POTENTIAL GRADIENT AND RADAR ECHOS FROM AN ISOLATED THUNDERSTORM

It was found by the simultaneous observations of the surface potential gradients and the radar echos from an isolated thundercloud that.the positiveward excursion of the gradient in the middle of the electrical disturbance was almost exactly associated with the sudden raising of the radar echo top. It is suggested from this observed fact that the lower positive pocket charge in a thundercloud is produced in a strong updraught during the growth of the cloud tower