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

Poleward leaping auroras, the substorm expansive and recovery phases and the recovery of the plasma sheet

The auroral motions and geomagnetic changes the characterize the substorm's expansive phase, maximum epoch, and recovery phase are discussed in the context of their possible associations with the dropout and, especially, the recovery of the magnetotail plasma sheet. The evidence that there may be an inordinately sudden large poleward excursion or displacement (a poleward leap) of the electrojet and the auroras at the expansive phase-recovery phase transition is described. The close temporal association of these signatures with the recovery of the plasma sheet, observed on many occasions, suggests a causal relationship between substorm maximum epoch and recovery phase on the one hand and plasma sheet recovery on the other

Field-aligned currents near the magnetosphere boundary

This paper reviews present thinking about the structure of magnetospheric boundary layers and their roles in the generation of the field-aligned currents that are observed in the polar regions. A principal effect of the momentum loss by magnetosheath plasma to the magnetosphere boundary regions just within the magnetopause, whether it be by a diffusive process or by magnetic reconnection, is the tailward pulling of surface flux tubes relative to those deeper below the surface. The dayside region 1 currents at low altitudes flow along field lines in the resulting regions of magnetic shear. The direction of the shear and its magnitude, measured in the boundary region, confirm tht the polarities and intensities of the dayside region 1 currents can be accounted for by this process. The low latitude boundary layer, formerly thought to be threaded entirely by closed field lines, now appears to contain at least some open field lines, newly reconnected, that are in the process of being swept into the high latitude tail to form the plasma mantle. The open flux tubes of the flux transfer events, thought to be the product of patchy reconnection have a spiral magnetic structure whose helicity is such as to suggest currents having the polarities of the region 1 currents

Plasma sheet behavior during substorms

Auroral or magnetic substorms are periods of enhanced auroral and geomagnetic activity lasting one to a few hours that signify increased dissipation of energy from the magnetosphere to the earth. Data acquired during the past decade from satellites in the near-earth sector of the magnetotail have suggested that during a substorm part of the plasma sheet is severed from earth by magnetic reconnection, forming a plasmoid, i.e., a body of plasma and closed magnetic loops, that flows out of the tail into the solar wind, thus returning plasma and energy that have earlier been accumulated from the solar wind. Very recently this picture has been dramatically confirmed by observations, with the ISEE 3 spacecraft in the magnetotail 220 R/sub E/ from earth, of plasmoids passing that location in clear delayed response to substorms. It now appears that plasmoid release is a fundamental process whereby the magnetosphere gives up excess stored energy and plasma, much like comets are seen to do, and that the phenomena of the substorm seen at earth are a by-product of that fundamental process

Characteristics of the magnetospheric boundary layer and magnetopause layer in high time resolution

A basic problem of magnetospheric physics is to determine how and where solar wind mass, momentum and energy is transferred to the magnetosphere. IMP 6 plasma and magnetic field data indicate that the closed magnetospheric boundary layer is always present adjacent to and earthward of the magnetopause layer at all locations equatorward of the entry layer and plasma mantle. All IMP 6 crossings show some magnetosheath-like plasma earthward of the magnetopause layer and the boundary layer electron spectra are often indistinguishable from the nearby magnetosheath electron spectra. In 24 out of 40 crossings, no change in density or electron spectra is observed near the magnetopause layer. In most remaining cases, changes in the plasma parameters occur primarily in the boundary layer. Observed boundary layer bulk plasma flow always has an anti-sunward component and often has a cross-field component. Energetic electron pitch angle distributions indicate that the boundary layer is on closed field lines. During six IMP 6 crossings near local noon, equatorward of the cusp regions, boundary layer plasma flow was observed to have an anti-sunward component consistent with flow away from the subsolar region or the nearby magnetosheath. The observations are not consistent with a primary source in the cusp region or any other nonlocal source. It is concluded that the boundary layer is populated primarily by direct plasma transport through the magnetopause layer

Magnetopause layer and plasma boundary layer of the magnetosphere. [Configuration, kinetics]

Due to recent availability and analyses of high time resolution satellite data (including IMP 6 and the ISEE-1 and -2 satellite pair), the study of the magnetopause and boundary layer has entered a period of renewed activity. Plasma observations from the VELA satellites first established the presence of magnetosheath-like plasma with reduced density and flow velocity in a relatively thin (approx.<1 R/sub E/) layer bordering the plasma sheet at low latitudes and bordering the lobe environment at high latitudes. Recent analyses of HEOS 2, Explorer 33 and IMP 6 data have established the presence of this ''plasma boundary layer'' (PBL) over the entire sunward magnetosphere near the magnetopause. This review gives a brief summary of recent published results on two distinct regions of the PBL: that bordering open field line regions and that bordering closed field line regions. The magnetopause layer (i.e., current layer) can usually be identified by a change in magnetic field direction and cannot be uniquely identified by any other field or plasma parameters. Immediately earthward of this magnetopause current layer, a PBL of magnetosheath-like plasma is usually observed that has dominantly magnetosheath-like energy spectra and flow characteristics. Observed plasma boundary layer thicknesses are highly variable and are generally much larger than the magnetopause layer thicknesses even near the subsolar region. Several suggested source mechanisms for the plasma boundary layer are discussed and compared

Evaluation of some geophysical events on 22 September 1979

TIROS-N plasma data and related geophysical data measured on 22 September 1979 were analyzed to determine whether the electron precipitation event detected by TIROS-N at 00:54:49 universal time could have been related to a surface nuclear burst (SNB). The occurrence of such a burst was inferred from light signals detected by two Vela bhangmeters approx. 2 min before the TIROS-N event. The precipitation was found to be unusually large but not unique. It probably resulted from passage of TIROS-N through The precipitating electrons above a pre-existing auroral arc that may have brightened to an unusually high intensity from natural causes approx. 3 min before the Vela signals. On the othe hand, no data were found that were inconsistent with the SNB interpretation of the 22 September Vela observations. In fact, a patch of auroral light that suddenly appeared in the sky near Syowa Base, Antarctica a few seconds after the Vela event can be interpreted (though not uniquely) as a consequence of the electromagnetic pulse of an SNB