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Global Density Structures and Reactive Feedback

Global GPS maps of ionospheric density showed, for the first time, large-scale dense plumes of plasma extending from middle latitudes to the auroral zone at the onset of magnetic storms (see Figure 3.3). During such events, plasmaspheric imaging of He+ ions by IMAGE showed corresponding structures in the inner magnetosphere, where plasma was sheared away from the plasmasphere and advected toward the magnetopause (see Figure 2.5).

The plasmaspheric structure was never expected to appear in the ionosphere, and the discovery points to a process critical to enhancing auroral ion outflow during storms. Localized structures in the neutral density were discovered by international geodesy programs. The CHAMP and NASA/German Gravity Recovery and Climate Experiment (GRACE) missions led to the discovery of localized neutral upwelling very near the poles associated with strong Joule heating that occurs during geomagnetically calm or moderate conditions.

This result demonstrated the surprising range of conditions wherein neutral densities are sufficiently altered to modify the decay rates of satellites in low Earth orbit. Understanding of the generation of these localized densities is not yet mature enough to predict their occurrence. Recent results from NASA’s FAST and IMAGE satellites revealed intense outflows of ionospheric ions during storms.

The solar wind-magnetosphere interaction on the dayside, that is, magnetopause reconnection, is a copious source of electromagnetic energy that propagates along the magnetic field into the ionosphere at high latitudes near noon. This energy is converted to heat and momentum through ion-neutral interactions and promotes resonant heating of O+ that drives outflows.

The O+ flows upward and is carried into the magnetotail by the reconnection-convection cycle. The resultant large O+ densities in the tail plasma sheet appear to change reconnection dynamics in the tail, leading to the ~3-hour planetary-scale (sawtooth) oscillations or quasi-periodic substorms in the magnetosphere.

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The influence of the O+ outflow on global dynamics is only one of a number of instances in which nonlinear reactive feedback leads to nonlinear dynamics.

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