IMF <i>B<sub>Y</sub></i> and the seasonal dependences of the electric field in the inner magnetosphere

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 B Y ) and season. In this study, we investigate the seasonal and B Y 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 B Z and B Y , 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 B Y 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 B Y and season into a realistic model of the inner magnetospheric convection electric field.

Derivation of inner magnetospheric electric field (UNH-IMEF) model using Cluster data set

“…The first choice is for instantaneous reaction. The second one is intermediate and also used in our previous studies (Matsui et al, 2003(Matsui et al, , 2004(Matsui et al, , 2005. The third one is the same time resolution as the K p index, which is known as a good organizing parameter of the inner magnetospheric electric field (Thomsen, 2004).…”

“…We have previously investigated statistical electric field patterns in the inner magnetosphere (Matsui et al, 2003(Matsui et al, , 2004(Matsui et al, , 2005 by using electric field data measured by the Electron Drift Instrument (EDI) on Cluster (Paschmann et al, 2001). We inferred that the inner magnetospheric electric field depends on interplanetary parameters.…”

Plasma convection in the magnetotail lobes: statistical results from Cluster EDI measurements

“…Cowley et al, 1991). This B y influence is also reflected in the convection in the lobes (Gosling et al, 1984(Gosling et al, , 1985Noda et al, 2003), the ecliptic plane Baumjohann et al, , 1986Maynard et al, 1990;Matsui et al, 2005), and in the polar cap ionosphere (Ruohoniemi and Baker, 1998;Haaland et al, 2007). In the case of northward IMF, reconnection can take place between the IMF and already open polar cap field lines at high latitudes.…”

Plasma transport in the magnetotail lobes

“…In the Northern Hemisphere a positive (negative) B y will cause a displacement of the reconnection region so that the newly opened flux tubes are transported towards dawn (dusk), and oppositely for the Southern Hemisphere (e.g., Cowley et al, 1991). This B y influence is also reflected in the convection in the lobes (Gosling et al, 1984(Gosling et al, , 1985Noda et al, 2003;Haaland et al, 2008), the ecliptic plane Baumjohann et al, , 1986Maynard et al, 1990;Matsui et al, 2005), and in the polar cap ionosphere (Ruohoniemi and Baker, 1998;Förster et al, 2007;Haaland et al, 2007). In the Published by Copernicus Publications on behalf of the European Geosciences Union.…”