Terms and Acronyms
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- Analog to Digital
- Air Base
- Air Conditioner
- Automatic Call Unit
- ADAPTATION (ADAPTABLE) PARAMETER:
- Generally, data related to a specific WSR-88D unit. These data may consist of meteorological
or hydrological parameters or of geographic boundaries, political boundaries, system
configuration, telephone numbers (auto dial), or other like data. Such data may be generated
at either a centralized location or locally at the WSR-88D unit.
- Automated Data Acquisition System
- Air Force Base
- Air Force Geophysics Laboratory
- Air Force Global Weather Central
- Automation of Field Operations and Services
- Automated Flight Service Station
- Automatic Gain Control
- Above Ground Level
- The process by which frequencies too high to be analyzed with the given sampling interval
appear at a frequency less than the Nyquist frequency.
- AMBIGUOUS VELOCITY:
- See VELOCITY ALIASING
- The maximun magnitude of a quantity.
- American Meteorological Society
- Class of devices in which the output varies continuously as a function of the input.
- ANOMALOUS PROPAGATION (AP):
- Non-standard atmospheric temperature or moisture gradients will cause all or part of the radar
beam to propagate along a non-normal path. When non-standard index-of-refraction distributions
prevail, "abnormal" or "anomalous" propagation occurs. When abnormal
downward bending occurs, it is called "superrefraction." If the beam is refracted
downward sufficiently, it will illuminate the ground and return signals to the radar from
distances further than is normally associated with ground targets. The term
"subrefraction" is applied when there is abnormal upward bending of the radar beam.
- ANTENNA GAIN:
- The measure of effectiveness of a directional antenna as compared to an isotropic radiator,
maximum value is called antenna gain by convention.
- Anomalous Propagation
- American Standard Code for Information Interchange
- Above Site (radar) Level
- Automated Surface Observing System
- Airport Surveillance Radar (FAA)
- ASSOCIATED PRINCIPAL USER:
- A Principal User with dedicated communications to a WSR-88D unit.
- Any process in which the flux density (power) of a beam of energy is dissipated.
- A measure of similarity between displaced and undisplaced (in time, space, etc.)
versions of the same function.
- AUTOMATIC GAIN CONTROL:
- Any method of automatically controlling the gain of a receiver, particularly one
that holds the output level constant regardless of the input level.
- Advanced Weather Interactive Processing System
- Air Weather Service
- A direction in terms of the 360-degree compass. The horizontal direction expressed as
an angle from the observation point. True north (or another fixed point) being 0 degrees.
- BACKING WIND:
- A change in wind direction in a counterclockwise sense representing cold-air advention.
- The portion of power scattered back in the incident direction.
- Binary Angular Measure
- BANDPASS FILTER:
- A filter whose frequencies are between given upper and lower cutoff values, while
substantially attenuating all frequencies outside these values (this band).
- BAND WIDTH:
- The number of cycles per second between the limits of a frequency band.
- BASE DATA:
- Those digital fields of reflectivity, mean radial velocity, and spectrum width data in
spherical coordinates provided at the finest resolution available from the radar.
- BASE PRODUCTS:
- Those products that present some representation of the base data. This representation
may not necessarily be either in full resolution or depict the full area of coverage.
Base products can be used to generate a graphic display or further processing.
- BEAM FILLING:
- The measure of variation of hydrometeor density throughout the radar sampling volume.
If there is no variation in density, the beam is considered to be filled.
- BEAM WIDTH:
- Angular width of antenna pattern. Usually that width where the power density is one-half
that of the axis beam. (Half-Power or 3 dB point)
- A systematic difference between an estimate of and the true value of a parameter.
- Radar sample volume.
- Built-In Test Equipment
- BOUNDARY LAYER:
- The layer of a fluid adjacent to a physical boundary in which the fluid motion is
affected by the boundary and has a mean velocity less than the free-stream value.
- BOUNDED WEAK ECHO REGION (BWER):
- A core of weak equivalent reflectivity in a thunderstorm that identifies the location of
a strong updraft. The updraft is so strong that large precipitation particles do not have
time to form in the lower and mid levels of the storm and are prevented from falling back
into the updraft core from above. The weak echo region is bounded when in a horizontal
section, the weak echo region is completely surrounded or bounded by higher reflectivity
values. See also Weak Echo Region.
- BOW ECHO:
- Rapidly moving cresent-shaped echo that is convex in the direction of motion. Typically
associated with strong straight-line winds. See also Line Echo Wave Pattern.
- Bright Band:
- The enhanced layer of radar echo caused by the difference in radar reflectivity of ice
and water particles. This echo is interpreted as the delineation on a radar display
between frozen and liquid precipitation.
- Bounded Weak Echo Region
- CARTESIAN COORDINATES:
- A coordinate system in which the locations of points in space are expressed by reference
to three planes, called coordinate planes, all three of which are prependicular to each
other. The three planes intersect in three straight lines, called coordinate axes. The
coordinate planes and coordinate axes intersect at a common point, called the origin.
- CARTESIAN GRID:
- The two-dimensional lattice used to identify the location of points. The grid is based on
an X-axis and a Y-axis that are perpendicular to each other. The unit spacing on each axis
is constant in all directions.
- A compact region of relatively strong vertical air motion (at least 10 m/sec; 19 knots).
- CENTRAL LIMIT THEOREM:
- Statistical theorem showing that averages approach a Gaussian distribution independent of
the input distribution.
- The center of mass of a storm.
- Central Flow Control Facility
- Central Flow Weather Service Unit
- Echoes that interfere with observation of desired signals on a radar display. Usually
applied to ground targets.
- Combined Moment
- COHERENT RADAR:
- A radar that utilizes both signal phase and amplitude to determine target characteristics.
- Coherent Oscillator
- A technique for estimating values of a spatial process (e.g. a precipitation field)
given point observations of the process (e.g. rain gage observations) and possibly
auxiliary observations (e.g. radar and satellite observations).
- COMPLEX SIGNAL:
- A signal containing both amplitude and phase information.
- CONTERMINOUS UNITED STATES:
- Those states of the United States enclosed within one common boundary. The conterminous
48 states of the United States.
- CONTOUR BASE VALUE:
- The lowest magnitude of a specific entity upon which contours are based.
- CONTOUR INTERVAL:
- Value between contours.
- Conterminous United States
- A measure of the contraction of a vector field.
- CORRELATED SHEAR:
- An output of the mesocyclone detection algorithm indicating a 3-dimensional shear region
(i.e. vertically correlated) that is not symmetrical.
- A measure of similarity between variables of functions.
- Adjacent maxima of radial velocities of opposite signs.
- A measure of the degree of association between two variables. In Doppler radars, the
argument (or angle) of the covariance of a complex signal is a measure of the Doppler
- Central Processing Unit
- Composite Reflectivity
- Composite Reflectivity Contour
- Central Radio Propagation Laboratories
- Console Replacement System (NOAA Weather Radio)
- Cathode Ray Tube
- Combined Shear
- Combined Shear Contour
- Continuous Wave
- County Warning Area
- Data Acquisition Program Manager
- DATA LEVEL:
- The specific range of data values represented by a single pixel when the data are
presented in a pixel image format; the specific value a datum may assume.
- DATA LEVEL CODE:
- A code representing a specific data level; used to assign color values when such are
assigned. Averaging and additional processing may reduce these resolutions. Because
of beam broadening, the geometric size of the resolution volume of the radar increases
with increasing range from the radar.
- DATA RESOLUTION:
- The resolution of the base data as produced by the signal processor, nominally 0.54
nautical mile (1 kilometer) x 1 degree in azimuth x 1 degree in elevation for reflectivity
values and 0.13 nautical mile (0.25 kilometer) x 1 degree x 1 degree for velocity values.
- Data Acquisition Unit
- Decibel (radar reflectivity ratio)
- Process of correcting for aliases in the velocity measurement. See also Velocity Aliasing.
- DECIBEL (dB):
- A logarithmic expression for a ratio of two quantities. A dBm is a decibel with respect
to 1 milliwatt.
- DEFAULT VALUES:
- A setting or value that will be used in a given software program unless changed.
- DIELECTRIC CONSTANT:
- For a given substance, the ratio of the capacity of a condenser with that substance
as dielectric to the capacity of the condenser with a vacuum as dielectric.
- DIELECTRIC MATERIAL:
- A substance that contains no or few free charges and that can support electromagnetic stress.
- Dual In-Line Package
- Equipment that measures and records the size distribution of raindrops.
- DISPLAY RESOLUTION:
- The area or two-dimensional product of the X and Y coordinates represented by one
picture element (pixel) of a raster scan display.
- Change in a signal resulting in gross non-linearities in signal processing or handling.
- A measure of the expansion of a vector field.
- Department of Commerce
- Department of Defense
- Department of Energy
- DOPPLER SHIFT:
- The change in frequency at a receiver due to the relative motion of the receiver and
the energy source.
- Department of Transportation
- A strong downdraft that induces an outburst of damaging winds on or near the ground.
- Current(s) of air with marked vertical downward motion.
- Digital Precipitation Array, One-hour precipitation accumulation product (Digital Array).
- A mesoscale feature with its own associated vertical circulation. It is a narrow, almost
vertical zone, across which a sharp moisture gradient, but little temperature gradient,
occurs at the earth's surface.
- The phenomenon by which the radar signal propagates along the boundary of two
dissimiliar air masses. The radar ranges with ducted propagation are greatly extended;
holes can also appear in the coverage. Ducting occurs when the upper air is exceptionally
warm and dry in comparison with the air at the surface. See also Anomalous Propagation.
- DWELL TIME:
- Time over which a signal estimate is made. Usually, the time required for the antenna
to traverse one degree.
- DYNAMIC RANGE:
- The ratio, usually expresses in decibels, of the maximum to the minimum signal that a
system can handle. Used to describe limits of receivers.
- Energy backscattered from a target as seen on the radar display.
- ECHO TOPS:
- The height of the greatest (in altitude) non-zero reflectivity value (greater than
the minimum significant reflectivity, 18.5 dBZ) for each 4 x 4 km (2.2 x 2.2 nmi) grid
box on the surface of the earth.
- Electronically Erasable Programmable Read Only Memory
- ELEVATION ANGLE:
- The vertical pointing angle of the radar (can vary from -1 degree to 60 degrees).
- ELEVATION SCAN:
- The process of the radar completing a full 360 degree rotation in azimuth for a
specific elevation angle.
- EQUIVALENT RADAR REFLECTIVITY (Ze):
- The concentration of uniformly distributed small (diameter one sixteenth wavelength
or less) water particles that would return the same amount of power received. Typically
expressed as: dBZ = 10 Log Ze.
- Environmental Research Laboratories
- A statement of the value of a quantity or function based on a finite number of samples.
- Echo Tops
- Echo Tops Contour
- EXTERNAL USER:
- Anyone other than a Principal User who has access to WSR-88D products, e.g., information
service companies, broadcast meteorologists, aviation interests, industrial meteorologists,
other government agencies, and universities.
- EYE WALL:
- The area of tall cumulonimbus storms surrounding the eye of the storm. Heavy rain and
very high winds occur in the eye wall. The area inside the eye wall is a roughly circular
area of comparitively light winds and fair weather found at the center of a severe
- Federal Aviation Administration
- A set of pattern vectors in close proximity.
- FEEDER CLOUD:
- The flanking lines of developing cumulus congestus clouds that sometimes merge with and
appear to intensify supercells.
- Forward Flank Downdraft
- Federal Meteorological Handbook
- Forward Overhang
- See Range Folding
- FREEZING LEVEL:
- The lowest altitude in the atmosphere over a given location where the air temperature
is 0 degrees Celsuis
- The number of recurrences of a periodic phenomenon per unit time. Electromagnetic energy
is usually specified in Hertz (Hz), which is a unit of frequency equal to one cycle per second.
- FREQUENT CARRIER:
- For the WSR-88D, the fundamental transmitted microwave frequency between 2,700 and
3,000 megahertz. It is modulated so that it exists for a few microseconds each pulse
repetition time. This limit is called the transmitted pulse.
- Flight Service Station
- Free Text Message
- GAGE DATA SUPPORT SYSTEM:
- A system external to the WSR-88D unit whose purpose is to collect and transfer
precipitation data from several rain gage sites to the WSR-88D unit. The data are
used by the RPG to calculate a mean field bias used in adjusting the precipitation estimates.
- A change in signal power, volatge or current. Usually applied to a change greater than
one and expressed in decibels.
- Global Atmospheric Research Program
- GARP Atlantic Tropical Experiment
- GATING (RANGE GATING):
- The use of electronic circuits in radar to eliminate or discard the target signals
from all targets falling outside certain desired range limits.
- Refers to the Normal distribution; phenomena whose events are normally distributed
are Gaussian distributed. This is the most common distribution encountered in physical
- Gage Data Support System
- Geostationary Operational Environmental Satellite
- GROUND CLUTTER:
- The pattern of radar echoes from fixed ground targets.
- GUST FRONT:
- The boundary between the horizontally propagating cold air outflow from a thunderstorm
and the surrounding environmental air.
- Precipitation in the form of spherical or irregular ice produced by convective clouds,
usually cumulonimbus. By convention, hail has a diameter of 5 mm or more. Smaller
particles of similar origin may be classified as ice or snow pellets.
- A unit of frequency equal to one cycle per second.
- Hail Index
- The transfer of signal intelligence from one carrier to another by mixing of signals
at different frequencies.
- HOOK ECHO:
- A pendant or hook on the right rear of an echo that often identifies mesocyclones on
the radar display. The hook is caused by precipitation drawn into a cyclonic spiral
by the winds, and the associated notch in the echo is caused by precipitation-free,
warm, moist air flowing into the storm.
- Hardwired Signal Processor
- Hail Weight
- International Civil Aviation Organization
- Interface Control Document
- Interdepartmental Committee for Meteorological Services and Supporting Research
- Institute of Electrical and Electronic Engineers
- Integrated Flood Observing and Warning System
- INCIDENT POWER DENSITY:
- Energy per unit area incident on the radar target.
- The component of a complex signal along the real axis in the complex plane. Two
waves of the same frequency that pass through their maximum and minimum values of
like polarity at the same instant.
- A contour of constant Doppler velocity values.
- ISOLATED STORM:
- An individual cell or a group of cells that are identifiable and separate from other
cells in a geographic area.
- Interference Suppression Unit
- Joint Doppler Operational Project
- Joint System Program Office
- KALMAN FILTER:
- A linear system in which the mean squared error between the desired output and
the actual output is minimized when the input is a random signal generated by white noise.
- Kilobit per Second
- An electron tube used as a low-power oscillator or a high-power amplifier at
ultrahigh frequencies. Noted for exceptional stability over long periods of transmission.
- LEVEL I DATA:
- The archive Level I interface is located in the RDA. Level I data are the analog,
time-domain output of the receiver. Information regarding synchronization, calibration,
date, time, antenna position, and status is also available. Level I data are not
- LEVEL II DATA:
- The archive Level II interface is also located at the RDA. The Level II data are
digital base data output from the signal processor and include base reflectivity,
mean radial velocity and spectrum width. The output also includes information on
synchronization, calibration, date, time, antenna position, and operational mode.
Level II data are recorded on 8 mm magnetic tape and sent to NCDC for permanent storage.
- LEVEL III DATA:
- The archive Level III interface is located at the RPG. A set of pre-determined
products defined in FMH-11 part A, comprise the Level III data which is archived on
WORM Optical Disk and sent to NCDC for permanent storage.
- LEVEL IV DATA:
- The archive Level IV interface is located at the PUP. Any data or information available
at the PUP may also be recorded on SCSI tape or WORM Optical disk at the discretion
of the PUP operator. These Level IV data are generally for local use and are not
permanently archived at NCDC.
- Line Echo Wave Pattern
- Limited Area Fine Mesh
- LIMITED-AREA FINE MESH (LFM):
- A rectangular grid based on a polar stereographic projection. The grid mesh length
of the LFM, 1/4 LFM, and 1/40 LFM at 60 degrees North and 105 degrees West are 190.5,
47.625, and 4.7625 km (102.9, 25.7, and 2.6 nmi), respectively.
- LINE ECHO WAVE PATTERN (LEWP):
- A radar echo pattern formed when a segment of a line of thunderstorms surges forward
at an accelerated rate. A meso high pressure area is usually present behind the
accelerating thunderstorms. A meso low pressure area is usually present at the crest
of the wave.
- Low Precipitation (storm)
- Layer Composite Reflectivity - Average
- Layer Composite Reflectivity - Maximum
- Layer Composite Turbulance - Average
- Layer Composite Turbulance - Maximum
- Large downburst with 4 km (2.2 nmi) or larger outflow size with damaging wind
lasting 5 to 20 minutes.
- The envelope of electromagnetic energy along the main axis of the beam.
- Modernization and Associated Restructuring
- Modernization and Associated Restructuring Demonstration
- MAXIMUM UNAMBIGUOUS RANGE:
- The maximum range to which a transmitted pulse wave can travel and return to
the radar before the next pulse is transmitted.
- Mesoscale Convective Complex
- Mesoscale Convective System
- MEAN DOPPLER VELOCITY:
- Reflectivity-weighted average velocity of targets in a given volume sample. Usually
determined from a large number of successive pulses. Also called mean radial velocity.
Doppler velocity usually refers to spectral density first moment; radial velocity to base data.
- MEAN RADIAL VELOCITY:
- The component of motion of the target toward or away from the radar.
- A 3-dimensional region in a storm that rotates cyclonically and is closely correlated
with severe weather.
- On the scale of 40 m to 4 km (130 ft to 2.2 nmi)
- MESOSCALE CONVECTIVE COMPLEX (MCC):
- A quasi-circular conglomeration of thunderstorms having a cloud-top area larger than
100,000 sq. km (29,000 sq. nmi) and persisting for more than 6 hours.
- MESOSCALE CONVECTIVE SYSTEM (MCS):
- Precipitation systems 20 to 500 km (11 to 270 nmi) wide that contain deep convection.
Examples in mid-latitudes are large isolated thunderstorms, squall lines, Mesoscale
Convective Complexes, and rainbands.
- Small downbursts, 1 to 5 km (0.5 to 2.7 nmi) in outflow size, with peak winds lasting
2 to 15 minutes.
- MIE SCATTERING or REGION:
- Radar backscattering by targets having dimensions somewhat greater than 1/10 the
wavelength of the radar but less than several radar wavelengths. Any scattering
produced by spherical particles without special regard to comparitive size of
radiation wavelength and particle diameter. Contrasted with Rayleigh scattering.
- Microwave Line of Sight
- Variation of the amplitude, frequency, or phase of a wave due to the mixing of two signals.
- MONOSTATIC RADAR:
- A radar that uses a common antenna for both transmitting and receiving.
- Mean Sea Level
- MULTICELL STORM:
- A storm that consists of a cluster of single cells that are often short-lived.
- Non-Associated, Not Applicable
- NATIONAL WEATHER RADAR NETWORK:
- Consists of WSR-88D sites dispersed throughout the conterminous United States.
A Department of Defense site or a non-CONUS Department of Transportation site.
- National Center for Atmospheric Research
- National Climatic Data Center
- No Data
- NETWORK SITE:
- A Department of Commerce WSR-88D site in the conterminous United States that
continuously collects, collates, and makes available radar data and products in
support of the National Weather Radar Netwrok.
- Next Generation Weather Radar
- NEXRAD PROGRAM COUNCIL:
- Composed of a representative from each of the Departments of Commerce, Defense,
and Transportation, and the Federal Coordinator for Meteorological Services and
- National Hurricane Center
- NEXRAD Information Dissemination System
- National Meteorological Center
- Nautical Mile
- National Oceanic and Atmospheric Administration
- NON-ASSOCIATED PRINCIPAL USER:
- A Principal User who has dial-in communications to WSR-88D units.
- NON-NETWORK SITE:
- A non-CONUS DOD site or a non-CONUS DOT site.
- NOTCH WIDTH:
- The 3 dB band width of a rejection filter.
- NEXRAD Program Council
- National Research Council
- National Severe Storms Forecast Center
- National Severe Storms Laboratory
- National Technical Information Service
- NEXRAD Technical Requirements
- National Weather Radio
- National Weather Service
- National Weather Service Forecast Office
- National Weather Service Modernization Committee
- National Weather Service Office, NEXRAD Weather Service Office
- NOAA Weather Wire Service
- NYQUIST FREQUENCY:
- The highest frequency that can be determined in data that have been discretely
sampled. For data sampled at frequency Fs, the Nyquist frequency is Fs/2.
- NYQUIST SAMPLING THEOREM:
- In order to unambiguously measure a frequency, a sampling rate of at least two
times this frequency is required. Doppler radar sampling rate is equal to the
pulse repetition frequency (PRF).
- Office of the Federal Coordinator for Meteorological Services and Supporting Research
- One-Hour Precipitation Accumulation (Graphic Image)
- OPERATIONAL MODE:
- A combination of one or more volume coverage patterns and product mixes tailored
to one or more meteorological situations. There are currently two modes of operation
each with two Volume Coverage Patterns, Clear Air Mode VCP 31 and 32 and Precipitation
Mode VCP 11 and 21.
- Operating System
- The general term for an electronic device that generates alternating currents or
voltages. The oscillator is classified according to frequency of the generated signal.
- Operational Support Facility
- A storm has overhang if the edge of the storm component at a given height range
(midlevels) extends outward beyond the edge of the storm component at the lowest
elevation by a specified distance.
- PARABOLIC ANTENNA:
- An antenna with a radiating element and a parabolic reflector that concentrates
the radiated power into a beam and also concentrates the return signal.
- PATTERN VECTOR:
- A pattern vector is formed by a series of azimuthally adjacent sample volumes
of increasing or decreasing Doppler velocity.
- A particular angular stage or point of advancement in a cycle; the fractional part
of the angular period through which the wave has advanced, measured from the phase reference.
- PHASE SHIFT:
- The angular difference of two periodic functions.
- Precipitation Intensity Exponent
- Planetary Boundary Layer:
- That layer of the atmosphere from the Earth's surface to the geostrophic wind level
(1.2 to 1.6 kilometers above the surface). Above this layer lies the free atmosphere
where the frictional influence of the Earth's surface on air motion is negligible.
- Program Management Committee
- POINT CLUTTER REJECTION:
- The rejection or removal of echoes having the characteristics of point targets.
- POLAR COORDINATES:
- A system of coordinates in which a point is isolated by its distance (range) and
angular direction (azimuth) from a fixed reference point. For radars, this reference
point is usually the location of the antenna.
- Plan Position Indicator
- Pulse Repetition Frequency
- PRINCIPAL USER:
- Principal Users are the National Weather Service, the Air Weather Service, the Naval
Oceanography Command, the Marine Corps Aviation Weather Service, and the Federal
- PRINCIPAL USER EXTERNAL SYSTEM:
- A communications port designed to interface with external systems that use a specific
(REDBOOK) communications format.
- PRODUCT RESOLUTION:
- The smallest spatial increment or data element that is distinguishable in a product.
- Program for Regional Observing and Forecasting Services
- PROGRAM MANAGEMENT COMMITTEE:
- A triagency Configuration Control Board for the configuration control of all WSR-88D
units deployed by three Principal Users (NWS, DOD, FAA).
- Transmission of electromagnetic energy as waves through or along a medium.
- Pulse Repetition Time
- Programmable Signal Processor
- PUP Text Message
- Principal User External System
- A single short duration transmission of electromagnetic energy.
- PULSE DURATION:
- Time occupied by a burst of transmitted radio energy. This may also be expressed
in units of range (pulse length). Also called pulse width.
- PULSE-PAIR PROCESSING:
- Nickname for the technique of mean velocity estimation by calculation of the signal
complex covariance argument. The calculation requires two consecutive pulses.
- PULSE RADAR (or PULSED RADAR):
- A type of radar, designed to facilitate range measurements, in which the transmitted
energy is emitted in periodic brief transmissions.
- PULSE REPETITION FREQUENCY (PRF):
- The number of pulses transmitted per second.
- PULSE REPETITION RATE:
- See Pulse Repetition Frequency.
- PULSE REPETITION TIME (PRT):
- The pulse interval from the beginning of one pulse to the beginning of the next
- PULSE WIDTH:
- The time occupied by an individual broadcast from a radar.
- Principal User Processor
- The component of the complex signal that is 90 degrees out of phase with the
inphase component. This component lies along the imaginary axis in the complex plane.
- RADAP II
- Radar Data Processor II -- a follow on to the NWS's DIGITIZED RADAR Experiment.
RADAP II equipment is installed at several NWS radar sites.
- RADAR CROSS SECTION:
- The area of a fictitious perfect reflector of electromagnetic waves that would
reflect the same amount of energy back to the radar as the actual target.
- RADIAL VELOCITY:
- The component of motion of the target toward or away from the radar.
- Radar Algorithm Display System, see WDSS
- Random Access Memory
- RANDOM VARIABLE (VARIATE):
- A variable characterized by random behavior in assuming its different possible
values. Mathematically, it is described by its probability distribution, which
specifies the possible values of a random variable together with the probability
associated (in an appropriate sense) with each value. A random variable is said
to be "continuous" if its possible values extend over a continuum,
"discrete" if its possible values are separated by finite intervals.
- RANGE BIN:
- A single data value derived from the mean WSR-88D-estimated reflectivity, velocity
or spectrum width. The WSR-88D uses these computed range bins for algorithm processing
and display purposes. Within the RDA, a range bin is computed from the mean value
received within the WSR-88D sample volume. Within the RPG, velocity and spectrum width
range bins also represent data from a single sample volume. However, to reduce the
variance of the reflectivity estimate, the RPG uses a reflectivity range bin made up
of four consecutive sample volumes.
- RANGE FOLDING:
- Apparent range placement of a multiple trip return. A multiple trip return appears
as the difference of the true range and a multiple of the unambiguous range.
- RANGE UNFOLDING:
- Process of removing range ambiguity in apparent range of a multitrip target.
- RANKINE VORTEX:
- Velocity profile for a systematic circulation in which the inner core is in solid
rotation, and tangential winds outside the core vary inversely with radial distance
from the center.
- RAYLEIGH SCATTERING:
- Scattering by spherical particles whose radii are smaller than about one-tenth
the radar wavelength.
- Radar Coded Message
- Cross Section - Reflectivity
- Radar Data Acquisition
- RDA Status and Control (Processor)
- The measure of the efficiency of a target in intercepting and returning radio energy.
With hydrometers it is a function of the drop size distribution, number of particles
per unit volume, physical state (ice or water), shape and aspect. A measure of the
fraction of radiation reflected by a given surface; defined as a ratio of the radiant
energy reflected to the total that is incident upon the surface.
- Changes in the direction of energy propagation (due to changes in speed) as a result
of density changes within the propagating medium.
- REFRACTIVE INDEX:
- A measure of the amount of refraction. Numerically equal to the ratio of wave velocity
in a vacuum to wave velocity in the medium.
- Radio Frequency
- Rear Flank Downdraft
- River Forecast Center
- Rain Gage Data Acquisition Computer (currently GDSS)
- Range Height Indicator
- Radar Interface and Data Distribution System.
- The RIDDS is the only approved interface to a WSR-88D to provide real-time wideband
data (base products) to external users. The RIDDS uses a SUN SPARC 5 workstation and
provides an Ethernet hub to permit multiple users to connect simultaneously. No products
or algorithm output are available. External access involves a formal procedure which
includes change requests, memoranda of agreement, approval by the local URC, and other
steps. The NWS/OSF/Systems Support Branch, SSB, can provide full information to offices
and universities interested in establishing such links.
- Root Mean Square
- Radar Products Generator
- RPG Operational Position
- Revolutions Per Minute
- Routine Product Set
- Radar Utilities and Data Distribution System, see WDSS
- Ratio of Signal Power to Clutter Power
- SAMPLE VOLUME:
- The volume of the atmosphere which is being instantaneously sampled by the radar;
the power returned at any one instant which is the total backscatter from a volume
of atmosphere equal to 1/2 the pulse length multiplied by the beam diameter.
- Systems and Applied Sciences Corporation
- Any object capable of reflecting the radar signal.
- Cross Section - Spectrum Width
- Small Computer Systems Interface - Tape subsystems connect to a workstation/computer
system through a SCSI bus, an ANSI standard interface for connecting peripherals to computers.
- SECTORIZED HYBRID SCAN:
- A single reflectivity scan composed of data from the lowest four elevation scans.
Close to the radar, higher tilts are used to reduce clutter. At further ranges,
either the maximum values from the lowest two scans are used or the second scan values
are used alone.
- As applied in the Storm Segments algorithm, segments are defined as runs of contiguous
radar sample volumes greater than or equal to the minimum reflectivity threshold and
having a combined length greater than or equal to the segment length threshold.
- SEVERE STORM:
- A storm with a tornado, surface hail equal to or greater than 3/4 inch, or wind gusts
equal to or greater than 50 knots, or any combination of the three.
- The rate of change of the vector wind in a specified direction on a horizontal plane.
Vertical shear is the variation of the horizontal wind in the vertical direction.
- Standard Hydrological Exchange Format
- SHELF CLOUD:
- A type of arcus (or roll) cloud. It is a low-level horizontal accessory cloud that
appears to be wedge-shaped as it approaches as seen along the leading edge of
approaching thunderstorms. It is accompanied by gusty straight-line winds and is
followed by precipitation.
- Secondary radiated energy maximum other than the radar main beam. Typically contains
a small percentage of energy compared to the main lobe.
- SIGNAL-TO-NOISE RATIO (SNR):
- A ratio that measures the comprehensibility of the data, usually expressed as the
signal power divided by the noise power.
- Severe Left-Moving Supercell
- Satellite and Meteorology Research Project
- Signal-to-Noise Ratio
- Science and Operations Officer
- Supplemental Precipitation Data
- SPEARHEAD ECHO:
- A radar echo associated with a downburst with a pointed appendage extending
toward the direction of the echo motion. The appendage moves much faster than
the parent echo, which is drawn into the appendage. During the mature stage, the
appendage turns into a major echo and the parent loses its identity.
- SPECIFIC HUMIDITY:
- In a system of moist air, the ratio of the mass of water vapor to the local mass of the system.
- SPECTRAL DENSITY:
- The distribution of power by frequency.
- SPECTRUM WIDTH:
- A measure of the dispersion of velocities within the radar sample volume. Standard
deviation of the velocity spectrum.
- Signal Processor Subsystem
- SQUALL LINE:
- Any line or narrow band of active thunderstorms.
- Severe Right-Moving Supercell
- Storm Relative Mean Radial Velocity (Map)
- Storm Relative Mean Radial Velocity (Region)
- Storm Structure
- Stable Local Oscillator
- STANDARD DEVIATION:
- The positive square root of the signal variance. In the WSR-88D, the velocity
standard deviation is called spectrum width.
- Storm Track Information
- Any disturbed state of the atmosphere, especially as affecting the Earth's surface,
and strongly implying destructive and otherwise unpleasant weather. Storms range in
scale from tornadoes and thunderstorms, through tropical cyclones, to widespread
- STORM MOTION:
- The velocity at which a storm travels.
- Storm-Total Precipitation Accumulation
- A large, long-lived (up to several hours) cell consisting of one quasi-steady
updraft-downdraft couplet that is generally capable of producing the most severe
weather (tornadoes, high winds, and giant hail).
- SUPPLEMENTAL SITE:
- A Department of Defense WSR-88D site in the conterminous United States. It
continuously collects, collates, and makes available radar data and products in
support of the DOD and the National Command Authority.
- Spectrum Width
- Severe Weather Analysis
- Severe Weather Probability
- Severe Weather Analysis - Reflectivity
- Severe Weather Analysis - Shear
- Severe Weather Analysis - Velocity
- Severe Weather Analysis - Spectrum Width
- SYNCHRONOUS DETECTION:
- Processing that retains the received signal amplitude and phase but that removes
the intermediate frequency carrier.
- System Calibration
- Precipitation or other phenomena that produce echoes.
- To Be Determined
- Terminal Doppler Weather Radar (FAA)
- THIN LINE ECHO:
- A narrow, elongated non-precipitating echo usually associated with thunderstorm
outflow, fronts, or other density discontinuities, also known as fine line.
- Three-Hour Precipitation Accumulation (Graphic Image)
- A storm is said to have tilt if a line connecting the centroid of the midlevel
storm component to the centroid of the lowest storm component is to the right or
rear of the direction of movement of the storm.
- TORNADIC VORTEX SIGNATURE:
- The radar "signature" of a vortex indicative of a tornado or tornadic
circulation. A small-scale, anomalous region of high shear associated with a tornado.
- The equipment used for generating and amplifying a radio frequency (rf) carrier
signal, modulating the carrier signal with intelligence, and feeding the modulated
carrier to an antenna for radiation into space as electromagnetic waves.
- TRELLIS ENCODING:
- A data transmission protocol that employs built-in error detection for more accurate
data flow, which generally does not require line conditioning.
- Tornado Vortex Signature
- User Alert Message
- Unit Control Position
- UNAMBIGUOUS RANGE:
- The range to which a transmitted pulse wave can travel and return to the
radar before the next pulse is transmitted. See Maximum Unambiguous Range.
- UNCORRELATED SHEAR:
- An output of the Mesocyclone detection algorithm indicating a region of shear
that is large and symmetrical but not vertically correlated.
- A distribution having only one localized maximum, i.e. only one peak.
- UNIT RADAR COMMITTEE:
- A coordinating committee, established by the Memorandum of Agreement for
Interagency Operation of the WSR-88D, composed of representatives of each
Principal User Agency associated with a particular WSR-88D unit.
- Current(s) of air with marked vertical upward motion.
- Unit Radar Committee
- Coordinated Universal Time
- Velocity Azimuth Display
- A measure of variability.
- Volume Coverage Pattern
- Cross Section - Velocity
- VEERING WIND:
- A change in wind direction in a clockwise sense representing warm air advection.
- VELOCITY ALIASING:
- Ambiguous detection of radial velocities outside the Nyquist co-interval.
- Vertically Integrated Liquid
- VOLUME COVERAGE PATTERN:
- A volumetric sampling procedure designed for the surveillance of one or more
particular meteorological phenomena. Clear Air Mode uses VCP 31 and 32. Each
has a Volume Scan consisting of 5 elevation angles (0.5 to 4.5 degrees) in
ten minutes. VCP 31 has a long pulse length and provides a better signal-to-noise
ratio permitting lower reflectivity returns to be detected. VCP 32 has a short
pulse length which provides for larger unambiguous velocity values. Precipitation
Mode uses VCP 11 and 21. VCP 11 provides better vertical sampling of weather echoes
near the antenna and is usually preferred in situations where convective precipitation
is within 60 nmi of the antenna. VCP 11 Volume Scan consists of 14 elevation angles
(0.5 to 19.5 degrees) in 5 minutes. VCP 21 has a slower antenna rotation rate and
provides better velocity and spectrum width estimates beyond 60 nmi. VCP 21 Volume
Scan consists of 9 elevation angles (0.5 to 19.5 degrees) in 6 minutes.
- VOLUME SCAN:
- The process of completing a series of specified scans in a specific sequence.
- In general, any flow possessing vorticity. More often the term refers to a flow
with closed streamlines.
- A vector measure of local rotation in a fluid flow.
- Velocity Azimuth Display Wind Profile
- WALL CLOUD:
- A local, abrupt lowering of a rain-free cumulonimbus base into a low-hanging
accessory cloud, from 1.6 to 6.4 km (1 to 4 nmi) in diameter. The wall cloud
is usually located in the southwestern part of a severe thunderstorm in the main
updraft to the southwest of the main precipitation region. Rapid upward motion and
visible rotation may be seen in wall clouds from several km away. Almost all strong
tornadoes develop from wall clouds.
- WSR-88D Algorithm Testing and Display System
- WATADS uses recorded Level II data only; no real-time data usage is possible. The
executable code is available for distribution to NEXRAD agencies, universities
and laboratories and other groups collaborating with the NEXRAD agencies. WATADS
runs on HP workstations and is used for developing case studies, conducting adaptable
parameter studies, and developing training sessions.
- The total area drained by a river and its tributaries.
- The unit of power in the meter-kilogram-second (mks) system of units; equal to
one joule per second.
- The distance a wave will travel in the time required to generate one cycle.
- Wideband Communications Control Module
- Warning Decision Support System
- The WDSS acquires data via a RIDDS and has two SPARC 20 workstations. One acts as a
radar product generator (RUDDS) and the other acts as a PUP interface (RADS). The
WDSS provides the capability to execute prototype algorithms and test new types of
displays in real-time. A limited number of WDSS systems have been implemented at WSR-88D sites.
- WEAK ECHO CHANNEL:
- A channel of weak reflectivity return, behind and near the center of a bow echo.
This is often evident as an echo assumes a bow shape.
- WEAK ECHO REGION (WER):
- Within a convective echo a localized minimum of equivalent reflectivity associated
with the strong updraft region.
- Weak Echo Region
- Weather Forecast Office
- Working Group for Doppler Radar Meteorological Observations
- Write Once Read Many
- Weather Surveillance Radar - 1957
- Weather Surveillance Radar - 1988, Doppler
- WSR-88D SYSTEM:
- The summation of all hardware, software, facilities, communications, logistics,
staffing, training, operations, and procedures specifically associated with the
collection, processing, analysis, dissemination and application of data from the WSR-88D unit.
- WSR-88D UNIT:
- Composed of a Doppler weather radar, computers, workstations, and communications
to link the components and distribute the products. The functional designations of
the first three components are: Radar Data Acquisition, Radar Product Generator,
and Principal User Processor. The combination of one RDA, one RPG and all associated
PUPs and the interconnecting communications.
- Reflectivity-Rain Rate
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