| Section I | I index | 151-159 of 513 terms |
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index of wetness—A numerical index, often expressed as a percentage, corresponding to the ratio of the runoff from a basin in a given year to the annual average. Could be restricted to a particular season of interest.
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Indian Deep Water—Occupies the depth range between 1500 and 3800 m in the Indian Ocean. It is characterized by a salinity maximum of 34.75–34.80 psu, indicating that its origin is North Atlantic Deep Water imported eastward past the Cape of Good Hope. See deep water.
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Indian equatorial jet—An intense eastward flow of about four-week duration found at the equator in the Indian Ocean during the transition periods between the monsoon seasons (April–June and October–December). Speeds at the equator can exceed 1 m s−1 but fall off to less than 0.2 m s−1 at 2°S and 2°N. The jet is the result of sea level adjustment to the change of wind direction from one monsoon season to the next.
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Indian National Satellite System—(Acronym INSAT.) A series of multipurpose geostationary satellites designed to support communications, television broadcasting, and meteorological observations. INSAT-1 (launched August 1983) was positioned at 74°E longitude, and was the first three- axis stabilized geostationary satellite. Not all satellites in the INSAT series have carried meteorological imagers.
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Indian spring low water—A tidal low water datum, designed for regions of mixed tides, that is depressed below mean sea level by the sum of the amplitudes of the principal semidiurnal lunar and solar tides and the principal diurnal tides (M2 + S2 + K1 + O1); originally developed for parts of the Indian Ocean.
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Indian summer—A period, in mid- or late autumn, of abnormally warm weather, generally clear skies, sunny but hazy days, and cool nights. In New England, at least one killing frost and preferably a substantial period of normally cool weather must precede this warm spell in order for it to be considered a true “Indian summer.” It does not occur every year, and in some years there may be two or three Indian summers. The term is most often heard in the northeastern United States, but its usage extends throughout English- speaking countries. It dates back at least to 1778, but its origin is not certain; the most probable suggestions relate it to the way that the American Indians availed themselves of this extra opportunity to increase their winter stores. The comparable period in Europe is termed the Old Wives' summer, and, poetically, may be referred to as halcyon days. In England, dependent upon dates of occurrence, such a period may be called St. Martin's summer, St. Luke's summer, and formerly All-hallown summer.
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indicated airspeed—(Abbreviated IAS.) The airspeed read or recorded directly from an airspeed indicator. Indicated airspeed is usually lower than the actual airspeed and must be corrected for both temperature and density to yield true airspeed. The correction is quickly accomplished on an ordinary navigational computer.
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indicated altitude—The altitude read directly from a pressure altimeter when set to the prescribed altimeter setting. This value differs from the corrected altitude as a function of the difference between the actual density of the underlying air and that of the standard atmosphere. The vertical separation of aircraft on airways is based on indicated altitude, and in general, standard aircraft operating procedure calls for the use of indicated altitude.
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