Total‐electron‐content signatures of plasmaspheric motions

Measurements of fluctuations in total electron content made with a radio interferometer reveal weak but frequent outbursts of total‐electron‐content disturbances, with trace azimuths roughly westward, with trace speeds up to ∼2 km/s, and with temporal periods in the range 100–500 seconds. Statistical tests of the dataset suggest that these disturbances are due to drift of plasmaspheric irregularities past the radio lines‐of‐sight. The phenomenon is likely to provide a new passive tracer of zonal convection in the inner magnetosphere.