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- Author or Editor: Norihiko Fukuta x
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Abstract
In order to improve the cloud seeding reaction, the basic processes in cloud microphysics and dynamics were critically examined. The disadvantage of the large temperature dependence in heterogeneous ice nucleation, as well as the advantage of there being almost no temperature dependence of strong coolants in homogeneous ice nucleation, was pointed out. A new horizontal seeding method using liquid carbon dioxide has been devised to maximize the effects of seeding, and simple devices for airborne and ground mobile applications were developed and tested in supercooled fogs and low-lying stratus clouds. Seeding tests revealed the development of vertical motions of the seeded plume and associated wind, the effective mixing of the plume with the surrounding supercooled fog and cloud volume, the resultant development of large crystals and their fall, the enlargement of the initial opening, the associated snowfall and its effects on traffic, and the accompanying optical effects. The developed ground mobile fog seeding method was found to be practical. A fundamental feedback reaction of the seeded plume at or near the overlying stabilization zone, which we call FILAS (falling-growth induced lateral air spreading), has been identified as an effective mechanism to cause precipitation in a large fog and cloud volume. Cellular motions and accompanying pseudoadiabatic lapse rates were confirmed in the fog and cloud.
Abstract
In order to improve the cloud seeding reaction, the basic processes in cloud microphysics and dynamics were critically examined. The disadvantage of the large temperature dependence in heterogeneous ice nucleation, as well as the advantage of there being almost no temperature dependence of strong coolants in homogeneous ice nucleation, was pointed out. A new horizontal seeding method using liquid carbon dioxide has been devised to maximize the effects of seeding, and simple devices for airborne and ground mobile applications were developed and tested in supercooled fogs and low-lying stratus clouds. Seeding tests revealed the development of vertical motions of the seeded plume and associated wind, the effective mixing of the plume with the surrounding supercooled fog and cloud volume, the resultant development of large crystals and their fall, the enlargement of the initial opening, the associated snowfall and its effects on traffic, and the accompanying optical effects. The developed ground mobile fog seeding method was found to be practical. A fundamental feedback reaction of the seeded plume at or near the overlying stabilization zone, which we call FILAS (falling-growth induced lateral air spreading), has been identified as an effective mechanism to cause precipitation in a large fog and cloud volume. Cellular motions and accompanying pseudoadiabatic lapse rates were confirmed in the fog and cloud.
Abstract
A detailed thermodynamical analysis of the glaciation of a supercooled cloud parcel has been carried out, applying a linear approximation to the vapor pressure curves for ice and water. The process can lead to three different final states: one in which partial glaciation of the supercooled cloud water brings the parcel temperature to 0C, one in which sublimation of water vapor takes place from the frozen phase, and one in which deposition occurs to it. It is pointed out that a treatment which considers only the release of latent heat of fusion, without taking into account the subsequent change in water vapor density, is a special, case and is generally incorrect.
Abstract
A detailed thermodynamical analysis of the glaciation of a supercooled cloud parcel has been carried out, applying a linear approximation to the vapor pressure curves for ice and water. The process can lead to three different final states: one in which partial glaciation of the supercooled cloud water brings the parcel temperature to 0C, one in which sublimation of water vapor takes place from the frozen phase, and one in which deposition occurs to it. It is pointed out that a treatment which considers only the release of latent heat of fusion, without taking into account the subsequent change in water vapor density, is a special, case and is generally incorrect.
Abstract
The nucleation of freezing of supercooled water drops by metaldehyde, phloroglucinol and 1,5–dihydroxynaphthalene was studied. It was found that the threshold temperature for nucleation by contact of the particles with the supercooled drops was 2–3°C warmer than the threshold when the same drops were melted and re–frozen with the nuclei already partly immersed. There was no evidence that the high threshold for contact nucleation was due to active sites that were subsequently destroyed. Rather, it was thought to be associated with the movement of the water front along the surface of the nucleus during the contact process. It is suggested that this process gives rise to a transient high free energy zone which facilitates nucleation. In support of this theory, measurements were made of the contact angles of water on the three compounds.
Abstract
The nucleation of freezing of supercooled water drops by metaldehyde, phloroglucinol and 1,5–dihydroxynaphthalene was studied. It was found that the threshold temperature for nucleation by contact of the particles with the supercooled drops was 2–3°C warmer than the threshold when the same drops were melted and re–frozen with the nuclei already partly immersed. There was no evidence that the high threshold for contact nucleation was due to active sites that were subsequently destroyed. Rather, it was thought to be associated with the movement of the water front along the surface of the nucleus during the contact process. It is suggested that this process gives rise to a transient high free energy zone which facilitates nucleation. In support of this theory, measurements were made of the contact angles of water on the three compounds.
Abstract
It is proposed, for the interpretation of infrared absorption spectra carrying information of a planetary atmosphere and the condensing clouds, that the following three conditions must be considered: 1) the exchange of the cloud constituents with overlying clear gas due to convective mixing; 2) the partition of constituent gases between the gaseous and the condensed phases, and that with respect to the cloud phase change; and 3) the loss of signal-giving molecules in the condensed phase due to dissociation.
In the Venus atmosphere, the presently available data suggest that the line formations of HCl and HF occur in the overlying clear layer if the condensate phase is liquid, and in the light-scattering cloud if the condensate is ice.
Abstract
It is proposed, for the interpretation of infrared absorption spectra carrying information of a planetary atmosphere and the condensing clouds, that the following three conditions must be considered: 1) the exchange of the cloud constituents with overlying clear gas due to convective mixing; 2) the partition of constituent gases between the gaseous and the condensed phases, and that with respect to the cloud phase change; and 3) the loss of signal-giving molecules in the condensed phase due to dissociation.
In the Venus atmosphere, the presently available data suggest that the line formations of HCl and HF occur in the overlying clear layer if the condensate phase is liquid, and in the light-scattering cloud if the condensate is ice.
Abstract
A careful survey of the methods for measuring ice nucleation was made. Errors of previous investigations based on the relationship between the time lag of ice formation and the falling velocity of ice particles through a temperature gradient zone were avoided. Experiments were made on a large number of chemicals by using a thermostat-type cloud chamber, the threshold temperatures for ice nucleation of these chemicals were determined precisely and found to be somewhat higher than those of previous workers. Analysis of the experimental data shows the following: 1. the highly effective nuclei are all insoluble in water; 2. particles with the greatest structural similarity to ice make the most effective nuclei; 3. the stronger the ionic nature of nuclei crystals, the more effective are they as ice nuclei. These latter two factors are mutually inter-dependent. An explanation of the mechanism of ice formation is presented.
Abstract
A careful survey of the methods for measuring ice nucleation was made. Errors of previous investigations based on the relationship between the time lag of ice formation and the falling velocity of ice particles through a temperature gradient zone were avoided. Experiments were made on a large number of chemicals by using a thermostat-type cloud chamber, the threshold temperatures for ice nucleation of these chemicals were determined precisely and found to be somewhat higher than those of previous workers. Analysis of the experimental data shows the following: 1. the highly effective nuclei are all insoluble in water; 2. particles with the greatest structural similarity to ice make the most effective nuclei; 3. the stronger the ionic nature of nuclei crystals, the more effective are they as ice nuclei. These latter two factors are mutually inter-dependent. An explanation of the mechanism of ice formation is presented.
Abstract
In a rising cloud parcel, a small droplet establishes quasi-steady-state fields of vapor density ρ and temperature T around it, approximately satisfying the common relationship, ∇2ρ=∇2 T=0, where ∇2 is the Laplacian operator. The fields at this stage merely transfer vapor and heat between the droplet surface and the infinite environment without changing their distributions in space; lowering of ρ and T fields is primarily due to cloud parcel lifting and not by the droplet growth. As the growth continues, the fields begin to compete with others of adjacent droplets and limit their expanse within each territory referred to as “cell.” The supersaturation reaches the maximum shortly thereafter, and the growth mode becomes totally competitive. Under this cell boundary-controlled competitive kinetics, the fields establish a new steady state and transfer properties between the droplet surface and the space inside the cell where ∇2ρ and ∇2 T take nonzero constant values. Under this condition, the ρ and T fields are lowered due to both parcel lifting and droplet growth.
To evaluate the difference between the droplet growth of conventional theories and the competitive growth under steady-state conditions, equations describing the latter vapor and temperature fields as well as the mass growth rates are analytically obtained in closed forms under both Maxwellian and diffusion-kinetic conditions. A factor responsible for the competitive kinetics is identified as a function of only the ratio between the droplet radius and the distance between the droplet center and the boundary with the surrounding droplets. Deviation of droplet mass growth rate for the competitive kinetics from that for noncompetitive growth is found to be negligible under the ordinary range of cloud conditions. However, it is pointed out that under unusual situations, laboratory processes in particular, consideration of the deviation may become necessary.
Abstract
In a rising cloud parcel, a small droplet establishes quasi-steady-state fields of vapor density ρ and temperature T around it, approximately satisfying the common relationship, ∇2ρ=∇2 T=0, where ∇2 is the Laplacian operator. The fields at this stage merely transfer vapor and heat between the droplet surface and the infinite environment without changing their distributions in space; lowering of ρ and T fields is primarily due to cloud parcel lifting and not by the droplet growth. As the growth continues, the fields begin to compete with others of adjacent droplets and limit their expanse within each territory referred to as “cell.” The supersaturation reaches the maximum shortly thereafter, and the growth mode becomes totally competitive. Under this cell boundary-controlled competitive kinetics, the fields establish a new steady state and transfer properties between the droplet surface and the space inside the cell where ∇2ρ and ∇2 T take nonzero constant values. Under this condition, the ρ and T fields are lowered due to both parcel lifting and droplet growth.
To evaluate the difference between the droplet growth of conventional theories and the competitive growth under steady-state conditions, equations describing the latter vapor and temperature fields as well as the mass growth rates are analytically obtained in closed forms under both Maxwellian and diffusion-kinetic conditions. A factor responsible for the competitive kinetics is identified as a function of only the ratio between the droplet radius and the distance between the droplet center and the boundary with the surrounding droplets. Deviation of droplet mass growth rate for the competitive kinetics from that for noncompetitive growth is found to be negligible under the ordinary range of cloud conditions. However, it is pointed out that under unusual situations, laboratory processes in particular, consideration of the deviation may become necessary.
Abstract
A high-output airborne metaldehyde smoke generator was designed for cloud seeding purposes and tested on the ground and in cumulus clouds.
The condensation method was employed for smoke production. Hot exhaust gas from the aircraft engine was diluted with air and used as the carrier gas for metaldehyde powder to evaporate and recondense. An output of 1012 nuclei sec−1 was estimated, effective at −5C.
Abstract
A high-output airborne metaldehyde smoke generator was designed for cloud seeding purposes and tested on the ground and in cumulus clouds.
The condensation method was employed for smoke production. Hot exhaust gas from the aircraft engine was diluted with air and used as the carrier gas for metaldehyde powder to evaporate and recondense. An output of 1012 nuclei sec−1 was estimated, effective at −5C.
Japanese weather modification activities have been surveyed. The principal works have evolved in three stages. During the early program from 1947 to 1960, the research was carried out in the major universities with sponsorship derived from the electric power companies. Many technical developments concerning the generation, detection, and behavior of artificial ice nuclei took place during this period. Experimental work was concentrated on ground seeding programs. Around the end of this period, the lack of basic knowledge in cloud seeding was realized while the practical program, although curtailed in some areas, continued operation. Tokyo Metropolitan Office of City Water Supply started developing a comprehensive but routine seeding program in order to secure the water supply in dry seasons.
The second period occurred between 1961 and 1967 when the Science and Technology Agency funded a five year project to the Japanese Artificial Rainfall Research Corporation for the purpose of obtaining more basic information on clouds and cloud seeding. This research was carried out in Kwanto and Kyushu Branches of the corporation.
In the third and most recent period starting in 1968, the research trend has been toward microphysics and dynamics of clouds with continuing effort on instrumentation development. Weather modification research of the hazard prevention type is currently emphasized.
Japanese weather modification activities have been surveyed. The principal works have evolved in three stages. During the early program from 1947 to 1960, the research was carried out in the major universities with sponsorship derived from the electric power companies. Many technical developments concerning the generation, detection, and behavior of artificial ice nuclei took place during this period. Experimental work was concentrated on ground seeding programs. Around the end of this period, the lack of basic knowledge in cloud seeding was realized while the practical program, although curtailed in some areas, continued operation. Tokyo Metropolitan Office of City Water Supply started developing a comprehensive but routine seeding program in order to secure the water supply in dry seasons.
The second period occurred between 1961 and 1967 when the Science and Technology Agency funded a five year project to the Japanese Artificial Rainfall Research Corporation for the purpose of obtaining more basic information on clouds and cloud seeding. This research was carried out in Kwanto and Kyushu Branches of the corporation.
In the third and most recent period starting in 1968, the research trend has been toward microphysics and dynamics of clouds with continuing effort on instrumentation development. Weather modification research of the hazard prevention type is currently emphasized.
Abstract
The nonsteady-state kinetics of droplet growth or evaporation is studied theoretically for two types of changing boundary conditions: changes in the distant environment, and changes at the droplet surface. The treatment assumes Maxwellian boundary conditions at the droplet surface. The nonsteady-state kinetics during rapid environmental changes is reviewed, and compared with the simulation of the process obtained by applying the quasi-steady-state theory in a stepwise manner. A method for estimating the errors arising from use of the quasi-steady-state theory to determine temperature and vapor fields and growth or evaporation rates is explained. The nonsteady-state kinetics for changing surface conditions is treated, taking a freezing supercooled droplet as an example. It is shown that a freezing supercooled droplet generates a wave of supersaturation around it. The head of the wave moves outward to a position about one droplet diameter away from the surface, and remains there until the droplet is completely frozen. Satellite droplet formation around a freezing droplet is explained by nucleation on unactivated condensation nuclei under the influence of this supersaturation. It is suggested that the supersaturation near a droplet which freezes may activate nearby ice nuclei which would be inactive under normal environmental conditions in a cloud.
Abstract
The nonsteady-state kinetics of droplet growth or evaporation is studied theoretically for two types of changing boundary conditions: changes in the distant environment, and changes at the droplet surface. The treatment assumes Maxwellian boundary conditions at the droplet surface. The nonsteady-state kinetics during rapid environmental changes is reviewed, and compared with the simulation of the process obtained by applying the quasi-steady-state theory in a stepwise manner. A method for estimating the errors arising from use of the quasi-steady-state theory to determine temperature and vapor fields and growth or evaporation rates is explained. The nonsteady-state kinetics for changing surface conditions is treated, taking a freezing supercooled droplet as an example. It is shown that a freezing supercooled droplet generates a wave of supersaturation around it. The head of the wave moves outward to a position about one droplet diameter away from the surface, and remains there until the droplet is completely frozen. Satellite droplet formation around a freezing droplet is explained by nucleation on unactivated condensation nuclei under the influence of this supersaturation. It is suggested that the supersaturation near a droplet which freezes may activate nearby ice nuclei which would be inactive under normal environmental conditions in a cloud.
Abstract
The ice forming ability of solid particles was tested at −2 to −3C after first cooling them to −35 to −78C. During the cooling process, the water vapor pressure over the solid particles was kept below ice saturation, in order to avoid any ice formation on them. All of the treated samples of nine test materials showed ice-forming ability at −2 or −3C which is much warmer than their ordinary threshold temperatures. This ability was lost after warming above 0C.
Abstract
The ice forming ability of solid particles was tested at −2 to −3C after first cooling them to −35 to −78C. During the cooling process, the water vapor pressure over the solid particles was kept below ice saturation, in order to avoid any ice formation on them. All of the treated samples of nine test materials showed ice-forming ability at −2 or −3C which is much warmer than their ordinary threshold temperatures. This ability was lost after warming above 0C.
