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2019 
Empirical Modeling of the Geomagnetosphere for SIR and CMEDriven Magnetic Storms During geomagnetic disturbances, the solar wind arrives in the form of characteristic sequences lasting from tens of hours to days. The most important magnetic storm drivers are the coronal mass ejections (CMEs) and the slowfast stream interaction regions (SIRs). Previous databased magnetic field models did not distinguish between these types of the solar wind driving. In the present work we retained the basic structure of the Tsyganenko and Andreeva (2015) model but fitted it to data samples corresponding to (1) SIRdriven storms, (2) CMEdriven storms preceded with a shock ahead of the CME, and (3) CMEdriven storms without such shocks. The storm time dynamics of the model current systems has been represented using the parametrization method developed by Tsyganenko and Sitnov (2005), based on dynamical variables Wi, calculated from concurrent solar wind characteristics and their previous history. The database included observations of THEMIS, Polar, Cluster, Geotail, and Van Allen Probes missions during 155 storms in 1997\textendash2016. The model current systems drastically differ from each other with respect to decay rate and total current magnitudes. During SIRinduced storms, all current systems saturate, while during CMEinduced disturbances, the saturation occurs only for the symmetric ring current and the tail current. The partial ring current parameters are drastically different between SIR and CMEinduced storm sets. In the case of SIRdriven storms, the total partial ring current is comparable with symmetric ring current, whereas for all CMEinduced events it is nearly twice higher. The results are compared with GOES 15 magnetometer observations. Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2018JA026008 Magnetic Storms; Magnetosphere; Modeling; Solar wind; spacecraft data; Van Allen Probes 
2017 
Empirical modeling of the quiet and stormtime geosynchronous magnetic field A dynamical empirical model of the neargeosynchronous magnetic field has been constructed, based on a recently developed RBF approach and a multiyear set of spacecraft data taken by THEMIS, Polar, Cluster, and Van Allen Probes missions including 133 geomagnetic storms in the time interval between 1996 and 2016. The model describes the field as a function of Cartesian solarmagnetic coordinates, dipole tilt angle, solar wind ram pressure, and of a set of dynamic variables representing the response of the magnetosphere to the external driving/loading during the active phase of a space weather event, followed by the internal relaxation/dissipation during the storm recovery. In terms of the disturbance level, the model\textquoterights validity range extends to intense storms with peak SymH values down to 150 nT. The spatial validity domain is a toroidal volume bounded by the inner (L\~4) and outer (L\~9) dipolar Lshells, which allows the model to be used for tracing field lines to magnetically map geosynchronous spacecraft locations down to low altitudes. The model has been validated on independent outofsample magnetic field data and compared with an earlier empirical model and GOES15 data taken in 2012 and 2015. Published by: Space Weather Published on: 12/2017 YEAR: 2017 DOI: 10.1002/2017SW001684 geomagnetic field; geostationary orbit; Modeling; spacecraft data; Van Allen Probes 
2016 
Reconstructing the magnetosphere from data using radial basis functions 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 (RBF) with their nodes regularly distributed over the 3D modeling domain. The method was tested by reconstructing the inner and highlatitude field within geocentric distances up to 12RE on the basis of magnetometer data of Geotail, Polar, Cluster, THEMIS, and Van Allen space probes, taken during 1995\textendash2015. Four characteristic states of the magnetosphere before and during a disturbance have been modeled: a quiet prestorm period, storm deepening phase with progressively decreasing SymH index, the storm maximum around the negative peak of SymH, 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 largescale effect of the fieldaligned currents. For two main phase conditions, the model field exhibited a strong dawndusk asymmetry of the lowlatitude 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 databased studies of the magnetospheric currents. Andreeva, Varvara; Tsyganenko, Nikolai; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2016 YEAR: 2016 DOI: 10.1002/2015JA022242 current systems; magnetospheric modeling; polar cusps; Van Allen Probes 
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