|
advection fog
Fog that forms when warm moist air moves over a cooler surface and is
cooled from below to the point of saturation and condensation.
angle of deflection
The amount of deflection of the horizontal wind component from
geostrophic balance due primarily to frictional effects in the surface
boundary layer.
This angle can vary from 20 to 40 degrees to the left of the isobar,
depending on the surface roughness, and results in flow across isobars
from high
to low pressure.
arctic sea smoke
Fog that forms when cold air moves over a much warmer water surface
(a differential typically being at least 15 degrees F between the
two surfaces), causing considerable amounts of water vapor to
enter the adjacent air to
the point of saturation and condensation. Same as steam fog.
bathymetry
The study of water depths or the form of the bottom surface
of a body of water.
Beaufort wind scale
A method of estimating wind speed based on the roughness or condition
of the sea (i.e., sea state) or on the motion of objects on land.
brightness
Refers in satellite imaging to the amount of light being reflected
by cloud tops in a visible image or to cloud-top temperature in
infrared images. Brightness is considered higher when the reflection
appears white
and lower when the reflection appears dark gray or black. Brightness
is measured in digital counts.
Catalina eddy
A localized atmospheric circulation occurring near Santa Catalina
Island and over the Gulf of Santa Catalina off the coast of Southern
California.
Due to coastal topography, winds blowing offshore from the Los Angeles
region create an eddy resulting in onshore flow in the vicinity of
San Diego. Offshore subsidence dissipates fog over Santa Catalina
Island while it increases fog along the San Diego coastline.
centrifugal force
An apparent force in a rotating system, deflecting masses radially
outward from the axis of rotation. Its magnitude can be expressed
as V2/R, where R is the radius of curvature of the path and V is
the linear speed of the particle. Per unit mass, this force is
equal and opposite to the centripetal acceleration.
centripetal acceleration
The acceleration of a particle moving in a curved path directed toward
the instantaneous center of curvature of the path. Its magnitude
can be expressed as V2/R, where R is the radius of curvature of
the path and V is the velocity of the particle. Per unit mass,
this acceleration
is equal and opposite to the centrifugal force.
coastal-marine automated network (C-MAN)
A network of marine weather observation sites.
cold upwelling
The rising of cold water toward the surface from the subsurface layers
of a body of water. Upwelling is most prominent where persistent
winds blow parallel to the coast (e.g., along the West Coast
of the United States), causing the current to set away from the
coast.
Water
from subsurface layers must then rise to the surface near the
coast to replace the water being driven away. See upwelling.
Coriolis force
A deflecting force arising solely from the earth's rotation. This
force is normal to the particle velocity, to the right in the Northern
Hemisphere and to the left in the Southern Hemisphere.
deep water wave
A wave with a length less than two times the water depth.
digital counts
The assignment of a number in measuring the brightness of a cloud
top. The numbers range from 0 for black to 255 for the brightest
white.
dry adiabatic lapse rate
The rate of temperature decrease with height of a parcel of dry air
lifted adiabatically through the atmosphere where gravity and the
pressure gradient force are in balance (hydrostatic equilibrium).
This rate equals 9.67 degrees C/km (5.4 degrees F/1000 ft).
dry adiabatic layer
A layer of the atmosphere in which the lapse rate is equal to the
dry adiabatic lapse rate throughout the entire layer.
dual channel differencing
A technique used to detect the extent of a fog layer at night on
GOES (geostationary operational environmental satellite) by which
differences in cloud radiance (temperature) are registered by two
infrared channels. A long-wave IR (11.0 microns) and a short-wave
IR (3.9 microns) capture vertical temperature differences within
the
layer of fog.
eddy viscosity
The turbulent transfer of momentum by eddies, giving rise to
an internal fluid friction.
effective conductivity
A measurement of the ability of a fluid to transport heat throughout
the fluid or within a layer through conduction processes.
Ekman layer
The layer of transition between the surface boundary
layer, where the shearing stress is constant, and the free atmosphere,
where the
atmosphere is in approximate geostrophic balance.
elevated inversion
A region within the atmosphere, suspended above the earth's surface,
in which the temperature increases with increasing height.
emissivity
The ratio of the emittance from a surface to the emittance of a body
that absorbs all radiation striking it for a given wavelength and
at the same temperature.
emittance
A measure of energy radiated per unit time per unit area from an
emitting surface.
fetch duration
The amount of time a fetch region with specific wind speed
and direction continues over the same ocean surface area.
fetch length
The length of the ocean surface over which wind of a specific speed
and direction blows. Fetch length is measured parallel to the wind
direction.
fetch region
The area of winds that encompass a wave-generation region. The fetch
region has fetch width and fetch length.
first-guess field
A numerical model forecast field derived from a short-range forecast,
usually of 6 or 12 hours, and used as an initial analysis field,
from which a subsequent model forecast sequence is run.
fog
Condensed water vapor in the atmosphere adjacent to the earth's surface--the
condensation resulting either from air being cooled to its saturation
point or from water being vaporized into the atmosphere until saturation
is reached.
forward scattering
The scattering of electromagnetic energy bounded by a plane perpendicular
to the direction of incident radiation where the electromagnetic
energy is scattered in the same direction in which it is advancing.
friction velocity
A reference wind velocity that is usually applied to motion near
the ground, where shearing stress is often assumed to be independent
of height and approximately proportional to the square of the mean
wind velocity.
frictional convergence
The tightening (or converging) of a vector wind field due to the
resistive force of friction.
geostrophic balance
In the atmosphere, the balance between the horizontal Coriolis force
and the horizontal pressure gradient force. The free atmosphere frequently
approaches geostrophic balance.
geostrophic wind
The horizontal wind velocity for which the Coriolis acceleration
exactly balances the horizontal pressure gradient force. The geostrophic
wind is directed along contour lines on a constant pressure surface
or along isobars on a geopotential surface.
gradient wind level
Also called the geostrophic wind level. The lowest level at which
the flow becomes geostrophic. This level marks the upper limit
of frictional influence of the earth's surface.
gradient wind
A horizontal wind velocity blowing tangent to a contour line on a
constant pressure surface or to an isobar on a geopotential surface
at a particular point. At this point, the Coriolis and centripetal
accelerations, together, will exactly balance the horizontal
pressure gradient force.
great-circle track
The path that waves (or swells) follow in deep water. The great circle
represents a track corresponding to the shortest distance between
two points on a sphere.
ground fog
A very shallow fog layer (extending usually no more than a few meters
from the ground) that forms when the radiational cooling of the
earth's surface cools the immediate air layer to the point of saturation
and condensation.
haze
An obstruction to visibility caused by dust, smoke, or pollution
particulates suspended in the atmosphere.
heat capacity
The ratio of the heat absorbed or released by a system to the corresponding
temperature rise or fall.
ice accretion
The accumulation on objects of freezing precipitation, sea spray, or
both.
inversion
A layer within the vertical profile of the atmosphere in which the
temperature increases with increasing height or within large bodies
of water in which the temperature increases with increasing depth.
isallobaric wind
A horizontal wind directed normal to lines of equal change in pressure
(isallobars) toward falling pressure and away from rising pressure,
with a magnitude proportional to the strength of the pressure tendency
gradient.
isothermal layer
A layer within the vertical profile of the atmosphere in which there
is no temperature change with height, or a layer within large bodies
of water in which there is no temperature change with depth.
marginal ice edge
The region of sea ice near an open ocean boundary and therefore particularly
subject to a number of processes related to ice-oceanic-atmospheric
interactions.
maximum combined seas (MCS)
The maximum height of the sea at a location where two or more wave
groups or swell groups pass at the same time.
mixed layer
The surface layer of a body of water whose vertical temperature profile
is nearly isothermal.
momentum flux
Within a fluid system, such as the atmosphere, the properties of
mass and velocity of a particular parcel are at some level capable
of being
transferred upward or downward through eddies or turbulent mixing processes.
numerical wave model
A numerical model for ocean waves which includes equations for wave
growth, propagation, and decay in order to forecast the future
state of ocean waves in a specified region.
ocean wind wave
A surface wave generated by wind stress on the ocean surface. Same
as wind wave.
parametric model
A type of model that is based on a collection of observations of a phenomenon
to which characteristic curves are fit in relation to the variables
that produce or affect the phenomenon's characteristics. These curves
can then be used to forecast the particular phenomenon of interest based
on the value of the variables as input. For example, the wave nomogram
is a parametric model for the forecasting of wave heights and periods
using the variables of fetch length, wind speed, and wind duration as
inputs.
peak period
The period corresponding to the highest peak in the one-dimensional
frequency spectrum of the wave field.
planetary boundary layer
Also called the "friction layer." The layer of the atmosphere
from the earth's surface to the geostrophic or gradient wind level. It
includes the surface boundary layer and the Ekman layer. Above this layer
lies the free atmosphere.
plunging breaker
A violently breaking wave in shallow water.
pressure gradient force
The force due to differences of pressure within a fluid mass. The
vector force is directed from higher toward lower pressure.
radiance temperature
The concentration of the radiant flux of a body, where radiant flux
is defined as energy radiated from a source. Radiance temperature may
be measured remotely by sensors that detect electromagnetic radiation
in the thermal IR wavelength region.
rogue wave
A single wave crest much higher than usual, caused by constructive interference.
Waves of different wavelengths and heights that converge at a point
from different directions can form this type of wave which can be three
to four times higher than the theoretical maximum wave that could be
sustained in a fully developed sea. Sometimes the term rogue wave is
used to describe a sudden growth of a wave that encounters a swift opposing
current even though this growth is not due to constructive interference.
The Agulhas Current off the southeastern tip of Africa is an example
of where this occurs. Rogue waves can also be though of as an unexpectedly
occurring wave of large height such as the pressure induced wave caused
by an atmospheric gravity wave.
roughness parameter
Also called "roughness length." It is a measure of the roughness
of a surface over which a fluid is flowing. The roughness of a surface
is gauged primarily on the average height of its irregularities.
salinity
A measure of the mass of dissolved salts in one kilogram of sea water--most
often expressed as grams of dissolved salts per kilogram of sea water.
sea state
Properties of wind-generated waves on the surface of the sea.
sensible heat flux
The rate of change of sensible heat over a given area, sensible heat
being heat that can be felt and measured by a thermometer.
shallow water wave
A wave with a length greater than 20 times the water depth.
shamal
A hot and drynorthwest wind that occasionally occurs in the lower valleys
of the Tigris and Euphrates Rivers in southern Iraq, Iran, and
Kuwait.
significant wave height (Hs)
The objectively averaged height of the highest one-third of all waves
passing a point in the ocean. The wave height subjectively estimated
by observers is often very close to Hs.
significant wave period (Ps)
The averaged period of the waves used to compute significant wave
height.
spatial
Occurring in space.
spectral wave model
A model using a frequency spectrum through space and time measuring
a finite sum of wave components of different length and amplitude.
spilling breaker
A gently breaking wave in shallow water. Water gradually spills over
the crest as the wave approaches the shore.
SST
Sea surface temperature.
SST gradient
The change in sea surface temperature (SST) expressed in degrees
per unit distance.
steam fog
See arctic sea smoke or fog.
subgradient wind
A wind of lower speed than the gradient wind, caused by the existing
pressure gradient and centrifugal forces.
subsidence
Sinking motion of air in the atmosphere.
supergradient wind
A wind of greater speed than the gradient wind, caused by the existing
pressure gradient and centrifugal forces.
superstructure icing
The accumulation on a ship's exposed surfaces of freezing precipitation,
sea spray, or both.
surface-based inversion
A layer in the atmosphere extending to the earth's surface in which
temperature increases with increasing height.
surface boundary layer
Also called "ground layer" or "surface layer." It
is a thin layer of air adjacent to the earth's surface extending up to
the base of the Ekman layer. Within this layer, the wind distribution
is largely determined by the vertical temperature gradient and the nature
of the contours of the underlying surface. Shearing stresses are approximately
constant throughout the layer.
surging breaker
A surge of wave onto a beach. The wave crest never actually breaks
before reaching the beach.
swell
Waves that have moved out of the wind-generation region.
swell forerunner
A long-period swell within a wave group that "outruns" the
shorter-period swell and reaches a destination first, giving an initial
warning of the swell to follow.
swell travel time
The time necessary for a swell of a specific period to reach a given
destination.
temporal
Occurring over a period of time.
trajectory
The path of a particle in motion. In meteorology, trajectories typically
refer to air parcels.
upwelling
Refers to a process in bodies of water whereby the lower layers of water
rise to the surface, usually resulting in cooler surface water. See cold
upwelling.
wave angular spreading
The lateral spreading of wave energy as it moves away from the wave-generation
region.
wave celerity (C)
The speed of an individual ocean wave.
wave direction
The direction from which waves travel.
wave dispersion
The phenomenon of wave group components separating according to their
wave length and period. Long-period/long-length waves move faster and
away from short-period/short-length waves within a given wave group.
wave group velocity (Cg)
The speed of an ensemble of waves propagating through the ocean.
wave growth
The growth of wind waves. Growth is related to wind speed, fetch
area, and wind duration.
wave height
The vertical height measured between a wave's trough and its crest.
wave length
The distance between successive wave crests or successive wave troughs.
wave period
The time interval between successive wave-crest or successive wave-trough
passage at a fixed point.
wave refraction
Bending or turning of the wave direction as the wave encounters shallow
water.
wave shoaling
Changes in wave characteristics as they move from deep to shallow
water. As waves encounter shallow water, the wave height increases
while the
wave length and the velocity decrease because the wave period is conserved
in shallow water.
wave spectrum
The distribution of varying wave periods within a wave group.
wave steepness
The measure of the ratio of wave height to wave length.
wave/swell decay
The transformation of wave period and wave height as swells move
away from the wave-generation region.
wave water particle motion
The actual movement of individual water particles within a wave.
wind stress
The force of the wind on a given area (in marine meteorology, on
the water surface).
wind wave
See ocean wind wave.
Back to Top
|