NWS Doppler Radar Dual Pol - Tornado Debris

NWS Doppler Radar (WSR-88D) Example Products

Conventional Doppler radar sends out a horizontal energy pulse providing a one dimensional view of precipitation. Dual pol radar sends both horizontal and vertical pulses, providing a two dimensional view. Thus, it provides much better information about the size, shape, and estimated amount of precipitation, distinguishing between rain, snow, and hail. Basic dual pol products include correlation coefficient (CC), differential reflectivity (ZDR), and specific differential phase (KDP). More information is available on our Dual Pol webpage.

Above, base reflectivity (lower left) showed a classic supercell with a hook echo on its southern side. Corresponding storm-relative velocity data (upper left) showed a strong low-level mesocyclone (dark blue-red couplet) that was associated with a tornado at this time. Dual pol CC data (right 2 panels at different elevation angles) showed a definitive area of blue, or very low values of around 0.7 in the location of the mesocyclone and tornado. The low CC values indicates a concentrated cluster of particles of different sizes, thus producing entities that are not correlated in size and shape. This is dual pol's depiction of a "debris ball" at the location of the tornado, i.e., various debris caught within and rotating around the tornado, and lifted up into the parent thunderstorm. This CC signature would be less evident for weaker tornadoes and for storms distant from the radar. Reflectivity and velocity structure and trends are the primary data sources needed to determine tornado potential and evolution.

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