Plasma and energetic particle properties of dispersionless substorm injections at geosynchronous orbit

Using a full year of geosynchronous spacecraft data, we survey the substorm-associated behavior of the thermal plasma (30 eV < E < 40 keV) in the plasma sheet in relation to energetic particle injections (E > 50 keV). Five classes of injection events are found, well ordered by their average local times: Ion injections without accompanying electron injection at ∼21 LT, ion injections followed a few minutes later by an electron injection at ∼22 LT, simultaneous ion and electron injections close to midnight, electron injections that are followed by an ion injection at ∼1 LT, and finally pure electron injections at ∼2 LT. The thermal electrons show a significant increase in temperature (from ∼1 keV to ∼2 keV) and pressure at substorm onset, while the density and the thermal ion signatures (below ∼30 keV) are typically weak. However, energetic ions (above ∼30 keV) contribute significantly to the total ion pressure and temperature, leading to a rise in the total temperature from ∼10 keV to ∼16 keV. Preexisting perpendicular anisotropies in the thermal electrons and ions are reduced during the substorm growth phase but become enhanced again after onset, sometimes after a brief period of parallel anisotropy.