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haarA name applied to a wet sea fog or very fine drizzle that drifts in from the sea in coastal districts of eastern Scotland and northeastern England. It occurs most frequently in summer.
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haboob(Many variant spellings, including habbub, habub, haboub, hubbob, hubbub.) A strong wind and sandstorm or duststorm in northern and central Sudan, especially around Khartoum, where the average number is about 24 a year. The name comes from the Arabic word habb, meaning “wind.” Haboobs are most frequent from May through September, especially in June, but they have occurred in every month except November. Their average duration is three hours; they are most severe in April and May when the soil is driest. They may approach from any direction, but most commonly from the north in winter and from the south, southeast, or east in summer. The average maximum wind velocity is over 13 m s−1 (30 mph) and a speed of 28 m s−1 (62 mph) has been recorded. The sand and dust form a dense whirling wall that may be 1000 m (3000 ft) high; it is often preceded by isolated dust whirls. During these storms, enormous quantities of sand are deposited. Haboobs usually occur after a few days of rising temperature and falling pressure.
Sutton, L. J., 1925: Haboobs. Quart. J. Roy. Meteor. Soc., 51, 25–30.
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Hadley cellA direct thermally driven and zonally symmetric circulation under the strong influence of the earth's rotation, first proposed by George Hadley in1735 as an explanation for the trade winds. It consists of the equatorward movement of the trade winds between about latitude 30° and the equator in each hemisphere, with rising wind components near the equator, poleward flow aloft, and, finally, descending components at about latitude 30° again. In a dishpan experiment, a Hadley cell is any direct thermally driven vertical cell of the approximate scale of the dishpan.
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Hadley regimeIn a dishpan experiment, a flow dominated by a single large Hadley cell.
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hailPrecipitation 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.
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hailpadA device used to obtain data on the size distribution and mass of hailstones. A hailpad usually consists of a plastic foam panel covered by aluminum foil or white latex paint and set in a frame that is hammered into the ground. Hail that impinges on the pad leaves dents in it. The dimensions of the dents are analyzed to obtain the hailstone size and mass data.
Long, A. B., et al., 1980: The hailpad: materials, data reduction and calibration. J. Appl. Meteor., 19, 1300– 1313.
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hailstoneA single unit of hail, ranging in size from that of a pea to that of a grapefruit (i.e., from 5 mm to more than 15 cm in diameter). Hailstones may be spheroidal, conical, or generally irregular in shape. The spheroidal stones often exhibit a layered internal structure, with layers of ice containing many air bubbles alternating with layers of relatively clear ice. These probably correspond to dry growth and wet growth and are called rime and glaze, respectively. The conical stones fall with their bases downward without much tumbling and are often smaller and not as layered. Irregular hailstones often have a lobate structure and are not composed of smaller hailstones frozen together. Hailstones grow by accretion of supercooled water drops and sometimes also by accretion of minor amounts of small ice particles. Large hail may contain liquid water and be spongy (an intimate mixture of ice and water) in some regions; it is usually solid ice with density greater than 0.8 g cm−3. Small hail may be indistinguishable from large graupel (snow pellets) except for the convention that hail must be larger than 5 mm in diameter. The density of small hail can be much less than 0.8 g cm−3 if they are dry; if partly melted such hailstones become spongy. The largest recorded hailstone in the United States fell in a hailstorm in Coffeyville, Kansas on 3 September 1970. It weighed 766 g, had a longest dimension about 15 cm, and had protrusions (lobes) several centimeters long on one side that formed as it grew.
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hailstormAny storm that produces hailstones that fall to the ground; usually used when the amount or size of the hail is considered significant.
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