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WSR-88D (NEXRAD)
Terms and Acronyms



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Top button A

A/D
Analog to Digital
AB
Air Base
AC
Air Conditioner
ACU
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.
ADAS
Automated Data Acquisition System
AFB
Air Force Base
AFGL
Air Force Geophysics Laboratory
AFGWC
Air Force Global Weather Central
AFOS
Automation of Field Operations and Services
AFSS
Automated Flight Service Station
AGC
Automatic Gain Control
AGL
Above Ground Level
ALIASING:
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
AMPLITUDE:
The maximun magnitude of a quantity.
AMS
American Meteorological Society
ANALOG:
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.
AP
Anomalous Propagation
ASCII
American Standard Code for Information Interchange
ASL
Above Site (radar) Level
ASOS
Automated Surface Observing System
ASR-9
Airport Surveillance Radar (FAA)
ASSOCIATED PRINCIPAL USER:
A Principal User with dedicated communications to a WSR-88D unit.
ATTENUATION:
Any process in which the flux density (power) of a beam of energy is dissipated.
AUTOCORRELATION:
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.
AWIPS
Advanced Weather Interactive Processing System
AWS
Air Weather Service
AZIMUTH:
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.

Top button B

BACKING WIND:
A change in wind direction in a counterclockwise sense representing cold-air advention.
BACKSCATTER:
The portion of power scattered back in the incident direction.
BAM
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)
BIAS:
A systematic difference between an estimate of and the true value of a parameter.
BIN:
Radar sample volume.
BITE
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.
BWER
Bounded Weak Echo Region

Top button C

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.
CELL:
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.
CENTROID:
The center of mass of a storm.
CFCF
Central Flow Control Facility
CFWSU
Central Flow Weather Service Unit
CLUTTER:
Echoes that interfere with observation of desired signals on a radar display. Usually applied to ground targets.
cm
Centimeter
CM
Combined Moment
COHERENT RADAR:
A radar that utilizes both signal phase and amplitude to determine target characteristics.
COHO
Coherent Oscillator
COKRIGING:
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.
CONUS
Conterminous United States
CONVERGENCE:
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.
CORRELATION:
A measure of similarity between variables of functions.
COUPLET:
Adjacent maxima of radial velocities of opposite signs.
COVARIANCE:
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 frequency.
CPU
Central Processing Unit
CR
Composite Reflectivity
CRC
Composite Reflectivity Contour
CRPL
Central Radio Propagation Laboratories
CRS
Console Replacement System (NOAA Weather Radio)
CRT
Cathode Ray Tube
CS
Combined Shear
CSC
Combined Shear Contour
CW
Continuous Wave
CWA
County Warning Area

Top button D

DAPM
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.
DAU
Data Acquisition Unit
dB
Decibel
dBz
Decibel (radar reflectivity ratio)
DEALIASING:
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.
DIP
Dual In-Line Package
DISDROMETER:
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.
DISTORTION:
Change in a signal resulting in gross non-linearities in signal processing or handling.
DIVERGENCE:
A measure of the expansion of a vector field.
DOC
Department of Commerce
DOD
Department of Defense
DOE
Department of Energy
DOPPLER SHIFT:
The change in frequency at a receiver due to the relative motion of the receiver and the energy source.
DOT
Department of Transportation
DOWNBURST:
A strong downdraft that induces an outburst of damaging winds on or near the ground.
DOWNDRAFT:
Current(s) of air with marked vertical downward motion.
DPA
Digital Precipitation Array, One-hour precipitation accumulation product (Digital Array).
DRYLINE:
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.
DUCTING:
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.

Top button E

ECHO:
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.
EEPROM
Electronically Erasable Programmable Read Only Memory
Elev
Elevation
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.
ERL
Environmental Research Laboratories
ESTIMATE:
A statement of the value of a quantity or function based on a finite number of samples.
ET
Echo Tops
ETC
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 tropical cyclone.

Top button F

FAA
Federal Aviation Administration
FEATURE:
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.
FFD
Forward Flank Downdraft
FMH
Federal Meteorological Handbook
FO
Forward Overhang
FOLDING:
See Range Folding
FREEZING LEVEL:
The lowest altitude in the atmosphere over a given location where the air temperature is 0 degrees Celsuis
FREQUENCY:
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.
FSS
Flight Service Station
ft
Foot
FTM
Free Text Message

Top button G

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.
GAIN:
A change in signal power, volatge or current. Usually applied to a change greater than one and expressed in decibels.
GARP
Global Atmospheric Research Program
GATE
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.
GAUSSIAN:
Refers to the Normal distribution; phenomena whose events are normally distributed are Gaussian distributed. This is the most common distribution encountered in physical processes.
GDSS
Gage Data Support System
GOES
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.
G/R
Gage/Radar

Top button H

HAIL:
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.
HERTZ:
A unit of frequency equal to one cycle per second.
HI
Hail Index
HOMODYNING:
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.
HSP
Hardwired Signal Processor
HW
Hail Weight
Hz
Hertz

Top button I

I
Inphase
ICAO
International Civil Aviation Organization
ICD
Interface Control Document
ICMSSR
Interdepartmental Committee for Meteorological Services and Supporting Research
ID
Identifier
IEEE
Institute of Electrical and Electronic Engineers
IFLOWS
Integrated Flood Observing and Warning System
INCIDENT POWER DENSITY:
Energy per unit area incident on the radar target.
INPHASE:
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.
ISODOP:
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.
ISU
Interference Suppression Unit

Top button J

JDOP
Joint Doppler Operational Project
JSPO
Joint System Program Office

Top button K

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.
kbs
Kilobit per Second
kg
Kilogram
KLYSTRON:
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.
km
Kilometer

Top button L

Lat
Latitude
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 permanently archived.
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.
LEWP
Line Echo Wave Pattern
LFM
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.
LOG
Logarithmic
Long
Longitude
LP
Low Precipitation (storm)
LRA
Layer Composite Reflectivity - Average
LRM
Layer Composite Reflectivity - Maximum
LTA
Layer Composite Turbulance - Average
LTM
Layer Composite Turbulance - Maximum

Top button M

m
Meter
M
Mesocyclone
MACROBURST:
Large downburst with 4 km (2.2 nmi) or larger outflow size with damaging wind lasting 5 to 20 minutes.
MAINLOBE:
The envelope of electromagnetic energy along the main axis of the beam.
MAR
Modernization and Associated Restructuring
MARD
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.
MCC
Mesoscale Convective Complex
MCS
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.
MESOCYCLONE:
A 3-dimensional region in a storm that rotates cyclonically and is closely correlated with severe weather.
MESOSCALE:
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.
mHz
Megahertz
MIC
Meteorologist-in-Charge
MICROBURST:
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.
MLOS
Microwave Line of Sight
MODULATION:
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.
MSL
Mean Sea Level
MULTICELL STORM:
A storm that consists of a cluster of single cells that are often short-lived.

Top button N

NA
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.
NCAR
National Center for Atmospheric Research
NCDC
National Climatic Data Center
ND
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.
NEXRAD
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 Supporting Research.
NHC
National Hurricane Center
NIDS
NEXRAD Information Dissemination System
NMC
National Meteorological Center
nmi
Nautical Mile
NOAA
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.
NPC
NEXRAD Program Council
NRC
National Research Council
NSSFC
National Severe Storms Forecast Center
NSSL
National Severe Storms Laboratory
NTIS
National Technical Information Service
NTR
NEXRAD Technical Requirements
NWR
National Weather Radio
NWS
National Weather Service
NWSFO
National Weather Service Forecast Office
NWSMC
National Weather Service Modernization Committee
NWSO
National Weather Service Office, NEXRAD Weather Service Office
NWWS
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).

Top button O

OFCM
Office of the Federal Coordinator for Meteorological Services and Supporting Research
OHP
One-Hour Precipitation Accumulation (Graphic Image)
OIC
Official-in-Charge
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.
OS
Operating System
OSCILLATOR:
The general term for an electronic device that generates alternating currents or voltages. The oscillator is classified according to frequency of the generated signal.
OSF
Operational Support Facility
OVERHANG:
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.

Top button P

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.
Param
Parameter
PATTERN VECTOR:
A pattern vector is formed by a series of azimuthally adjacent sample volumes of increasing or decreasing Doppler velocity.
PHASE:
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.
PIE
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.
PMC
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.
PPI
Plan Position Indicator
PRF
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 Aviation Administration.
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.
PROFS
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).
PROPAGATION:
Transmission of electromagnetic energy as waves through or along a medium.
PRT
Pulse Repetition Time
PSP
Programmable Signal Processor
PTM
PUP Text Message
PUES
Principal User External System
PULSE:
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 succeeding pulse.
PULSE WIDTH:
The time occupied by an individual broadcast from a radar.
PUP
Principal User Processor

Top button Q

Q
Quadrature
QUADRATURE:
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.

Top button R

R
Reflectivity
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.
RADS
Radar Algorithm Display System, see WDSS
RAM
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.
RCM
Radar Coded Message
RCS
Cross Section - Reflectivity
RDA
Radar Data Acquisition
RDASC
RDA Status and Control (Processor)
REFLECTIVITY:
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.
REFRACTION:
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.
rf
Radio Frequency
RFD
Rear Flank Downdraft
RFC
River Forecast Center
RGDAC
Rain Gage Data Acquisition Computer (currently GDSS)
RHI
Range Height Indicator
RIDDS
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.
RMS
Root Mean Square
RPG
Radar Products Generator
RPGOP
RPG Operational Position
rpm
Revolutions Per Minute
RPS
Routine Product Set
RUDDS
Radar Utilities and Data Distribution System, see WDSS

Top button S

S/C
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.
SASC
Systems and Applied Sciences Corporation
SCATTERER:
Any object capable of reflecting the radar signal.
SCS
Cross Section - Spectrum Width
SCSI
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.
SEGMENT:
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.
Sfc
Surface
SHEAR:
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.
SHEF
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.
SIDELOBE:
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.
SL
Severe Left-Moving Supercell
SMRP
Satellite and Meteorology Research Project
SNR
Signal-to-Noise Ratio
SOO
Science and Operations Officer
SPD
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.
SPS
Signal Processor Subsystem
SQUALL LINE:
Any line or narrow band of active thunderstorms.
SR
Severe Right-Moving Supercell
SRM
Storm Relative Mean Radial Velocity (Map)
SRR
Storm Relative Mean Radial Velocity (Region)
SS
Storm Structure
STALO
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.
STI
Storm Track Information
STORM:
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 extratropical cyclones.
STORM MOTION:
The velocity at which a storm travels.
STP
Storm-Total Precipitation Accumulation
SUPERCELL:
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.
SW
Spectrum Width
SWA
Severe Weather Analysis
SWP
Severe Weather Probability
SWR
Severe Weather Analysis - Reflectivity
SWS
Severe Weather Analysis - Shear
SWV
Severe Weather Analysis - Velocity
SWW
Severe Weather Analysis - Spectrum Width
SYNCHRONOUS DETECTION:
Processing that retains the received signal amplitude and phase but that removes the intermediate frequency carrier.
SYSCAL
System Calibration

Top button T

TARGET:
Precipitation or other phenomena that produce echoes.
TBD
To Be Determined
TDWR
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.
THP
Three-Hour Precipitation Accumulation (Graphic Image)
TILT:
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.
TRANSMITTER:
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.
TVS
Tornado Vortex Signature

Top button U

UAM
User Alert Message
UCP
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.
UNIMODAL:
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.
UPDRAFT:
Current(s) of air with marked vertical upward motion.
URC
Unit Radar Committee
UTC
Coordinated Universal Time

Top button V

v
Volt
V
Velocity
VAD
Velocity Azimuth Display
VARIANCE:
A measure of variability.
VCP
Volume Coverage Pattern
VCS
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.
VIL
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.
VORTEX:
In general, any flow possessing vorticity. More often the term refers to a flow with closed streamlines.
VORTICITY:
A vector measure of local rotation in a fluid flow.
VWP
Velocity Azimuth Display Wind Profile

Top button W

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.
WATADS
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.
WATERSHED:
The total area drained by a river and its tributaries.
WATT:
The unit of power in the meter-kilogram-second (mks) system of units; equal to one joule per second.
WAVELENGTH:
The distance a wave will travel in the time required to generate one cycle.
WCCM
Wideband Communications Control Module
WDSS
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.
WER
Weak Echo Region
WFO
Weather Forecast Office
WG/DRMO
Working Group for Doppler Radar Meteorological Observations
WORM
Write Once Read Many
WSR-57
Weather Surveillance Radar - 1957
WSR-88D
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.

Top button Z

Z-R
Reflectivity-Rain Rate

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