V. Smirnov

Different types of low‐latitude boundary layer as observed by Interball Tail probe

Interball Tail probe crossed dayside magnetopause during late winter to middle autumn months. The high-latitude magnetopause was crossed outbound orbit, while the low- latitude magnetopause was crossed inbound. We analyze 31 low-latitude magnetopause/low- latitude boundary layer (LLBL) crossings recorded in 1996 in the fast mode of SCA-1 ion spectrometer. Data from the MIF/FM-3 magnetometers and ELECTRON spectrometer are also used. The majority of magnetopause/LLBL crossings fall into two categories: (1) highly structured LLBL (14 cases) and (2) weakly structured LLBL (9 cases). The highly structured LLBL usually consists of short-time (0.5-5 min) transients including fast-moving (of an order of magnetosheath velocity) plasma as well as density transients that are nearly stationary relative to the magnetospheric plasma. The observed ensemble of transients shows evolution of plasma parameters from magnetosheath-like to magnetosphere-like. Fast-moving transients frequently have flux transfer event (FTE) magnetic signatures. This type of LLBL is usually accompanied by various reconnection signatures and is more frequently observed when the interplanetary magnetic field (IMF) and/or magnetosheath magnetic field has a negative Bz component. The weakly structured LLBL shows a significantly smaller variation of number density and hotter plasma temperature. Strong velocity shear is frequently observed at the magnetopause in the weakly structured case. Dispersed ion signatures are often seen within this type of LLBL. The ion and electron temperatures within the weakly structured LLBL are more elevated in respect to the magnetosheath values compared to the highly structured LLBL. The weakly structured LLBL has a tendency to occur at positive IMF and/or magnetosheath magnetic field Bz. The cause of significant differences between the two kinds of LLBL lies, apparently, in the significantly larger distance of the plasma entry site from the observation point, for weakly structured LLBL, as opposed to highly structured LLBL. While the highly structured LLBL originates at low latitudes, the weakly structured LLBL is most probably formed at high latitudes.

Relaxation of plasma at the shock front

Abstract Brief overview of previous studies of ion thermalization at the shock transition is given. One non-quite typical Prognoz-8 quasi-perpendicular bow shock crossing on 11 February 1981 is considered for which high-time resolution data on plasma and ELF electric field fluctuations are available. Strong turbulence in LH-range that is associated with two-stream ion motion upstream of shock transition is characterized by an exponential growth and saturation of these fluctuations at a level of ∼100 mV/m. The heating of ions at the main shock transition is associated with pulse-like increase of these waves amplitude. Relaxation of gyrating beams downstream of the main shock transition appears to be associated with ion-cyclotron waves and additional heating of ions and passes through two phases: hydrodynamic and kinetic ones. Linear and time scales of the events are estimated.

ION POPULATIONS IN THE TAIL OF VENUS

Abstract Plasma measurements in the tails of Venus showed the existence of several ion populations. Measurements performed on Venera and Pioneer Venus spacecraft at different planetocentric distances showed the evolution of the plasma parameters along the tail. Low-energy ion fluxes measured in the tail at close downstream distances, are also observed farther downstream, and show low acceleration from 0.5 Rv to 12 Rv. High energy ions (energetic O+ ions) reported from PVO observations in the tail bt 10–12 Rv seem to be the same ion component that was observed as energetic ions at the tail boundary close to the planet have on Venera spacecraft. We give evidences that these ions are accelerated in the narrow shear layer near the tail boundary.

Transients at the dusk side magnetospheric boundary: Surface waves or isolated plasma blobs?

We revisit Interball-Tail and Magion-4 observations of the dusk side magnetospheric boundary on February 15-16, 1996. The observed transient behavior of the boundary can be interpreted in terms of surface waves or as the manifestation of isolated magnetosheath plasma entities embedded in the magnetosphere. We examine the arguments for each of these interpretations with high time resolution magnetic field and plasma data and by exploiting the dual-satellite nature of the observations. We find strong evidence for magnetic field and flow vortices near the magnetospheric boundary and hence for the existence of flux tubes with helicoidal field lines; such structures can be associated with both interpretations. The cross-correlation between the dual satellite observations and the apparent periodicity strongly suggest a Kelvin-Helmholtz surface wave, although other interpretations are not impossible. In any case, the observations for this particular event allow us to derive constraints on surface wave generation mechanisms and on scenarios that could account for the presence of isolated plasma elements in the magnetosphere.

Observation of Isolated Structures of the Low Latitude Boundary Layer with the INTERBALL/Tail Probe

Abstract. We analyze the structure of magnetospheric tran- sients observed at the dusk-side low-latitude magnetopause with the Interball Tail Probe. Ion and magnetic field meas- urements are used to investigate one particular transient in more detail. This transient has distinct non-symmetric struc- ture with the plasma characteristics and the flow properties of the leading part of the transient being quite different from those in the trailing part of the transient. The region separat- ing these two parts corresponds to the change of the sign in the Bn component. These observations support an earlier con- clusion that some plasma irregularities within the Low Lati- tude Boundary Layer (LLBL), formed as a result of sporadic reconnection, disconnect from the magnetopause, propagate and dissipate in the magnetosphere, and form what we call Disconnected Magnetosheath Transfer Events (DMTEs). Introduction Flux Transfer Events (FTE) with bipolar Bn signatures, discovered by Russell and Elphic [1978], are identified as re- connected flux tubes resulting from sporadic and localized re- connection. The occurrence of dayside FTEs is strongly cor- related with southward magnetosheath fields, consistent with dayside magnetic merging. Both magnetosheath and magne- tospheric FTEs contain magnetosphere-like and magne- tosheath-like plasmas [Paschmann et al., 1982, Thomsen et al., 1987] and display unique ion composition [Klumpar et al., 1990]. Several regions within FTEs have been identified: the reconnected flux tube and its associated external perturba- tions [Russell and Elphic, 1978], and, more recently, the fuzzy region between the open flux tube and the external perturbation [Rijnbeek et al., 1987]. Farrugia et al. [1988] de- fined four distinct nested regions in an FTE: a disturbed mag- netospheric region, the plasma mixing region, the magne- tosheath-like region (more isotropic and less dense plasma than in the magnetosheath), and the central region where the plasma is indistinguishable from the magnetosheath plasma. These regions are most easily distinguished by the ratio of the plasma to the magnetic field pressure, [3. Smith and Owen [1992] found D-shaped ion distributions in magnetosheath- like and central regions of the same event, caused by a paral-

Bow shock motion with two-point observations: Prognoz 7, 8 and ISEE 1, 2; Prognoz 10 and IMP 8

Abstract Observations of multiple crossings of the Earths bow shock allow us to estimate the nature and velocity of bow shock motion. We have studied this motion with Prognoz 7, 8, 10, ISEE 1, 2 and IMP observations in two ways: by the time delay of bow shock crossings with two well separated satellites and by the difference in time between the bow shock crossings observed by one spacecraft and jumps in solar wind dynamic pressure observed by the other one. The qualitative interpretation of these data as a “surface wave” moving along the bow shock front allows us to estimate its velocity to be about several tens up to several hundreds km/s with mean value ∼100 km/s.

Ion distribution function dynamics near the strong shock front (Project Intershock)

Thestructureof the iondistributionfunctiondownstreamof thebowshockfrontisanalyzedwith theuseof ionenergyspectrameasuredwithhightemporalresolution(0.64sec) by severaldifferentlyorientednarrow—angleelectrostatic analyzersonboardPrognoz-1OIntercosmossatellite.Withina relativelyextendedregiondownstreamof the shockthe ionenergyspectraexhibitfinestructureconsistingof severalrapidlyvaryingnarrow peaks. Someevidenceexiststhatthe iondistributionfunctionbehinda strongquasiperpendicular shockconsistsof manynarrowbunches. Theelectrostaticpotentialjumpat thefrontof an obliqueshockmayoccurin a distanceof about2 km. Observations of the iondistributionfunctionis an importanttestand information source forthetheoreticaldescriptionof thecollisionlessshock. Observationsof doublepeakedionflowat theshockfront/1/provedtheimportanceof thereflectedbeamin the shockprocesses.Subsequentobservationson ISEE—1and—2 /2,3,4/and Prognoz-8/5/as wellas theoreticaldevelopments(e.g.,/6/)showeda moredetailedpictureof the reflectedbeamdynamicsand theroleof reflectedinnsin thedissipativeprocessesnear theshockfront. Itwasone of the importanttopicsof the INTERSHOCKproject/7/to provideadditionaldataon thestructureof theiondistribution function. Itwasexpectedthatthehighertemporalresolutionwouldhelpthedevelopmentof the incompletely solvedproblemof thedissipationin theshock.

INTERBALL observations of the dayside magnetopause

Abstract The high-apogee Interball Tail Probe crosses the magnetopause in two latitude ranges: one is close to the equator, and the other is at middle and high latitudes. A brief description of dayside magnetopause observations from the fast plasma analyzer SCA-1 is given. We give examples of plasma regimes observed at low latitudes that show evidence for plasma cloud penetration into the magnetosphere. Nonstationary reconnection is suggested as a possible mechanism for the observed near-magnetopause structures.

Dependence of amplitude and spectrum of ELF turbulence on ΘBn

Abstract Analysis of several low Mach number interplanetary shocks have shown that the steepness of the amplitude spectrum of electric field fluctuations in the frequency range from several Hz to about 20 Hz is different at quasi-parallel shock front compared to the front of quasi-perpendicular shock. The amplitude of electric field fluctuations in the ion sound frequency range is also varying with the angle between the shock normal and magnetic field direction, Θ Bn . We extend our analysis to sample of bow shock crossings using the data of Prognoz-8 in order to verify the Θ Bn dependence of ELF noise for supercritical shocks.

INTERBALL tail observations of dayside magnetopause oscillations and simultaneous POLAR cusp measurements

On April 13, 1996, while Russias Interball Tail spacecraft was travelling through the dayside magnetosheath, NASAs Polar spacecraft traversed the northern cusp. Ob- served transients seen in the SCA-1 Interball Tail data are shown to be multiple crossings of the magnetopause. Analysis of the moments data from the SCA-1 instrument and magnetic field data from the MIF instrument on Interball Tail show quasi-periodic motion of the magnetopause. Simultaneous ob- servations of changes in the He2+/H + density ratio in the cusp by the Polar/TIMAS instrument show variations on the same time scale. We conclude that the variations in cusp data ob- served by Polar are the result of changes in the reconnection rate at the magnetopause and that these changes are associated with the magnetopause oscillations observed by Interball. neous measurements at the magnetopause, may well be the best approach to relating magnetopause oscillations to changes in the reconnection rate. In this paper, we present a propitious conjunction when Polar was in the cusp and Interball Tail was near the dayside magnetopause (Fig. 1). Changes in the reconnection rate, in- dicated by changes in the He2+/H + ratio in the cusp, were ac- companied by magnetopause oscillations on a similar time scale. While previous studies have suggested correlations between observations in the cusp and, for example, the loca- tion of the magnetopause, we present here direct simultaneous plasma observations in the two regions.