Subj : Wx Terms (R)(1)
To : All
From : Daryl Stout
Date : Tue Sep 19 2017 12:08 am
R
Rain
RA
Rain
RADAP II
RAdar DAta Processor II, attached to some WSR-57 and WSR-74 radar units.
It automatically controls the tilt sequence and computes several
radar-derived quantities at regular intervals, including VIL, storm tops,
accumulated rainfall, etc.
RADAR
Acronym for RAdio Detection And Ranging; a radio device or system for
locating an object by means of ultrahigh-frequency radio waves reflected
from the object and received, observed, and analyzed by the receiving
part of the device in such a way that characteristics (as distance and
direction) of the object may be determined.
Radar Beam
The straight line that a radar pulse travels along. As the radar beam
gets further away from the radar, it gets wider and wider. In order for
a precipitation target to be detected by the radar, it must fill the
entire radar beam; therefore, the radar will have a difficult time
detecting small showers and thunderstorms at a great distance from the
radar.
Radar Coded Message
This is an alphanumeric coded message which will be used in preparation of
a national radar summary chart. It is automatically produced by the
WSR-88D's Radar Product Generator (RPG) in 3 parts (reflectivities, storm
motion, and echo tops).
Radar Cross Section
The area of a fictitious, perfect reflector of electromagnetic waves
(e.g., metal sphere) that would reflect the same amount of energy back to
the radar as the actual target (e.g., lumpy snowflake).
Radar Data Acquisition
An acronym for Radar Data Acquisition. The RDA is the hardware component
of the NEXRAD system that consists of the radar antenna, transmitter,
receiver, tower, and controlling computer. The RDA collects the
unprocessed, analog voltages from the radar antenna and converts the
signal to base reflectivity , base velocity, and spectrum width (in polar
coordinate form). These "wide-band" products are transmitted to the RPG,
which creates and disseminates end-user products. Also: The RDA is the
origination point of the WSR-88D radar data that will be eventually used
by the radar operator. This WSR-88D component group is made up of several
subcomponents which generate and radiate radio frequency (RF) pulses,
receive reflected energy from those pulses, and process this received
energy into digital base data. The RDA is also the site of the first two
of four data recording levels used by the WSR-88D to record and store
radar data.
Radar Meteorology
Branch of meteorology that uses radars for weather observations and
forecasts.
Radar Mosaic
A radar product that combines information from multiple radars to give a
regional or national view of reflectivity or precipitation. An individual
NEXRAD radar is limited to a range of about 200 miles. Typically, a
mosaic product is produced for regions spanning several hundreds to
several thousands of miles. Mosaic products are produced by vendors
external to the NEXRAD system.
Radar Product Generator (RPG)
The RPG is the computer in the NEXRAD system that receives
polar-coordinate base radar data from the RDA and processes these data
into end-user products. Algorithms are utilized for pattern-recognition,
rainfall estimation, computation of VIL and other products. The RPG
communicates these products to end-users. A specific subset of available
products is always generated for the NIDS vendors for distribution
outside of the NWS, DoD, and FAA. Other products are generated by the
RPG upon request from a PUP.
Radar Range
Distance from the radar antenna. The WSR-88D radar has a range for
velocity products out to 124 nautical miles and reflectivity products
out to 248 nautical miles.
Radar Reflectivity
The sum of all backscattering cross-sections (e.g., precipitation
particles) in a pulse resolution volume divided by that volume. The
radar reflectivity can be related to the radar reflectivity factor
through the dielectric constant term |K|^2, and the radar wavelength.
Radar Reflectivity Factor (z)
z = the sum (over i) of (N_i * D_i^6), where N_i is the number of drops
of diameter D_i in a pulse resolution volume. Note that z may be
expressed in linear or logarithmic units. The radar reflectivity factor
is simply a more meteorologically meaningful way of expressing the radar
reflectivity.
Radial Velocity
Component of motion toward or away from a given location. As "seen" by
Doppler radar, it is the component of motion parallel to the radar beam.
(The component of motion perpendicular to the beam cannot be seen by the
radar. Therefore, strong winds blowing strictly from left to right or
from right to left, relative to the radar, can not be detected.)
Radiance
A measure of the intensity of the radiant energy flux emitted by a body
in a given direction.
Radiation
Energy transport through electromagnetic waves. See shortwave radiation
and longwave radiation.
Radiation Fog
A fog that forms when outgoing longwave radiation cools the near-surface
air below its dew point temperature.
Radiation Laws
The four physical laws which fundamentally describe the behavior of
blackbody radiation: Kirchhoff's law, Planck's law, Stefan-Boltzmann law
and Wien's displacement law.
Radiational Cooling
The cooling of the Earth's surface. At night, the Earth suffers a net
heat loss to space due to terrestrial cooling. This is more pronounced
when you have a clear sky.
Radiational Inversion
Used interchangably with Nocturnal Inversion; a temperature inversion that
develops during the night as a result of radiational cooling of the
surface. Because the immediate surface (lower Boundary Layer) cools much
more rapidly during these conditions than the air just above (upper
Boundary Layer), a temperature inversion can be created overnight, but
typically erodes quickly after sunrise.
Radio Emission
Emissions of the sun in radio wavelengths from centimeters to dekameters,
under both quiet and disturbed conditions.
Type I. A noise storm composed of many short, narrow-band bursts in the
metric range (300 - 50 MHz).
Type II. Narrow-band emission that begins in the meter range (300 MHz)
and sweeps slowly (tens of minutes) toward dekameter wavelengths
(10 MHz). Type II emissions occur in loose association with major FLAREs
and are indicative of a shock wave moving through the solar atmosphere.
Type III. Narrow-band bursts that sweep rapidly (seconds) from decimeter
to dekameter wavelengths (500 - 0.5 MHz). They often occur in groups and
are an occasional feature of complex solar ACTIVE REGIONs.
Type IV. A smooth continuum of broad-band bursts primarily in the meter
range (300 - 30 MHz). These bursts are associated with some major flare
events beginning 10 to 20 minutes after the flare maximum, and can last
for hours.
Radio Event
Flares with Centimetric Bursts and/or definite Ionospheric Event (SID).
Radiofacsimile
Also known as HF FAX, radiofax or weatherfax, is a means of broadcasting
graphic weather maps and other graphic images via HF radio. HF radiofax is
also known as WEFAX, although this term is generally used to refer to the
reception of weather charts and imagery via satellite. Maps are received
using a dedicated radiofax receiver or a single sideband shortwave
receiver connected to an external facsimile recorder or PC equipped with
a radiofax interface and application software.
Radiofax
Abbreviation for radiofacsimile
Radioisotope Snow Gage
A snow water equivalent gage based on the absorption of gamma radiation
by snow; this gage can measure up to 55 inches water equivalent with a
2 to 5 percent error.
Radiosonde
An instrument that is carried aloft by a balloon to send back information
on atmospheric temperature, pressure and humidity by means of a small,
expendable radio transmitter. Radiosondes can be tracked by radar, radio
direction finding, or navigation systems (such as the satellite Global
Positioning System) to obtain wind data. See also rawinsonde.
Radius of Maximum Winds
The distance from the center of a tropical cyclone to the location of the
cyclone's maximum winds. In well-developed hurricanes, the radius of
maximum winds is generally found at the inner edge of the eyewall.
RAFC
Regional Area Forecast Center
RAFS
Regional Analysis and Forecasting System
Rain
Precipitation that falls to earth in drops more than 0.5 mm in diameter.
Rain Foot
Slang for a horizontal bulging near the surface in a precipitation shaft,
forming a foot-shaped prominence. It is a visual indication of a wet
microburst.
Rain Forest
A forest which grows in a region of heavy annual precipitation. There are
two major types, tropical and temperate.
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