Time correlation of low‐altitude relativistic trapped electron fluxes with solar wind speeds

Abstract

We present the results from a study of time correlation between the low‐altitude relativistic trapped electron fluxes and the solar wind speeds. Our trapped electron observations in the energy range of 0.19–3.2 MeV were obtained by the OHZORA spacecraft in an altitude range of 350–850 km, near a solar minimum period (1984–87). The solar wind data with a 5‐minute time resolution were obtained from IMP‐8 observations. Linear correlation analyses between the two data sets have been performed for relative time lags varying from 12 minutes to 60 days. The 2.5–day, 13‐day, 27‐day and 54‐day correlation peaks previously reported for energetic electrons near geosynchronous orbits are clearly seen in our results. However, the use of higher time resolution solar wind data than in previous studies allows correlation analyses to be performed at shorter time lags. We report here that correlation at shorter time lags (<10 hrs) exists and that while such correlation is stronger than those observed at longer lag times, it can not be entirely attributed to storm or substorm injections. The correlation is also found to decrease with drift shell magnetic equatorial radii, rt. In addition, local‐time and radial variations in the responses of different drift shells to solar wind speed enhancements indicate that the energetic electron population enters the inner magnetosphere predominantly through the midnight sector.