The Partition of Energy Flux Transport at Bursty Bulk Flows

Abstract

Bursty bulk flows (BBFs) are fast flows of plasma in the tail and are responsible for much of the energy flux transport earthward from the tail into the inner magnetosphere despite being relatively short‐lived. BBFs are often accompanied by injections in which particles that have been accelerated to 10–100s of keV are transported earthward. We quantify kinetic energy transport by both the thermal plasma of the BBF and the energetic particles of the injections to see how significantly injections contribute. We studied three different cases. In the first, a BBF with no observed injections, we found that the thermal ion population was responsible for almost all the kinetic energy transport. In the second, a BBF with only an electron injection, the thermal ions were again dominant, suggesting that neither electron population is a major contributor to energy transport. Finally, the third event contained an ion injection. This time, the energetic ions transported a comparable amount of energy as the thermal ions. The energy transport from the thermal ions alone is similar to the other events and the total energy transport is higher, suggesting that the ion injection is adding extra energy transport to the process. Global magnetospheric modeling shows that this is a straightforward reconnection event, so unique conditions are not necessary for energetic ions to be a significant contributor to earthward kinetic energy transport during a BBF. Therefore, an energy transport calculation assuming a solely thermal flow can lead to an underestimate if there is a concurrent ion injection.