Space radiation environment in low earth orbit during solar-activity minimum period from 2006 through 2011

摘要

The Technical Data Acquisition Equipment on board the Advanced Land Observing Satellite had been operated in low earth orbit at 700. km altitude from 2006 through 2011 in order to evaluate space radiation environment, especially the proton environment and the electron environment in the radiation belts, during solar-activity minimum period. The activation of the electron environment in the inner radiation belt along with the 24th solar-activity cycle started in the beginning of 2010, 1 year after the beginning of the 24th solar-activity cycle itself in the end of 2008. The electron environment in the outer radiation belt was almost always modulated by solar wind variations; however, it showed very low activities in the beginning of 2010 which was the same time when the lowest activities were seen in the inner radiation belt. On the other hand, the proton environment in the inner radiation belt showed a slight increase as solar activity went lower, and had a peak also in the beginning of 2010, the same time when there was maximum galactic cosmic ray flux. 1-year delay of the response of space radiation environment around the Earth is suggested to be because the beginning of the 24th solar-activity cycle was very quiet as compared with the several former solar-activity cycles.