Transcript Corporate Profile - University of Oklahoma

METR 2413
6 February 2004
WSR-88D
Radar Products
Radar Products
-
Base Reflectivity (BREF)
Base Velocity (BVEL)
Composite Reflectivity (CREF)
Layer Composite Reflectivity (LCREF)
Rainfall Accumulation (RAIN)
Echo Tops (ECHO)
Storm-Relative Radial Velocity (SRVEL)
Vertically Integrated Liquid (VIL)
VAD Wind Profile (VAD)
More Radar Background
Precipitation Mode:
-Volume Coverage Patterns (VCP) 21: 9 elevation
angles with a complete vertical scan every 6
minutes
-VCP 11: 14 elevation angles, every 5 minutes
Clear-Air Mode:
-VCP 31: 5 low level elevation angles, every 10
minutes
Precipitation Mode: VCP-11
Precipitation Mode: VCP-21
Clear Air Mode: VCP-31
Base Reflectivity (BREF)
- Image corresponds to
the amount of radiation
that is scattered or
reflected back to the
radar by targets (in dBZ)
- Colors on the Base
Reflectivity product
correspond to the
intensity of the radiation
that was received by the
radar antenna from a
given location.
(Precipitation Mode)
Base Reflectivity (BREF)
- Targets can be
hydrometeors (snow,
rain drops, hail, cloud
drops or ice particles) or
other targets (dust,
smoke, birds, airplanes,
insects).
(Clear-Air Mode)
-Two modes: Precipitation mode, Clear-Air mode
Base Velocity (BVEL)
Like Base Reflectivity, Base Velocity is a base
product measured by the radar. Base Velocity is
the average radial velocity of the targets in the
radar beam at a given location. Radial velocity is
the component of the target's motion that is along
the direction of the radar beam. Positive values
(warm colors) denote out-bound velocities that
are directed away from the radar. Negative
values (cool colors) are in-bound velocities that
are directed towards the radar.
Base Velocity (BVEL)
How do we interpret the Base Velocity Image?
Use the “zero” line as a reference. The
environmental wind will be perpendicular to
this line, at the elevation of the radar beam.
Keep in mind that the radar beam is increasing
in elevation as it travels away form the radar.
Base Velocity (BVEL)
Composite Reflectivity (CREF)
Composite Reflectivity is the maximum base reflectivity
value that occurs in a given vertical column in the radar
umbrella. NEXRAD scans in several pre-defined "volume
coverage patterns (VCPs), where the radar makes a 360degree horizontal sweep with the radar antenna tilted at a
given angle above the horizontal, then changes the
elevation angle, and completes another 360-degree
sweep, and so on. Composite reflectivity gives a plan
view of the most intense portions of thunderstorms, and
can be compared with Base Reflectivity to help
determine the 3-D structure of a thunderstorm.
Composite Reflectivity (CREF)
Rainfall Accumulation (RAIN)
The Rainfall Accumulation products attempt to estimate
the amount of rainfall that has fallen in a given area under
the radar's umbrella. NEXRAD does this by making
certain assumptions about the number and kind of
raindrops it detects. There are certain limitations involved
with radar estimation of rainfall, which is a subject of
current meteorological research, and there are plans to
improve the way that NEXRAD produces its rainfall
estimates. A given rainfall product should generally be
compared with a product from another radar or with rain
gage reports, if they're available.
Rainfall Accumulation (RAIN)
Rainfall Accumulation (RAIN)
Echo Tops (ECHO)
- This image gives the approximate top of
the precipitation core. When a specific
threshold (18 dBZ) is reached vertically, the
product declares this height to be the “echo
top” (the storm top).
Echo Tops (ECHO)
Base Reflectivity
Echo Tops
Echo Tops (ECHO)
- Echo Top Problems:
Be careful when interpreting an echo-top image. A storm top might be
too close to the radar to be accurately estimated. Specifically, the
highest elevation scan (19.5º) might still pass through the
precipitation core of the storm. The echo-top will therefore be
underestimated on the image. (topping)
Also, if a storm or echo is too far away from the radar, then less
confidence should be placed in the echo-top image. This is because
the centers of the beams will eventually be too far apart to accurately
resolve the echo top. The radar mode (VCP-21 or VCP-11) should be
taken into account when determining the validity of a distant echo-top.
S-R Radial Velocity (SRVEL)
Storm-Relative Radial Velocity is Base
Velocity with the average motion of all storm
centroids subtracted out. Storm-Relative
Radial Velocity can be useful in finding
mesocyclones or other circulation patterns.
S-R Radial Velocity (SRVEL)
VIL
Vertically Integrated Liquid, or VIL, is a
calculation that converts a column of
reflectivity into its liquid water equivalent.
However, it turns out that VIL is seasonally
and geographically correlated to hail size.
VIL
VAD Wind Profile
The VAD Wind Profile is a time series of
estimate of the horizontal wind at specific
heights above the radar. It is useful in
diagnosing the locations and structure of
fronts, the movement of moisture from the
Gulf of Mexico, and other meteorological
phenomena (Low/Mid level Jets, vertical
wind shear, etc.)
VAD Wind Profile