Comparison of the observed dependence of large-scale Birkeland currents on solar wind parameters with that obtained from global simulations

Abstract

Spatial distributions of the large-scale Birkeland currents derived from magnetic field data acquired by the constellation of Iridium Communications satellites have been compared with global-magnetosphere magneto-hydrodynamic (MHD) simulations. The Iridium data, spanning the interval from February 1999 to December 2007, were first sorted into 45°-wide bins of the interplanetary magnetic field (IMF) clock angle, and the dependencies of the Birkeland currents on solar wind electric field magnitude, <I>E</I><sub>yz</sub>, ram pressure, <I>p</I><sub>sw</sub>, and Alfvén Mach number, <I>M</I><sub>A</sub>, were then examined within each bin. The simulations have been conducted at the publicly-accessible Community Coordinated Modeling Center using the University of Michigan Space Weather modeling Framework, which features a global magnetosphere model coupled to the Rice Convection Model. In excess of 120 simulations with steady-state conditions were executed to yield the dependencies of the Birkeland currents on the solar wind and IMF parameters of the coupled model. Averaged over all IMF orientations, the simulation reproduces the Iridium statistical Birkeland current distributions with a two-dimensional correlation coefficient of about 0.8, and the total current agrees with the climatology averages to within 10%. The total current for individual events regularly exceeds those computed from statistical distributions by factors of ≥2, resulting in larger disparities between observations and simulations. The simulation results also qualitatively reflect the observed increases in total current with increasing <I>E</I><sub>yz</sub> and <I>p</I><sub>sw</sub>, but the model underestimates the rate of increase by up to 50%. The equatorward expansion and shift of the large-scale currents toward noon observed for increasing <I>E</I><sub>yz</sub> are also evident in the simulation current patterns. Consistent with the observations, the simulation does not show a significant dependence of the total current on <I>M</I><sub>A</sub>

Magnetospheric “Penetration” of IMF Viewed Through the Lens of an Empirical RBF Modeling

“…This is a well-known effect due to the latitudinal splitting and longitudinal overlapping of Region 1 field-aligned currents, observed both in the AMPERE data and in the MHD simulations (Korth et al, 2011), and also reproduced in a recent empirical modeling study . In the case of southward IMF B z (right panel), the induced model B actually rises to ∼10 nT at X = 6 and Z = 10, that is, twice the IMF B = 5 nT (the color scale saturates at 5 nT and cannot reproduce larger values).…”

Global MHD modeling of ionospheric convection and field‐aligned currents associated with IMF By triggered theta auroras

“…As we see below in Figures d and d, during B y > 0 periods, the Northern Hemisphere pattern and the Southern Hemisphere pattern switch. Real existence of such IMF B y control is not clear from the available observations [e.g., Green et al ., ; Korth et al ., ]. Our MHD model cannot reproduce realistic region 2 FACs, because MHD approximation does not necessarily hold in the inner magnetosphere.…”

Exploring predictive performance: A reanalysis of the geospace model transition challenge

“…This is especially applicable in the tail, where explosive reconnection is a requirement for capturing realistic substorm dynamics which contribute strongly to nightside d B /d t . This is less of a concern on the dayside, as MHD models have shown the ability to successfully mimic Petscheck reconnection rates [ Ouellette et al , , ] and reproduce the immediate ionospheric consequences of dayside reconnection: cross polar cap potential dynamics and region 1 field‐aligned current patterns [ Ridley et al , , Korth et al , , ]. The MHD models have many settings and parameters that affect the results [e.g., Ridley et al , ], including grid resolution.…”