Analysis of a major conjunction activity sequence from THEMIS observations
Abstract
We investigate in detail a sequence of magnetotail activity observed during a major conjunction interval of THEMIS satellites. During this interval, all THEMIS satellites were closely aligned along the tail axis near midnight and were bracketed in local time by GOES 11 and 12. The radial distances covered by these satellites range from the geosynchronous altitude to 30 RE in the tail. This sequence consists of three activations detected by the THEMIS satellites with good ground all-sky-camera observations of auroral activity. Analysis of this sequence suggests that the first activation is a small substorm with spatially limited disturbance in the tail and the temporal development is consistent with the inside-out scenario. The onset arc was equatorward of some undisturbed poleward arcs. The second activation is a moderate size substorm with the onset arc also being equatorward of an undisturbed poleward auroral arc that marks the poleward boundary of the auroral oval. The temporal development of this substorm activity is also consistent with the inside-out scenario. The third activation is associated with further poleward expansion of auroral activity initiated by the second activation and is interpreted as an intensification of the second activation. The temporal development of this activity is consistent with the outside-in scenario. Broadband oblique whistler waves were detected intermittently during the dipolarizations observed in these three activations. These observations suggest that (1) a small substorm may be initiated in the near-Earth region and may not involve magnetic reconnection of open magnetic field lines, and (2) a moderate size substorm may also be initiated in the near-Earth region but can proceed to involve magnetic reconnection of open magnetic field lines as a subsequent substorm intensification. The overall temporal development of the second and third activations appears to be in good agreement with the substorm synthesis model.
- Publication:
-
37th COSPAR Scientific Assembly
- Pub Date:
- 2008
- Bibcode:
- 2008cosp...37.1843L