SAFFIR-SIMPSON DAMAGE-POTENTIAL SCALE
Developed
in the early 1970s by Herbert Saffir, a consulting engineer, and Robert
Simpson, then Director of the National Hurricane
Center, it is a measure of hurricane intensity on a scale of 1 to 5. The scale categorizes potential damage
based on barometric pressure, wind speeds, and surge. Related term: Saffir Simpson Scale
ST. ELMO'S FIRE
A luminous, and often audible, electric discharge that is sporadic in nature. It
occurs from objects, especially pointed ones, when the electrical field
strength near their surfaces attains a value near 1000 volts per centimeter.
It often occurs during stormy weather and might be seen on a ship's
mast or yardarm, aircraft, lightning rods, and steeples. Also known
as corposant or corona discharge.
SALINITY
A measure of the quantity of dissolved salts in sea
water. The total amount of dissolved solids in sea water in parts
per thousand by weight.
SALT WATER
The water of the ocean, distinguished from fresh water by its appreciable salinity.
SAND
Loose particles of hard, broken rock or minerals. In observing, sand is reported when particles
of sand are raised to sufficient height that reduces visibility.
It is reported as "SA" in an observation and on the METAR.
SANDSTORM
A strong wind carrying sand particles through the air.
They are low level occurences, 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 predominate during the day
and die out in the night. Visibility is reduced to between 5/8ths and 6/16ths statute mile, 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
Bernadino 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.
SARGASSO SEA
An area of the North Atlantic Ocean
between Bermuda and the Azores. It is in the middle of the North Atlantic oceanic gyre, with converging
surface waters. Consequently, it has less biological features than any
other region of the ocean because the lack of mixing with more nutrient-rich
waters.
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.
View WALTER Satellite Tutorial
SATELLITE IMAGES
Images taken by a weather satellite
that reveal information, such as the flow of water vapor, the movement
of frontal system, and the development of a tropical system. Looping
individual images aids meteorologists in forecasting. One way a picture
can be taken is as a visible shot, that is best during times of visible
light (daylight). Another way is as an IR (infrared)
shot, that reveals cloud temperatures and can be used day or night.
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.
SCATTERING
The process by which small particles suspended in the air diffuse
a portion of the incident radiation in all directions. This is a primary reason for colors, such as blue
skies, rainbows, and orange sunsets. When working with radars, this often
refers to the more or less random changes in direction of radio energy.
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 diurnal coastal breeze that blows onshore, from the sea to the land. It is caused by
the temperature difference when the surface of the land is warmer than
the adjacent body of water. Predominate during the day, it reaches its
maximum early to mid afternoon. It blows in the opposite direction of
a land breeze.
SEA BREEZE FRONT
A coastal phenomena, it is restricted to large bodies of water and their immediate coast lines. This is usually
the landward extent of the sea breeze. Due to the imbalance of heating
between land and water, a region of maximum upward motion or convergence
occurs by mid-afternoon in the summer some 10 to 15 miles inland. Air
mass thunderstorms or a line of towering cumulus clouds with showers can form along the front. At the beach, there are
blue skies and a light breeze. This often occurs along the coast of
the Gulf of Mexico and Florida's east coast.
SEA FOG
A type of advection fog which forms in warm moist air cooled to saturation
as the air moves across cold water. Related term: Arctic
Sea Smoke
SEA ICE
Ice that is formed by the freezing of sea water. It forms first as small
crystals, thickens into sludge, and coagulates into sheet ice, pancake
ice, or ice floes of various shapes and sizes.
SEA LEVEL
The height or level of the sea surface at any time. It is used as a reference for
elevations above and below. Related term: mean
sea level
SEA LEVEL PRESSURE
The atmospheric pressure
at mean sea level, usually determined from the observed station pressure.
SEA MILE
A unit of length distinguished from a nautical
mile. One sea mile is equivalent to 1,000 fathoms (6,000 feet).
SEASON
A division of the year
according to some regularly recurring phenomena, usually astronomical
or climatic. For example, in the Northern Hemisphere, winter is said
to begin on the winter solstice and end on the
vernal equinox when spring begins,
covering the months of December, January, and February. In the tropics,
there is the dry and the rainy season, depending on the amount of precipitation.
SEA SPRAY
Sometimes called salt spray, it is the drops of sea water (salt water) blown from the
top of a wave. Related terms: blowing spray and condensation
nuclei
SEA SURFACE TEMPERATURE (SST)
The temperature of the water's surface. It is measured using buoy and ship data, infrared
satellite imagery, and coastal observations.
SEMI-PERMANENT PRESSURE SYSTEMS
A relatively stable, stationary pressure-and-wind system where
the pressure is predominately high or low with the changing season.
They are not of a transitory nature, like migratory lows that develop
from temperature and density differences. Related terms: Icelandic
Low, Aleutian Low, North Pacific High, Siberian High, and Bermuda High
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.
Related term: supercell
SHEAR
It is the rate of change over a short duration. In wind shear, it can refer to the frequent change
in wind speed within a short distance. It can occur vertically or horizontally. Directional shear
is a frequent change in direction within a short distance, which can
also occur vertically or horizontally. When used in reference to Doppler
radar, it describes the change in radial velocity
over short distances horizontally.
SHEAR LINE
A line of maximum horizontal wind shear. A narrow zone across which there is an abrupt
change in the horizontal wind component parallel to it.
SHORT WAVE
A progressive wave of smaller amplitude, wave length, and duration than a long
wave. It moves in the same direction as the basic current in which
it is embedded and may induce upward vertical motion ahead of it. They
are more numerous than long waves and often disappear with height in
the atmosphere.
SHOWALTER STABILITY INDEX
A measure of the local static stability of the atmosphere.
It is determined by lifting an air parcel to 500 millibars
and then comparing its temperature to that of the environment. If the
parcel is colder than its new environment, then the atmosphere is more
stable. If the parcel is warmer than its new environment,
then the atmosphere is unstable and the potential for thunderstorm development and severe weather increases.
SHOWER
Precipitation from a convective cloud that
is characterized by its sudden beginning and ending, changes in intensity,
and rapid changes in the appearance of the sky. It occurs in the form
of rain (SHRA), snow (SHSN), or ice (SHPE). It is reported as "SH" in
an observation and on the METAR.
SIBERIAN EXPRESS
A fierce, cold flow of air that originates in Siberia, then moves into
Alaska and northern Canada before moving southward into the United States.
SIBERIAN HIGH
The semi-permanent high pressure area that forms over Siberia during the winter. The
average central pressure exceeds 1030 millibars from late November to
early March. It is characterized by clear, dry weather. Over southern
Asia, the predominate surface wind is northeasterly, just the opposite
of the predominate summer winds which bring the monsoon.
SIDEREAL TIME
The measure of time as defined by
the diurnal motion of the vernal equinox. A sidereal day is equivalent
to one complete rotation of the earth relative to the equinox, which
is 23 hours, 56 minutes, and 4.091 seconds. A sidereal year is the interval
required for the earth to make one absolute revolution around the sun,
which is 365 days, 6 hours, 9 minutes, and 9.5 seconds. Compare with
the solar day.
SKEW T-LOG P DIAGRAM
A thermodynamic diagram, using the temperature and the logarithm of pressure as coordinates.
It is used to evaluate and forecast air parcel properties. Some values
that can be determined are the Convective Condensation Level (CCL), the Lifting
Condensation Level (LCL), and the Level of Free Convection (LFC).
SKY
The vault-like apparent surface against which all aerial objects are seen from the earth.
SKY COVER - The amount of the celestial dome that is hidden by clouds and/or obscurations.
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.
SMALL CRAFT ADVISORY
An advisory issued for marine interests, especially for operators of small boats
or other vessels. Conditions include wind
speeds between 20 knots (23 mph) and 34 knots (39 mph).
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 ADVISORY
A statement or advisory issued when snow is
expected to create hazardous travel conditions. It warns of less severe
weather conditions than a winter storm
SNOW BANNER
A plume of snow blown off a mountain crest, resembling smoke blowing from a volcano.
SNOW BLINDNESS
Temporary blindness or impaired vision that results from bright sunlight reflected off the snow surface.
The medical term is niphablepsia.
SNOWBURN
A burn of the skin, like a sunburn, but caused by the sun's rays reflected off the snow
surface.
SNOW COVER
The areal extent of ground covered by the snow. It is usually expressed as a percent
of the total area of a given region.
SNOW CREEP
A continuous, extremely slow, downhill movement of a layer of snow.
SNOW CRUST - The crisp, almost icy, surface on fallen snow, usually formed by the slight melting and
refreezing of the surface snow.
SNOW DEPTH
The actual depth of snow on the ground at any instant during a storm, or after any single snowstorm or series
of storms.
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 EATER
Any warm downslope wind, or foehn, that blows over
snowy terrain and melts the snow. Related term: Chinook
SNOWFALL
The rate at which snow falls, usually expressed in inches of snow depth over a six hour
period.
SNOWFLAKES
An ice crystal or an aggregate of ice crystals which fall from clouds.
SNOW FLURRY/FLURRIES
Light showers of snow, generally very brief without
any measurable accumulation. May be reported as "SHSN--" in an observation
and on the METAR.
SNOW GARLAND
Snow appearing as a beautiful long
thick rope draped on trees, fences and other objects. Formed by the
surface tension of thin films of water bonding individual snow crystals.
SNOW GRAINS
Frozen precipitation in the form of very small, white, opaque grains of ice. The solid equivalent
of drizzle. It is reported as "SG" in an observation and on the METAR.
SNOW LEVEL
The elevation in mountainous terrain where the precipitation
changes from rain to snow, depending on the temperature structure of
the associated air mass.
SNOW LINE
The lowest elevation area of a perennial snow field on high terrain, such as a mountain range.
SNOWPACK
The amount of annual accumulation of snow at higher elevations.
SNOW PELLETS
Frozen precipitation
in the form of white, round or conical opaque grains of ice. Their diameter
ranges from 0.08 to 0.2 inch (2 to 5 mm). They are easily crushed and
generally break up after rebounding from a hard surface, unlike hail.
Sometimes it is called small or soft hail. It is reported as "GS" in
an observation and on the METAR.
SNOW ROLLER
The product of moist, cohesive snow
that when initiated by wind rolls across the landscape, gathering snow
until it can no longer move. It is shaped like a rolled sleeping bag,
some reaching four feet across and seven feet in diameter.
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.
SNOW SQUALL
A heavy snow shower accompanied by sudden strong winds, or a squall.
SOLAR DAY
The complete rotation of the earth in relation to the sun. Although it varies, an average has determined a
mean solar day of 24 hours. It is universally used for civil purposes.
Related term: sidereal day
SOLAR ECLIPSE
An eclipse of the sun occurs when the moon is in a direct line between the sun
and the earth, casting some of the earth's surface in its shadow. The
moon's disk shaped outline appears to cover the sun's brighter surface,
or photosphere. That part of the earth that is directly in the moon's shadow will see a total
eclipse of the sun, while the areas around it will see a partial eclipse.
SOLSTICE
The point at which the sun is the furthest on the ecliptic from the celestial equator.
The point at which sun is at maximum distance from the equator and days
and nights are most unequal in duration. The Tropic
of Cancer and the Tropic of Capricorn are those parallels of latitude
which lies directly beneath a solstice. In the Northern Hemisphere,
the winter solstice falls on or about December 21 and the summer solstice
on or about June 21.
SOUNDING
A plot of the atmosphere, using data rom upper air or radiosonde
observations. Usually confined to a vertical profile of the temperatures,
dew points, and winds above a fixed location.
SOUTHERN OSCILLATION
A periodic reversal of the pressurepattern across the tropical
Pacific Ocean during El Niņo events. It is represents the distribution of temperature
and pressure over an oceanic area.
SPECIFIC HUMIDITY
The ratio of the density of
the water vapor to the density of the air, a mix of dry air and water vapor. It is expressed in grams
per gram or in grams per kilograms. The specific humidity of an air
parcel remains constant unless water vapor is added to or taken from
the parcel.
SPRING
The season of the year which occurs as the sun approaches the summer solstice,
and characterized by increasing temperatures in the mid-latitudes. Customarily,
this refers to the months of March, April, and May in the North Hemisphere,
and the months of September, October, and November in the Southern Hemisphere.
Astronomically, this is the period between the vernal equinox and the
summer solstice.
SPRING TIDE
A tide of increased range, which occurs about every two weeks when the moon is
new or full. Related term: neap tide
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"s 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/STABILITY
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. Contrast
with unstable air and instability.
STAGNATION AREA
An area that has a combination of stable stratification, weak horizontal wind speed, and little, if
any, significant precipitation. It is usually associated with an area
of high pressure. Related terms: Tule
fog
STANDARD ATMOSPHERE
A standard atmosphere has been
defined by the International Civil Aeronautical Organization (ICAO).
It assumes a mean sea level temperature of 15 degrees 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 degrees C per 100 meters up to 11 kilometers in the atmosphere.
STANDARD SURFACE PRESSURE
The measurement of one atmosphere
of pressure under standard conditions. It is equivalent to 1,013.25
millibars, 29.92 inches of mercury, 760 millimeters of mercury,
14.7 pounds per square inch, or 1.033 grams per square centimeter.
STANDING CLOUD
Any type of isolated cloud, generally
formed over peaks or ridges of mountainous areas, that appears stationary
or standing over the terrain. Related term: altocumulus lenticularis
STANDING WAVE
An atmospheric wave that is stationary with respect to the medium in which it is embedded. Related term: mountain wave
STATIONARY FRONT
A front which is nearly stationary
or moves very little since the last synoptic position. May be known as a quasi-stationary front.
STATION ELEVATION
The vertical distance above mean sea level that is the reference level
for all current measurements of atmospheric pressure at that station.
STATION PRESSURE
The atmospheric pressure with respect to the station elevation.
STEAM FOG
A type of advection fog that is produced by evaporation when cool air passes over a warm
wet surface and the fog rises, giving the appearance of steam. Also called sea smoke when it occurs over the
ocean. Related term: Arctic Sea Smoke
STORM
An individual low pressure disturbance, complete with
winds, clouds, and precipitation. The name is associated with destructive
or unpleasant weather. Storm-scale refers to disturbances the size of
individual thunderstorms. Related terms: thunderstorms, tornadoes, and tropical cyclones
STORM PREDICTION CENTER (SPC)
A branch of the National
Centers for Environmental Prediction, the Center monitors and forecasts
severe and non-severe thunderstorms, tornadoes, and other hazardous
weather phenomena across the United States. Formerly known as the Severe
Local Storms (SELS) unit of the National Severe Storms Forecast Center.
For further information, contact the SPC, located in Norman, Oklahoma.
STORM TRACKS
The path or tracks generally followed by a cyclonic disturbance.
STORM WINDS
On the Beaufort Wind Scale, a wind
with speeds from 56 to 63 knots (64 to 72 miles per hour).
STRAIGHT-LINE WINDS
Any surface wind that is not
associated with rotation. An example is the first gust from a thunderstorm,
as opposed to tornadic winds.
STRATIFORM
Clouds composed of water droplets that exhibit no or have very little vertical development.
The density of the droplets often blocks sunlight, casting shadows on
the earth's surface. Bases of these clouds are generally no more than
6,000 feet above the ground. They are classified as low clouds, and
include all varieties of stratus and stratocumulus. The opposite
in type are the vertical development of cumuliform clouds.
STRATOCUMULUS
A low cloud composed of layers or patches
of cloud elements. It can form from cumulus clouds becoming more stratiformed
and often appears as regularly arranged elements that may be tessellated,
rounded, or roll-shaped with relatively flat tops and bases. It is light
or dark gray in color, depending on the size of the water droplets and
the amount of sunlight that is passing through them.
STRATOPAUSE
The boundary zone or transition layer between the stratosphere
and the mesosphere. Characterized by a decrease in temperature with increasing altitude.
STRATOSPHERE
The layer of the atmosphere located between
the troposphere and the mesosphere, characterized by a slight temperature increase and absence of clouds.
It extends between 11 and 31 miles (17 to 50 kilometers) above the earth's
surface. It is the location of the earth's ozone layer.
STRATUS
One of the three basic cloud forms (the others are cirrus
and cumulus. It is also one of the two low cloud types. It is a sheetlike cloud that does not exhibit
individual elements, and is, perhaps, the most common of all low clouds.
Thick and gray, it is seen in low, uniform layers and rarely extends
higher than 5,000 feet above the earth's surface. A veil of stratus
may give the sky a hazy appearance. Fog may form from a stratus cloud
that touches the ground. Although it can produce drizzle
or snow, it rarely produces heavy precipitation. Clouds producing
heavy precipitation may exist above a layer of stratus.
STRATUS FRACTUS
Stratus clouds that appear in irregular fragments, as if they had been shred
or torn. Also appears in cumulus clouds (called cumulus fractus), but not in cirrus clouds.
SUBLIMATION
The process of a solid (ice) changing directly into a gas (water vapor), or
water vapor changing directly into ice, at the same temperature, without
ever going through the liquid state (water). The opposite of crystallization.
SUBPOLAR
The region bordering the polar region, between 50 degrees and 70 degrees North and South latitude. This
is generally an area of semi-permanent low pressure that exists and
where the Aleutian and Icelandic Lows may be found. However, a dome of high pressure may form over
the cold continental surfaces during the winter, for example, the North
American High and the Siberian High.
SUBREFRACTION
Less than normal bending of light or a radar beam as it passes through a
zone of contrasting properties, such as atmospheric
density, water vapor, or temperature. Related term: superrefraction
SUBSIDENCE
A sinking or downward motion of air, often seen in anticyclones. It is most prevalent
when there is colder, denser air aloft. It is often used to imply the
opposite of atmospheric convection.
SUBTROPICAL
The region between the tropical and temperate regions, an area between 35 degrees and
40 degrees North and South latitude. This is generally an area of semi-permanent
high pressure that exists and is where the Azores and North Pacific
Highs may be found.
SUBTROPICAL AIR
An air mass that forms over the subtropical region. The air is typically
warm with a high moisture content due to the low evaporative process.
SUBTROPICAL JET
Marked by a concentration of isotherms
and vertical shear, this jet is the boundary between the subtropical
air and the tropical air. It is found approximately between 25 degrees and
35 degrees North latitude and usually above an altitude of 40,000 feet. Its position tends to migrate south
in the Northern Hemispheric winter and north in the summer.
SUMMATION LAYER AMOUNT
The amount of sky cover
for each layer is given in eighths of sky cover attributable to clouds
or obscurations. The summation amount for any given layer is equal to
the sum of the sky cover for the layer being evaluated plus the sky
cover for all lower layers, including partial obscuration.
A summation amount for a layer can not exceed 8/8ths.
SUMMER
Astronomically, this is the period between the summer solstice and
the autumnal equinox. It is characterized as having the warmest temperatures
of the year, except in some tropical regions. Customarily, this refers
to the months of June, July, and August in the North Hemisphere, and
the months of December, January, and February in the Southern Hemisphere.
SUN DOG
Either of two colored luminous spots
that appear at roughly 22 degrees on both sides of the sun at the same
elevation. They are caused by the refraction of sunlight passing
through ice crystals. They are most commonly seen during winter
in the middle latitudes and are exclusively associated with cirriform clouds. The scientific
name for sun dogs is parhelion and they are also known as mock
suns.
SUN PILLAR
Horizontal
ice crystals in the form of plates, which occur in clouds and
ice fog near the earth's surface, reflect sunlight into vertical
sun pillars for a spectacular display.
SUNRISE
The daily appearance of the sun on the eastern horizon as a result of the earth's rotation.
In the United States, it is considered as that instant when the upper
edge of the sun appears on the sea level horizon. In Great Britain,
the center of the sun's disk is used instead. Time of sunrise is calculated
for mean sea level. related term: sunset
SUNSET
The daily disappearance of the sun below the western horizon as a result of the earth's rotation.
In the United States, it is considered as that instant when the upper
edge of the sun just disappears below the sea level horizon. In Great
Britain, the center of the sun's disk is used instead. Time of sunset
is calculated for mean sea level. Related terms: sunrise
SURGE
The increase in sea water height from the level that would normally occur were there no storm.
Although the most dramatic surges are associated with hurricanes, even
smaller low pressure systems can cause a slight increase in the sea level if the wind and fetch
is just right. It is estimated by subtracting the normal astronomic
tide from the observed storm tide.
SUPERCELL
A severe thunderstorm characterized by a rotating, long-lived, intense updraft.
Although not very common, they produce a relatively large amount of
severe weather, in particular, extremely large hail, damaging straight-line
winds, and practically all violent tornadoes.
SUPERCOOLING
The reduction of the temperature
of any liquid below the melting point of that substance's solid phase. Cooling a substance beyond
its nominal freezing point. Supercooled water is water that remains in a liquid state when it is
at a temperature that is well below freezing. The smaller and purer
the water droplets, the more likely they can become supercooled.
SUPERREFRACTION
Greater than normal bending of light or radar beam as it passes through a zone
of contrasting properties, such as atmospheric
density, water vapor, or temperature.
Related term: subrefraction
SURFACE BOUNDARY LAYER
The lowest layer of the
earth's atmosphere, usually up to 3,300 feet, or one kilometer, from
the earth's surface, where the wind is influenced by the friction of the earth's surface and the objects
on it. Related terms: boundary layer and friction layer
SWELL
Ocean waves that have traveled out of their generating area. Swell characteristically exhibits
a more regular and longer period and has flatter wave
crests than waves within their fetch.
SYNOPTIC CHART
Any map or chart that depicts meteorological or atmospheric
conditions over a large area at any given time.
SYNOPTIC SCALE
The size of migratory high and low
pressure systems in the lower troposphere that cover a horizontal area of several hundred miles or more. Related
terms: macroscale, mesoscale, and storms
SYZYGY
The points in the moon's orbit about the earth at which the moon is new or full.
