Abstract
Abstract. We introduce the effect of enhanced ionospheric conductivity into a low-order, physics-based nonlinear model of the nightside magnetosphere called WINDMI. The model uses solar wind and interplanetary magnetic field (IMF) parameters from the ACE satellite located at the L1 point to predict substorm growth, onset, expansion and recovery measured by the AL index roughly 50–60 min in advance. The dynamics introduced by the conductivity enhancement into the model behavior is described, and illustrated through using synthetically constructed solar wind parameters as input. We use the new model to analyze two well-documented isolated substorms: one that occurred on 31 July 1997 from Aksnes et al. (2002), and another on 13 April 2000 from Huang et al. (2004). These two substorms have a common feature in that the solar wind driver sharply decreases in the early part of the recovery phase, and that neither of them are triggered by northward turning of the IMF Bz. By controlling the model parameters such that the onset time of the substorm is closely adhered to, the westward auroral electrojet peaks during substorm expansion are qualitatively reproduced. Furthermore, the electrojet recovers more slowly with enhanced conductivity playing a role, which explains the data more accurately.
Highlights
We use the new model to analyze two well-documenteDdisiscou-ssionsnated Modeling Center for near real time forecasts of space lated substorms: one that occurred on 31 July 1997 from Ak- weather activity (Mays et al, 2009)
Geoscientificnote that a strongly fluctuating solar wind may trigger bursts in the auroral electrojet (AE) index (Pulkkinen et al, 2006), Model Developmentbut this effect is not represented in the nonlinear dynamical geomagnetic process DinistchuessionsWINDMI model
The function (u2) is in the same form as the function in Eq (3) except that in this case u2 = (K − K0)/ K, where K0 is a lower limit for the parallel kinetic energy above which the conductivity becomes enhanced at the altitude of the auroral electrojet
Summary
The plasma-physics-based WINDMI model uses the solar wind dynamo voltage Vsw generated by a particular solar wind–magnetosphere coupling function to drive eight ordinary differential equations describing the transfer of power between the major energy components of the nightside magnetosphere. The remaining terms describe the loss of energy from the magnetosphere–ionosphere system through plasma injection, ionospheric losses and ring current energy losses. The effective width of the magnetosphere is Ly, and the transition region magnetic field is given by Btr. The pressure-gradient-driven current is given by Ips = Lx(p/μ0)1/2, where Lx is the effective length of the magnetotail. Where u1 = (I − Ic)/ I in Eq (3) is specified by a critical current Ic and the interval I for the transition to loss of plasma along newly opened magnetic field lines with a parallel thermal flux q||. For northward or zero BsIMF, a nominal viscous voltage of 4 kV is used to drive the system
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