Substorm-associated pressure variations in the magnetotail plasma sheet and lobe

Simultaneous pressure measurements by Interball‐Tail in the high‐latitude lobe and by Geotail in the equatorial plasma sheet were analyzed for 30 substorms which exhibited significant pressure changes. At the onset of a few substorms we observed equatorial pressure peaks with magnitudes up to 50% higher than those in the lobe. These pileups are probably rather localized, and their properties are consistent with plasma sheet thickening between two active regions in the tail. During expansion and recovery phases of more than half of substorms, we observed equatorial pressure depletions relative to the high‐latitude lobe pressure. These depletions can last more than 2 hours and are likely formed during the substorm expansion phase near the equatorial plane behind (tailward of) the strongly dipolar near‐Earth magnetotail region. The observed pressure gradient is probably a nonstationary feature and can be compensated partially by magnetic tension on the curved field lines. Magnitude and history of the solar wind dynamic pressure appear to significantly influence substorm scenarios in the magnetotail. Possible existence of the pressure difference should be taken into account in single‐spacecraft substorm studies.