Formation of new electron radiation belt during magnetospheric compression event Original Research Article

The rapid formation of the new electron belts during March 24–28, 1991 magnetic storm was investigated by using Akebono RDM (radiation monitor) observations. Immediately after the storm sudden commencement (SSC) at 03:41 UT on March 24, highly energetic (>2.5MeV) electrons were promptly enhanced deep in the inner magnetosphere, forming a new radiation belt peaked around L=2.6. There was a very big magnetic storm activity around 22 UT on March 24; e.g. AE reached 2300 nT and Dst went down to −300 nT, and the new radiation belt moved further toward the Earth with its peak at L=2.2. Measurements from the Akebono RDM instrument show that plenty of intermediate-energy (0.3–0.95MeV) electrons were supplied in regions around L=2.8 by early March 25. These electrons could be the source populations, forming another radiation belt there. The increase in the intensity of MeV electrons around the peak (Lr2.8) was somewhat smooth. It took several days for MeV electrons to reach a saturation level. The prolonged substorm activities during the recovery phase of the magnetic storm got these electrons more energetic. The new radiation belt formed around L=2.2 persisted for almost one year, while the other radiation belt formed around L=2.8 persisted for only one month and half. This difference would be the difference of the loss rate of the MeV electrons in both locations.