Satellite Magnetometer Data Research Articles

Energetic electrons at 6.6REduring the January 13-14, 1967, geomagnetic storm

The trapped, energetic (Eϵ > 0.4 Mev to > 3.0 Mev) electron fluxes at synchronous altitude are examined during the January 13–14, 1967, geomagnetic storm. Except for a short period after the sudden commencement (sc) at 1202 UT, day 13 (0202 local time), the measured electrons were observed to be stably trapped for about the first twelve hours after the sc. However, the values of the electron fluxes in the local morning and at local noon were quite different than those generally observed during quiet periods. About two hours after local noon, at 2324 UT, day 13, the electron flux dropped sharply by two orders of magnitude in response to a sudden decrease in the magnetic field observed at the satellite. Recovery of the electron flux occurred in a few minutes. About 40 minutes later, 0007 UT, day 14, the electron fluxes were essentially wiped out at the time of an observed reversal in the magnetic field at the satellite. During two separate approximately 10-minute periods after this 0007 UT, day 14, wipeout, the observed particle fluxes indicate that the satellite encountered a region of space with characteristics very different from the normal magnetospheric trapping region. The data during these times are consistent with the interpretation from the magnetic field observations that the satellite was outside the magnetopause. Correlation of the electron data during the storm is made with the satellite magnetometer data and with the magnetometer data from several ground stations.

Magnetopause structure and attitude from Explorer 12 observations

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.