Discovery of a low-latitude ionospheric trough associated with the inner radiation belt

The dynamics of ionospheric troughs that developed during a great geomagnetic storm on 11-13 April 2001 are studied using measurements of electron density obtained by the CHAMP satellite at an altitude of 410-465 km. Subauroral, mid-latitude and low-latitude troughs were observed at nighttime, sometimes simultaneously. The subauroral trough is usually defined as the main ionospheric trough, whereas the mid-latitude trough is associated with the magnetospheric ring current. It appeared at the beginning of the storm recovery phase around latitudes of 40 degrees-45 degrees GMLat (L=1.7-2.0) and existed for a long period of time throughout the late recovery phase of the residual ring current at latitudes of 50 degrees-55 degrees GMLat (L similar to 2.4-3.0). For the first time, a low-latitude trough was revealed. It developed at latitudes of 34 degrees-45 degrees GMLat (L=1.45-2.00) in association with the precipitation of energetic particles from the inner radiation belt.