Observations by the Voyager imaging instrument has shown an organized train of features moving in a westerly current at 9 ¿N with a zonal speed of 100--120 m s-1. The measurement reports show that the number of plumes varied between 13 at the time of the Voyager 1 encounter, and 11 at the time of the second spacecraft passage. The infrared interferometer spectromer (Iris) measurements suggest that the effect of these plume features propagates throughout the Jovian troposphere. A mechanism is suggested for the origin of the plumes in terms of wave interactions with the Jovian flow.