To investigate the universality of magnetic turbulence in space plasmas, we analyze seven time periods in the free solar wind under different plasma conditions. Three instruments on Cluster spacecraft operating in different frequency ranges give us the possibility to resolve spectra up to 300 Hz. We show that the spectra form a quasiuniversal spectrum following the Kolmogorov's law approximately k(-5/3) at MHD scales, a approximately k(-2.8) power law at ion scales, and an exponential approximately exp[-sqrt[k(rho)e]] at scales k(rho)e approximately [0.1,1], where rho(e) is the electron gyroradius. This is the first observation of an exponential magnetic spectrum in space plasmas that may indicate the onset of dissipation. We distinguish for the first time between the role of different spatial kinetic plasma scales and show that the electron Larmor radius plays the role of a dissipation scale in space plasma turbulence.

Individual multispacecraft case studies confirm that the underlying current sheets are tangential discontinuities, but most I-t•As have relatively small jumps in field magnitude from before to after and thus would fail traditional identification tests as definite tangential discontinuities. The combination of our results suggests that HFAs should occur at a rate of several per day, and thus they may play a significant role in the solar-terrestrial dynamics.

The electron heating and the electrostatic potential jump across collisionless shocks play an important, if not dominant, role in the electron momentum balance. We present here a survey of these two quantities over a large sample of fast mode collisionless shocks. Results for estimates of the electrostatic potential (as measured in the de Hoffmann‐Teller reference frame) based on an estimate of the jump in electron enthalpy and on Liouville's theorem correlate well with each other, although the latter are consistently higher, perhaps due to irreversible processes affecting the shock electron dynamics. The size of the potential does not appear to be strongly controlled by any of the various upstream parameters (shock geometry, Mach number, etc.) and represents approximately 12% of the incident ion ram kinetic energy, this figure showing some tendency to decrease with increasing Mach number. The electron contribution to the total (ion plus electron) heating across the shock varies systematically from 50% or more at subcritical Mach numbers to less than 10% at the highest Mach number shocks in the sample. The electron heating shows only modest, but systematic, departure from that which would result by preserving the ratio of the perpendicular temperature to the magnetic field strength.

We have conducted a detailed analysis of a set of events termed short large-arnphtude magnetic structures (SLAMS) observed at an encounter of the quasi-parallel bow shock by the AMPTE UKS and IBM satellites. Both the satellite configuration and the solar wind conditions are favorable for the case study presented here. We have identified isolated SLAMS, surrounded by solar wind conditions, and embedded SLAMS, which lie within or form the boundary with regions of significant heating and deceleration. The duration, polarization, and other characteristics of SLAMS are all consistent with their growth directly out of the ULF wave field, including the common occurrence of an attached whistler as found in ULF shocklets. The plasma rest iYmne propagation speeds, where they can be determined, and two-spacecraft time delays for all cases show that the SLAMS attempt to propagate upstream against the oncoming flow, but are convected back downstream. The speeds and delays vary systematically with SLAMS amphtude in the way anticipated from nonlinear wave theory, as do their polarization features. Inter-SLAMS regions, and boundary regions with the solar wind, contain hot deflected ions of lesser density than within the SLAMS. The amplitude of the SLAMS requires an active growth mechanism. Following earlier inferences about the limited transverse extent of SLAMS, we highlight the importance of determining the thickness of the transition zone over which SLAMS grow and the bulk heating and deceleration is effected. From this case study it appears that, at least under some circumstances, the quasi-parallel shock cannot be regarded as an undulating, cychcally re-forming simply connected surface. Instead, the transition zone is better represented as a set of ULF waves, some of which grow to become SLAMS which gradually decelerate and merge to form the downstream state. conditions and that these instabilities cause the shock to cyclically re-form. pulsations was dictated primarily by the Larmor radii of the backstreaming particles found in abundance upstream of the bow shock but downstream of the foreshock boundary. This boundary is defined by the upstream field line which is tangent to the curved bow shock, or by the trajectory of field-aligned ion beams of a given energy originating at the point of tangency. The turbulence associated with the shock apparently saturates some distance, typically 10 R•, downstream of this ion foreshock boundary [Bonifazi et al., 1983], downstream of which nearly isotropic distributions of "diffuse" energetic ions are found. The curved nature of the bow shock led early workers to suggest that the turbulent appearance of the quasi-parallel shock was due to debris which originated under more quasi-perpendicular configura-4209

Abstract. We present a comprehensive observational study of the magnetospheric response to an interplanetary magnetic field (IMF) tangential discontinuity, which first struck the postnoon bow shock and magnetopause and then swept past the prenoon bow shock and magnetopause on July 24, 1996. Although unaccompanied by any significant plasma variation, the discontinuity interacted with the bow shock to form a hot flow anomaly (HFA), which was observed by Interball-1 just upstream from the prenoon bow shock. Pressures within and Earthward of the HFA were depressed by an order of magnitude, which allowed the magnetopause to briefly (-7 min) move outward some 5 R E beyond its nominal position and engulf Interball-1.A timing study employing nearby Interball-1 and Magion-4 observations demonstrates that this motion corresponded to an antisunward and northward moving wave on the magnetopause. The same wave then engulfed Geotail, which was nominally located downstream in the outer dawn magnetosheath. Despite its large amplitude, the wave produced only minor effects in GOES-8 geosynchronous observations near local dawn. Polar Ultraviolet Imager (UVI) observed a sudden brightening of the afternoon aurora, followed by an even more intense transient brightening of the morning aurora. Consistent with this asymmetry, the discontinuity produced only weak near-simultaneous perturbations in highlatitude postnoon ground magnetometers but a transient convection vortex in the prenoon Greenland ground magnetograms. The results of this study indicate that the solar wind interaction with the bow shock is far more dynamic than previously imagined and far more significant to the solar wind-magnetosphere interaction.