading is about 250 mg m −2 . The transparency of the haze is high for wavelengths above 1 μm because the haze material becomes almost purely scattering and the optical depth decreases with increasing wavelength. The particles in the main haze deck are probably fractal in structure with an equivalent volume radius of 0.2 μm . The haze material is organic and, if similar to laboratory tholin, has a C/N ratio in the range of 2–4 and a C/H ratio of about unity. The haze significantly affects the thermal balance of Titan, causing an antigreenhouse effect that cools the surface by 9 K. Titan's faintly banded appearance suggests strong zonal winds in the lower stratosphere. Condensate clouds of ethane or methane, if present, are thin, patchy, or transient. Stratospheric clouds of condensed nitriles and (possibly) hydrocarbons appear to be associated with, though not contained entirely in, the polar shadow, suggesting abundances may vary with the season. Precipitating condensate particles from the stratosphere probably act as nucleating centers for the formation and rapid growth of methane ice particles in the troposphere, where the gas phase appears to be highly supersaturated. Once formed, fallout times for these hailstones are ∼2 h or less. Melting, and possible subsequent fragmentation of methane raindrops should occur at ∼12 km and below. Almost complete evaporation should occur just above the surface. A thin residue of ethane-enriched fog particles would then slowly settle to the surface, steadily modifying an existing surface or subsurface residue of liquid hydrocarbons. The optical properties of the haze in the 1 to 3 μm spectral region and the implications for the visibility of the surface are probably the most pressing current research questions. Other key questions include the nature of the high altitude detached haze layer, altitude and seasonal changes in composition of the haze, the role of haze particles as condensation nuclei for clouds, and the nature of any condensate clouds.

Radiative Effects on the Diffusional Growth of Ice Particles in Cirrus Clouds

Abstract At Colorado State University the Regional Atmospheric Modeling System (RAMS) has been used to study the radiative effect on the diffusional growth of ice particles in cirrus clouds. Using soundings extracted from a mesoscale simulation of the 26 November 1991 cirrus event, the radiative effect was studied using a two-dimensional cloud-resolving model (CRM) version of RAMS, coupled to an explicit bin-resolving microphysics. The CRM simulations of the 26 November 1991 cirrus event demonstrate that the radiative impact on the diffusional growth (or sublimation) of ice crystals is significant. Even in a radiatively cooled atmospheric environment, ice particles may experience radiative warming because the net radiation received by an ice particle depends upon the emission from the particle, and the local upwelling and downwelling radiative fluxes. Model results show that radiative feedbacks on the diffusional growth of ice particles can be very complex. Radiative warming of an ice particle will restri...

Effect of HNO3 and HCl on D2O Desorption Kinetics from Crystalline D2O Ice

The presence of trace species may perturb H2O desorption kinetics from ice surfaces and alter the stability of atmospheric ice particles. To investigate the effects of atmospheric species on H2O desorption kinetics from crystalline ice, the D2O desorption kinetics from pure and HNO3- and HCl-dosed crystalline D2O ice multilayers on Ru(001) were investigated using isothermal laser-induced thermal desorption (LITD) measurements. The D2O desorption kinetics were studied for D2O ice film thicknesses of 25−200 BL (90−730 Å) and initial acid coverages of 0.5−3.0 BL for HNO3 and 0.3−5.0 BL for HCl. Arrhenius analysis of the D2O desorption rates from pure D2O crystalline ice at T = 150−171 K yielded a desorption activation energy of Ed = 13.7 ± 0.5 kcal/mol and a zero-order desorption preexponential of νo = (3.3 ± 0.7) × 1032 molecules/(cm2 s). The absolute D2O desorption rates were ∼3−5 times smaller for D2O ice films exposed to HNO3. The D2O desorption kinetics from HNO3-dosed ice were Ed = 11.3 ± 0.4 kcal/mol and νo = (5.0 ± 0.9) × 1028 molecules/(cm2 s). In contrast, the absolute D2O desorption rates were ∼2 times larger for D2O ice films exposed to HCl. The D2O desorption kinetics from HCl-dosed ice were Ed = 14.2 ± 0.6 kcal/mol and νo = (3.7 ± 0.8) × 1033 molecules/(cm2 s). The changes in the D2O isothermal desorption kinetics were independent of DNO3 and DCl coverages. The adsorbate-induced perturbations are believed to be associated with the formation of stable hydrate cages and reduced D2O mobility in HNO3-dosed ice and the creation of defects and enhanced D2O mobility in HCl-dosed ice. The effects of HNO3 and HCl on the D2O desorption kinetics indicate that the growth, stability, and lifetimes of atmospheric ice particles should be altered by the presence of adsorbates on the ice surface.

A simple model of the ice particle size distribution in noctilucent clouds

A timescale analysis indicates that at noctilucent cloud (NLC) heights near 83 km, the growth and decay of ice particles and their transport by tide‐ and gravity‐wave‐associated vertical velocity components are the dominant processes that determine the particle size distribution. Other processes including sedimentation are of minor importance, so that the formation of NLCs should, in general, not depend on atmospheric conditions at the mesopause, in agreement with recent findings from simultaneous lidar and rocket experiments. Then a simple NLC model can be constructed consisting essentially of a partial differential equation which describes the temporal behavior of the particle size distribution in particle parcels moving with the wave‐associated air velocity. Contrary to previous ones, the present model yields a steady state oscillation within an integration time of 1 day because the optically active ice particles have lifetimes of a few hours only. NLC simulations yield particle concentrations, mean radii, and scatter ratios which are in good agreement with observational results. The model also predicts an occasional coexistence of small populations of optically active particles and large populations of microscopic particles, which may be of basic importance for the interpretation of recent observations indicating a more or less tight coupling between NLCs and simultaneously occurring polar mesosphere summer echoes.

Formation and growth of ice particles in stationary ultrasonic fields

The formation of ice particles in stationary ultrasonic fields (SUSFs) from ice aerosol was observed. Under suitable experimental conditions aerosol particles gather in stable ellipsoidal systems at temperatures down to <50 K below ambient. We call these systems cold gas traps. The aerosol concentrates in the pressure node areas of the SUSF and conglomerates to form larger particles and snowflakes with diameters up to 10 mm. The resulting shapes are shown. Most of them are similar to those occurring in nature. An attempt is made to explain the effect. Three different processes of ice particle formation are visualized and discussed. Here the existence of a quasiliquid layer (QLL) on the particle surfaces seems to be essential because both the formation of ice particles and the QLL occur only at temperatures higher than about −25 °C. The observed trapping and generation process can be used, for example, in atmospheric physics for the study of particle aggregation, precipitation formation, and water and radiation transport phenomena.

Dehumidification of air flow through cooling at sub-freezing temperatures

An experimental and numerical study is presented in which laminar air flow with low water-vapour concentration is cooled at temperatures well below 0°C to remove the humidity contained in the carrier gas. The experiment uses a cold trap that consists of a vertical tube-bundle immersed in a cold shell. The analysis is carried out with the help of a model that simulates heat and mass transfer, as well as aerosol dynamics in the tube flow. It is found that an optimal temperature range exists for the efficiency of the process. The results are interpreted in terms of the competition between vapour diffusion to the wall and ice particle formation and growth.