We have computed the pressure from the field tension yielding the specific entropy as shown in the plot. As one can see in Figure 1, there is a two order of magnitude change in the entropy such that steady convection is impossible without loss of particles and energy from the flux tube. It should be noted that similar conservation laws also apply to the total number of particles on a flux tube. Synthesis and Conclusions We have constructed an equatorial map of specific entropy in Figure 3. Stars indicate the location of the magnetopause.
Lines are contours of constant specific entropy, i.e., paths along which convection is preferable.
The most pronounced effects would be found about 9 R E and 10 R E . The result of this divergent flow is a decrease of B z in the near-Earth tail. We expect that the evacuation of this region, together with the decrease of B z , leads to the formation of a thin current sheet with decreasing thickness. Thus the proposed mechanism can explain the location of the strongest current sheet thinning and the approximate duration of the growth phase. It should also be noted that the formation of the current layer implies the transition from dipolar to tail-like magnetic field in the region around 10 R E , implying the equatorward expansion of the trapping boundary.