Multiple-satellite studies of magnetospheric substorms: Plasma sheet recovery and the poleward leap of auroral-zone activity

Particle observations from pairs of satellites (Ogo 5, Vela 4A and 5B, Imp 3) during the recovery of plasma sheet thickness late in substorms were examined. Six of the nine events occurred within about 5 min in locations near the estimated position of the neutral sheet, but over wide ranges of east-west and radial separations. The time of occurrence and spatial extent of the recovery were related to the onset (defined by ground Pi 2 pulsations) and approximate location (estimated from ground mid-latitude magnetic signatures) of substorm expansions. It was found that the plasma sheet recovery occurred 10 - 30 min after the last in a series of Pi bursts, which were interpreted to indicate that the recovery was not due directly to a late, high latitude substorm expansion. The recovery was also observed to occur after the substorm current wedge had moved into the evening sector and to extend far to the east of the center of the last preceding substorm expansion

The theory of pulsar winds and nebulae

We review current theoretical ideas on pulsar winds and their surrounding nebulae. Relativistic MHD models of the wind of the aligned rotator, and of the striped wind, together with models of magnetic dissipation are discussed. It is shown that the observational signature of this dissipation is likely to be point-like, rather than extended, and that pulsed emission may be produced. The possible pulse shapes and polarisation properties are described. Particle acceleration at the termination shock of the wind is discussed, and it is argued that two distinct mechanisms must be operating, with the first-order Fermi mechanism producing the high-energy electrons (above 1 TeV) and either magnetic annihilation or resonant absorption of ion cyclotron waves responsible for the 100 MeV to 1 TeV electrons. Finally, MHD models of the morphology of the nebula are discussed and compared with observation.Comment: 33 pages, to appear in Springer Lecture Notes on "Neutron stars and pulsars, 40 years after the discovery", ed W.Becke

The Scientific Foundations of Forecasting Magnetospheric Space Weather

The magnetosphere is the lens through which solar space weather phenomena are focused and directed towards the Earth. In particular, the non-linear interaction of the solar wind with the Earth's magnetic field leads to the formation of highly inhomogenous electrical currents in the ionosphere which can ultimately result in damage to and problems with the operation of power distribution networks. Since electric power is the fundamental cornerstone of modern life, the interruption of power is the primary pathway by which space weather has impact on human activity and technology. Consequently, in the context of space weather, it is the ability to predict geomagnetic activity that is of key importance. This is usually stated in terms of geomagnetic storms, but we argue that in fact it is the substorm phenomenon which contains the crucial physics, and therefore prediction of substorm occurrence, severity and duration, either within the context of a longer-lasting geomagnetic storm, but potentially also as an isolated event, is of critical importance. Here we review the physics of the magnetosphere in the frame of space weather forecasting, focusing on recent results, current understanding, and an assessment of probable future developments.Peer reviewe

The Earth: Plasma Sources, Losses, and Transport Processes

This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed

Magnetospheric and auroral activity during the April 18, 2002 sawtooth event.

We examine the 18 April 2002 sawtooth event. We find that the strong magnetic field dipolarizations observed in association with each tooth are not global in occurrence but are rather confined to the nightside. In addition, we find that the flux increases are not globally dispersionless. Instead, each tooth is associated with a nonglobal, but wider-than-usual, dispersionless injection region that is consistent with the high Kp versions of the standard injection boundary model (which places the entire nightside segment of geosynchronous orbit tailward of the injection boundary for values of Kp above about 5). We also find evidence that at least one of the teeth was likely triggered by a pressure pulse. The auroral distribution shows a repeatable evolution in which a wide double-oval configuration gradually thins. Following this, a localized substorm-like brightening in the dusk to midnight sector occurs on the lower branch of the double oval which subsequently expands rapidly poleward and azimuthally. A new expanded double oval configuration emerges from this expansion phase activity and the cycle repeats itself for the duration of the sawtooth event. The observations presented give considerable support to the contention that sawtooth events are actually sequences of quasi-periodic substorms. We suggest that sawtooth events can be viewed as a magnetospheric mode similar to Steady Magnetospheric Convection intervals (SMCs) except that for sawtooth events, the flow of energy from the solar wind into the magnetosphere becomes too large to dissipate without the periodic occurrence of substorms. We further suggest that the quasi-periodicity arises because the magnetosphere may only become susceptible to external or internal triggering after it has been driven beyond a stability threshold. This hypothesis can account for the existence of more potential external triggers (in the interplanetary magnetic field or solar wind) than teeth in that the magnetosphere may be selectively responsive to them