Effect of Solar Cycle Activity on High Energy Proton of Inner Radiation Belt in the Low Altitude Region

The NOAA-15 high energy proton observation from 1998 to 2011 is used to analyze the effect of solar cycle activity on high energy proton flux. The statistic research indicates that there is an inverse correlative relationship between the proton flux in inner radiation belt and solar activity. This anti-correlation is related to geomagnetic coordinates L and B, and more significant with the increasing of L and decreasing of B. There is also a phase lag between the solar activity and the proton flux. This hysteresis effect is more obvious in the region with smaller L or larger B. The lag can reach one year in some regions. This hysteresis effect means it takes a long time to reach the dynamic balance between the source and the loss for the proton of inner radiation belt in the low altitude region. The unbalance between the source and loss is the reason why the intensity of proton flux at the same solar activity is different. The comparison with the result of AP8 model indicates the energetic proton flux from AP8 is higher than the satellite's observation in the region with large B, which suggests that the AP8 model may overstate the proton flux enhancement at inner radiation belt in the low altitude region if only the long-term variation of magnetic field is considered.