Pictured is a mesocyclone with a tight circulation as revealed by looking at velocity data. Doppler radar "sees" if detected particles carried by the wind has any compontent along the beam itself. Greens are used for particles moving toward the radar while reds are away.
Therefore, a "couplet" as shown here implies strong cyclonic (counterclockwise) circulation. The radar beam comes in from Wichita from the WSW in this image.
FYI, the green triangle is a a software-driven symbol indicating a possible tornado. This is derived by looking at the entire volume of the storm for rotation. The tightest, most persistent and deepest areas of spin will be tagged in this fashion. This software is used extensively "behind the scenes" at KOLR and KSFX.
Ted Keller
Senior Meteorologist
KOLR/KSFX-TV