The new radiation belt of the earth from trapped anomalous cosmic rays

In this review we briefly present the observational results on the new radiation belt of the Earth originating from the anomalous cosmic rays (ACR) and their implications. Firstly, a brief historical account of the development of our knowledge and ideas on the trapped particles in the geomagnetic field is presented. We then discuss briefly the first observations of the anomalous cosmic rays inside the magnetosphere in the Skylab experiment in 1973-1974 (Biswas et al., 1975). This showed that the measured ACR oxygen flux was at least 25 times higher than the calculated flux from the interplanetary value, indicating the presence of trapped ACR component originating from the Blake-Freisen mechanism (Biswas and Durgaprasad, 1980). In the 'Cosmos' experiment of the USSR, the presence of trapped ACR oxygen was indicated from the observations of double peaked angular distributution (Grigorov el al., 1990). In the recent satellite experiment, MAST-SAMPEX the new results were obtained which confirmed the earlier indications and established the presence of the trapped ACR component in the geomagnetic field from the spatially separated components of the ACR (Cummings et al., 1993). The properties of the trapped ACR ions as measured in the SAMPEX are briefly discussed. The theoretical model of trapped ACR oxygen by Blake and Freisen are briefly summarised. The implications of the new observations are noted.