METR 24136 February 2004

WSR-88DWSR-88D

Radar ProductsRadar Products

Radar Products

- Base Reflectivity (BREF)Base Reflectivity (BREF)- Base Velocity (BVEL)Base Velocity (BVEL)- Composite Reflectivity (CREF)Composite Reflectivity (CREF)- Layer Composite Reflectivity (LCREF)Layer Composite Reflectivity (LCREF)- Rainfall Accumulation (RAIN)Rainfall Accumulation (RAIN)- Echo Tops (ECHO)Echo Tops (ECHO)- Storm-Relative Radial Velocity (SRVEL)Storm-Relative Radial Velocity (SRVEL)- Vertically Integrated Liquid (VIL)Vertically Integrated Liquid (VIL)- VAD Wind Profile (VAD)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

- 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.

Base Reflectivity (BREF)

(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).

-Two modes: Precipitation mode, Clear-Air mode

(Clear-Air Mode)

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)

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 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 360-degree 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)

Composite Reflectivity (CREF)

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)

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.

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)

S-R Radial Velocity (SRVEL)

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

VIL

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

VAD Wind Profile