Abstract
Energetic protons, alpha particles, and electrons are measured with the Space Environment Monitor (SEM) on the Geostationary Meteorological Satellite (GMS, GMS-2, and GMS-3) “Himawari”. SEM on GMS-2 and GMS-3 (GMS) has six (seven) channels P1-P6 (P7) for protons with energies of 0.8-100 MeV (1.2-500MeV), five channels A1-A5 for alpha particles with energies of 8-370 MeV (9-370 MeV), and one channel EL for electrons with energies of > 2 MeV. However, the P1 channel is contaminated by pile-up electrons so that the proton response in the P1 channel is masked. The P2 and A1 channels from GMS provide data of good quality, but other channels from GMS respond to sunlight. Failure of detectors causes trouble in some data sets.
Solar particle events (SPE's) are observed in the P2-P6 (P7) and A1-A5 channels. Some events show a sharp rise and a gradual decay of the particle fluxes, but most events show a gradual rise and a further gradual decay of the particle fluxes. The differential energy spectral index in the SPE's is around 3 for both protons and alpha particles. The flux behavior seen in the A1 channel is quite similar to that seen in the P2 channel. The long-term trend of high energy particle ejection from the sun during the Solar Cycle 21 could be monitored with the A1 and P6 channels, which were noise-free throughout the whole period. SPE's frequently occurred in 1978-1979 and 1981-1982. SPE's in 1980 were not large and were less energetic, although the sunspot number and the solar flare number were quite high. After 1983, SPE's were less frequent, but there occurred several large and energetic SPE's. Therefore, the long-term trend in the high energy particle ejection from the sun is quite different from that in the sunspot number.
The EL and P1 channel response is largely due to energetic particles trapped in the earth's magnetic field. The fluxes from these channels show substorm-induced variations. Characteristics of these substorm-induced flux variations depend highly on local time. The flux levels in these channels diminish just after the onset of high geomagnetic activities and then they rapidly increase above the pre-storm level. Finally, the fluxes gradually decrease to the normal level. The high flux level generally corresponds to the high geomagnetic activity. The fluxes from these channels show a clear 27-day recurrent pattern in 1983-1986, which can be recognized in the geomagnetic activities. The fluxes in the EL and P1 channels can be used as a monitor of geomagnetic activities.
Thus the GMS/SEM provides excellent data bases on the high energy particle ejection from the sun, the cosmic ray intensity, the geomagnetically trapped particle flux level and others. This is valuable for the study of the Solar-Terrestrial relationship.
