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.

593The region downstream of a supercritical collisionless shock, the magnetosheath (MSH), is known to be in a highly disturbed turbulent state [1][2][3]. The undisturbed solar wind (SW) streams with supermagnetosonic velocity V > c ms at a magnetosonic Mach number up to M ms ~ 15. At the Earth's bow shock (BS), the SW decelerates to Mach numbers M ms < 1, thermalizes, and, when entering the MSH, is compressed by roughly a factor of 4. The flow downstream of the BS is highly disturbed and turbulent. However, the MSH is not spacious enough for the turbulence to reach a quasi-sta- ¶ The text was submitted by the authors in English.tionarity. It remains not fully developed, intermittent, and structured in time and space. In this framework, high-energy density jets have been observed in the past in the magnetosheath [1,5]. As a development of such earlier studies, we have found more than 140 events of an anomalously high kinetic energy density in the MSH during 20 orbits of Interball-1 , Cluster , Polar , and Geotail . Here, we concentrate on two MSH crossings-by Interball-1 and Cluster [11], respectively-characterized by the bursts of an extraordinarily high ion flux and kinetic energy density. High energy density jets in the magnetosheath near the Earth magnetopause were observed by Interball-1 [1]. In this paper, we continue the investigation of this important physical phenomenon. New data provided by Cluster show that the magnetosheath kinetic energy density during more than one hour exhibits an average level and a series of peaks far exceeding the kinetic energy density in the undisturbed solar wind. This is a surprising finding because the kinetic energy of the upstream solar wind in equilibrium should be significantly diminished downstream in the magnetosheath due to plasma braking and thermalization at the bow shock. We suggest resolving the energy conservation problem by the fact that the nonequilibrium jets appear to be locally superimposed on the background equilibrium magnetosheath, and, thus, the energy balance should be settled globally on the spatial scales of the entire dayside magnetosheath. We show that both the Cluster and Interball jets are accompanied by plasma superdiffusion and suggest that they are important for the energy dissipation and plasma transport. The character of the jet-related turbulence strongly differs from that of known standard cascade models. We infer that these jets may represent the phenomenon of the general physical occurrence observed in other natural systems, such as heliosphere, astrophysical, and fusion plasmas [2][3][4][5][6][7][8][9][10]. High Energy Jets in the Earth

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Abstract. At 1130 UT on November 28, 1995, two spacecraft, Interball-Tail and Geotail, were in a favorable position to study the plasma sheet activity and an auroral breakup observed on the ground near the spacecraft ionospheric footpoints. Both spacecraft were near the neutral sheet, and they were nearly aligned along the magnetic meridian. During the auroral breakup observed at the equatorward half of the auroral oval (also registered as an AKR burst at Interball) both spacecraft

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