Growth phase signature in the magnetotail associated with sawtooth injections

We have examined magnetic field and plasma signatures observed by the Geotail spacecraft during the magnetic storm event of April 2002. On April 18 and19 during this storm, Los Alamos National Laboratory (LANL) satellites observed sawtooth injections at geosynchronous orbit. Geotail was staying in the mid-tail region at R ~ 27 Re and observed an increase and then decrease of total (kinetic plus magnetic) pressure associated with each sawtooth injection. A detailed examination shows that the total pressure started to increase tens of minutes before each injection and then decreased to even below the previous levels after the injection. These features are similar to what we observe for regular substorms, and the observed increase and decrease in the total pressure are probably related to the substorm growth and expansion phases, respectively. The IMF and solar wind data acquired from the ACE satellite show no clear change of plasma or magnetic field parameters that can be associated with the trigger of injections, but the IMF BZ gradually changed from southward to northward. Therefore the present results suggest that for the sawtooth injection, energy is continuously provided by the solar wind to the magnetosphere but is released only periodically by a certain internal process rather than a change of external conditions.