Comparative studies of multi-scale convective transport through the Earth's plasma sheet

In this dissertation we explore multi-scale, convective transport through the Earth's plasma sheet using in situ observations and global terrestrial magnetospheric simulations. We statistically test the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model with observations from the Geotail spacecraft at a variety of spatial and temporal scales within the plasma sheet. These comparisons, in addition to quantifying the LFM range of validity, illuminate model shortcomings and highlight the additional physics necessary to resolve data/model discrepancies. First, we perform the first ever comprehensive validation of the LFM in the plasma sheet. We show that the LFM largely reproduces global, long-term average plasma sheet properties and variability, but we also identify and characterize its systematic deficiencies. We find that the LFM overestimates the average plasma sheet velocity, and show that a portion of this overestimate is reflected in excessive LFM ionospheric transpolar potential (15%), and a portion of it is due to insufficient simulation resolution (15%). By characterizing the LFM plasma sheet velocity distribution as a function of simulation resolution, we find that increased resolution inherently changes the nature of the dynamics and transport within the LFM plasma sheet, bringing it into closer agreement with magnetotail observations containing fast, localized bulk flows. To perform the data/model comparisons described thus far, we construct one of the largest central plasma sheet data set of Geotail observations to date. Using this comprehensive data set, we investigate the equatorial distributions of fast, convective flows and infer that the Earthward extent of the average neutral line, the most likely location of near-Earth reconnection, is convex relative to the Earth and offset toward dusk. Due to the importance of these fast flows to mass, momentum, and energy transport in both the observed and simulated plasma sheets, we use the LFM to establish that locally-reconnecting magnetic lobe field lines initiate simulated "flow channels", explore the instability governing their subsequent evolution, and examine their similarity to observations of bursty bulk flows. This dissertation demonstrates the fruitful augmentation of sparse, statistical plasma sheet data sets with global MHD models, thereby enabling further exploration of the multi-scale nature of convective transport within the global, time-dependent plasma sheet.