A forecasting model of the magnetosphere driven by an optimal solar wind coupling function

2016

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.

Section: Testing the Methodsmentioning

confidence: 99%

Reconstructing the magnetosphere from data using radial basis functions

2016

“…For the sake of brevity, they will be referred to below, respectively, as Subsets 1 and 2, with the following statistical characteristics. To better visualize the coverage in the context of the magnetospheric geometry, the magnetic field lines are also plotted in the left panel, calculated on the basis of the TA15 model (Tsyganenko & Andreeva, 2015) for quiet conditions and zero dipole tilt angle. The latitude resolution of the grid was set at 6.5 • , which provided a spatial resolution at the inner and outer boundaries of the modeling region equal to 0.68 and 1.73 R E , respectively.…”

Section: Data/grid In the Global Modelmentioning

confidence: 99%

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

2020

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The spiral structure of the interplanetary magnetic field (IMF) is known to induce intramagnetospheric azimuthal magnetic field B , which strongly correlates with the IMF B . We reconstruct this effect for the first time in 3-D, using a large set of data taken in the near/inner magnetosphere and a flexible magnetic field model based on expansions in radial basis functions (RBF). The RBF model serves here as a magnifying glass with tunable resolution, focused on the specific region of interest. In this study, we used it to explore the IMF-induced B both on a global scale (i.e., for the entire range of local times) and in the night sector only, to better visualize details in the region with the strongest "penetration" magnitude. The induced B was found to maximize on the nightside at distances R ∼10-12 R E , where it concentrates around the solar-magnetic equator and bifurcates into a pair of peaks located in predawn and postdusk sectors. The B "penetration" is associated with the IMF-induced asymmetry of field-aligned currents at the plasma sheet boundary. Even on a statistical level, the peak values of the induced B can substantially exceed the external IMF B . The effect is significantly stronger under southward IMF B z conditions and grows with increasing geodipole tilt angle. Key Points: • Global/local 3-D distributions of IMF-induced B are derived in closed field line domain using a new technique and large multiyear database • The induced B maximizes near SM equator at Xsm ∼ −10 R E where it splits into a pair of duskside/dawnside peaks and can significantly exceed IMF B • The effect is associated with asymmetry of Birkeland currents and increases under southward IMF

“…Each spherical surface holds 144 nearly equidistant nodes per hemisphere, so that the average distance between neighboring nodes ranges between ∼0.7 R E at r = R 1 and ∼3 R E at r = R 9 . The deformation parameters in were set at R H =8 R E and α = 3, corresponding to their average estimates obtained in our earlier studies of the tilt‐related effects [e.g., Tsyganenko and Fairfield , ; Tsyganenko and Andreeva , , hereinafter TA15]. The radial, latitudinal, and longitudinal distributions of the RBF nodes in the untilted case ψ = 0 are also illustrated below in the top left panels of Figures and .…”

Section: Rbf Model Formulationmentioning

confidence: 99%

An empirical RBF model of the magnetosphere parameterized by interplanetary and ground‐based drivers

2016

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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.