Abstract
Abstract. It is known that the electric field pattern at high latitudes depends on the polarity of the Y component of the interplanetary magnetic field (IMF BY) and season. In this study, we investigate the seasonal and BY dependences in the inner magnetosphere using the perigee (4<L<10) Cluster data taken from low magnetic latitudes. The data consist of both components of the electric field perpendicular to the magnetic field, obtained by the electron drift instrument (EDI), which is based on a newly developed technique, well suited for measurement of the electric fields in the inner magnetosphere. These data are sorted by the polarities of IMF BZ and BY, and by seasons or hemispheres. It is demonstrated from our statistics that the electric fields in the inner magnetosphere depend on these quantities. The following three points are inferred: 1) The electric fields exhibit some differences statistically between Cluster locations at the Northern and Southern Hemispheres with the same dipole L and magnetic local time (MLT) values and during the same IMF conditions. These differences in the electric fields might result from hemispherical differences in magnetic field geometry and/or those in field-aligned potential difference. 2) The IMF BY and seasonal dependence of the dawnside and duskside electric fields at 4<L<10 is consistent with that seen in the polar convection cell. In addition, it is possible that these dependences are affected by the ionospheric conductivity and the field-aligned current. 3) The nightside electric field in the inner magnetosphere measured by Cluster is often similar to that in the magnetotail lobe. In the future, it will be necessary to incorporate these dependencies on IMF BY and season into a realistic model of the inner magnetospheric convection electric field. Keywords. Magnetospheric physics (Electric fields; Magnetosphere-ionosphere interactions; Solar windmagnetosphere interactions)
Highlights
The electric field induced by the interaction of the solar wind and the magnetosphere is modified by the effects of magnetosphereionosphere coupling, such as ionospheric shielding (Vasyliunas, 1970, 1972). Another reason is that the IMF BZ component is a more important parameter controlling the electric field in the inner magnetosphere than the IMF BY component and season, so that the IMF BZ component is often chosen for studies (e.g. Baumjohann and Haerendel, 1985; Goldstein et al, 2002)
The electric potential patterns are calculated for all combinations of the following three conditions: 1) IMF BZ>0,
The electric fields are obtained around perigee from 4
Summary
It is known that electric fields in the polar magnetosphere and ionosphere depend on the Y component of the interplanetary magnetic field (IMF BY ) (e.g. Cowley, 1981; Burch et al, 1985; Reiff and Burch, 1985; Heppner and Maynard, 1987; Weimer, 1995; Vaith et al, 2004), as well as the season or the tilt angle (e.g. de la Beaujardiere et al, 1991; Crooker and Rich, 1993; Weimer, 1995). One work by Baumjohann et al (1986) investigated the dependence of the strength of the inner magnetospheric electric field on IMF BY polarity by using data from a geosynchronous satellite GEOS-2 located in the Northern Hemisphere and slightly off the equator. We examine the origin of the IMF BY and seasonal dependence by referring to the size and location of the convection cell, as well as the convection in the magnetotail lobe This type of study is useful to address which parameter does/does not control the dynamics of the inner magnetosphere in terms of the electric field.
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