Abstract. The origin of multiple energetic particle injections into the inner magnetosphere is addressed using a rare opportunity of measuring the energetic particle fluxes at different radial distances under known electric and magnetic fields. During a strong substorm on February 10, 1991, the CRRES spacecraft measured E and B fields and high-energy particle fluxes near the magnetic equator at r •-5 Re, whereas particle injections, their azimuthal locations, and some other parameters were simultaneously monitored by three geostationary spacecraft and ground networks. We show a multitude of impulsive short-duration injection events which correlate with 1-2 rain long pulses of dawn-dusk electric field. The observations suggest that some E field pulses recorded deep in the inner magnetosphere were fast magnetosonic waves radiated by the current disruption region. This supports the concept of impulsive dissipation event as an elementary building block of substorm expansion. Furthermore, our modeling results indicate that most of the flux variations of energetic particles can be explained by the global convective transport and corresponding particle acceleration. However, we emphasize that, depending on particle spectra and r•dial flux gradient, one can observe either flux increase, or decrease, or no variation (often seen in different energy ranges simultaneously and at the same point) as a response to the electric field pulse. Both the cloud of injected particles and magnetic field dipolarization region had a sharp inner boundary (injection front) which propagated inward at the convection speed. We document the complicatad structure of this front, consisting of a diamagnetic hot proton layer followed by the dipolarization front which contains enhanced energetic electron fluxes. Further study is required to understand how common this structure is and, if common, how it may be formed.

Abstract. We present a comprehensive study of a sequence of two substorms and multiple pseudobreakups using optical, magnetic and incoherent scatter radar measurements, energetic particles from two geosynchronous satellites and particle and field data from the Geotail spacecraft located at Xasm • -86 Re. Following conventional nomenclature, we classified as pseudobreakups those auroral breakups which did not exhibit significant poleward expansion (< 2 ø magnetic latitude).Auroral intensifications following substorm breakups were also observed, and were classified separately. Pseudobreakups were found not to differ from substorm breakups in longitudinal extent (from 1.3 to 6.1 hours of magnetic local time), or in duration (from 5 to 16 minutes). In general, the ionospheric currents producing ground magnetic disturbances were more intense during substorms than pseudobreakups. We found that pseudobreakups are associated with the same magnetospheric processes as substorm breakups which involve current wedge formation, midlatitude magnetic Pi2 pulsations and energetic particle injections at the geosynchronous altitude. Moreover, pseudobreakups are associated with magnetic reconnection in the near-Earth region, evidenced by the typical subsequent detection of a plasmoid at Geotail. This implies that the magnetotail volume influenced by a pseudobreakup is qui•e large in radial distance. We conclude that there is no definitive qualitative distinction between pseudobreakups and substorms but there is a continuum of states between the small pseudobreakups and large substorms.

Abstract. Quantitative relationships allowing one to compute the lobe magnetic field, flaring angle and tail radius, and to evaluate magnetic flux based on solar wind/IMF parameters and spacecraft position are obtained for the middle magnetotail, X=(−15, −35) R E , using 3.5 years of simultaneous Geotail and Wind spacecraft observations. For the first time it was done separately for different states of magnetotail including the substorm onset (SO) epoch, the steady magnetospheric convection (SMC) and quiet periods (Q). In the explored distance range the magnetotail parameters appeared to be similar (within the error bar) for Q and SMC states, whereas at SO their values are considerably larger. In particular, the tail radius is larger by 1−3 R E at substorm onset than during Q and SMC states, for which the radius value is close to previous magnetopause model values. The calculated lobe magnetic flux value at substorm onset is ∼1 GWb, exceeding that at Q (SMC) states by ∼50%. The model magnetic flux values at substorm onset and SMC show little dependence on the solar wind dynamic pressure and distance in the tail, so the magnetic flux value can serve as an important discriminator of the state of the middle magnetotail.

[1] According to the loading-unloading substorm scenario, the magnetic flux, stored in the magnetotail during the substorm growth phase,is dissipated in the course of the expansion phase. However so far only separate estimates of both accumulated and dissipated flux values were made due to the lack of methods to calculate those quantities, doing their direct comparison impossible. First, we analyzed the magnetotail magnetic flux at substorm onset as a function of solar wind parameters to show that the tail magnetic flux, stored during the growth phase (DF T ), depends mainly (CC = 0.95) on the merging electric field E m = V SW B t sin 3 q/2. It implies the lack of threshold magnetic flux at substorm onset. Also, the magnetic flux through the auroral bulge at substorm maximum (