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Section S S index 731-739 of 1376 terms
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spark discharge—That type of gaseous electrical discharge in which the charge transfer occurs transiently along a relatively constricted path of high ion density, resulting in high luminosity. It is of short duration and to be contrasted with the nonluminous point discharge, the corona discharge, and the continuous arc discharge. The exact meaning to be attached to the term “spark discharge” varies somewhat in the literature. It is frequently applied to just the transient phase of the establishment of any arc discharge. A lightning discharge can be considered a large- scale spark discharge.
spatial average—The mathematical mean value over multiple points in space. These can be points along a line or path (line average), along a surface (area average), or within a volume (volume average). Compare time average, ensemble average; see also ergodic condition.
spatial dendrite—A complex ice crystal with dendritic arms that extend in many directions (spatially) from a central nucleus, probably a frozen droplet that originally froze as a polycrystal. Its form is roughly spherical. See dendritic crystal.
SPCZ—Abbreviation for South Pacific convergence zone.
SPECI—In the METAR observation program, a surface observation issued on a nonroutine basis as dictated by changing meteorological conditions.
National Oceanographic and Atmospheric Administration (NOAA), 1995: Federal Meteorological Handbook No. 1 (FMH-1), chap. 9
special observation—A category of aviation weather observation taken to report significant changes in one or more of the observed elements since the last record observation. The specific criteria demanding a special observation change from time to time. Basically they cover 1) significant changes in ceiling and visibility, particularly in the low ranges; 2) the appearance of low clouds; 3) the appearance and disappearance of a tornado or thunderstorm; 4) the beginning and ending of frozen or freezing precipitation; 5) pressure jumps; and 6) significant changes in the wind.
Special Sensor Microwave Imager—(Abbreviated SSM/I.) A passive conical-scanning multichannel microwave radiometer on DMSP satellites that is used to derive parameters such as land and sea surface temperature, ocean surface wind speed, precipitable water, rainfall rate, and snow/ ice cover.
Special Sensor Microwave Temperature—(Abbreviated SSM/T.) The microwave temperature and water vapor sounders on the DMSP polar-orbiting satellites. SSM/T is a temperature sounder, while SSM/T2 is a water vapor profiler. Many of the capabilities of the SSM/T and SSM/T2 instruments will be duplicated on the AMSU.
special weather report—The encoded and transmitted report of a special observation. This has been replaced by the SPECI observation in the METAR code.
special weather statements—Statements issued by a weather service that discuss weather situations including long-term events that describe phenomena of interest or concern to a number of users. These are used when a warning is in progress to provide additional detail, describe events, and provide appropriate response recommendations. These statements may refer to inclement or hazardous weather, but are not so limited.
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