Classificazione delle idrometeore

gb · 04/03/2006, 14:33

ciao

cerco una classificazione delle idrometeore che sia seria ed affidabile nonchÃ¨ particolareggiata e completa

grazie

ciao

gb · 04/03/2006, 16:19

provo a costruirla partendo dal glossario della American Metorological Society

rain—Precipitation in the form of liquid water drops that have diameters greater than 0.5 mm, or, if widely scattered, the drops may be smaller. The only other form of liquid precipitation, drizzle, is to be distinguished from rain in that drizzle drops are generally less than 0.5 mm in diameter, are very much more numerous, and reduce visibility much more than does light rain. For observing purposes, the intensity of rainfall at any given time and place may be classified as 1) “light,” the rate of fall varying between a trace and 0.25 cm (0.10 in.) per hour, the maximum rate of fall being no more than 0.025 cm (0.01 in.) in six minutes; 2) “moderate,” from 0.26 to 0.76 cm (0.11 to 0.30 in.) per hour, the maximum rate of fall being no more than 0.076 cm (0.03 in.) in six minutes; 3) “heavy,” over 0.76 cm (0.30 in.) per hour or more than 0.076 cm (0.03 in.) in six minutes. When rain gauge measurements are not readily available to determine the rainfall intensity, estimates may be made according to a descriptive system set forth in observing manuals.

drizzle—(Sometimes popularly called mist.) Very small, numerous, and uniformly distributed water drops that may appear to float while following air currents. Unlike fog droplets, drizzle falls to the ground. It usually falls from low stratus clouds and is frequently accompanied by low visibility and fog. In weather observations, drizzle is classified as 1) light, the rate of fall being from a trace to 0.3 mm (0.01 in.) per hour; 2) moderate, the rate of fall being from 0.3 to 0.5 mm (0.01–0.02 in.) per hour, and 3) heavy, the rate of fall being greater than 0.5 mm (0.02 in.) per hour. When precipitation equals or exceeds 1 mm (0.04 in.) per hour, all or part of the precipitation is usually rain. However, true drizzle falling as heavily as 1.3 mm (0.05 in.) per hour has been observed. By convention, drizzle drops are taken to be less than 0.5 mm (0.02 in.) in diameter. Larger drops are considered raindrops. Compare mist.

freezing precipitation—Any form of liquid precipitation that freezes upon impact with the ground or exposed objects, that is, freezing rain, freezing drizzle, or freezing fog. Compare frozen precipitation.

sleet—1. See ice pellets. 2. In British terminology, and colloquially in some parts of the United States, precipitation in the form of a mixture of rain and snow.

hail—Precipitation in the form of balls or irregular lumps of ice, always produced by convective clouds, nearly always cumulonimbus. An individual unit of hail is called a hailstone. By convention, hail has a diameter of 5 mm or more, while smaller particles of similar origin, formerly called small hail, may be classed as either ice pellets or snow pellets. Thunderstorms that are characterized by strong updrafts, large liquid water contents, large cloud-drop sizes, and great vertical height are favorable to hail formation. The destructive effects of hailstorms upon plant and animal life, buildings and property, and aircraft in flight render them a prime object of weather modification studies. In aviation weather observations, hail is encoded A.

snow—Precipitation composed of white or translucent ice crystals, chiefly in complex branch hexagonal form and often agglomerated into snowflakes. For weather-observing purposes, the intensity of snow is characterized as 1) light when the visibility is 1 km (5/8 statute mile) or more; 2) moderate when the visibility is less than 1 km (5/8 statute mile) but not more than 1/2 km (5/16 statute mile); and 3) heavy when the visibility is less than 1/2 km (5/16 statute mile).

snow pellets—(Also called soft hail, graupel, tapioca snow.) Precipitation consisting of white, opaque, approximately round (sometimes conical) ice particles having a snowlike structure, and about 2–5 mm in diameter. Snow pellets are crisp and easily crushed, differing in this respect from snow grains. They rebound when they fall on a hard surface and often break up. In most cases, snow pellets fall in shower form, often before or together with snow, and chiefly on occasions when the surface temperature is at or slightly below 0Â°C (32Â°F). It is formed as a result of accretion of supercooled droplets collected on what is initially a falling ice crystal (probably of the spatial aggregate type).

soft hail—Same as snow pellets.

grains of ice—A British term for ice pellets (sleet). Sleet, in turn, has a different meaning in Great Britain than it does in the United States. In British terminology, sleet is precipitation in the form of a mixture of rain and snow.

ice crystal—Any one of a number of macroscopic, crystalline forms in which ice appears, including hexagonal columns, hexagonal platelets, dendritic crystals, ice needles, and combinations of these forms. The crystal lattice of ice is hexagonal in its symmetry under most atmospheric conditions. Varying conditions of temperature and vapor pressure can lead to growth of crystalline forms in which the simple hexagonal pattern is present in widely different habits (a thin hexagonal plate or a long thin hexagonal column). In many ice crystals, trigonal symmetry can be observed, suggesting an influence of a cubic symmetry. The principal axis (c axis) of a single crystal of ice is perpendicular to the axis of hexagonal symmetry. Planes perpendicular to this axis are called basal planes (a axes related to the prism facets) and present a hexagonal cross section. Ice is anisotropic in both its optical and electrical properties and has a high dielectric constant (even higher than water) resulting from its water dipole structure. The electrical relaxation time for water is much shorter than for ice (109 Hz compared with 104 Hz), resulting from a chain reaction requirement for molecules to relax through defects in the ice lattice. In the free air, ice crystals compose cirrus-type clouds, and near the ground they form the hydrometeor called, remarkably enough, “ice crystals” (or ice prisms). They are one constituent of ice fog, the other constituent being droxtals. On terrestrial objects the ice crystal is the elemental unit of hoarfrost in all of its various forms. Ice crystals that form in slightly supercooled water are termed frazil. Ice originating as frozen water (e.g., hail, graupel, and lake ice) still has hexagonal symmetry but lacks any external hexagonal form. Analysis of their sections (0.5 mm) in polarized light reveals different crystal shapes and orientations, depending on the freezing and any annealing and subsequent recrystallization process.

gb · 04/03/2006, 16:22

snow grains—(Also called granular snow.) Precipitation in the form of very small, white opaque particles of ice; the solid equivalent of drizzle. They resemble snow pellets in external appearance, but are more flattened and elongated, and generally have diameters of less than 1 mm; they neither shatter nor bounce when they hit a hard surface. Descriptions of the physical structure of snow grains vary widely and include very fine, simple ice crystals; tiny, complex snow crystals; small, compact bundles of rime; and particles with a rime core and a fine glaze coating. It is agreed that snow grains usually fall in very small quantities, mostly from stratus clouds or from fog, and never in the form of a shower.

gb · 04/03/2006, 16:45

bellissime immagini al microscopio elettronico del graupel e del rime (che non saprei tradurre in italiano)

http://emu.arsusda.gov/snowsite/rimegraupel/rg.html

Cornour · 05/03/2006, 16:40

Originariamente Scritto da gb

bellissime immagini al microscopio elettronico del graupel e del rime (che non saprei tradurre in italiano)

http://emu.arsusda.gov/snowsite/rimegraupel/rg.html

Veramente bolto belle ed esplicative!

Purtroppo non posso aiutarti per la classificazione delle idrometeore. L'unica che mi viene in mente, su internet, Ã¨ quella che ho trovato su Nivoland.com (sito sulle valanghe tra l'altro consigliatissimo!):

http://www.nivoland.net/ItIdrometeore.htm

weathermaster · 05/03/2006, 18:46

Originariamente Scritto da gb

bellissime immagini al microscopio elettronico del graupel e del rime (che non saprei tradurre in italiano)

http://emu.arsusda.gov/snowsite/rimegraupel/rg.html

credo sia una specie di galaverna?

Aspetta che guardo in un bel libro americano....

Enrico