Find in Library

From 1995 to 2000, the Wind spacecraft spent over 500h in the magnetotail, much of it within ~2x10⁴km of the predicted location of the neutral sheet. Wind passed through the near magnetotail at distances of -15 <i>R_E</i>&lt;<i>X</i> GSM&lt;-6 <i>R_E</i> on 35 occasions. Another 10 passes took place at distances of -30 <i>R_E</i>&lt;<i>X</i> GSM&lt;-15 <i>R_E</i>. We identified 65 dipolarization events in the Wind magnetic field data set between <i>Y</i> GSM~-16 and +16 <i>R_E</i> based upon our requirements that the magnetic field inclination had to change by more than 15&deg;, the maximum inclination angle had to be greater than 20&deg;, and the inclination angle had to increase by a factor of at least 1.5. Most of the dipolarization events occurred in the pre-midnight region of the magnetotail and were accompanied by earthward flows with speeds greater than 100km/s. The properties of the dipolarization events did not depend upon the <i>Y</i> GSM position. However, they did vary with the distance to the neutral sheet. Isolated dipolarization events, defined as occurring more than 20min apart, were characterized by a decrease in <i>B_x</i> GSM and <i>B_TOTAL</i>, and an increase in <i>B_z</i> GSM and the magnetic field inclination. Dipolarizations that occurred as part of a series of small dipolarizations spaced less than 20min apart were characterized by a transient increase in <i>B_z</i> GSM and the magnetic field inclination, but no significant change in <i>B_x</i> GSM and <i>B_TOTAL</i>. The events consisting of a series of small dipolarizations occurred predominantly near midnight. We interpret these results in terms of two different modes of magnetotail convection: 1) a classical substorm pattern featuring storage of magnetic energy in the tail lobes which is explosively released at onset, and 2) a directly driven process.