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A major question in solar–terrestrial physics concerns the nature of the interaction between the solar wind and the Earth's magnetosphere and ionosphere, and how this depends on the direction of the interplanetary magnetic field (IMF). We report here simultaneous observations of the IMF by the AMPTE–UKS (Active Magnetospheric Particle Tracer Explorers–UK Satellite), and of plasma flow in the high-latitude ionosphere by the EISCAT radar with better time resolution than has been achieved hitherto. We discuss one event in which a sharp southwards turning of the IMF is followed by the onset of rapid ionospheric plasma flow near local noon, demonstrating the close control of ionospheric flows by the IMF. We discuss the causes of the observed 13-min delay, and study the ionospheric heating that accompanies the acceleration.

The physical processes which give rise to convection in the earth's magnetosphere have been the subject of active debate for many years. Most of the discussion has centered on two basic pictures, one in which closed magnetospheric flux tubes are transported from dayside to nightside in a boundary layer around the flanks of the magnetosphere by a ‘viscouslike’ process occurring at the magnetopause and the other in which open flux tubes are transported over the poles of the earth after reconnection has taken place with the interplanetary magnetic field. These processes may coexist on a continuous basis, and the question then arises as to their relative contributions to usual total cross-magnetospheric voltages of ∼40–100 kV. The first detailed observations of plasmas and fields in the vicinity of the dayside magnetopause have recently been made during the International Magnetospheric Study by the ISEE 1 and 2 spacecraft and are discussed in this paper in relation to this question. Observations which relate to the occurrence of ‘quasi-steady’ as well as impulsive flux transfer event (FTE) reconnection are reviewed in detail in the paper, together with measurements of the properties of the boundary layer on the magnetospheric flanks. Particular emphasis is given to the interpretation of these data in terms of the physical processes occurring. It is argued that the ISEE observations of quasi-steady reconnection are indeed compatible with the process playing a major role in magnetospheric dynamics. The observed frequency of these events at the magnetopause indicates that they are associated either with infrequent intervals of intense magnetospheric convection or with more frequent contributions of lesser intensity (i.e., ∼40 kV whenever IMF Bz is negative). The latter seems the more likely situation at the present time. In addition, a rough estimate of ∼20 kV is made for the contribution due to FTE's, this figure having the nature of a lower limit. It is therefore argued that the in situ ISEE observations pertaining to reconnection processes are consistent with the view that these provide a major contribution to magnetospheric flows. A preliminary picture is suggested from our inferences based on ISEE data in which quasi-steady subsolar reconnection occurs essentially continuously in a band ∼2 hours LT wide when IMF Bz ≤ 0, centered often near the noon meridian, while at other local times, reconnection also occurs but in an unsteady, sporadic manner. Examination of the unsteady flows observed in the boundary layers on the flanks of the magnetosphere yields voltages of typically ∼5–20 kV for dusk and dawn layers combined. Similar values are obtained from studies of low-altitude spacecraft observations, although there is some disagreement in the literature concerning the exact identification of the boundary layer in such data. This latter topic is also reviewed. It is also argued that part, at least, of the boundary layer flow could occur on open field lines and indeed that some of the boundary layer observations correspond closely to what one would expect for the magnetospheric counterpart of magnetosheath FTE's. Finally, recent analyses of the variation of the transpolar voltage (measured at low altitudes) with solar wind conditions suggest an average ∼30-kV contribution from the boundary layers, a rather higher value than is indicated by the in situ measurements. However, all these estimates suggest that the layers generally provide a small but sometimes significant contribution to the magnetospheric voltage. We conclude that dayside reconnection is the dominant contributor under usual conditions, in agreement with conclusions reached previously on the basis of less direct information.

To understand the purpose of the IMS Assessment Symposium, held at Goddard Space Flight Center, May 21–23, 1981, we should first say a few words about the International Magnetospheric Study (IMS) itself. Broadly speaking, the ’active‘ phase of the IMS, which ran from 1976 to 1979, was conceived as an intensive period of worldwide data acquisition on magnetospheric processes, with emphasis on closely coordinated multi-spacecraft and ground-based observations. As a result, many high-quality data sets were generated during this period from spacecraft projects, such as GEOS and ISEE, and from extensive ground arrays of magnetometers and auroral cameras. However, the mere gathering of data is obviously a futile activity in itself if the data are not then subsequently turned into science by an equally vigorously pursued period of data analysis and interpretation. Therefore, although the active phase of the IMS ended in December 1979, the IMS exercise is by no means over yet. It was to promote effective worldwide participation in the data analysis phase (DAP) that IMSAS was held. Internationally, the IMS DAP is guided by a working group convened under the auspices of SCOSTEP (the ICSU Special Committee for Solar-Terrestrial Physics), which is chaired by Gordon Rostoker (Alberta). It was with the backing of this working group that the concept that Chris Russell and David Southwood had of the IMSAS meeting came to fruition.

The properties of energetic ions (>35 keV) observed in plasmoids and in the postplasmoid plasma sheet in the distant geomagnetic tail by the energetic particle anisotropy spectrometer instrument on ISEE 3 are investigated and compared with simultaneous thermal electron and magnetic field data. Two representative plasmoid-associated bursts are discussed in detail, followed by the results of a survey of 37 such events. It is found that the bulk speeds deduced from the angular anisotropies of the energetic ions, assumed to be protons, agree with those deduced from the thermal electrons to within ∼200 km s−1 in the hot plasma regions, showing that the ions are convected with the plasma. Average speeds are 660 km s−1 in plasmoids and 840 km s−1 in the postplasmoid plasma sheet. In the energetic particle boundary layers surrounding the hot plasma regions, however, the ion anisotropies are consistent with energetic proton bulk speeds (∼1000 km s−1) which considerably exceed local plasma speeds (∼200 km s−1) such that the ions form a beam, originating in the plasma sheet, which flows along newly reconnected magnetic field lines through plasma which has tail lobe characteristics. In the plasma sheet regions a correlation is found between the energetic proton intensity and the thermal electron temperature Te, such that the intensity increases by 2 orders of magnitude as kTe increases from ∼50 to ∼200 eV. To investigate this further, the thermal ion temperature Ti, not measured on ISEE 3, is estimated from pressure balance arguments. It is found that Ti and Te are correlated, with Ti ≈ 8Te in the plasmoids and with Ti ≈ 11Te in the postplasmoid plasma sheet, such that the energetic ion fluxes are also correlated with (and presumably controlled by) Ti. Characterizing the energetic protons as a Maxwellian distribution with density np* and temperature Tp* then yields typical energies kTp* ≃ 10 keV, compared with kTi ≃ 1 keV and kTe ≃ 100 eV, and densities np* ≃ 6 × 10−3 cm−3, compared with ni ≃ ne ≃ 0.16 cm−3. Thus the energetic protons form a tail to the thermal population which is “non-Maxwellian” in the sense that their characteristic temperature is much larger than thermal values. The energetic proton bulk speeds are also integrated to investigate plasmoid lengths. It is found that one-loop plasmoids (as inferred from field data) have an average length ∼60 RE, while multiple-loop plasmoids have an average length ∼110 RE. For single-loop plasmoids the observed time delay in their appearance in the distant tail following substorm onset is consistent with pinching off at a near-Earth neutral line (given some acceleration as the plasmoid moves downtail), while for multiple-loop plasmoids, agreement is found only if the first loop alone is considered. This result suggests that subsequent loops are formed after substorm onset, either through tailward retreat of the substorm neutral line and further pinching off or through loop formation within the postplasmoid plasma sheet.

Fifteen years ago, when I first became involved in space physics research and started to attend conferences, the refereeing of proceedings papers was rarely regarded as a serious business. The relaxed attitudes then prevailing doubtless allowed fringe material to be published which might better not have been inflicted upon the community, but a few pages of such a nature at least provided some light relief in an otherwise solid diet of scientific progress. On the positive side, the freedom given to authors to express their views in a more unbuttoned manner than would be appropriate in a formal journal paper encouraged interesting, individual, and thought-provoking contributions. The writing of conference papers could be a pleasurable and hassle-free experience.

Flux transfer events (FTEs), observed on both the interior and exterior of the dayside magnetopause region by the ISEE 1 and 2 spacecraft, are noted to be a feature of the magnetopause region covered by the spacecraft when the magnetic field in the magnetosheath has a southward component, but not when it is northward. During periods of southward magnetosheath field, the average number and recurrence time of FTE signatures/magnetopause crossing are similar to those observed in the magnetopause interior, implying that the magnetosheath and magnetosphere FTEs are aspects of the same physical phenomenon. It is speculated that FTEs may provide the dominant means of flux transfer required for the driving of geomagnetic disturbances.

Examples of the onset of a resonant ion beam instability are illustrated on the basis of ISEE 3 observations of 66 large amplitude wave events at the plasma sheet boundary layer. Analysis of the observational data showed that the observed wave and ion beam parameters were, in general, in agreement with linear theoretical predictions of resonant ion beam instability. The distribution of ion energies at the onset of the instability is given in a table.

Solar-terrestrial monitoring is under threat. The circumstances vary from one country to another, but the threat is widespread. Monitoring activities have been closed with little or no warning. Important activities such as the production of the international sunspot number and well-used facilities, for example, the World Data Center at Boulder, Colo., have in recent years been saved only by timely and concerted action by the scientific community.

Observations made by the ISEE 3 spacecraft in the distant geomagnetic tail during the eight CDAW 8 intervals are discussed, along with their relation to concurrent geomagnetic activity. This extensive multiinstrument case study of distant tail data covers a wide range of geomagnetic conditions from extended intervals of magnetic quiet with isolated substorms to prolonged periods of intense disturbance. Plasmoids are observed in the distant tail following disturbance enhancements, the time of their appearance being generally consistent with disconnection from the near-earth region at the time of the enhancement. Their structure is entirely consistent with the neutral line model. However, not all enhancements in geomagnetic activity result in the observation of plasmoids. In particular, the CDAW 8 data suggest that, during extended intervals of strong activity, a continuous neutral line may reside in the near-earth tail and some disturbance enhancements may then relate to an increase in the reconnection rate at a preexisting neutral line, rather than to new neutral line and plasmoid formation.