S Sierra

SA (Surface Aviation Weather Reports) - A report that provides pilots with an observation of surface weather and includes the following information: station reporting, time of report, sky condition and ceiling, visibility, weather obstructions, pressure, temperature and dewpoint, wind information and altimeter setting.

sand storm - A strong wind carrying sand particles through the air. They are low level occurrences, usually only ten feet in height to not more than fifty feet above the surface. Due to the frequent winds created by surface heating, they are most predominant during the day and out in the night. Visibility is reduced to between 5/8ths and 6/16ths statute miles, and if less than 5/16ths, then the storm is considered a heavy sandstorm. It is reported as "SS" in an observation and on the METAR.

Santa Ana Winds - The hot, dry winds, generally from the east, that funnel through the Santa Ana river valley south of the San Gabriel and San Bernardino Mountains in southern California, including the Los Angeles basin. Classified as katabatic, it occurs most often during the winter and it is an example of a foehn wind.

satellite - Any object that orbits a celestial body, such as a moon. However, the term is often used in reference to the manufactured objects that orbit the earth, either in a geostationary or a polar manner. Some of the information that is gathered by weather satellites, such as GOES9, includes upper air temperatures and humidity, recording the temperatures of cloud tops, land, and ocean, monitoring the movement of clouds to determine upper level wind speeds, tracing the movement of water vapor, monitoring the sun and solar activity, and relaying data from weather instruments around the world.

SATS (Small Aircraft Transportation System) - A proposed plan by NASA to develop technology that will provide a new framework for the national transportation system.

saturate - To treat or charge something to the point where no more can be absorbed, dissolved, or retained. In meteorology, it is used when discussing the amount of water vapor in a volume of air.

saturation point - The point when the water vapor in the atmosphere is at its maximum level for the existing temperature.

scattered - The amount of sky cover for a cloud layer between 3/8ths and 4/8ths, based on the summation layer amount for that layer.

scientific method - A systematic way of solving a problem or answering a question using observation and measurement. The six steps of the scientific method are: state the problem, create a hypothesis, design an experiment, perform the experiment, organize and analyze the data, draw
conclusions.

scud - Low fragments of clouds, usually stratus fractus, that are unattached and below a layer of higher clouds, either nimbostratus or cumulonimbus. They are often along and behind cold fronts and gust fronts, being associated with cool moist air, such as an outflow from a thunderstorm. When observed from a distance, they are sometimes mistaken for tornadoes.

sea breeze - A coastal breeze blowing from sea to land, caused by temperature difference when the land surface is warmer than the sea surface.

sea fog - A type of advection fog which forms in warm moist air cooled to saturation as the air moves across cold water.

sea level - The height or level of the sea surface at any time. It is used as a reference for elevations above and below.

sectional chart - An aeronautical chart designed for visual navigation of slow or medium speed aircraft. Topographic information on these charts features the portrayal of relief and a judicious selection of visual checkpoints for VFR flight. Aeronautical information includes visual and radio aids to navigation, airports, controlled airspace, restricted areas, obstructions, and related data.

sector - Airspace that is split up into small manageable pieces that have vertical as well as horizontal boundaries.

sequencing - A method of efficiently placing aircraft safely into a line of smoothly flowing air traffic.

severe weather - Generally, any destructive weather event, but usually applies to localized storms, such as blizzards, intense thunderstorms, or tornadoes.

severe thunderstorm - A thunderstorm with winds measuring 50 knots (58 mph) or greater, 3/4 inch hail or larger, or tornadoes. Severe thunderstorms may also produce torrential rain and frequent lightning.

shear zone - The area in which a wind shear occurs usually between two wind currents moving at different speeds and/or in opposite directions.

Sierra - Designator for the letter "S" in the International Phonetic Alphabet.

SIGMET (SIGnificant METeorological information) - In-flight advisory concerning severe icing, severe and extreme turbulence, widespread dust storms, or volcanic ash lowering visibility to less than 3 miles.

simulation - The use of a computer to calculate and visualize the effects of a given process.

simulator - A device that creates an environment that is as close as possible to reality. In flight simulators, engineers create a cockpit environment identical to the one in a real airplane. In a flight simulator a pilot will see, hear and feel like he or she is in a real aircraft.

skids - A runner used on an aircraft landing gear instead of tires.

sky cover - The amount of the celestial dome that is hidden by clouds and/or obscurations.

slant range - Direct line distance, not along the ground.

sleet - Also known as ice pellets, it is winter precipitation in the form of small bits or pellets of ice that rebound after striking the ground or any other hard surface. It is reported as "PE" in an observation and on the METAR.

slush - Snow or ice on the ground that has been reduced to a softy watery mixture by rain and/or warm temperatures.

SMA (Surface Movement Advisor) - A joint FAA and NASA project to help current airport facilities operate more efficiently.

smog - A low-lying perceptible layer of polluted air. The word was coined to mean a noxious mixture of smoke and fog.

smoke - Small particles produced by combustion that are suspended in the air. A transition to haze may occur when the smoke particles have traveled great distance (25 to 100 miles or more), and when the larger particles have settled out. The remaining particles become widely scattered through the atmosphere. It is reported as "FU" in an observation and on the METAR.

snow - Frozen precipitation in the form of white or translucent ice crystals in complex branched hexagonal form. It most often falls from stratiform clouds, but can fall as snow showers from cumuliform ones. It usually appears clustered into snowflakes. It is reported as "SN" in an observation and on the METAR.

snow banner - A plume of snow blown off a mountain crest, resembling smoke blowing from a volcano.

snow devil - A small, rotating wind that picks up loose snow instead of dirt (like a dust devil) or water (like a waterspout). Formed mechanically by the convergence of local air currents. May be called a snowspout.

snow shower - Frozen precipitation in the form of snow, characterized by its sudden beginning and ending. It is reported as "SHSN" in an observation and on the METAR.

solar radiation - The electromagnetic radiation (energy) emitted by the sun.

speed of sound - The speed at which sound waves travel. If you stand a distance away from a friend and say something to him, the sound waves of your voice will travel very quickly to the ear of your friend. The speed of sound is the speed at which those waves traveled.

spoiler - A device, normally located on the top of the wing, for changing the airflow around a wing to reduce lift. Pilots deploy spoilers when they land so that the airplane is no longer "lifted" into the air.

squall - A sudden onset of strong winds with speeds increasing to at least 16 knots (18 miles per hour) and sustained at 22 or more knots (25 miles per hour) for at least one minute. The intensity and duration is longer than that of a gust. It is reported as "SQ" in an observation and on the METAR.

squall line - A narrow band or line of active thunderstorms that is not associated with a cold front. It may form from an outflow boundary or the leading edge of a mesohigh.

stable air - Occurs when a rising air parcel becomes denser than the surrounding air. It will then return to its original position. When the density of the air parcel remains the same as the surrounding air after being lifted, it is also considered stable, since it does not have the tendency to rise or sink further.

stability - The condition of being steady. A motion of an aircraft is said to have stability, or be stable, if the aircraft will return to that motion after a disturbance, without the pilot having to move the controls.

stabilizer - A surface that helps to provide stability for an aircraft. An airplane has two stabilizers: a vertical stabilizer and a horizontal stabilizer. Stabilizers are like the feathers on an arrow, which keep the arrow pointed in the right direction.

stall - A condition in which an improper angle of attack and a lack of airspeed combine to disrupt the airflow around an airfoil enough to result in the loss of lift which forces the aircraft to drop.

standard atmosphere - A standard atmosphere has been defined by the International Civil Aeronautical Organization (ICAO). It assumes a mean sea level temperature of 15°C a standard sea level pressure of 1,013.25 millibars or 29.92 inches of mercury, and a temperature lapse rate of 0.65°C per 100 meters up to 11 kilometers in the atmosphere.

standard atmospheric pressure - For aviation purposes, 29.92 in. Hg (1013.2 hPa).

standard briefing - A complete and concise weather report including preparatory instructions and /or advice, NOTAMS, military activities, flow control information, and other items as requested.

standard temperature - For aviation purposes, 59°F (15°C).

STAR (Standard Terminal Arrival Route) - A preplanned instrument flight rule (IFR) ATC arrival procedure published for pilot use in graphic and textual form. STARs provide transition from the en route structure to an outer fix or an instrument approach fix/arrival waypoint in the terminal area

station - structure on the ground, perhaps containing VOR or TACAN.

station model - A symbolic illustration used on a surface analysis chart that represents and reflects the weather occurring at a given weather reporting point.

statute miles - A unit of linear measure (5280 feet). There are 0.87 nautical miles in one statute mile and 1.15 statute miles in one nautical mile.

straight wing - A wing that sticks straight out (approximately perpendicular) from the fuselage - it does not slant to the front or the rear. The ER-2 is an example of an aircraft that has straight wings.

stratocumulus - A low cloud of predominantly horizontal development in gray and/or whitish patches or layers.

stratosphere - The atmospheric layer above the tropopause which is very stable and characterized by low moisture content and absence of clouds.

stratus - A low, gray cloud layer with a fairly uniform base.

streamline - To shape an object so that it creates less drag and moves smoothly and easily through the air. Airfoils are streamlined, as is the fuselage.

strips - See flight progress strips.

subsonic - Velocity less than the speed of sound. The MD-11 is a subsonic aircraft because it never flies above the speed of sound.

supercomputer - A computer that is especially designed to receive, process and present very large amounts of data very quickly. The Cray Y-MP is an example of a supercomputer that is resident at NASA Ames
Research Center and is used for CFD.

supercooled water - water that has been cooled below the freezing point, but is still in a liquid state.

supersonic - Velocity greater than the speed of sound. The SR-71 is characterized as a supersonic aircraft because it travels from three to four times the speed of sound. A supersonic aircraft can fly from New York to
London in less than two hours.

Surface Analysis Chart (SA) - An aviation weather chart used to show air pressure patterns, high and low pressure areas, fronts, and station models

Surface Weather Chart - see Surface Analysis Chart.

sweepback wing - A wing that is slanted toward the rear of the aircraft which are designed to be more efficient at high speeds. The F-18 aircraft is an example of a supersonic jet that has sweepback wings.