Composite reflectivity

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#1 the fuchsia colored region, visible on the composite image, is all but missing on the base reflectivity
#2 and #3, show more rain supported by strong updrafts. Baserefl composite comparison fr.svg
#1 the fuchsia colored region, visible on the composite image, is all but missing on the base reflectivity
#2 and #3, show more rain supported by strong updrafts.

The composite reflectivity is the maximum dBZ reflectivity from any of the reflectivity angles of the NEXRAD weather radar. In the Composite, the highest intensities amongst those available in the different angles above each point of the image will be displayed. In the Canadian weather radar network, this is called MAXR, for Maximum reflectivity in the column.

Contents

Principle

Scans at different angles by a weather radar. Composite reflecitivty principle.png
Scans at different angles by a weather radar.

A weather radar sequentially surveys a series of vertical angles over 360 degrees in azimuth. The reflectivity at each of these angles represents the rate of precipitation along a cone that rises away from the radar. Every angle can be seen on a PPI image. However, this rate varies with altitude and an individual PPI does not give a complete idea of the vertical structure of precipitation. In the United States NEXRAD network some of these angles are .5, 1.45, 2.4, and 3.35 degrees with the radar having up to 14 angles when it is in Severe Mode. [1] [2]

In the composite reflectivity product, the highest intensities among those available on the different angles above each point in the image will be displayed. It is a radar product created to compare low-level reflectivity with total reflectivity in the air column in order to identify certain cloud characteristics or artifacts in radar data. [1]

Variants

One might want to only compare the precipitation in a certain layer above ground, instead of the whole column, and the base level reflectivity. Such subset composite radar products used by the National Weather Service with the NEXRAD data are: [3]

Use

When compared to the base angle reflectivity, the lowest angle of elevation sounding, the composite reflectivity, including higher elevation scan information, may appear to indicate more widespread rain. This could indicate one of different things:

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References

  1. 1 2 National Weather Service (August 29, 2007). "Composite Reflectivity". JetStream - Online School for Weather. NOAA . Retrieved 2008-10-03.
  2. US Department of Commerce, NOAA. "About our WSR 88-D Radar". www.weather.gov. Retrieved 2023-03-11.
  3. "Layer Composite Reflectivity Average and Maximum". National Weather Service. Retrieved 2023-11-07.