Statistical distribution of ring current ions observed by NOAA/POES satellites

The dynamics of the ring current ions are studied in detail by using the observations of the NOAA/POES satellites (N15, N16, N17) from 2001 until now. These satellites observe energetic (keV - MeV) particles at altitudes of about 800 km and across the magnetic footprint of the ring current region. The orbit of three satellites can cover all magnetic local times (MLT) during a storm event. From the two-dimensional statistical analysis, we have confirmed that the ring current ions observed by the P0 (30-80 keV) channel show asymmetric distribution. The time variation of the ion flux during magnetic storm appears as intensity and special variation. Intensity of the ion flux shows MLT asymmetry; strongest in the pre-midnight sector (20-24 MLT). The flux in the post-midnight sector (0-4 MLT) tends to intense rather than that in the dusk sector (16-20 MLT). In comparison with the post-midnight sectors, the flux enhancement is very weak in the dawn and pre-noon sector (4-8 and 8-12 MLT) during storm times. The timing of ion flux enhancement during storm time is typically as the following: the ions in the pre-midnight sector increase firstly (in the initial phase) at about L = 6 and those in the post-noon sector increase finally (in the main phase). In the main phase, the peak flux of the ions is at about L = 4. In the recovery phase the ion fluxes in the all sectors decrease while these latitudes (L-values) increase. However, such asymmetric distribution still remains after the storm event. Even during non-storm period, the ring current ions exist in the pre-midnight and its neighbor sectors at L = 5 to 7. Only during Kp < 1 (very quiet period) such asymmetry disappears. This suggests that substorm injection play a role of ion distribution during non-storm time. The relationship between asymmetry of ring current ions and that of magnetic field variations observed on the ground will be discussed in this presentation.