Multiple Flux Rope Events at the High‐Latitude Magnetopause: Cluster/Rapid Observation on January 26, 2001

Abstract

AbstractFrom 11:10 to 11:40UT on January 26, 2001 the four Cluster II spacecraft were located in the duskside high latitude regions of the magnetosheath and magnetosheath boundary layer (MSBL). During this time Interval the interplanetary magnetic field (IMF) had a negative Bz component. A detailed study on the multiple flux ropes (MFRs) observed in this period is conducted in this paper. It is found that: (1) The multiple flux ropes in the high latitude MSBL appeared quasi‐periodically with a repeated time period of about 78s, which is much shorter than the averaged occurring period (about 8–11min) of the flux transfer events (FTEs) at the dayside magnetopause (MP). (2) All the flux ropes observed in this event had a strong core magnetic field. The axial orientation of the most flux ropes is found to lie in the direction of the minimum magnetic field variance; a few flux ropes had their axes lying in the direction of the middle magnetic field variance; while for the remainders their principle axes could not be determined by the method of Principal Axis Analysis (PAA). The reason that causes this complexity relys on the different trajectories of the spacecraft passing through the flux ropes. (3) Each flux rope had a good corresponding HT frame of reference in which it was in a quasi‐steady state. All flux ropes moved along the surface of the MP in a similar direction indicating that these flux ropes all came from the dawnside low latitude. Their radial scale is 1– 2RE, comparable to the normal diameter of FTEs observed atthe dayside MP. (4) The energetic ions originated from the magnetosphere flowed out to the magnetosheath on the whole, while the solar wind plasma flowed into the magnetosphere along the axis of the flux ropes. The flux ropes offered channels for the transport of the solar wind plasma into the magnetosphere and the escaping of the magnetospheric plasma into the interplanetary space. (5) Each event was accompanied by an enhanced reversal of the dusk‐dawn electric field, which could be identified to be the convective electric field in nature.