ALBERT

Notes: A light-weight, low-power, plasma analyzer is described that can be used for measuring the plasma environments of spacecraft with constrained resources. A unique system using a single electrostatic analyzer coupled to a single array of channel electron multipliers allows measurement of the three-dimensional energy per charge distributions of both ions and electrons over E/q ranges from ∼1 eV/q to (approximately-greater-than)40 keV/q. Particles selected by the analyzer are post-accelerated into the multipliers to maintain sensitivity for the lowest energy particles. An instrument using this concept called the magnetospheric plasma analyzer (MPA) is described. Presently, three MPAs are in geosynchronous orbits (GEO) aboard spacecraft with International Designators of 1989-046, 1990-095, and 1991-080. The MPA and its response characteristics are described, and examples of on-orbit data showing some of the MPA capabilities are presented.

Notes: Coronal mass ejections are spectacular manifestations of solar activity in which 10+15–10+16 g of solar material are propelled outward into interplanetary space. Recent work has demonstrated that these events are the prime link between solar activity and large, nonrecurrent geomagnetic storms, closing a loop in a body of research extending back more than 130 years.

Notes: Abstract Two types of flows dominate the large-scale structure of the solar wind: corotating flows and transient disturbances. Corotating flows are associated with spatial variability in the coronal expansion and solar rotation, whereas transient disturbances are associated with episodic ejections of material into interplanetary space from coronal regions not previously participating in the solar wind expansion. Ulysses' recent epic journey over the poles of the Sun has provided new insights on the three-dimensional nature of both corotating flows and transient disturbances in the solar wind and their evolution with heliocentric distance and latitude. This paper provides a simple physical description of the origins and dynamics of both of these types of solar wind flows, highlighting new understanding gained from the unique Ulysses high-latitude observations.

Notes: [Auszug] A characteristic of magnetic field reconnection is the acceleration of plasma as it flows across a rotational discontinuity. At the Earth's magnetopause this effect has only been observed recently during a few magnetopause crossings by the ISEE satellites. For one example analysed in detail ...

Notes: [Auszug] Magnetic reconnection in a current sheet converts magnetic energy into particle energy, a process that is important in many laboratory, space and astrophysical contexts. It is not known at present whether reconnection is fundamentally a process that can occur over an extended region in space or ...

Notes: Abstract We analyse the fluctuations of the electron density and of the magnetic field in the Earth’s magnetosheath to identify the waves observed below the proton gyrofrequency. We consider two quiet magnetosheath crossings i.e. 2 days characterized by small-amplitude waves, for which the solar wind dynamic pressure was low. On 2 August 1978 the spacecraft were in the outer magnetosheath. We compare the properties of the observed narrow-band waves with those of the unstable linear wave modes calculated for an homogeneous plasma with Maxwellian electron and bi-Maxwellian (anisotropic) proton and alpha particle distributions. The Alfvén ion cyclotron (AIC) mode appears to be dominant in the data, but there are also density fluctuations nearly in phase with the magnetic fluctuations parallel to the magnetic field. Such a phase relation can be explained neither by the presence of a proton or helium AIC mode nor by the presence of a fast mode in a bi-Maxwellian plasma. We invoke the presence of the helium cut-off mode which is marginally stable in a bi-Maxwellian plasma with 〈alpha〉 particles: the observed phase relation could be due to a hybrid mode (proton AIC + helium cut-off) generated by a non-Maxwellian or a non-gyrotropic part of the ion distribution functions in the upstream magnetosheath. On 2 September 1981 the properties of the fluctuations observed in the middle of the magnetosheath can be explained by pure AIC waves generated by protons which have reached a bi-Maxwellian equilibrium. For a given wave mode, the phase difference between B\Vert and the density is sensitive to the shape of the ion and electron distribution functions: it can be a diagnosis tool for natural and simulated plasmas.

Notes: Abstract The mechanism by which ions are accelerated near the Earth's bow shock and near shocks propagating outward from the Sun in response to solar activity appears to be essentially the same. For both types of shock the solar wind thermal distribution acts as a seed population. Leaked magnetospheric ions and resident flare ions are additional seed populations for the bow shock and outward propagating shocks respectively. The acceleration of solar wind ions at these shocks begins with either the reflection of ions off the shock or leakage of shocked plasma back through the shock. Interaction with a disruption wave field self-generated by these backstreaming ions is responsible for the remainder of the acceleration at the bow shock. Both the disruption wave field and the ambient interplanetary wave field play important roles in accelerating ions at outward propagating shocks, but on different time scales. The geometry of the shock and the duration of field line connection to the shock play decisive roles in determining what is observed.

Notes: Abstract The early ISEE orbits provided the opportunity to study the magnetopause and its environs only a few Earth radii above the subsolar point. Measurements of complete two-dimensional ion and electron distributions every 3 or 12 s, and of three-dimensional distributions every 12 or 48 s by the LASL/MPI instrumentation on both spacecraft allow a detailed study of the plasma properties with unprecedented temporal resolution. This paper presents observations obtained during four successive inbound orbits in November 1977, containing a total of 9 magnetopause crossings, which occurred under widely differing orientations of the external magnetic field. The main findings are: (1) The magnetosheath flow near the magnetopause is characterized by large fluctuations, which often appear to be temporal in nature. (2) Between ∼ 0.1 and ∼ 0.3R E outside the magnetopause, the plasma density and pressure often start to gradually decrease as the magnetopause is approached, in conjunction with an increase in magnetic field strength. These observations are in accordance with the formation of a depletion layer due to the compression of magnetic flux tubes. (3) In cases where the magnetopause can be well resolved, it exhibits fluctuations in density, and especially pressure and bulk velocity around average magnetosheath values. The pressure fluctuations are anticorrelated with simultaneous magnetic field pressure changes. (4) In ope case the magnetopause is characterized by substantially displaced electron and proton boundaries and a proton flow direction change from upwards along the magnetopause to a direction tranverse to the geomagnetic field. These features are in agreement with a model of the magnetopause described by Parker. (5) The character of the magnetopause sometimes varies strongly between ISEE-1 and -2 crossings which occur ∼ 1 min apart. At times this is clearly the result of highly non-uniform motions. There are also cases where there is very good agreement between the structures observed by the two satellites. (6) In three of the nine crossings no boundary layer was present adjacent to the magnetopause. More remarkably, two of the three occurred while the external magnetic field had a substantial southward component, in clear contradiction to expectations from current reconnection models. (7) The only thick (low-latitude) boundary layer (LLBL) observed was characterized by sharp changes at its inner and outer edges. This profile is difficult to reconcile with local plasma entry by either direct influx or diffusion. (8) During the crossings which showed no boundary layer adjacent to the magnetopause, magnetosheath-like plasma was encountered sometime later. Possible explanations include the sudden formation of a boundary layer at this location right at the time of the encounter, and a crossing of an ‘inclusion’ of magnetosheath plasma within the magnetosphere. (9) The flow in the LLBL is highly variable, observed directions include flow towards and away from the subsolar point, along the geomagnetic field and across it, tangential and normal to the magnetopause. Some of these features clearly are nonstationary. The scale size over which the flow directions change exceeds the separation distance (several hundred km) of the two spacecraft.

Notes: Abstract High temporal resolution measurements of solar wind electrons at the Earth's bow shock on the dawn side have been made with the LASL/MPI fast plasma experiments on ISEE-1 and 2. One dimensional, 1-d, temperatures, T e , and densities, N e , are obtained every 0.3 s and 2-d values are obtained every 3 s. Profiles of T e and N e at the shock usually are found to be similar to one another and also to the profile of the magnetic field magnitude. The time scale of electron thermalization varies from about 0.5 s to greater than 1 min, depending importantly on the shock motion and the orientation of the magnetic field. Typical thermalization times from 05:00–12:00 LT are ∼10 s, considerably shorter than proton thermalization times at the shock. This time scale corresponds to a distance of ∼100 km, comparable to but somewhat larger than the typical ion inertial length. The electron thermalization times are significantly longer than some of the values frequently cited in the past. At the end of the electron thermalization there typically is an overshoot in electron thermal pressure followed by an undershoot which give the pressure profile of the shock the appearance of a damped wave. Ion thermalization is essentially completed by the time the electron pressure wave is ‘damped’. The most probable value of the electron temperature ratio across the shock is 1.7, and this value is relatively independent of the Sun-Earth-satellite angle, θ ss , for θ ss between 25° and 100°. The Los Alamos Scientific Laboratory requests that the publisher identify this article as work performed under the auspices of the Department of Energy.

Notes: Abstract Ulysses plasma observations reveal that the forward shocks that commonly bound the leading edges of corotating interaction regions (CIRs) beyond ∼2 AU from the Sun at low heliographic latitudes nearly disappeared at a latitude of S26°. On the other hand, the reverse shocks that commonly bound the trailing edges of the CIRs were observed regularly up to S41.5°, but became weaker with increasing latitude. Only three CIR shocks have been observed poleward of S41.5°; all of these were weak reverse shocks. The above effects are a result of the forward waves propagating to lower heliographic latitudes and the reverse waves to higher latitudes with increasing heliocentric distance. These observational results are in excellent agreement with the predictions of a global model of solar wind flows that originate in a simple tilted-dipole geometry back at the Sun.