Radar signatures#radar#velocity#rotation
Velocity couplet
At a glance
Two neighbouring radar pixels showing opposite-direction winds — one coming at the radar, one going away. That's rotation.
Deep dive
On a Doppler velocity product, rotation appears as adjacent pixels with opposite-sign velocities. Strength is measured as gate-to-gate shear (inbound + outbound velocities, absolute values summed). Anything above ~40 m/s combined in the lowest 2 km is a strong signal.
Rotation can be real (mesocyclone, mesovortex) or range-folding artifact — always cross-check reflectivity and velocity at multiple elevation angles before trusting a couplet.