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Annales Geophysicae Sun, Earth, planets, and planetary systems An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/angeo-2018-31
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Regular paper
25 Apr 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).
Dynamics of the electrojet during intense magnetic disturbances
Liudmila I. Gromova1, Matthias Förster2,3, Iakov I. Feldstein1, and Patricia Ritter2 1Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation of the Russian Academy of Sciences (IZMIRAN), 142090 Troitsk, Moscow region, Russia
2Helmholtz-Centre Potsdam, GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany
3Max-Planck-Institut für Sonnensystemforschung, 37077 Göttingen, Germany
Abstract. Hall current variations in different time sectors during six magnetic storms of the summer seasons in 2003 and 2005 are examined in detail: three storms in the day-night meridional sector and three storms in the dawn-dusk sector. We investigate the sequence of the phenomena, their structure, positions and the density of the polar (PE) and the auroral (AE) Hall electrojets using scalar magnetic field measurements obtained from the CHAMP satellite in accordance with the study of Ritter et al. (2004a). Particular attention is devoted to the spatial-temporal behaviour of the PE at ionospheric altitudes during daytime hours both under geomagnetically quiet and under magnetic storm conditions. We analyze the correlations of the PE and AE with various activity indices like SYM/H and ASYM/H, that stand for large-scale current systems in the magnetosphere, AL for ionospheric currents, and the IndN coupling function for the state of the solar wind. We obtain regression relations of the magnetic latitude MLat and the electrojet current density I with those indices and with the interplanetary By and Bz magnetic field components. For the geomagnetic storms during summer seasons investigated here, we obtain the following typical characteristics for the electrojets' dynamics:

1. The PE appears at magnetic latitudes (MLat) and local times (MLT) of the cusp position.
2. This occurs in the day-time sector at MLat ∼ 73°–80° with a westward or an eastward direction, depending on the orientation of the IMF By component. Changes of current flow direction in the PE can occur repeatedly during the storm, but only due to changes of the IMF By orientation.
3. The current density in the PE increases with the intensity of the IMF By component from I ∼ 0.4 A/m for By ∼ 0 nT up to I ∼ 1.0 A/m for By ∼ 23 nT.
4. The MLat position of the PE does not depend on the orientation and the strength of the IMF By component. It depends, however, on the strength of the IMF Bz component.
5. The PE is situated at MLat ∼ 73° on the dayside during geomagnetically quiet periods and the recovery phase of a magnetic storm, and it shifts equatorward during intense substorms and the main phase of a storm.
6. There is no connection between MLat and the current density I in the PE with the magnetospheric ring current DR (index SYM/H).
7. There is a correlation between the current density I in the PE and the partial ring current in the magnetosphere (PRC, index ASYM/H), but practically no correlation of this index with MLat of the PE.
8. Substorms that occur before and during the beginning of a storm main phase are accompanied in the daytime by the appearance of an eastward electrojet (EE) at MLat ∼ 64° and then also by a westward electrojet (WE). In the nighttime sector the WE appears at MLat ∼ 64°.
9. During the development of the main storm phase, the daytime EE and the nighttime WE shift toward subauroral latitudes of MLat ∼ 56° and intensify up to I ∼ 1.5 A/m. Both electrojets persist during the main phase of the storm. The WE is then located about 6° closer to the pole than the EE during evening hours and about 2°–3° during daytime hours.

Citation: Gromova, L. I., Förster, M., Feldstein, I. I., and Ritter, P.: Dynamics of the electrojet during intense magnetic disturbances, Ann. Geophys. Discuss., https://doi.org/10.5194/angeo-2018-31, in review, 2018.
Liudmila I. Gromova et al.
Liudmila I. Gromova et al.
Liudmila I. Gromova et al.

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