## 3 Event Monitoring by Sensor Systems for Multiple Satellites
### Case Study 2: Rapid Decrease of High-Energy Electron Flux by a Coronal Mass Ejection  
Another crucial space weather event is CMEs. Next, we demonstrate the prediction for CMEs by our proposed model. Figure 10 shows the time development of sensor data for the CME happened at 26 April 2008. All the plots were created from 30 April 2008 at 00:00:00 UTC to 4 May 2008 at 23:00:00 UTC. In this event, several days later, the solar wind is ejected in front of the Earth from the surface of the Sun. The rapid increase of the solar wind speed was observed by ACE at the time 20 h from the beginning of the sensor data. Simultaneously, the north-south component of IMF also rapid decreased to the south direction. Other observation data for the north-south component of IMF and solar wind speed for STEREO-A and TEREO-B showed monthly variation originated from a coronal hole. The high-energy electron flux usually rapid decreases a few days later when the rapid increase of solar wind speed is observed by ACE. The high-energy electron flux shows the smallest value at the time 100 h from the start of the sensor data. Then, the high-energy electron flux rapidly increases and keeps its level several days.  
Figure 11 shows the time development of the credibility of each sensor. The test data is shown in Figure 10. The two sensors for solar wind speed of ACE and STEREO-A indicate high credibility for the whole of the sensor data. The solar wind speed of STEREO-B, however, shows the rapid variation of the credibility in the beginning of the sensor data. This is induced by the sudden changes of the solar wind speed and north-south component observed by STEREO-B at the time a day ago.  
For the high-energy electron flux of GOES-10, the sensor node is diagnosed as abnormal because the credibility shows 0.0 in short duration several times. This diagnosis result corresponds to the changes of the high-energy electron flux observed by GOES-10. For the sensor of the high-energy electron flux 24 h  
Figure 10: Time development of sensor data for five days from 30 April 2008 at 00:00:00 UTC. This plot contains an event of high-speed solar wind flowing from a coronal hole. In the first and second rows, the plots of the columns correspond to the satellites of ACE, STEREO-A, and STEREO-B, respectively. In the third row, the plot corresponds to GOES-10.  
ahead, the credibility follows the observed flux except the duration from about 35 to 45 h. The proposed model also predicts the decrease of the high-energy electron flux in the recovery phase.  
In the eight-sensor model, the deviations in the predefined conditions are detected as a result of the many relations among sensor nodes. These detections contribute to preventing oscillation in sensor credibility. The predictions of the high-energy electron flux 24 h ahead by the eight-sensor model are more reliable than those by the four-sensor model. Solar activity can be observed with higher accuracy by sensors located at distinct locations. Having multiple sensors with different satellites plays a significant role in prediction of the high-energy electron flux 24 h ahead.