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[en] Complete text of publication follows. Based on a comprehensive catalogue with more than 4000 substorm entries from the years 2000--2005, the spatial distribution of the substorm-related magnetic signature at mid and low latitudes around local midnight is investigated. Superposed epoch analysis of a larger number of recent observatory data from mid and low latitudes revealed a field strength increase that is consistent with the results of earlier studies. For the first time, the magnetic signature of the substorm current wedge formation is studied also in near-Earth satellite data from CHAMP. The average maximal deflection measured on board the satellite is smaller by a factor of 2 than that determined from ground observations. The near-Earth and ground-based magnetic field observations cannot be described adequately by a simple current wedge model. A satisfactory agreement between model results and observations at satellite height and on ground can be achieved only if the current reconfiguration scenario combines the following four elements: (1) a gradual decrease of the tail lobe field; (2) a re-routing of a part of the cross-tail current through the ionosphere; (3) eastward ionospheric currents at low and mid latitudes driven by Region-2 field-aligned currents; and (4) a partial ring current connected to these Region-2 FACs.
[en] Complete text of publication follows. The Harang discontinuity is known as the region in the near magnetospheric tail where the earthward plasma flow is divided into the parts passing the Earth on the dawnward or duskward sides. The importance of this bifurcation point for the substorm onset has long been discussed controversially. Presently there is more and more observational evidence provided that the intense field-aligned current (FAC) associated with the substorm break-up is connected to the Harang discontinuity. Based on a catalogue of more than 4000 substorms a statistical study of the onset characteristics has been performed. For about 50 cases nearby CHAMP observations are available. They show systematically the presence of a strong upward FAC in the center flanked by weaker downward currents on the poleward and equatorward sides. In certain cases the magnetic field variations exhibit some helical signatures. We will try to explain the observations in a global picture.
[en] Complete text of publication follows. The effects of the solar wind dynamic pressure (P), the z component of the interplanetary magnetic field (Bz), the merging electric field (Em), season and the Kp index on the R1 and R2 field-aligned currents are studied statistically using magnetic field data from the CHAMP satellite during 2001-2005. The ionospheric and field-aligned currents are determined from the magnetic field data by the 1-D Spherical Elementary Current System (SECS) method. During southward IMF, increasing |Bz| is observed to clearly increase the total field-aligned current, while during northward IMF, the amount of field-aligned current remains fairly constant regardless of |Bz|. The dependence of the field-aligned current on Bz is given by |Ir[MA]| = 0.054 Bz[nT]2 - 0.34 Bz2[nT] + 2.4. With increasing P, the intensity of the field-aligned current is also found to increase according to |Ir[MA]| = 0.62 P[nPa] + 1.6, and the auroral oval is observed to move equatorward. Increasing Em produces similar behaviour, described by |Ir[MA]| = 1.41 Em[mV/m] + 1.4. While the absolute intensity of the ionospheric current is stronger during negative than during positive Bz, the relative change in the intensity of the currents produced by a more intense solar wind dynamic pressure is observed to be approximately the same regardless of the Bz direction. Increasing Kp from 0 to ≥5 widens the auroral oval and moves it equatorward from between 66deg-74deg AACGM latitude to 59deg-71deg latitude. The total field-aligned current as a function of Kp is given by |Ir[MA]| = 1.1 Kp + 0.6. In agreement with previous studies, total field-aligned current in the summer is found to be 1.4 times stronger than in the winter.
[en] Complete text of publication follows. We analyse Field-Aligned Current (FAC) measurements on board the CHAMP satellite, conducted on days 30.06-02.07.2008. In general, there are 91 crossings over polar regions (46 in the Northern hemisphere and 45 - in the Southern hemisphere). The data are gathered under quiet geomagnetic conditions (Kp < 1, Vsw < 450 km/s, and IMF Bz is within ±3.5nT). On these days most of the FAC measurements fall in the noon (MLT =10-14, Mlat = 55-85) and midnight (MLT =16-12, Mlat = 55-85) sectors. Our preliminary analysis reveals a multitude of alternating medium-scale (at least 1-2 degrees) FAC sheets of reverse sign and with increasing amplitude. Determination of FAC by single satellite measurement however is accompanied with the following uncertainties: i) underestimation of the FAC density and ii) appearance of false FAC structures. Consecutively we apply several procedures to reduce the occurrence of such errors. First, FAC structures of density less than 0.1 μmA/m2 were neglected; secondly, all FAC obtained at attack angles (the angle between the satellite trajectory and polar oval) considerably different from 90 degrees (e.g. for angle less than 65 degrees) were discarded. Despite these methodological constraints, the existence of multiple FAC close to the noon-midnight meridian under quiet geomagnetic conditions remains. The multiple FAC structure is more frequent in the night sector, with as much as 7 sheets of alternate sign for IMF Bz > 0. This issue is verified for both Northern (summer) and Southern (winter) hemispheres. The number of all FAC sheets observed in the Southern hemisphere, however, is less than in the Northern one. FAC sheets poleward of FAC Region 1 were also detected. Possible mechanisms of multiple FAC structures under quiet geomagnetic conditions are considered.