LONG-TERM VARIABILITY OF ELECTRON-RADIATION DOSE IN GEOSYNCHRONOUS ORBIT

A neural network that was developed to model the temporal variations o f relativistic (>3 MeV) electrons at geosynchronous orbit has been use d to estimate the long-term variability of the radiation dose to geosy nchronous spacecraft. The input to the neural network consists of 10 c onsecutive days of the daily sum of the planetary magnetic index SIGMA Kp. The output is an estimate of the daily-averaged electron flux for the tenth day. The model was used to compute the daily-averaged electr on flux for energies >3 MeV for each day from January 1933 through Dec ember 1988. Assuming that the average energy spectrum is independent o f time, the annual radiation dose of electrons >300 keV is obtained by scaling the model output to 300 keV and summing the daily-averaged fl ux for each year. The annual dose is found to vary from 0.25 to 3.4 ti mes its average value. The dose is found to correlate only weakly with the annual mean sunspot number. The results are also applicable to st udies of the affect on the middle atmosphere of the long-term variabil ity of the precipitation of these electrons into the atmosphere.