Abstract
The global dynamics of substorms are controlled by several key magnetospheric parameters. In this work we obtain quantitative measures of these parameters from a low-order nonlinear model of the nightside magnetosphere called WINDMI. The model uses solar wind and IMF measurements from the ACE spacecraft as input into a system of 8 nonlinear ordinary differential equations. The state variables of the differential equations represent the energy stored in the geomagnetic tail, central plasma sheet, ring current and field-aligned currents. The output from the model is the geomagnetic westward auroral electrojet (AL) index and the Dst index. Intermediate variables of the model are the plasma sheet pressure, geotail current, cross-tail electric field, parallel ion velocity and the pressure gradient current. The values of these variables are controlled by physical parameters of the model, consisting of spatially averaged quantities that are analogous to electric circuit elements. We tune the model to re-produce substorm events, comparing model capability against observations of auroral brightening and the auroral electrojet indices AL from WDC Kyoto and SML from SuperMAG. The model is capable of capturing events within a 10–12-min interval of occurrence, with level of activity comparable to the measured indices.
Highlights
The fundamental processes that result in triggering of a substorm have been a topic of intense debate and research over several decades
Because the model is driven by solar wind conditions measured at ACE and propagated to the nose of the earth’s magnetosphere, the model can only produce a substorm if the solar wind energy is present and sufficient for triggering to occur
The parameters do not vary over large ranges, except that the model onset times are distributed over a 10–12-min interval around the observed auroral brightening times
Summary
The fundamental processes that result in triggering of a substorm have been a topic of intense debate and research over several decades. Using these onset times as a rough guide, and combining them with AL and SML (SuperMAG lower auroral electrojet index) indices obtained from WDC Kyoto and SuperMAG, respectively, we tune the WINDMI model to produce substorms to establish bounds for the model parameters under different magnetospheric and solar wind conditions.
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