Mathematics – Logic
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsm22a..01m&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #SM22A-01
Mathematics
Logic
2407 Auroral Ionosphere (2704), 2723 Magnetic Reconnection (7526, 7835), 2740 Magnetospheric Configuration And Dynamics, 2744 Magnetotail, 2790 Substorms
Scientific paper
The concept of a magnetospheric substorm has developed over the years into a phenomenological model called the near Earth neutral line model (NENL). In this talk we review the development of this model and some of its testable predictions. The initial motivation for the NENL model was the observation that major auroral zone activity only occurs when the interplanetary magnetic field (IMF) is southward. Dungey had anticipated this possibility and suggested that reconnection between the IMF both on the dayside magnetopause and in the tail could account for auroral motions and ionospheric convection. The NENL model incorporates a sequence of physical processes through which magnetic flux from the dayside is moved to the nightside and stored in the tail lobes. A sequence of changes in configuration of the magnetopause and plasma sheet during the growth phase lead to the onset of reconnection in the plasma sheet. In the expansion phase the energy stored in the lobe magnetic field is released by reconnection heating the plasma and causing it to jet Earthward (and tailward) releasing a flux rope that is ejected from the tail. Plasma flowing Earthward piles up in the inner region and is then diverted towards the flanks. Precipitation of this heated and turbulent plasma creates an auroral disturbance that propagates poleward as the pileup moves tailward. At the same time the pressure gradients and vorticity of the plasma flow produce the substorm current wedge. The outward current in the current wedge accelerates electrons into the ionosphere generating bright discrete aurora in the westward surge. When the pileup of plasma and flux approaches the location of the neutral line the neutral line begins to move tailward. This initiates the recovery phase of the substorm with a global expansion of the plasma sheet and a broadening of the auroral oval over most of the night side. The initial cause and location of the plasma sheet instability is a subject of intense controversy. Some believe that a process other than reconnection first occurs at the inner edge of the plasma sheet and only later triggers reconnection further down the tail. The NASA Themis (Greek Goddess of Justice) mission successfully launched in February 2007 is designed to resolve this controversy. It will test the NENL concept by timing the onset of different phenomena in the tail as a function of distance. Themis is supported by the most extensive collection of ground magnetometers, all sky cameras, riometers, and radars ever deployed. This ground instrumentation will help to time and to localize the onset of various ionospheric phenomena for comparison with space observations.
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