Abstract
Abstract. Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for more than seven and a half years (2001–2008) have been used to derive a statistical model of the high-latitude electric potential distribution for summer conditions. Based on potential pattern for different orientations of the interplanetary magnetic field (IMF) in the GSM y-z-plane, basic convection pattern (BCP) were derived, that represent the main characteristics of the electric potential distribution in dependence on the IMF. The BCPs comprise the IMF-independent potential distribution as well as patterns, which describe the dependence on positive and negative IMFBz and IMFBy variations. The full set of BCPs allows to describe the spatial and temporal variation of the high-latitude electric potential (ionospheric convection) for any solar wind IMF condition near the Earth's magnetopause within reasonable ranges. The comparison of the Cluster/EDI model with the IZMEM ionospheric convection model, which was derived from ground-based magnetometer observations, shows a good agreement of the basic patterns and its variation with the IMF. According to the statistical models, there is a two-cell antisunward convection within the polar cap for northward IMFBz+≤2 nT, while for increasing northward IMFBz+ there appears a region of sunward convection within the high-latitude daytime sector, which assumes the form of two additional cells with sunward convection between them for IMFBz+≈4–5 nT. This results in a four-cell convection pattern of the high-latitude convection. In dependence of the ±IMFBy contribution during sufficiently strong northward IMFBz conditions, a transformation to three-cell convection patterns takes place.
Highlights
Magnetospheric convection and its appearance as highlatitude ionospheric plasma convection depends strongly on the orientation of the Interplanetary Magnetic Field (IMF) carried by the solar wind and to a smaller extent on other solar wind parameters like solar wind speed and plasma density
A small fraction of the anti-sunward flow may occur on closed magnetic field lines due to quasi-viscous interaction between the solar wind and the magnetosphere at the magnetopause, as it was proposed by Axford and Hines (1961)
We present a model of high-latitude plasma convection based on measurements in the distant magnetosphere by use of the Electron Drift Instrument (EDI) onboard Cluster (Paschmann et al, 1997, 2001)
Summary
Magnetospheric convection and its appearance as highlatitude ionospheric plasma convection depends strongly on the orientation of the Interplanetary Magnetic Field (IMF) carried by the solar wind and to a smaller extent on other solar wind parameters like solar wind speed and plasma density. For northward IMF, Russell (1972) suggested that reconnection between the IMF and lobe field lines poleward of the cusp region can result in twin cell pattern at high latitudes in the ionosphere with sunward convection between them. This pattern is known as lobe cell convection, which circulates exclusively in the open field line region of the polar cap. The IZMIRAN Electrodynamic Model (IZMEM) describes several high-latitude electodynamic parameters like the equivalent ionospheric current, the field-aligned current system, Joule heating rates, and the ionospheric plasma convection in dependence of the solar wind parameters It is based on correlation analyses of the three-component magnetic field measurements of high-latitudes geomagnetic observatories with the observed IMF and solar wind variations. In contrast to those studies, we merge electric field measurements of the Southern and Northern Hemisphere in order to get a unified data set that represent summer season conditions of one hemisphere (North) to be compared with ground-based observations of a magnetometer network which forms the data base for the IZMEM model
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