A study of orientation and motion of flux transfer events observed at the high-latitude dayside magnetopause
高纬向阳侧磁层顶通量传输事件的特性研究——通量管轴线方位及运动分析

We investigate 13 FTEs,which were detected by the Cluster II in the magnetosheath near the cusp region during February to March 2001.The orientation of the FTE tube axis is derived by virtue of minimum variance analysis(MVA) using magnetic field data from the four Cluster spacecraft.Of 13 events,6 axis directions are determined reliably,most of them are closer to the L axis than to the M axis in the boundary normal coordinate system LMN.This implies that there are some differences between them and those events observed at the low-latitude magnetopause,whose axes tend to lie in east-west directions.The deHoffmann-Teller(HT) frame for 13 events are also obtained,and there are good HT frames for all FTEs.The correlation coefficients between the convection electric field and the HT electric field are larger than 0.96 except two of them are about 0.9. This means that the event passes the spacecraft as a moving quasi-static structure at V-(HT)(velocity of the HT frame).The FTE moving in the direction perpendicular to its axis is not convected with the ambient magnetosheath plasma,and the velocity of FTE tube may be slower or faster than the ambient plasma.The motion direction of FTE tube is about the same as the ambient plasma,but there may be a small angle between them.The plasma velocity in the HT frame approximates to zero for ten FTEs,and is only about 14% of the local Alfven speed for the others,which are all not satisfied with the Walen relation.The slope of the Walen plot is positive in the northern hemisphere and negative in the southern hemisphere.This implies that the plasma flows along the magnetic field into the magnetosphere(parallel magnetic field in the northern hemisphere and anti-parallel magnetic field in the southern hemisphere).