Successive Westward Traveling Surges Driven by Sequential Plasma-Sheet Bubble Injections

The westward traveling surge (WTS) is one of the most notable manifestations of auroral substorms. Using the Rice Convection Model, previous study confirmed that a single plasma-sheet bubble injection can result in the formation of WTS. In reality, however, earthward-propagating bubbles are persistently injected from the magnetotail during substorms; hence it is worth further investigating how sequential bubble injections would affect the features of WTS. In this study, we find that the successive WTSs observed by all-sky imagers correspond well with continual plasma-sheet bubble injections detected by the Time History of Events and Macroscale Interaction during Substorms satellite in the magnetosphere. Numerical simulations are carried out to reveal that the multiple plasma-sheet bubble injections lead to sequential surges in the ionosphere. Interestingly, our results indicate that the propagation speeds of WTSs are well correlated with the magnetic field dipolarization in the magnetosphere.