Total pressure variations in the magnetotail as a function of the position and the substorm magnitude

The present study investigates the energy storage and release processes of substorms as a function of both position and substorm intensity in a model-independent manner. As an index of the substorm intensity, we use the amplitude of the positive bay observed at middle and low latitudes. As an index of the energy storage and release in the magnetotail, we use the total pressure measured by Geotail. We have performed a superposed epoch analysis of the total pressure for each substorm group binned in terms of the position and the substorm intensity. We have found that (1) both the magnitude and the increasing rate of the total pressure (i.e., energy density) in the near-tail region (-15 R_E < X_GSM < -6 R_E and -8 R_E < Y_GSM <8 R_E) are highly correlated with the substorm intensity, while those in the midtail (-25 R_E < X _GSM < -15 R_E and - 10 R_E < Y _GSM <10 R_E) are not correlated with the substorm intensity. We have also found that (2) the start of the energy release of small substorms in the near-tail region tends to be delayed from the first Pi2 onset.