Abstract
A multidimensional superposed epoch analysis of plasma and magnetic field data from the Geotail spacecraft was used to visualize the time evolution of plasmoids in the Earth's magnetotail statistically. The substorm events were identified by Pi2 events at midlatitude ground stations when Geotail was in the downtail region from −30 RE to −200 RE. Plasma density, velocity, temperature, and magnetic field data were sorted and analyzed according to the Pi2 onset time. We selected 156 substorm events that were either a single onset or the first onset of multiple onsets. In the statistical visualization, we found that plasma acceleration does not take place in a small region around X ∼ −30 RE, but occurs in a more widely spread region extending from X ∼ −30 RE down to X ∼ −90 RE. The spatial structure of the plasmoid is characterized by a bilatitudinal structure where the fast plasma flow in the plasma sheet boundary stretches from the equator and a relatively slow plasma sheet flow is encountered with preexisting plasma sheet populations. Finite By fields are created in the inner plasma sheet boundary, and the total pressure is enhanced inside the plasmoid. The evolution of the plasma and magnetic fields as well as the deduced parameters, such as the number flux of plasma or energy fluxes, agreed well with a magnetic reconnection model.
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