Friday, February 1, 2013

The Value of Dual Polarization Radar

Doppler radar, installed in the early and mid-90's across the United States, was a huge step forward in the field of tornado warnings. Doppler radar senses the winds within a thunderstorm to detect rotation as in the Oklahoma example below. The problem is that the radar detects the rotation aloft and there are times when the rotation does not reach the ground. So, meteorologists are not sure whether a tornado is on the ground or not.

Dual polarization radar has a product called "correlation coefficient." Precipitation (rain, hail, snow) have relatively high signal correlations as compared to debris (wood, metal).
Above is the debris lifted by the fatal Adairsville, Georgia, tornado on Tuesday. The blue-green pixels are a sure sign of a tornado on the ground. It is surrounded by the more highly correlated precipitation returns. This display is especially valuable at night and in remote areas.

2 comments:

  1. Is correlation coefficient product for a specific radar elevation angle?

    From this product can you infer whether a tornado is rain-wrapped or not?

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  2. No, this doesn't tell us whether a tornado is rain-wrapped. That is the reflectivity display.

    The CC is available for all tilts. According to the Atlanta NWS office, they could see debris in the CC products up to 20,000 ft.

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