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Ice crystals with threefold symmetry in the atmosphere may not be made of hexagonal ice. In late 1611, Johannes Kepler was pondering what he should give his friend and patron, Baron Wackher von Wackhenfels, as a New Year’s gift when a snowflake landed on his coat. He was struck with a perfect philosophical present for his patron: why do snowflakes have six corners rather than some other number, say, seven or five? In the pamphlet that Kepler produced as a gift for his friend, he presented the
Ice crystals with threefold symmetry in the atmosphere may not be made of hexagonal ice. In late 1611, Johannes Kepler was pondering what he should give his friend and patron, Baron Wackher von Wackhenfels, as a New Year’s gift when a snowflake landed on his coat. He was struck with a perfect philosophical present for his patron: why do snowflakes have six corners rather than some other number, say, seven or five? In the pamphlet that Kepler produced as a gift for his friend, he presented the
Ingestion of large amounts of ice crystals by jet engines, known as the ice crystal icing (ICI) hazard, appears to be the culprit in more than 150 jet engine power-loss and damage events during the past two decades ( Fig. 1 ). Typically occurring near tropical convective systems, ICI events may also impact heated inlets used by an aircraft’s air data system. Although the heat within an engine or inlet would presumably prevent any ice buildup, analyses of engine power-loss events attributed to
Ingestion of large amounts of ice crystals by jet engines, known as the ice crystal icing (ICI) hazard, appears to be the culprit in more than 150 jet engine power-loss and damage events during the past two decades ( Fig. 1 ). Typically occurring near tropical convective systems, ICI events may also impact heated inlets used by an aircraft’s air data system. Although the heat within an engine or inlet would presumably prevent any ice buildup, analyses of engine power-loss events attributed to
Some cumulus clouds appear to be capable of producing ice crystals in concentrations of 10–100l −1 at temperatures approaching −5C. This has serious implications for cloud seeding with ice nuclei. We discuss various possible mechanisms by which these unexpectedly high concentrations may originate. Circumstantial evidence from field work points to their production in the riming process, but laboratory confirmation is lacking.
Some cumulus clouds appear to be capable of producing ice crystals in concentrations of 10–100l −1 at temperatures approaching −5C. This has serious implications for cloud seeding with ice nuclei. We discuss various possible mechanisms by which these unexpectedly high concentrations may originate. Circumstantial evidence from field work points to their production in the riming process, but laboratory confirmation is lacking.
Ice crystals in supercooled clouds may form upon ice nuclei, or they may arise through secondary processes. Two of these secondary ice “multiplication” mechanisms are discussed in some detail: the rime-splintering process and the mechanical fracture of ice particles. The nature of the water-drop size distribution has an important bearing on secondary ice production. Confident predictions of ice particle concentration can only be made in a few limited cloud situations. This is a serious handicap in assessing the feasibility of artificial rainmaking through the ice crystal process.
Ice crystals in supercooled clouds may form upon ice nuclei, or they may arise through secondary processes. Two of these secondary ice “multiplication” mechanisms are discussed in some detail: the rime-splintering process and the mechanical fracture of ice particles. The nature of the water-drop size distribution has an important bearing on secondary ice production. Confident predictions of ice particle concentration can only be made in a few limited cloud situations. This is a serious handicap in assessing the feasibility of artificial rainmaking through the ice crystal process.
The basic laboratory experiment in which a supercooled cloud may be seeded and converted to ice crystals is described in considerable detail. Such information is given as type and preparation of the cold chamber, light sources which are effective for different purposes, methods to follow in forming supercooled clouds, and procedures to follow in seeding them.
The transition temperature at which ice crystals form spontaneously is given as − 39°C ± 0.1°C as the result of a recent study. A simple replica technique for preserving the exact structure of the crystals in plastic is described.
The basic laboratory experiment in which a supercooled cloud may be seeded and converted to ice crystals is described in considerable detail. Such information is given as type and preparation of the cold chamber, light sources which are effective for different purposes, methods to follow in forming supercooled clouds, and procedures to follow in seeding them.
The transition temperature at which ice crystals form spontaneously is given as − 39°C ± 0.1°C as the result of a recent study. A simple replica technique for preserving the exact structure of the crystals in plastic is described.
Increased understanding of ice fog microphysics can improve frost and ice fog prediction using forecast models and remote-sensing retrievals, thereby reducing potential hazards to aviation. Ice fog occurs usually at temperatures less than −15°C because of direct deposition of water vapor into ice nuclei. It significantly affects aviation and transportation in northern latitudes because ice fog causes low visibilities and ice crystal accumulation on the surface of structures. Ice fog may also be
Increased understanding of ice fog microphysics can improve frost and ice fog prediction using forecast models and remote-sensing retrievals, thereby reducing potential hazards to aviation. Ice fog occurs usually at temperatures less than −15°C because of direct deposition of water vapor into ice nuclei. It significantly affects aviation and transportation in northern latitudes because ice fog causes low visibilities and ice crystal accumulation on the surface of structures. Ice fog may also be
; Matsuo and Sasyo 1981a , b , c ; Fujiyoshi 1986 ; Mitra et al. 1990 ), liquid droplets first appear at the tips of a snowflake during melting and then within the crystal lattice, but the snowflake does not collapse. This is wet snow. Only later, after more melting has occurred, does the snowflake collapse into a semispherical particle composed of both liquid and solid. We will refer to this as an almost melted particle in the rest of this article. The ice eventually fully melts to form a drop. It
; Matsuo and Sasyo 1981a , b , c ; Fujiyoshi 1986 ; Mitra et al. 1990 ), liquid droplets first appear at the tips of a snowflake during melting and then within the crystal lattice, but the snowflake does not collapse. This is wet snow. Only later, after more melting has occurred, does the snowflake collapse into a semispherical particle composed of both liquid and solid. We will refer to this as an almost melted particle in the rest of this article. The ice eventually fully melts to form a drop. It
