Magnetosphere Sawtooth Oscillations Induced by Ionospheric Outflow

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Science  03 Jun 2011:
Vol. 332, Issue 6034, pp. 1183-1186
DOI: 10.1126/science.1202869

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The sawtooth mode of convection of Earth’s magnetosphere is a 2- to 4-hour planetary-scale oscillation powered by the solar wind–magnetosphere–ionosphere (SW-M-I) interaction. Using global simulations of geospace, we have shown that ionospheric O+ outflows can generate sawtooth oscillations. As the outflowing ions fill the inner magnetosphere, their pressure distends the nightside magnetic field. When the outflow fluence exceeds a threshold, magnetic field tension cannot confine the accumulating fluid; an O+-rich plasmoid is ejected, and the field dipolarizes. Below the threshold, the magnetosphere undergoes quasi-steady convection. Repetition and the sawtooth period are controlled by the strength of the SW-M-I interaction, which regulates the outflow fluence.

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