Magnetic effects of the substorm current wedge in a “spread-out wire” model and their comparison with ground, geosynchronous, and tail lobe data

Abstract

[1] Although the substorm current wedge (SCW) is recognized as a basic 3-D current system of the substorm expansion phase, its existing models still do not extend beyond a cartoon-like sketch, and very little is known of how well they reproduce magnetic variations observed in the magnetosphere during substorms. A lack of a realistic quantitative SCW model hampers testing model predictions against large sets of spacecraft data. This paper (1) presents a computationally efficient and flexible model with a realistic geometry of field-aligned currents, conveniently parameterized by the SCW strength, longitudinal width, and position, all derived from ground-based midlatitude magnetic variations; and (2) tests the model against INTERMAGNET network observations during substorms and compares its predictions with space magnetometer data. The testing demonstrated significant and systematic discrepancies between the observed and predicted magnetic variations, depending on spacecraft location, concurrent magnetotail configuration, and substorm phase. In particular, we found that the net SCW current derived from the midlatitude field variations corresponds to only a relatively small and variable fraction of the distant 3-D substorm current, inferred from spacecraft data in the lobe and at geosynchronous distance. The discrepancy can be partly attributed to additional region 2 polarity field-aligned currents in the same longitudinal sector, associated with azimuthal diversion of the earthward plasma flow when it encounters the region of strong quasi-dipolar field in the inner magnetosphere.

Data-based modelling of the Earth's dynamic magnetosphere: a review

“…A separate interesting and yet largely untapped area is empirical data-based modelling of substorm reconfigurations of the magnetosphere, including the dynamics of the substorm current wedge. First advances in this field have already been made (Sergeev et al, 2011(Sergeev et al, , 2013.…”

“…5. We used that method in constructing a numerical model of the substorm current wedge (Sergeev et al, 2011). A similar approach was developed independently by Ontiveros et al (2006) in their model of the R2 FACs and the magnetopause currents.…”

“…Moreover, since the critical value of γ in Eq. (37) is energy-dependent and the latitudinal positions of IBs are routinely observed on each spacecraft pass in a wide range of energies, it becomes in principle possible to adjust standard field models so that they more accurately reproduce the actual field configuration in specific events (Sergeev et al, 1993;Sergeev and Gvozdevsky, 1995). Combining the low-altitude IB observations with simultaneous data from several equatorial satellites and properly adapted magnetic field models can further improve the mapping accuracy and reveal interesting features of the magnetospheric dynamics during disturbances (e.g., Kubyshkina et al, 2009;Shevchenko et al, 2010).…”

Aspects of magnetosphere–ionosphere coupling in sawtooth substorms: a case study

“…A central feature of this sector is the boundary between the EEJ and WEJ in the evening to premidnight sector -also delimiting the southern and northern branches of the aurora, marked by a dashed curved line -is the Harang reversal boundary (HRB). The northern auroral branch in this sector (HR-N) is characterized by equatorward-moving auroral forms (streamers) which are coupled to earthwardmoving plasma-depleted flux tubes (Chen and Wolf, 1993) and associated bursty bulk flows (BBFs) in the PS (Sergeev et al, 2004(Sergeev et al, , 2012Sandholt et al, 2014). During "classical" substorms the HR is typically found in the 19:00-24:00 MLT sector (Nielsen and Greenwald, 1979).…”

“…At present there are still unresolved questions on the temporal evolution of these M-I coupling processes taking place during substorms (see e.g. Sergeev et al, 2012;Sauvaud et al, 2012;Akasofu, 2013).…”