| We present a series of studies that utilize observations and modeling in order to characterize transport in the earth's plasma sheet out to distances of 23 R{dollar}sb{lcub}rm E{rcub}{dollar}. After a brief description of the dissertation's goals in Chapter 1, we analyze in Chapter 2 representative cases of high speed flows in the inner central plasma sheet along with the concurrent behavior of the plasma and magnetic field. We argue that such flows are organized in 10 min time scale entities of convection enhancements that we term bursty bulk flow (BBF) events. BBFs have substructure of a 1 min time scale, referred to as "flow bursts". BBFs represent intervals of enhanced, predominantly earthward transport of mass energy and magnetic flux. In Chapter 3 we use an algorithm to automatically detect BBFs and study their statistical properties. BBFs cause the plasma sheet to be in a more dipolarized, higher temperature state for a long time after their subsidence. Despite their short duration, BBFs can account for most of the measured earthward transport of particles, energy and magnetic flux in the plasma sheet. The concept of the BBFs as a particular state of transport in the plasma sheet is applied in Chapter 4 to the study of the non-BBF, quiet state of the inner plasma sheet. We construct the average ion velocity pattern in the quiet inner plasma sheet. We show that a semi-empirical magnetic field model of the magnetotail along with the inferred cross tail electric field and the measured average density reproduce the observed velocity averages assuming that the flow is the sum of corrotation, an E {dollar}times{dollar} B flow and a model-derived diamagnetic drift. Despite the qualitative agreement of the average flow pattern with our model calculations the flow exhibits variability much larger than its average. The non-BBF flow is highly irregular and fundamentally unsteady, a reason why convection in the quiet state of the plasma sheet may be able to avoid a pressure balance inconsistency with the lobes. Chapter 5 explores whether a segregation of plasma sheet states similar to the one applied to the inner plasma sheet can also be extended to the outer plasma sheet. We present a counter-example of an inactive outer plasma sheet and argue that the plasma sheet boundary encounters took place because of fluctuations of the solar wind velocity elevation angle. We suggest that the outer plasma sheet may be active only during plasma sheet expansions. In the last chapter we organize the existing evidence for two states of transport in the plasma sheet and we make suggestions for future work. |
