Magnetopause structure and attitude from Explorer 12 observations

Abstract

It is shown how satellite magnetometer data at a magnetopause penetration can be used to determine the vector normal to the magnetopause current layer and the magnetic‐field component along this normal. According to theory such a component is a measure of the amount of field reconnection at magnetopause. Results from 22 Explorer 12 boundary penetrations are presented indicating normal‐field components of less than 5 γ in two‐thirds of the cases. Measured field variations within the current layer are presented to demonstrate the existence of two fundamentally different types of boundary structure, the rotational and the tangential discontinuity. The former of these permits a nonzero normal field component, whereas the latter does not. The rotational discontinuity seems to occur predominantly during magnetic storms and two of these cases, involving substantial normal‐field components, provide compelling evidence that field reconnection takes place during the storm main phase. Finally, the calculated normal vector is compared with the normal to the surface of the Mead‐Beard magnetosphere model.

Phase‐steepened Alfvén waves, proton perpendicular energization and the creation of magnetic holes and magnetic decreases: The ponderomotive force

“…From the minimum variance analyses [Sonnerup and Cahill, 1967] taken for data between the dashed vertical lines, the wave is found to be circularly/ elliptically polarized (l 1 /l 2 > 3.2), is planar (l 2 /l 3 = 4.6), and is propagating at a highly oblique angle ($80°) relative to the ambient magnetic field.…”

“…Two instabilities which can be generated by such T ? /T k anisotropies are: the mirror instability [Southwood and Kivelson, 1993] and the proton cyclotron (loss-cone) instability [Anderson, 1995]. MDs.…”

Error estimates for minimum variance analysis

“…In its initial form, described by Sonnerup and Cahill [1967], the MVA was applied for the purpose of inferring, from spacecraft magnetic field measurements, the orientation of current layers and wave fronts in magnetized plasmas. With some modifications, the MVA (in this context understood as minimum/maximum variance analysis) has also been employed to analyze electric field and mass-flux data series [Sonnerup et al, 1987[Sonnerup et al, , 1990.…”

Energetic electrons associated with magnetic reconnection in the sheath of interplanetary coronal mass ejection

“…We firstly calculate the normal direction of the current sheet (i.e. the N component) through minimum variance analysis of the magnetic field [22]. We then employ the relation M = N × (B A  B B )/|B A  B B |, where B A and B B are the tangential magnetic field vectors on the two sides of the current sheet [8], to gain the X axis orientation.…”