Effect of solar wind density on relativistic electrons at geosynchronous orbit

Abstract

We examined the relationship between relativistic (>2 MeV) electron fluxes at geostationary orbit and two solar wind parameters, the speed and density. For the analysis, we used data of relativistic electron fluxes measured with GOES‐8 spacecraft for 1997–2002 and GOES‐10 spacecraft for 2003–2006, and solar wind data, provided by Goddard Space Flight Center. Using the correlation analysis, we found that not only solar wind speed but also solar wind density provides a strong effect on relativistic electrons: the relativistic electron fluxes increase with increasing solar wind speed and decrease with increasing solar wind density. In contrast to solar wind speed that shows the best correlation with electron fluxes after about two days only, the solar wind density shows the best correlation with the electron fluxes after about 15 hours. To separate the effects of solar wind speed and density, we examined events when solar wind speed varied insignificantly; in these events, the effect of solar wind density on the relativistic electrons remained strong. We found that the solar wind density, which may affect the loss of relativistic electrons, effectively controls the magnitude of relativistic electron fluxes at geostationary orbit, so that the strongest fluxes occurred almost exclusively during low‐density solar wind conditions. Thus, our study showed that solar wind density is an important parameter that may significantly affect the loss of relativistic electrons and, as a result, the resulting magnitude of the electron fluxes at geostationary orbit.