Abstract. We analyze ground magnetograms and magnetic field, ion, and electron data from Interball/tail (IT) for the period 0030-0530 UT on January 11, 1997, focusing on waves at the near-tail (-•-13 RE), duskside, equatorial flank, a locale whose physical and wave properties have not been as well studied as those on the dayside. Two major interplanetary features, monitored by Wind, are relevant to this work: The very high and variable dynamic pressure and the strongly northward and generally increasing magnetic field. In this paper, we report, first, on magnetosonic waves in the magnetosheath of frequency -•0.15 Hz, probably generated by the mirror instability, which are Doppler shifted with respect to similar waves on the dayside. Second, we discuss Kelvin-Helmholtz (KH) waves on the magnetopause, of wavelength -•13-14 RE and frequency -•3.6 mHz, i.e., in the Pc 5 range. At IT, these waves appear as an envelope modulation of the magnetosonics and are recorded on ground stations at dusk. We argue that the large magnetic shear across the magnetopause and a magnetosheath flow aligned almost normal to the field stabilized the magnetopause locally. Thus these waves were generated on the dayside and propagated to the flank. Third, we examine a low-latitude boundary layer (LLBL), whose tailward stretched field and average antisunward flow were perturbed quasi-periodically. This, together with the particle behavior, suggests a complex billowy structure where hot plasma sheet and cold magnetosheath populations wind around each other while drifting antisunward. A numerical calculation using IT parameters suggests that the inner edge of the LLBL was at this time KH unstable. Fourth, over the 5-hour period the power of the KH oscillations drifts to lower frequencies which we attribute to the progressive decrease in clock angle. Fifth, transients induced by dynamic pressure pulses include a 7.5-min single, free oscillation upon arrival of a fourfold pressure release. Sixth, the long-term effect on the magnetosphere of the increasing northward pointing magnetic field and the stepwise decreasing dynamic pressure is to make the shape of the cavity progressively less blunt. A conclusion of this work is that the equatorial magnetopause can be very oscillatory with various, distinct periodicities even when the interplanetary magnetic field is strongly north. The solar wind dynamic pressure, while responsible for some, cannot explain all of this wave activity.

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Abstract. The high time-resolution solar wind ion flux measurements from Interball-1 and IMP 8 show about one hundred large, rapid dynamic the pressure changes each year. We cataloged these events by the size and transition time of the pressure changes and present a statistical survey of these events. We find that the majority of the pressure changes of more than 1-2 nPa occur over a very short time period, on the order of a few minutes or less. Most of the large pressure changes not associated with shocks are due solely to density changes with speed remaining constant. We find that pressure balance between the thermal and magnetic pressures is not maintained across most of these events, so these events are still evolving.

We present a statistical survey of Prognoz 10 solar wind observations at the times of transient (step function and impulsive) variations in the dayside magnetospheric magnetic field strength measured by the GOES 5 and 6 geosynchronous satellites. The results indicate that 51% of the transient magnetospheric events can be associated with corresponding variations in the solar wind dynamic pressure. A further 17% of the events can be associated with fluctuations in the interplanetary magnetic field orientation in the sense previously associated with foreshock pressure pulses. We find no tendency for impulsive events at dayside geosynchronous orbit to be associated with north/south fluctuations in the interplanetary magnetic field (IMF) orientation, nor for the events to occur primarily during intervals of southward IMF. The success rate for associating transient events at dayside geosynchronous orbit with solar wind features decreases as Prognoz 10 moves farther from the Earth-Sun line. The observations indicate that variations in the solar wind dynamic pressure and foreshock pressure pulses associated with variations in the IMF cone angle are the predominant causes of large-amplitude transient events observed at dayside geosynchronous orbit. spn spheric magnetic field strength correspond to similar features in mid-and low-latitude ground magnetograms [e.g., Nishida and Cahill, 1964; Behannon and Ness, 1966; Patel, 1968; Pateland Coleman, 1970] and step function si and ssc events in ground magnetograms correspond to sudden sharp changes in the solar wind density (and therefore dynamic pressure) [Gosling et al., 1967a, b, 1968; Ogilvie et al., 1968], we can be reasonably certain that abrupt changes in the solar wind dynamic pressure produce almost equally sharp variations in B .. Occasional case spn studies using simultaneous solar wind and magnetospheric observations provide more direct evidence for a relationship between step function variations in the solar wind dynamic pressure and B• [Sugiuraetal 1968; Wilkenetal, 1982,1986; •h ß ' ß Sibeck et al., 1989a]. Consequently, statistical surveys of step function variations in Bsp h justifiably take for granted the relationship of the magnetospheric events to variations in the solar wind dynamic pressure and do not present simultaneous solar wind observations [e.g., Kokubun, 1983; Kuwashirna et al., 1985; Kuwashirna and Fukunishi, 1985]. Of course, not all solar wind dynamic pressure variations resemble step functions. Poternra et al. [ 1989] and Sibeck and Croley [ 1991 ] presented evidence for repetitive (5-10 min), impulsive (-1 min) variations in the solar wind dynamic pressure far upstream from the bow shock and showed that they produced similar fluctuations in Bsp h. Despite the strong evidence for a relationship between solar wind dynamic pressure variations and magnetospheric events, efforts to establish a one-to-one correspondence must surely fail. Solar wind monitors generally do not lie on the Earth-Sun line and therefore do not always observe features which...