Effects of solar wind ultralow-frequency fluctuations on plasma sheet electron temperature: Regression analysis with support vector machine

To investigate whether ultralow-frequency (ULF) fluctuations from 0.5 to 8.3 mHz in the solar wind and interplanetary magnetic field (IMF) can affect the plasma sheet electron temperature (T-e) near geosynchronous distances, we use a support vector regression machine technique to decouple the effects from different solar wind parameters and their ULF fluctuation power. T-e in this region varies from similar to 0.1 to 10 keV with a median of 1.3 keV.

We find that when the solar wind ULF power is weak, T-e increases with increasing southward IMF B-z and solar wind speed, while it varies weakly with solar wind density. As the ULF power becomes stronger during weak IMF B-z (similar to 0) or northward IMF, T-e becomes significantly enhanced, by a factor of up to 10. We also find that mesoscale disturbances in a time scale of a few to tens of minutes as indicated by AE during substorm expansion and recovery phases are more enhanced when the ULF power is stronger.