Abstract
We use IMAGE‐FUV observations of the polar aurora and measurements of the ionospheric convection from the SuperDARN radar network to study several sawtooth events previously reported in the literature. We estimate the amount of open magnetic flux in the Earth magnetosphere during a significant part of these sawtooth intervals as well as the magnetic flux opening and closure rates, that is, the dayside and nightside reconnection rates. We find that during the sawtooth intervals the magnetosphere is highly loaded with open flux as a result of the strongly southward IMF carried by the solar wind during these intervals. The magnetosphere tries to relax to a less loaded configuration through a sequence of substorm expansions. However, these substorms do not necessarily evolve to their end before reintensification of nightside reconnection occurs in response to continued loading of the magnetosphere on the dayside.
Highlights
[1] We use IMAGE-FUV observations of the polar aurora and measurements of the ionospheric convection from the SuperDARN radar network to study several sawtooth events previously reported in the literature
[12] The general picture that emerges from the case studies presented here is that a sawtooth event is a sequence of substorms taking place during an interval of strongly southward IMF that loads the magnetosphere with open flux, and keeps the amount of open flux at a high level despite the closure in the tail
As reported by Henderson et al [2006], the closure process can be triggered by a solar wind shock, because an increase of the solar wind dynamic pressure favours the formation of an X line in the plasma sheet, but it is not a necessary condition
Summary
[2] A sawtooth event is a prolonged interval during which quasiperiodic large intensifications of the particle fluxes occur at geosynchronous altitude [Belian et al, 1995; Henderson et al, 2006]. The shape of the proton flux vs time curve during these intervals exhibits quasi-periodic rapid increases followed by slow decreases, resembling the teeth of a saw blade [Henderson et al, 2006]. Substorms evolve on timescales of about three hours [Akasofu, 1964; McPherron, 1970], and consist essentially in a cycle of open flux production on the dayside and transport to the nightside where it is eventually closed This process is primarily responsible for convection in the Earth’s magnetosphereionosphere system [Dungey, 1961; Cowley and Lockwood, 1992]. [3] We have developed a method that combines ground based measurements of the ionospheric convection from the Super Dual Aurora Radar Network (SuperDARN) and images of the proton aurora from the Spectrographic Imager
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