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The solar wind has been seen as the major source of hot magnetospheric plasma since the early 1960’s. More recent theoretical and observational studies have shown that the cold (few eV) polar wind and warmer polar cusp plasma that flow continuously upward from the ionosphere can be a very significant source of ions in the magnetosphere and can become accelerated to the energies characteristic of the plasma sheet, ring current, and warm plasma cloak. Previous studies have also shown the presence of solar wind ions in these magnetospheric regions. These studies are based principally on proxy measurements of the ratios of He++/H+ and the high charge states of O+/H+. The resultant admixture of ionospheric ions and solar wind ions that results has been difficult to quantify, since the dominant H+ ions originating in the ionosphere and solar wind are indistinguishable. The ionospheric ions are already inside the magnetosphere and are filling it from the inside out with direct access from the ionosphere to the center of the magnetotail. The solar wind ions on the other hand must gain access through the outer boundaries of the magnetosphere, filling the magnetosphere from the outside in. These solar wind particles must then diffuse or drift from the flanks of the magnetosphere to the near-midnight reconnection region of the tail which takes more time to reach (hours) than the continuously large outflowing ionospheric polar wind (10’s of min). In this paper we examine the magnetospheric filling using the trajectories of the different ion sources to unravel the intermixing process rather than trying to interpret only the proxy ratios. We compare the timing of the access of the ionospheric and solar wind sources and we use new merged ionosphere-magnetosphere multi-fluid MHD modeling to separate and compare the ionospheric and solar wind H+ source strengths. The rapid access of the initially cold polar wind and warm polar cusp ions flowing down-tail in the lobes into the mid-plane of the magnetotail, suggests that, coupled with a southward turning of the IMF Bz, these ions can play a key triggering role in the onset of substorms and subsequent large storms.

Ionospheric ions (mainly H+, He+, and O+) escape from the ionosphere and populate the Earth's magnetosphere. Their thermal energies are usually low when they first escape the ionosphere, typically a few electron volt to tens of electron volt, but they are energized in their journey through the magnetosphere. The ionospheric population is variable, and it makes significant contributions to the magnetospheric mass density in key regions where magnetic reconnection is at work. Solar wind—magnetosphere coupling occurs primarily via magnetic reconnection, a key plasma process that enables transfer of mass and energy into the near-Earth space environment. Reconnection leads to the triggering of magnetospheric storms, auroras, energetic particle precipitation and a host of other magnetospheric phenomena. Several works in the last decades have attempted to statistically quantify the amount of ionospheric plasma supplied to the magnetosphere, including the two key regions where magnetic reconnection occurs: the dayside magnetopause and the magnetotail. Recent in situ observations by the Magnetospheric Multiscale spacecraft and associated modeling have advanced our current understanding of how ionospheric ions alter the magnetic reconnection process, including its onset and efficiency. This article compiles the current understanding of the ionospheric plasma supply to the magnetosphere. It reviews both the quantification of these sources and their effects on the process of magnetic reconnection. It also provides a global description of how the ionospheric ion contribution modifies the way the solar wind couples to the Earth's magnetosphere and how these ions modify the global dynamics of the near-Earth space environment. Plain Language Summary Above the neutral atmosphere, space is filled with charged particles, which are tied to the Earth's magnetic field. The particles come from two sources, the solar wind and the Earth's upper atmosphere. Most of the solar wind particles are deflected by the Earth´s magnetic field, but some can penetrate into near-Earth space. The ionized layer of the upper atmosphere is continuously ejecting particles into space, which have low energies and are difficult to measure. We investigate the relative importance of the two charged particle sources for the dynamics of plasma processes in near-Earth space. In particular, we consider the effects of these sources in magnetic reconnection. Magnetic reconnection allows initially separated plasma regions to become magnetically connected and mix, and converts magnetic energy to kinetic energy of charged particles. Magnetic reconnection is the main driver of geomagnetic activity in the near-Earth space, and is responsible for the release of energy that drives a variety of space weather effects. We highlight the fact that plasma from the ionized upper atmosphere contributes a significant part of the density in the key regions where magnetic reconnection is at work, and that this contribution is larger when the geomagnetic activity is high.

International audience; We present Magnetospheric Multiscale mission (MMS) observations of Hall physics in the magnetotail, which compared to dayside Hall physics is a relatively unexplored topic. The plasma consists of electrons, moderately cold ions (T ∼ 1.5 keV) and hot ions (T ∼ 20 keV). MMS can differentiate between the cold ion demagnetization region and hot ion demagnetization regions, which suggests that MMS was observing multiscale Hall physics. The observed Hall electric field is compared with a generalized Ohm's law, accounting for multiple ion populations. The cold ion population, despite its relatively high initial temperature, has a significant impact on the Hall electric field. These results show that multiscale Hall physics is relevant over a much larger temperature range than previously observed and is relevant for the whole magnetosphere as well as for other astrophysical plasma.

International audience; When the interplanetary magnetic field is northward for a period of time, O + from the high-latitude ionosphere escapes along reconnected magnetic field lines into the dayside magnetopause boundary layer. Dual-lobe reconnection closes these field lines, which traps O + and mass loads the boundary layer. This O + is an additional source of magnetospheric plasma that interacts with magnetosheath plasma through magnetic reconnection. This mass loading and interaction is illustrated through analysis of a magnetopause crossing by the Magnetospheric Multiscale spacecraft. While in the O +-rich boundary layer, the interplanetary magnetic field turns southward. As the Magnetospheric Multiscale spacecraft cross the high-shear magnetopause, reconnection signatures are observed. While the reconnection rate is likely reduced by the mass loading, reconnection is not suppressed at the magnetopause. The high-latitude dayside ionosphere is therefore a source of magnetospheric ions that contributes often to transient reduction in the reconnection rate at the dayside magnetopause.

The warm plasma cloak is a source of magnetospheric plasma that contain significant O+. When the O+ density in the magnetosphere near the magnetopause is >0.2 cm‐3 and the H+ density is 20% due to mass‐loading only about 2% to 4% of the time. However, during geomagnetic storms, O+ dominates the mass density of the warm plasma cloak and these mass densities are very high. Therefore, a separate study is conducted to determine the effect of the warm plasma cloak on magnetopause reconnection during geomagnetically disturbed times. This study shows that the warm plasma cloak reduces the reconnection rate significantly about 25% of the time during disturbed conditions. publishedVersion

Through the more than half century of space exploration, the perception and recognition of the fundamental role of the ionospheric plasma in populating the Earth’s magnetosphere has evolved dramatically. A brief history of this evolution in thinking is presented. Both theory and measurements have unveiled a surprising new understanding of this important ionosphere-magnetosphere mass coupling process. The highlights of the mystery surrounding the difficulty in measuring this largely invisible low energy plasma are also discussed. This mystery has been solved through the development of instrumentation capable of measuring these low energy positively-charged outflowing ions in the presence of positive spacecraft potentials. This has led to a significant new understanding of the ionospheric plasma as a significant driver of magnetospheric plasma content and dynamics.

More than 30 years after the prediction of the polar wind outflow from the high latitude ionosphere, the exact magnitude and ultimate fate of the ionospheric plasma supply remains unknown. Estimates made more than a decade ago suggested that the polar ion outflow might well be of sufficient strength to populate the different regions of the Earth’s magnetosphere. Direct measurements in the high altitude magnetosphere became possible only with the launch of the Polar spacecraft. The combination of the Thermal Ion Dynamics Experiment and the Plasma Source Instrument has revealed the presence of low energy (

[1] Previous studies of the magnetospheric plasma populations have concentrated on the low-energy (1 eV) plasma of the plasmasphere, the more energetic (1-100 keV) plasma of the plasma sheet and ring current, and the high-energy (approximately MeV) plasma of the radiation belts. A compilation of satellite measurements over the past 30 years augmented by recent observations from the Polar-TIDE instrument has revealed a new perspective on a plasma population in the middle magnetosphere. This population consists of ions with energies of a few eV to greater than several hundred eV which display a characteristic bidirectional field-aligned pitch angle distribution. Measurements from the ATS, ISEE, SCATHA, DE, and POLAR satellites establish the characteristics of this “warm plasma cloak” of particles that is draped over the nightside region of the plasmasphere and is blown into the morning and early afternoon dayside sector by the sunward convective wind in the magnetosphere. The satellite observations combined with the predictions of an ion trajectory model are used to describe the formation and dynamics of the warm plasma cloak.

[1] The contribution of ionospheric plasma to the Earth's magnetosphere has been recognized for more than 3 decades. The magnitude of this contribution has become more evident over that same time period with the observed magnitude of the low-energy ionospheric supply increasing as the measurement techniques improved. Estimates based on Dynamics Explorer measurements in the mid-1980s suggested that the ionospheric plasma supply is sufficient to populate the plasmasphere, plasma trough, plasma sheet, and magnetotail lobes. Recent measurements from the Thermal Ion Dynamics Experiment on the Polar spacecraft have been used in conjunction with an ion trajectory model to reexamine the process and magnitude of the ionospheric supply of magnetospheric plasma. These measurements reveal the energy, pitch angle, and flux characteristics of the upward flowing polar wind over broad regions of the high-latitude ionosphere. Onboard measurement of spacecraft potential is found to be a fundamental element in interpreting the measured ion outflow. Newly derived polar wind fluxes are determined to be near 6.0 × 107 ions cm−2 s−1 at 5000 km altitude during local winter and magnetically quiet conditions. Using the measured ionospheric source characteristics in combination with the trajectory code reveals the nature of the ionospheric/magnetosphere filling process and shows that the ionospheric source is sufficient to supply the observed densities and energies of the plasma sheet and magnetotail lobes. Many of the ionospheric particles are further transformed to ring current energies and locations after circulation through the plasma sheet. This measurement/calculation approach is able to show which regions of the high-latitude ionosphere are important for plasma sheet/ring current filling. The ionospheric sources used in the calculations include the dominant polar wind, the cleft ion fountain, and the auroral zone.

We consider the formation of the plasma sheet and geosynchronous region (nonstorm) ring current in the framework of collisionless test particle motions in three-dimensional magnetospheric fields obtained from self-consistent MHD simulations. Simulation results are compared with observations of the near-Earth plasma sheet from the Polar spacecraft during 2001 and 2002. Many particles were initiated in two regions representative of the solar wind source upstream of the bow shock and the polar wind source outside the plasmasphere, both of which are dominated by protons (H+). Proton trajectories are run until they precipitate into the atmosphere, escape from the simulation space, or become stably trapped. These calculations produce a database of proton characteristics in each 1 RE3 volume element of the magnetosphere and yield velocity distributions as well as bulk plasma properties. We report results reflecting steady growth phase conditions after 45 min of southward interplanetary field, BZ = −5 nT (BY = 0), and for conditions resulting after 2 hours of northward BZ = +5 nT. The results for simulated velocity distributions are consistent with the Polar soundings of the current sheet from lobe to lobe and with AMPTE/CCE observations of (nonstorm) ring current region protons. The simulations help us identify the differentiation between solar and polar wind H+ ions in observations. The weak NBZ ring current-like pressure is primarily polar wind protons, while the moderately active SBZ ring current-like pressure is primarily solar wind protons. The solar and polar wind contributions to the SBZ ring current are comparable in density, but the solar protons have a higher average energy. For SBZ, solar wind protons enter the nonstorm ring current region primarily via the dawn flank and to a lesser degree via the midnight plasma sheet. For NBZ, solar wind protons enter the ring current-like region via the cusp and flanks. Polar wind protons enter the nonstorm ring current through the midnight plasma sheet in both cases. Solar and ionospheric plasmas thus take different transport paths to the geosynchronous (nonstorm) ring current region and may thus be expected to respond differently to substorm dynamics of the magnetotail.

The ISTP Polar spacecraft is equipped with a unique plasma velocity analyzer system designed specifically for kinetic diagnostics of low-energy, low-density plasma ions. Such plasmas were previously unobservable in the polar cap region owing to their low velocities and the positive photoelectric charging of spacecraft in sunlight at low ambient plasma density. The thermal ion dynamics experiment (TIDE) incorporates seven large apertures, focusing electrostatic optics, and time-of-flight mass analysis, for enhanced sensitivity to low energy plasma ions. The plasma source instrument (PSI) limits and regulates the photoelectric charging of the Polar spacecraft at small potentials (∼+2V). Together, TIDE and PSI have produced new observations of i) the mixing of solar and ionospheric plasmas in the cleft regions; ii) auroral heating and plasma transport; iii) solar illumination control of the polar cap ionosphere; iv) the downward motion of O + at lower altitudes throughout the polar cap region; v) the high altitude polar wind; vi) the high altitude convection of the polar outflows; vii) the unexpected dynamism of polar wind outflows; and viii) the supply of plasma to the plasma sheet. These observations indicate that most polar cap O + out flow originates in the dayside plasma upwelling region, creating a plasma fountain effect in the polar cap. The observations support the evaluation of consequences of the ionospheric source of plasma for magnetospheric dynamics and storm phenomena. Preliminary global modeling results indicate that ionospheric plasma is the dominant contributor to both the density and pressure of the plasma within a corresponding geopause that extends to the persistent neutral line in the central plasma sheet. TIDE and PSI have contributed fundamentally to our knowledge that the dissipation of solar wind energy is not limited to the ionosphere proper, but is distributed throughout a much larger geosphere of dominantly terrestrial origin.

Quasi-static electric field data collected by the DE-1 spacecraft were used to study ionospheric ion upwelling events observed in the vicinity of the dayside cleft. Bulk plasma parameters such as ion-species density and field-aligned bulk velocity and flux were derived at points within several upwelling ion events for the H(+), He(+), O(+), and O(2+), and the ion-species bulk parameters near the source altitude were compared. It was found that O(+) ions comprise about 90 percent of the upwelling particle density, followed by H(+) at less than 10 percent; He(+) and O(2+) contribute about 1 percent each. The upwelling O(+) flux is also dominant, followed by upward H(+) flux, which is relatively more significant than the fractional H(+) density, due to its high upward flow velocity.

Earlier Ogo 5 discussions of high-latitude magnetospheric wave-particle interaction phenomena associated with field aligned current systems are extended by considering some September 7, 1968, out-bound measurements and corresponding March 11, 1969, observations, when the spacecraft was traversing auroral L shells in midafternoon. It is shown that during moderate magnetospheric disturbances the most intense waves and currents were detected near sharp boundaries in the density of polar cleft electrons, and it is possible that local wave-particle interactions produced anomalous resistivity. Some observed changes in the electron distribution functions might be explained in terms of local acceleration, but significant causal questions about the dynamics remain open if one can use only local data from a single spacecraft in this region.

Operating in a mass scanning mode, the Retarding Ion Mass Spectrometer (RIMS) has measured N+ and N++ ions in the magnetosphere. Both N+ and N++ are observed in the plasmasphere with N+ ions also seen flowing out of the northern polar cap at altitudes up to 3 RE. The N+ fluxes are 5 to 10% of the O+ fluxes with the N++ fluxes at 1 to 5% of the N+ fluxes.

A review is given of the development of ideas concerning the transport and distribution of ionospheric plasma in the magnetosphere. An unresolved dichotomy in these ideas is identified, in which two incompatible explanations have been given for the low plasma densities outside the plasmasphere, the convection/hot solar plasma model, and the convection/loss model. This dichotomy reveals a fundamental unresolved problem in magnetospheric physics whose resolution is essential if we are to adequately understand the transport of mass, momentum and energy through the magnetosphere, and the resulting contributions of terrestrial and solar plasma sources. Recent progress in understanding global ionospheric outflows is reviewed for clues which might help resolve this problem. Observations are compared with theoretical concepts dealing with (1) the low-altitude collisional and chemical processes affecting the character of ionospheric outflow, (2) the ambipolar outflow of plasma in the collisionless region above, and (3) the acceleration of ionospheric plasma by macroscopic magnetospheric electric fields associated with structured convection. We appear to need a hybrid model of magnetospheric plasma in which terrestrial plasma is both lost into the solar wind, and energized and trapped within the magnetosphere, inflating the geomagnetic field and excluding cold plasma from conjugate regions.

Regions of high-density cold plasma have been observed outside the plasmasphere in the plasma trough region of the magnetosphere. These detached plasma regions may have densities as high as several hundred ions per cubic centimeter in the normally low-density (∼1 ion/cm³) plasma trough. The detached plasma regions are found across the day side of the magnetosphere, particular concentrations being in the afternoon-dusk sector. The regions are located at the plasmapause at dusk and progressively farther away for earlier local times in the early afternoon and morning. Detached plasma regions are observed during moderate to disturbed magnetic activity conditions. They exhibit a very complex spatial structure with sizes varying from thousands of kilometers down to less than 50 km in extent. The detached regions may be generated by variations in the magnetospheric convection electric field, which occurs during substorm activity.

Plasmapause observations by ion spectrometer aboard OGO-5 vehicle for early orbits, obtaining O, He and H ion concentration profiles for geomagnetic parameter

Magnetosphere Alfven velocity profile relation to ELF chorus and hiss, indicating unstable wave generation by cyclotron resonance

Several spacecraft experimenters have reported on the detection of large temporal variations in trapped electron fluxes near L = 5 to 6 at midlatitudes in the night hemisphere. In this report we describe in detail the particle, wave, and field changes measured when Ogo 5 traversed an outer-zone trapping boundary of this type on September 7, 1968. It is shown that thermal proton concentrations and E greater than 50-keV electron fluxes abruptly decreased when electrons with (1-4) keV mean energy were detected. It is also shown that currents flowed along the average geomagnetic field direction near the plasma boundaries and that these were accompanied by intense VLF electrostatic waves. It is proposed that turbulent resistivity produced by current-driven plasma instabilities allows parallel dc electric fields to develop along this boundary.

A unique low energy (0–50 keV) electron accelerator has been developed which provides a broad, parallel, low intensity electron beam with excellent long term stability. The beam intensity is approximately 106 electrons·cm−2 ·sec−1 and the long term stability is better than 2%/day. A prototype of this accelerator is described and the results of its application to instrument calibration and channel electron multiplier (CEM) efficiency measurements are presented. The absolute electron detection efficiency for CEM's was found to vary from approximately 90% at 1 keV to 73% at 14 keV with a probable error of ±10%. The large disagreement among the various published measurements of CEM detection efficiency is discussed.

Plasmasphere bulge region morphology from hydrogen ion concentration measurement by mass spectrometer on OGO 5 satellite

Energy spectra and pitch angle distributions of auroral electrons have been measured in a premidnight multiple arc auroral display by a Javelin rocket containing two identical payloads that separated in flight. The rocket was launched from Fort Churchill, Canada, at 0459 UT on March 2, 1968, and covered an altitude range up to 800 km. The electron energy spectra between 40 eV and 20 keV show a 'continuum' spectrum with a superimposed energetic peak. The center energy of the peak was observed to shift from 10-12 keV over the arcs to 2-3 keV between the arcs. This spectral structure is shown to be similar to the inverted 'V' structure reported by other investigators. The in flight separation of the two payloads allowed investigation of spatial versus temporal effects in the auroral precipitation.

Magnetic activity effect on magnetospheric plasmapause position, measuring ion concentrations as function of local time from OGO 5 observations

Hydrogen ion concentration measurements by OGO 5 in plasmasphere during intense magnetic storms accompanied by stable auroral red arcs

New details of unsteady magnetospheric convection and gradual erosion of the plasmasphere during a weak magnetic storm are revealed in the light of presented ground data and OGO-4 and OGO-5 data for August 13-15, 1968. These new findings suggest that westward electric fields of the order of 0.5 mv/m were present in the midnight sector during the substorms studied.

The concentrations of H(+) ions in the dayside region of the plasmasphere, measured from March 1968 through February 1969 by the Lockheed light-ion mass spectrometer aboard the OGO 5 satellite, are presented and analyzed. The position of the plasmapause on the dayside appears to be determined by the level of magnetic activity present during the previous corotation of the dayside sector through the formative nightside region. Observations of the buildup of H(+) density versus local time following magnetic storms indicate that H(+) ions flow from the dayside ionosphere into the plasmasphere and plasma trough. Plasmapause density profiles in the afternoon-dusk sector show the effects of the dayside filling from the ionosphere. In addition, several of the dayside profiles display a steep drop in the H(+) density of about a factor of 10 inside the plasmapause position.

OGO 5 polar cusp observations showing dayside magnetosheath plasma penetration during magnetic storm

We use OGO 5 measurements made within the plasmapause on May 15, 1969, to investigate the possible association between changes in lightning whistler dispersion characteristics and local density fluctuations. It is shown that groups of whistlers with relatively constant dispersions tended to be detected in regions where the local ion concentration was significantly enhanced. It is assumed that these local density fluctuations represent characteristics of large-scale field-aligned variations. The results are then compared with ray refraction estimates appropriate for low-frequency whistler mode propagation (wave components with frequencies comparable to the local lower hybrid frequency) in a nonuniform medium.

Electron and plasma beams and neutral gas plumes were injected into the space environment by instruments on Spacelab 1, and various diagnostic measurements including television camera observations were performed. The results yield information on vehicle charging and neutralization, beam-plasma interactions, and ionization enhancement by neutral beam injection.

Since the early work of Dungey, Axford and Hines, and Piddington, the concept of magnetospheric convection has become more and more widely accepted as the fundamental driving force for magnetospheric processes. Although the early convection theories have been modified to include the effects of magnetospheric-ionospheric coupling, the original steady large-scale convection models remain largely intact. This paper discusses a variety of recent magnetospheric measurements which support the basic convection model. These measurements include the dynamics of thermal plasma, the drift patterns of medium-energy protons and electrons, and the direct measurement of magnetospheric electric fields by satellites and balloons. All of these measurements have added significantly to our understanding of convection processes, and taken collectively, they offer a fairly unified picture of magnetospheric convection.

The larger system of the earth environment is controlled externally by electromagnetic and particle energy from the sun. Recent studies have shown that the sun is a variable star with changes in its radiation which produce significant effects in the earth's climate and weather. The study of the solar-terrestrial system requires simultaneous, long-duration observations of the different elements or 'links' in the solar-terrestrial chain. Many investigations must be conducted in space from a vantage point above the earth's atmosphere where all of the sun's emissions can be observed free from atmospheric distortion, where the magnetospheric particles and fields can be measured directly, and where the atmosphere can be observed on a global scale. The extension of the Shuttle on-orbit capability in connection with the development of the power module will offer an important near-term step in an evolutionary process leading toward a permanent manned Solar Terrestrial Observatory capability in low-earth orbit. Attention is given to the required solar-terrestrial measurements, the operation of the Solar Terrestrial Observatory, and an evolutionary approach to the Solar Terrestrial Observatory.

The distribution and dynamics of thermal (∼ 1 eV) plasma are of fundamental importance for understanding many magnetospheric processes. Above the ionosphere the bulk of the thermal plasma is found in the plasmasphere, which displays varying characteristics in the different LT regions. These different characteristics are reviewed herein with specific interest placed on the H+ ion density profiles since the H+ ions are the main component of the plasmasphere. Plasmasphere dynamics and morphology can be explained in terms of a time varying convection model of the magnetosphere which incorporates the bulge region as part of the main flow pattern of the plasmasphere.

Concentrations of H+, He+, and O+ ions have been measured from an initial perigee height of ∼300 km to an apogee of ∼23 RE by the light ion mass spectrometer aboard OGO 5. The instrument has a sensitivity of less than 1 ion/cm3 and a range of 8 orders of magnitude. With these capabilities the instrument was able to measure ion concentrations from within the plasmasphere through the plasmapause and the ‘trough’ region of the outer magnetosphere. In this paper we are concerned with the position and density profile of the plasmapause which is generally located in the region ∼3≼L∼6.

Measurements of low-energy ions made by the retarding ion mass spectrometer (RIMS) onboard the Dynamics Explorer 1 (DE 1) satellite are used to study some aspects of 'body-plasma interactions' in the terrestrial plasmasphere. Preliminary results are presented, yielding the degree of H+ and He+ ion depletion in the wake of the satellite in terms of specific and average ion Mach numbers, average ion mass, body size normalized to ionic Debye length, and body potential normalized to ion thermal energy. Some results from the RIMS measurements are compared with relevant results from the Explorer 31 and the Atmosphere Explorer C ionospheric satellites. Wake depletion is found to vary approximately linearly for small bodies (R-sub-Di less than about 12) and exponentially for large bodies (R-sub-Di greater than 50).

The magnetospheric-Ionospheric Coupling (MIC) Conference was held on February 6–8, 1974, at the Ahwahnee Hotel amid the magnificence of Yosemite National Park. The Conference was organized so as to keep the final attendance to a manageable number (less than 100) who were directly involved in the conference topic. By keeping the number of attendees down, we were able to achieve a maximum interchange of ideas. The daily schedule was set up to give a reasonable mixture between the lecture and discussion periods and the recreational and leisure time. This approach was quite successful and created an atmosphere in which the attendees could exchange ideas on both a formal and an informal basis. The Yosemite location furnished the combined benefits of a somewhat secluded spot with the incomparable beauty of the park surroundings. This combination served to keep the spirits of the participants high and contributed significantly to the success of the conference.

Cold flowing hydrogen and helium ions have been observed using the retarding ion mass spectrometer on board the Dynamics Explorer 1 spacecraft in the dayside magnetosphere at subauroral latitudes. The ions show a marked flux asymmetry with respect to the relative wind direction. The observed data are fitted by a model of drifting Maxwellian distributions perturbed by a first order-Spritzer-Haerm heat flux distribution function. It is shown that both ion species are supersonic just equatorward of the auroral zone at L = 14, and the shape of asymmetry and direction of the asymmetry are consistent with the presence of an upward heat flux. At L = 6, both species evolve smoothly into warmer subsonic upward flows with downward heat fluxes. In the case of subsonic flows the downward heat flux implies a significant heat source at higher altitudes. Spin curves of the spectrometer count rate versus the spin phase angle are provided.