Abstract. Based on a data pool of 79 yearly files of space magnetometer data by Polar, Cluster, Geotail, and THEMIS satellites between 1995 and 2013, we developed a new quantitative model of the global shape of the magnetospheric equatorial current sheet as a function of the Earth's dipole tilt angle, solar wind ram pressure, and interplanetary magnetic field (IMF). This work upgrades and generalizes an earlier model of Tsyganenko and Fairfield (2004) by extending the modeling region to all local times, including the dayside sector. In particular, an essential feature of the new model is the bowl-shaped tilt-related deformation of the equatorial surface of minimum magnetic field, similar to that observed at Saturn, whose existence in the Earth's magnetosphere has been demonstrated in our recent work (Tsyganenko and Andreeva, 2014).

A new empirical magnetospheric magnetic field model is described, driven by interplanetary parameters including a coupling function by Newell et al. (2007), termed henceforth as “N index.” The model uses data from Polar, Geotail, Cluster, and Time History of Events and Macroscale Interactions during Substorms satellites, obtained in 1995–2013 at distances 3–60  RE. The model magnetopause is based on Lin et al. (2010) boundary driven by the solar wind pressure, IMF Bz, and the geodipole tilt. The model field includes contributions from the symmetric ring current (SRC), partial ring current (PRC) with associated Region 2 field‐aligned currents (R2 FAC), tail, Region 1 (R1) FAC, and a penetrated IMF. Increase in the N index results in progressively larger magnitudes of all the field sources, the most dramatic and virtually linear growth being found for the PRC and R1 FAC. The solar wind dynamic pressure Pdyn affects the model magnetotail current in proportion to the factor []Pdyn/〈Pdyn〉ζ, where the exponent ζ on the order of 0.4–0.6 steadily decreases with increasing N index. The PRC peaks near midnight at N ∼ 0 but turns duskward with growing N. At ionospheric altitudes, both R1 and R2 FAC expand equatorward with growing N and Pdyn, and the R2 zone rotates westward. Larger values of N result in a more efficient penetration of the IMF into the magnetosphere and larger magnetic flux connection across the magnetopause. Growing dipole tilt is accompanied by a persistent and significant decrease of the total current in all magnetospheric field sources.

In our recent paper (Andreeva and Tsyganenko, 2016), a novel method was proposed to model the magnetosphere directly from spacecraft data, with no a priori knowledge nor ad hoc assumptions about the geometry of the magnetic field sources. The idea was to split the field into the toroidal and poloidal parts and then expand each part into a weighted sum of radial basis functions (RBF). In the present work we take the next step forward by having developed a full‐fledged model of the near magnetosphere, based on a multiyear set of space magnetometer data (1995–2015) and driven by ground‐based and interplanetary input parameters. The model consolidates the largest ever amount of data and has been found to provide the best ever merit parameters, in terms of both the overall RMS residual field and record‐high correlation coefficients between the observed and model field components. By experimenting with different combinations of input parameters and their time‐averaging intervals, we found the best so far results to be given by the ram pressure Pd, SYM‐H, and N‐index by Newell et al. (2007). In addition, the IMF By has also been included as a model driver, with a goal to more accurately represent the IMF penetration effects. The model faithfully reproduces both externally and internally induced variations in the global distribution of the geomagnetic field and electric currents. Stronger solar wind driving results in a deepening of the equatorial field depression and a dramatic increase of its dawn‐dusk asymmetry. The Earth's dipole tilt causes a consistent deformation of the magnetotail current sheet and a significant north‐south asymmetry of the polar cusp depressions on the dayside. Next steps to further develop the new approach are also discussed.

A new method is proposed to derive from data magnetospheric magnetic field configurations without any a priori assumptions on the geometry of electric currents. The approach utilizes large sets of archived satellite data and uses an advanced technique to represent the field as a sum of toroidal and poloidal parts, whose generating potentials Ψ1 and Ψ2 are expanded into series of radial basis functions (RBFs) with their nodes regularly distributed over the 3‐D modeling domain. The method was tested by reconstructing the inner and high‐latitude field within geocentric distances up to 12RE on the basis of magnetometer data of Geotail, Polar, Cluster, Time History of Events and Macroscale Interactions during Substorms, and Van Allen space probes, taken during 1995–2015. Four characteristic states of the magnetosphere before and during a disturbance have been modeled: a quiet prestorm period, storm deepening phase with progressively decreasing SYM‐H index, the storm maximum around the negative peak of SYM‐H, and the recovery phase. Fitting the RBF model to data faithfully resolved contributions to the total magnetic field from all principal sources, including the westward and eastward ring current, the tail current, diamagnetic currents associated with the polar cusps, and the large‐scale effect of the field‐aligned currents. For two main phase conditions, the model field exhibited a strong dawn‐dusk asymmetry of the low‐latitude magnetic depression, extending to low altitudes and partly spreading sunward from the terminator plane in the dusk sector. The RBF model was found to resolve even finer details, such as the bifurcation of the innermost tail current. The method can be further developed into a powerful tool for data‐based studies of the magnetospheric currents.

To study further the factors and mechanisms controlling 10-150 keV particle fluxes in the inner magnetosphere, we investigate empirically their behavior in the nightside transition region (6-14 Re) depending on solar wind parameters taken at different time lags. We aim to establish the hierarchy of predictors (V, N, Pd, Ekl = VByz sin 2 (θ/2), etc.) and the optimal range of their time delays, both depending on the distance and local time. We use THEMIS 5-min averaged observations of energetic proton and electron fluxes in 2007-2018 near the plasma sheet midplane and build regression models exploring the combination of predictors, taken at time delays up to 24 h. The model obtained shows that protons and electrons are controlled differently by solar wind parameters: electrons are influenced equally by Vsw and Ekl, whereas protons are controlled mostly by Vsw and Pd and less by Ekl. We found that a wide range of time delays is involved depending on distance and particle energy. Specifically, the Ekl affects the energetic fluxes with time delays up to 24 h (or more), exhibiting the long delays in the innermost regions. As regards the mechanism of Vsw influence, the Vsw-related flux changes are large and, to a large extent, established on the route of the energy flow from solar wind to the plasma sheet and, eventually, the inner magnetosphere. We also identified a new parameter, NBL = VByz cos 2 (θ/2), which helps to reveal the loss processes in the plasma sheet transition region.STEPANOV ET AL.