Satellite observations indicate that multiple components often exist in the plasma sheet, particularly during impulsive fast flow events. In this paper, we perform a kinetic analysis of the energy transport of plasma sheet ion flow using a model of two‐component plasma sheet ion flows (Background convection flow represented by subscript “b” and Fast flow represented by subscript “f”) and compare the energy transport calculated by kinetic approach Qk with those obtained from magnetohydrodynamic (MHD) approach QMHD. The ratio of Qk/QMHD is always larger than unity and is positively proportional to the ratios of Vf/Vb and Tf/Tb. The maximum values of Qk/QMHD occur in the low‐speed ranges (i.e., small density ratio Nf/N). When Nf/N exceeds 0.4, the ratio of Qk/QMHD is almost the same for a wide parameter ranges of Vf, Tf, and Vb. Heat flux is important in low‐speed range and is neglectable in the high‐speed range. The adiabatic polytropic index 5/3 cannot correctly describe energy transport rate. A density ratio Nf/N of 0.3% of high‐speed ion flow can make the effective polytropic index obviously deviate from adiabatic polytropic index (5/3). The above theoretic results can well explain previously reported satellite in situ observations.
We use 9 years data of Cluster to study the dependencies of plasma parameters and energy transport in the plasma sheet on the lasting time of northward/southward interplanetary magnetic field (IMF). The plasma parameters and energy transport in the plasma sheet always respond to the change of IMF direction by more or less time. The ion density starts to increase/decrease remarkably at 80 min after northward/southward IMF turning. The ion temperature starts to decrease at 25 min after northward IMF turning, whereas it starts to increase at 80 min after southward IMF turning. The earthward convection velocity within 15 min after northward IMF turning almost equals to that within 15 min period after southward IMF turning. However at time greater than 15 min after southward IMF turning, the earthward convection velocity under southward IMF starts to remarkably increase. The response time (15 min) of magnetospheric convection velocity is well consistent with the response times of nightside ionospheric convection to southward IMF turning. The enthalpy flux is larger than kinetic flux by about three orders of magnitudes, and thus the enthalpy flux plays a dominant role in the plasma sheet energy transport. The enthalpy flux does not weaken immediately after northward IMF turning. The enthalpy flux within 15 min after northward IMF turning is comparable to or even slightly larger than that within 15 min after southward IMF. The enthalpy flux starts to decrease at times greater than 15 min after northward IMF turning, whereas it starts to increase at times greater than 15 min after southward IMF turning. The result that the enhanced energy transport during the 15 min period after northward IMF turning may explain previous observation that substorms frequently occur shortly after northward IMF turning.
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