Abstract
Abstract. Hall current variations in different time sectors during six magnetic storms from the summer seasons in 2003 and 2005 (Ritter, 2018) are examined, namely three storms in the day–night meridional sector and three storms in the dawn–dusk sector. The sequence of the phenomena, their structure and positions, and the strength of the polar (PE) and the auroral (AE) Hall electrojets were investigated using scalar magnetic field measurements obtained from the CHAllenging Minisatellite Payload (CHAMP) satellite in accordance with the study of Ritter et al. (2004a). We analyzed the correlations of the PE and AE as well as the obtained regression relations of the magnetic latitude MLat and the electrojet current intensity I with auroral and ring current activity, the interplanetary magnetic field, and the Newell et al. (2007) coupling function for the state of the solar wind. The following typical characteristics of the electrojets were revealed: The PE appears in the daytime sector at MLat ∼80∘–73∘, with a westward or an eastward direction depending on the interplanetary magnetic field (IMF) By component (By < 0 nT or By > 0 nT). Changes in the current flow direction in the PE can occur repeatedly during the storm, but only due to changes in the IMF By orientation. The PE increases with the intensity of the IMF By component from I∼0.4 A m−1 for By∼0 nT up to I∼1.0 A m−1 for By∼23 nT. The MLat position of the PE does not depend on the direction and intensity of the By component. There is no connection between MLat and I in the PE and the symmetric part of the magnetospheric ring current (index SymH). There is a correlation between I in the PE and the AsyH index, but only a very weak interconnection of this index with the MLat of the PE. Substorms occurring before the storm's main phase are accompanied by the appearance of an eastward electrojet (EE) at MLat ∼64∘ as well as that of a westward electrojet (WE). In the nighttime sector, a WE appears at MLat ∼64∘. During the main phase both electrojets persist. The daytime EE and the nighttime WE shift toward sub-auroral latitudes of MLat ∼56∘ and grow in intensity up to I∼1.5 A m−1. The WE is then located about 6∘ closer to the pole than the EE during evening hours and about 2∘–3∘ closer during daytime hours.
Highlights
The pioneering work of Dungey (1961) about the open nature of the magnetosphere and the role of magnetic reconnection processes between the interplanetary magnetic field (IMF) and the geomagnetic main field paved the way for the understanding of the large-scale structure and dynamics of the Earth’s spatial environment
In this paper we investigated the strength and spatial– temporal distribution of Hall currents at high latitudes
The currents were determined from measurements of scalar magnetic field data, sampled on board the CHAllenging Minisatellite Payload (CHAMP) satellite at ionospheric altitudes of ∼ 430 km (Ritter et al, 2004a) during a selection of six magnetic storms
Summary
The pioneering work of Dungey (1961) about the open nature of the magnetosphere and the role of magnetic reconnection processes between the interplanetary magnetic field (IMF) and the geomagnetic main field paved the way for the understanding of the large-scale structure and dynamics of the Earth’s spatial environment. Using MAGSAT satellite data, Iijima et al (1984) showed the existence of a particular FAC system in the dayside sector of the polar cap, the so-called NBZ Birkeland currents for intervals of positive IMF Bz. From ground-based magnetometer observations, the highlatitude electrojets have already been studied prior to the space era (cf Chapman and Bartels, 1940). An intense study of the polar electrojet (PE) at the highlatitude daytime ionosphere was initiated by the works of Svalgaard (1968) and Mansurov (1969) They demonstrated that its characteristic magnetic field variation depends on the sector structure of the IMF that is much like the average magnetic field of the solar photosphere. For the determination of all indices throughout this study we used time averages of the overflight intervals
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